Genetic Variation Flashcards

Question

Define codominance

Answer 1

Codominance is where both alleles in a heterozygous organism are fully and equally expressed in the phenotype. As in, both traits are visible simultaneously without blending, with each allele contributing distinctly to the organism’s appearance. (e.g., AB blood type showing both A and B antigens). Co-dominance provides genetic diversity, as more phenotypes can be expressed within a population. In co-dominance, neither allele is recessive; both contribute equally to the organism's traits.

Answer 2

Incomplete dominance is where both alleles are 'mixed' or expressed together, creating a (new) intermediate phenotype. As in, neither allele is completely dominant, so the traits of both alleles blend to form a third distinct new phenotype. (e.g., pink flowers from red and white parents).

Answer 3

> Lethal alleles are alleles that cause death when expressed in homozygous conditions. >Types of Lethal Alleles: - Recessive Lethal Allele: causes death only when an organism inherits two copies (homozygous recessive). - Dominant Lethal Allele: causes death in both heterozygous and homozygous dominant states. It is often observed in late-onset conditions, where the organism may reach reproductive age before symptoms appear. > The effect of lethal alleles on a population and its genetic variation is that they reduce the number of viable offspring and can influence the frequency of alleles in a population. And dominant lethal conditions often result in the death of individuals before they reproduce, thereby reducing the allele frequency in the population.

Answer 4

Linked genes are genes located close together on the same chromosome, which tend to be inherited together. Linked genes do not assort independently. They are more likely to be inherited together in the same gamete. Crossing over which occurs during prophase I of meiosis, potentially separates linked genes. However, genes closer together are less likely to be separated by crossing over.

Answer 5

Dihybrid Inheritance is the inheritance of two different traits, each controlled by a separate gene with different alleles. Traits are typically located on different chromosomes, allowing for independent assortment during gamete formation.

Answer 6

Without crossing over, linked alleles are inherited together, maintaining specific allele combinations. With crossing over, linked alleles increase genetic variation by producing new allele combinations, enhancing diversity in a population, allowing populations to adapt to changing environments.

Answer 7

A test cross is a genetic cross used to determine the genotype of an individual with a dominant phenotype but an unknown genotype. The cross is to ascertain whether the individual with the dominant phenotype is homozygous dominant (AA) or heterozygous (Aa). If Homozygous Dominant (AA): All offspring will exhibit the dominant phenotype. The dominant allele (A) will always mask the recessive allele (a) from the recessive parent. If Heterozygous (Aa): Approximately 50% dominant phenotype, 50% recessive phenotype. The dominant and recessive alleles will segregate during gamete formation, resulting in a 1:1 ratio in the offspring. This confirms the genotype of an organism exhibiting a dominant phenotype. And helps predict the likelihood of specific traits appearing in future generations.

Answer 8

>Small numbers of offspring may not accurately reflect the true genotype of the parent. And alleles segregate randomly during meiosis, leading to variable ratios in offspring. Therefore, small sample sizes might not show the expected 1:1 ratio in a heterozygous cross, complicating the interpretation. >To mitigate uncertainty, use a large number of offspring to achieve more reliable and representative results, and conduct multiple test crosses to confirm the genotype of the dominant phenotype organism.

Answer 9

>The total number of genetic characteristics within the genetic makeup of a species. >The components of genetic diversity includes... - the range of different alleles present for each gene in a population. - the genetic variation necessary for natural selection to act upon. - High genetic diversity enables populations to adapt to changing environments. - enhances the likelihood of survival by ensuring that some individuals have advantageous traits that can help them survive and reproduce in varied conditions. > Benefits of genetic diversity: - Populations with high genetic diversity are less likely to face extinction because they have a greater chance of possessing traits that are beneficial under new or changing conditions. - Genetic diversity contributes to overall health and robustness of a population, enabling it to withstand diseases and environmental stresses. >Mechanisms for Increasing Diversity: - Sexual Reproduction: Introduces new allele combinations through recombination and independent assortment. - Mutations: Create new alleles, adding to genetic variation. - Migration and Gene Flow: Introduce new alleles into a population from other populations.

Answer 10

- Populations with high genetic diversity are more likely to contain individuals with traits that provide a survival advantage under new conditions. - Higher genetic diversity enhances the ability of a population to adapt and persist through environmental changes. - Populations with low genetic diversity may lack necessary traits for survival, leading to higher risk of extinction.

Answer 11

Natural selection is the process through which individuals with traits better suited to their environment are more likely to survive and reproduce, leading to a gradual adaptation of the population.

Answer 12

> Advantageous Alleles: Alleles that provide a survival or reproductive benefit to organisms possessing them, like an increased likelihood of survival in their environment. Resulting in a higher chance of reproducing and passing these alleles to offspring. The frequency of advantageous alleles rises as they become more common due to their positive effects on survival and reproduction. Leads to populations becoming better adapted to their environment as advantageous traits become prevalent. > Disadvantageous alleles: Alleles that decrease an organism's chances of survival or reproduction. Individuals with these alleles are less likely to survive. Therefore, a lower chance of passing these alleles to offspring. The frequency of disadvantageous alleles declines as they are less likely to be passed on and are gradually removed by natural selection. This results in a population that is less burdened by traits detrimental to survival, improving overall fitness.

Answer 13

> Genetic Drift: a mechanism of evolution involving random changes in allele frequencies within a population over time. - Unlike natural selection, genetic drift occurs by chance. - More pronounced in small populations where each individual's genetic contribution has a larger effect on allele frequencies. - Can lead to significant shifts in allele frequencies due to random events, rather than environmental pressures. - The surviving population may not represent the genetic diversity of the original population. Reduced genetic diversity can affect the population's ability to adapt and survive in the long term. -Over time, genetic drift can lead to an allele becoming fixed in a population (frequency = 100%). Or alleles can be lost entirely from the population due to random chance. The two common causes of genetic drift include population bottleneck, and the founder effect.

Answer 14

>Migration is the movement of individuals into (immigration) a population. Migration allows the introduction of new individuals with different genetic backgrounds into a population. New alleles are added to the gene pool, enhancing genetic variation. New alleles can introduce traits that may be subject to natural selection. >Emigration is the process by which individuals leave their current population to move to another location. Alleles carried by emigrants are lost from the original population's gene pool. If emigrants carried alleles that were unique or advantageous, their departure reduces the genetic diversity and adaptability of the original population. >High Migration Rates: Can rapidly alter allele frequencies and increase genetic diversity. >Low Migration Rates: Changes may be gradual and less noticeable but still significant over long periods.

Answer 15

>The founder effect is a type of genetic drift occurring when a limited number of individuals from a parent population of a diverse gene pool becomes isolated from this larger population, and colonises a new area. The smaller founder population has reduced genetic diversity. This means: - The isolated group is small and may not represent the full genetic diversity of the original population. - The alleles present in the founder group are randomly selected from the larger population. - Certain alleles may become more common, while others may be completely absent. - Limited genetic variation can reduce the population's ability to adapt to environmental changes. - Deleterious alleles may become more prevalent, potentially leading to higher rates of genetic disorders. - The isolated population may evolve differently from the original population due to its reduced genetic diversity. - Over time, the founder population could diverge significantly, possibly leading to the emergence of new species or subspecies.

Answer 16

- Because the founding group carries only a portion of the genetic variation present in the original, larger population. - Some alleles from the original population may be lost entirely in the founding group due to the small sample size. - The alleles in the founding population are a random sample of the original gene pool. Therefore, certain alleles may be overrepresented or underrepresented due to chance, affecting the genetic makeup of the new population. - The smaller population size means fewer possible mating combinations, limiting genetic variation introduced by new combinations. - There is a higher likelihood of mating between relatives in a small population, which increases the chances of recessive allele expression and further reduces genetic diversity. - Inbreeding increases the probability of individuals inheriting genetic disorders and reduces overall fitness. - With lower genetic variation, the population may struggle to adapt to new environmental changes or challenges.

Answer 17

> The bottle neck effect is a genetic phenomenon where a population undergoes a dramatic reduction in size due to a catastrophic event, leading to a loss of genetic diversity.

Answer 18

>Natural Disasters: Earthquakes, volcanic eruptions, floods, tsunamis. These events can cause immediate and widespread death, significantly reducing population size. Only a small, random sample of individuals survives, leading to a loss of genetic diversity and potential loss of rare alleles. The surviving individuals repopulate but with reduced genetic diversity, impacting adaptability and evolutionary potential. >Climate Change: Extreme weather conditions (heatwaves, cold snaps), prolonged droughts, severe storms. Changes in climate can make existing habitats inhospitable, leading to reduced living conditions for many species. Species that cannot adapt to new conditions or migrate to more suitable habitats face population declines. As populations shrink, only a subset of the original genetic diversity remains, affecting future adaptability. >Human Activities: Habitat destruction (deforestation, urbanization), pollution, overhunting, introduction of invasive species. Habitat destruction and pollution directly reduce the population size and survival rates. Overhunting and invasive species further decrease the population. The drastic reduction in population size limits genetic variation and can lead to a genetic bottleneck. The reduced genetic diversity can make populations more vulnerable to diseases and environmental changes, affecting long-term survival. >Disease Outbreaks: Epidemics (influenza, Ebola), pandemics (COVID-19). Diseases that spread rapidly can significantly decrease population size and genetic diversity. The surviving individuals may carry different genetic traits compared to the pre-outbreak population, leading to reduced genetic variation. Post-outbreak populations may have altered genetic compositions and face different evolutionary pressures.

Answer 19

1. Before the bottleneck, the population has a wide range of alleles and high genetic diversity. Then a catastrophic event occurs that wipes out some of the population. The event is usually random with respect to genetic traits, meaning it does not selectively remove individuals based on their genetic make-up. 2. The population is drastically reduced to a small number of individuals. Only a fraction of the original genetic variation survives in these few individuals. The survivors’ genetic makeup may not represent the full genetic diversity of the original population. 3. The new, larger population, derived from these survivors, may have lower genetic diversity and may be less adaptable to environmental changes or disease. The gene pool of the post-bottleneck population is less diverse than that of the pre-bottleneck population. Meaning, the population may be more vulnerable to diseases and environmental changes due to reduced genetic variability. 4. The reduced genetic diversity can limit the population’s ability to adapt to new conditions which may increase the risk of extinction in changing environments. 5. Resultantly, the population may follow a different evolutionary path compared to the original, potentially leading to different adaptations or evolutionary outcomes, which could either be good or bad.

Answer 20

Cell containing double set of chromosomes (2n)

Answer 21

Altering the genetic makeup of an organism

Answer 22

Having only one set of chromosomes, all chromosomes different (n).

Answer 23

The gametes produced as a result of crossing over.

Answer 24

The points on chromatids where the homologous chromosomes cross.

Answer 25

Fertilised egg

Answer 26

During cell division chromosomes are not pulled correctly to the poles resulting in incorrect chromosome numbers.

Answer 27

A map of sorted chromosomes used to detect nondisjunction or sex of the child.

Answer 28

A sex-linked disease where the blood cells are unable to clot.

Answer 29

An allele where more than two forms can fit at a locus on a chromosome.

Answer 30

> Little finger: Small population size. The population can shrink. If the population shrinks, then chance can take over. For example, if only four individuals survive an epidemic, then their genes will represent the new gene pool. > Ring finger: non-random mating, because a ring represents a couple. If individuals choose a mate based on their appearance or location, the frequency may change. If redheaded individuals only mate with redheaded individuals, they could eventually form a new population. If no one ever mates with redheaded individuals, these genes could decrease. > Middle finger. The M in the middle finger should remind you of the M in the word "mutation." If a new gene is added through mutation, it can affect the frequency. Imagine a gene mutation creates a new colour of hair. This would obviously change the frequency in the gene pool. >Pointer finger: Movement (Gene flow). If new individuals flow into an area, or immigrate, the frequency will change. If individuals flow out of an area, or emigrate, then the frequency will change. >Thumb: Natural selection, the process that creates organisms better adapted to their local environment. Nature votes thumbs up for adaptations that will do well in their environment, and thumbs down to adaptations that will do poorly. The genes for individuals that are not adapted for their environment will gradually be replaced by those that are better adapted. All four of the processes represented by our fingers can cause evolution. However, none of them lead to adaptation, except for the thumb.

Answer 31

* Temperature - increasing or decreasing * Climate changes - be specific if possible * Major events like floods, droughts etc * Salinity * Humidity * Wind * Moisture levels / dryness * Light intensity * Chemicals (eg antibiotics, pesticides, herbicides, disinfectants etc)

Answer 32

* Competition for resources (always name or give eg's of resources - light, food, space etc) * Predation - S.P. on prey to avoid predation and S.P. on the predator to catch prey more efficiently * Grazing / browsing -S.P. on plants to avoid being grazed by animals and S.P. on animals to graze more efficiently * Parasitism / parasites * disease (specify the name of the disease viral, bacterial, fungal, protozoan). Note resistance to disease is a phenotype that results from the presence of a particular allele or alleles.

Answer 33

Gene flow is the movement of genes into or out of a population (immigration and emigration). A population may gain or lose alleles through gene flow. Gene flow tends to reduce the differences between populations because the gene pools become more similar.

Answer 34

Natural selection is any selective process that occurs due to the fitness of an organism to its environment. Whereas artificial selection is the selective breeding, imposed by an outside entity, typically humans, in order to increase the frequency of desired traits. Simply put, natural selection does not involve human intervention.

Answer 35

Allele frequency refers to how common an allele is in a population. It is determined by counting how many times the allele appears in the population then dividing by the total number of copies of the gene.

Answer 36

Homologous chromosomes are best described as carrying the same genes in the same sequence but not necessarily identical genetic information. They come from the same parent, one from the mother and one from the father.

Answer 37

Genetic drift is a mechanism of evolution that causes changes in allele frequencies in a population due to random chance. * Key causes of genetic drift include: Small Population Size: Genetic drift has a stronger effect in smaller populations, where random events can significantly impact allele frequencies. Bottleneck Effect: A sharp reduction in population size due to events like natural disasters, disease, or human activity can reduce genetic diversity. The small surviving population's allele frequencies may differ from the original population's. Founder Effect: When a small group of individuals establishes a new population, the allele frequencies in this new population may differ from the original population due to the limited genetic diversity of the founders. Random Mating and Reproduction: In each generation, certain alleles may be passed on more or less frequently simply by chance, leading to shifts in allele frequencies over time. These random processes can lead to reduced genetic variation and fixation (where one allele becomes the only variant in the population) or loss of alleles in the population.

Answer 38

Phenotypic range refers to the variety of observable traits (phenotypes) displayed by individuals in a population. It results from the interaction between an individual's genotype and the environment. A wide phenotypic range indicates significant variation in traits within a population. Traits with a phenotypic range are often controlled by polygenic inheritance (involving multiple genes). Examples include height, skin colour, and weight in humans, which are influenced by both genetic factors and environmental conditions like nutrition or exposure to sunlight. The phenotypic range is important for adaptation and survival, as it provides a population with flexibility to cope with environmental changes.

Answer 39

Definition: Stabilising selection is a type of natural selection that favours the average phenotype, reducing variation in a population. Outcome: Extreme phenotypes (e.g., very small or very large traits) are selected against, while intermediate phenotypes are more likely to survive and reproduce. Impact on Variation: Decreases genetic variation as individuals with extreme traits have lower fitness. Example: Human birth weight – very low and very high birth weights have higher mortality rates, so average weights are more common in the population. Adaptive Advantage: Helps populations maintain traits that are well-suited to stable environments.

Answer 40

Definition: A type of natural selection where individuals with extreme phenotypes at both ends of a trait spectrum are favored over individuals with intermediate phenotypes. Effect: Results in increased genetic variation within a population as the two extremes are selected for. Example: Birds with either very small or very large beaks may be favoured if their food sources require specialised feeding adaptations, while birds with medium-sized beaks may be at a disadvantage. Outcome: Over time, this can lead to the development of two distinct groups within a population or even speciation. Graph Representation: The curve showing the frequency of traits becomes bimodal, with peaks at the extremes and a dip in the middle.

Answer 41

Definition: Directional selection is a type of natural selection where one extreme phenotype is favored over others, causing a shift in the population's genetic makeup. Outcome: The population's allele frequencies shift toward the advantageous trait over generations. Environmental Influence: This often occurs in response to a changing environment or new selective pressures. Example: The development of antibiotic resistance in bacteria or the increase in beak size of finches during droughts. Key Points: Increases the prevalence of the beneficial extreme trait while reducing genetic diversity for other traits in the population.

Answer 42

Definition: Polyploidy is the condition where an organism has more than two sets of chromosomes (e.g., triploid (3n) or tetraploid (4n)). Causes: Errors during meiosis, such as non-disjunction, result in gametes with extra sets of chromosomes. Errors during mitosis in early embryonic cells can also result in polyploid cells. Fertilization: A diploid gamete (2n) may fuse with a haploid gamete (n), creating a triploid (3n) zygote. Alternatively, two diploid gametes (2n + 2n) can fuse, forming a tetraploid (4n) zygote. Artificial Induction: Polyploidy can be artificially induced in plants using chemicals like colchicine, which disrupts spindle fiber formation during cell division. Significance in Plants: Polyploidy often leads to increased size, vigor, and improved traits in plants. It is common in agriculture (e.g., wheat, strawberries). Uncommon in Animals: Polyploidy is less common in animals due to complications in meiosis and reproduction.

Answer 43

Definition: Ploidy refers to the number of complete sets of chromosomes in a cell. Haploid (n): Cells with one complete set of chromosomes. Examples include gametes (sperm and egg cells in humans). Diploid (2n): Cells with two complete sets of chromosomes, one from each parent. Most human somatic (body) cells are diploid. Polyploidy: Cells with more than two sets of chromosomes (e.g., triploid, tetraploid). Common in plants but rare in animals. Importance in Variation: During meiosis, changes in ploidy, such as the production of haploid gametes, ensure genetic diversity through fertilization. Role in Speciation: Polyploidy can lead to new species, especially in plants, by preventing interbreeding with the parent population.

Answer 44

1. Autopolyploidy Occurs when an organism has multiple sets of chromosomes from the same species. Results from errors during cell division, such as nondisjunction in meiosis or mitosis. Produces individuals with extra chromosome sets (e.g., 3n, 4n). Common in plants, leading to larger cells, bigger fruits, and flowers. 2. Allopolyploidy Occurs when an organism has multiple sets of chromosomes from two different species. Results from hybridization between species, followed by chromosome doubling. Allows fertility in hybrids by providing homologous chromosome pairing during meiosis. Common in crops like wheat (e.g., hexaploid wheat with chromosomes from three species).

Answer 45

Definition of Polyploidy: Polyploidy occurs when an organism has more than two complete sets of chromosomes, often due to errors in meiosis or mitosis. Formation of Polyploid Individuals: This can result from processes like nondisjunction, where chromosomes fail to separate properly, leading to gametes with extra chromosome sets. Reproductive Isolation: A polyploid organism is often reproductively isolated from its diploid ancestors because it cannot produce fertile offspring with them due to differences in chromosome numbers. Instant Speciation: Since the polyploid organism can only mate successfully with others of the same ploidy level (e.g., tetraploids with tetraploids), it effectively becomes a new species in one generation. Common in Plants: Polyploidy is particularly common in plants, enabling them to adapt to new environments and exploit ecological niches. Hybrid Polyploidy: Sometimes, polyploidy arises in hybrids between species, where chromosome doubling allows the hybrid to become fertile and form a new species. Evolutionary Significance: Polyploidy contributes to biodiversity and speciation events, with many crops (e.g., wheat, bananas) having polyploid origins.

Answer 46

A group of organisms that share common characteristics and can interbreed successfully in nature. Members of the same species produce fertile offspring. They are reproductively isolated from other groups, meaning they cannot produce fertile offspring with members of different species. Share a common gene pool, enabling genetic variation within the species.

Answer 47

A group of populations of a species distributed around a geographic barrier in a ring-like formation. Adjacent populations in the ring can interbreed and produce fertile offspring. Populations at the ends of the ring, which are geographically adjacent, are genetically distinct and cannot interbreed. Provides evidence for speciation as it demonstrates how genetic differences accumulate over distance. Highlights the role of geographic isolation and gene flow in evolution.

Answer 48

Varied Definitions: Different species concepts (e.g., biological, morphological, phylogenetic) emphasize distinct criteria such as reproduction, appearance, or evolutionary lineage. Asexual Reproduction: Many organisms reproduce asexually (e.g., bacteria), making it hard to apply the biological species concept, which focuses on interbreeding. Hybridization: Some species can interbreed and produce viable offspring (e.g., ligers, mules), challenging the notion of reproductive isolation. Fossil Evidence: Defining extinct species relies on morphology alone, which can lead to subjective classification. Ring Species: Populations that can interbreed with neighboring groups but not distant ones blur species boundaries. Continuous Variation: Gradual changes across populations (cline) make it hard to draw clear distinctions. Genetic Divergence: Variability in genetic data may not always align with observable traits or reproductive capabilities. Human Influence: Artificial selection and habitat changes complicate natural species definitions.

Answer 49

* Allopatric Speciation Occurs when populations are geographically isolated. Physical barriers like mountains, rivers, or oceans prevent gene flow. Populations evolve independently through mutation, natural selection, and genetic drift. * Sympatric Speciation Occurs within the same geographical area. Results from reproductive isolation due to factors like ecological niches, behavioral differences, or chromosomal changes (e.g., polyploidy). Gene flow between groups is restricted despite the lack of physical barriers.

Answer 50

Definition: Allopatric speciation occurs when populations of the same species become geographically isolated, leading to the formation of new species. Geographical Barrier: A physical barrier (e.g., mountains, rivers, or oceans) prevents gene flow between populations. Genetic Divergence: Over time, mutations, genetic drift, and natural selection cause genetic differences to accumulate in the isolated populations. Reproductive Isolation: Once genetic differences are significant, the populations can no longer interbreed to produce fertile offspring, even if the barrier is removed. Result: Two distinct species evolve from the original population. Example: Darwin’s finches on the Galápagos Islands, where geographic isolation led to the evolution of different species adapted to specific ecological niches.

Answer 51

Geographic isolation occurs when a population is divided by a physical barrier, such as a mountain range, river, or ocean. The isolated populations are prevented from interbreeding, meaning gene flow is restricted between them. Over time, the populations adapt to their different environments through natural selection, leading to changes in traits such as behaviour, morphology, or physiology. Genetic mutations accumulate independently in each population, further increasing genetic differences. If the genetic differences become significant enough (e.g., through reproductive isolation mechanisms like behavioral or temporal differences), the populations can no longer interbreed even if the physical barrier is removed. This results in the formation of two distinct species, a process known as speciation. This process is a form of allopatric speciation, which is the most common form of speciation due to geographic isolation.

Answer 52

Sympatric speciation occurs when a new species evolves from a population without geographical separation. It is driven by factors such as mutations, changes in behaviour, or ecological niches. Involves reproductive isolation where members of the same population can no longer interbreed. Can occur through mechanisms like polyploidy (increase in chromosome number) or disruptive selection (favoring extreme traits). Leads to the formation of two or more distinct species over time, despite living in the same area.

Answer 53

Reproductive Isolation: Populations may become reproductively isolated due to differences in mating behaviors, timing (temporal isolation), or physical characteristics that prevent successful mating. Behavioral Isolation: Differences in mating rituals or behaviors can prevent interbreeding between populations, leading to speciation. Ecological Isolation: Populations may occupy different ecological niches within the same environment, reducing interactions and gene flow. Mechanical Isolation: Physical differences in reproductive organs can prevent successful mating, even if populations are in the same area. Genetic Divergence: Over time, genetic differences accumulate between populations due to mutations, genetic drift, or natural selection, resulting in reproductive isolation. Polyploidy: In some cases, mutations lead to an increase in the number of chromosomes, creating a new species that cannot interbreed with the parent population.

Answer 54

Reproductive isolating mechanisms are factors that prevent different species or populations from interbreeding, maintaining species boundaries. Pre-zygotic isolating mechanisms (prevent fertilization from occurring): Temporal isolation: Species reproduce at different times (e.g., seasons, times of day). Behavioral isolation: Differences in mating behavior or rituals prevent interbreeding. Mechanical isolation: Physical differences in reproductive organs prevent successful mating. Gametic isolation: Incompatibility of sperm and egg cells prevents fertilization. Post-zygotic isolating mechanisms (act after fertilization): Hybrid inviability: The hybrid offspring do not develop properly or die early. Hybrid sterility: The hybrid offspring are sterile and cannot reproduce (e.g., mules).

Answer 55

* Prezygotic isolating mechanisms: These prevent fertilization from occurring, even if individuals from different populations come into contact. Examples include: Temporal isolation (different mating times) Behavioural isolation (different mating behaviors) Mechanical isolation (differences in reproductive organs) Gametic isolation (incompatibility of sperm and egg) * Postzygotic isolating mechanisms: These occur after fertilization and affect the viability or fertility of the offspring. Examples include: Hybrid inviability (offspring do not develop properly or die early) Hybrid sterility (offspring are sterile, e.g., mules)

Answer 56

* Allopatric Speciation: Geographical Isolation: A physical barrier (e.g., mountains, rivers) separates populations of the same species. Reproductive Isolation: Over time, due to geographical isolation, genetic differences accumulate in the two populations, preventing interbreeding even if they are brought back together. Types of Isolation: Pre-zygotic (before fertilization): Temporal Isolation: Mating seasons differ. Behavioural Isolation: Differences in courtship behavior. Mechanical Isolation: Physical differences preventing mating. Post-zygotic (after fertilization): Hybrid Inviability: Offspring do not develop properly or die early. Hybrid Sterility: Offspring are sterile (e.g., mules). * Sympatric Speciation: No Geographical Barrier: Species arise from a single population within the same geographic area. Reproductive Isolation develops due to factors other than geographical isolation. Types of Isolation: Temporal Isolation: Different mating times prevent interbreeding. Behavioral Isolation: Changes in behavior or mating rituals that cause reproductive barriers. Ecological Isolation: Different ecological niches or habitats within the same area lead to reduced interbreeding. Genetic Isolation: Mutations or chromosomal changes (e.g., polyploidy) cause individuals to be reproductively incompatible. Mechanical Isolation: Physical differences in reproductive structures prevent mating.

Answer 57

Reproductive isolating mechanisms are factors that prevent different species from interbreeding, leading to speciation. They ensure that gene flow between populations is restricted, allowing them to evolve independently. * Prezygotic mechanisms (before fertilization): Temporal isolation: Species reproduce at different times (e.g., different seasons). Behavioral isolation: Species have different mating behaviors (e.g., different courtship rituals). Mechanical isolation: Physical differences in reproductive organs prevent mating. Gametic isolation: Sperm and egg from different species are incompatible. * Postzygotic mechanisms (after fertilization): Hybrid inviability: Offspring from different species do not develop properly or die early. Hybrid sterility: Hybrids are sterile (e.g., mule, a cross between a horse and a donkey). These mechanisms can occur due to genetic differences between populations, leading to the formation of new species over time.

Answer 58

Definition: A barrier that prevents fertilization from occurring between individuals of different species or populations. Function: Ensures reproductive isolation by stopping gametes from combining to form a zygote. Types: Temporal Isolation: Species reproduce at different times (e.g., seasons, times of day). Behavioral Isolation: Differences in mating behaviors or courtship rituals prevent interbreeding. Mechanical Isolation: Differences in reproductive structures make mating physically impossible. Ecological (Habitat) Isolation: Species occupy different habitats and rarely encounter each other. Gametic Isolation: Gametes cannot fuse due to incompatibilities in biochemical signals or conditions.

Answer 59

Habitat Isolation: Populations live in different environments and are unlikely to encounter each other for mating. Prevention of Gene Flow: These isolating mechanisms stop the exchange of genetic material between populations. Divergence of Populations: Without gene flow, populations accumulate genetic differences over time due to mutation, genetic drift, and natural selection. Formation of New Species: Eventually, the genetic differences are significant enough that populations can no longer interbreed, even if barriers are removed, resulting in speciation.

Answer 60

A type of reproductive barrier that occurs after fertilization of the egg by the sperm. Prevents the resulting zygote from developing into a viable, fertile offspring. Reduces gene flow between populations by ensuring offspring are either: - Inviable (zygote does not survive or develop properly). - Sterile (offspring cannot produce functional gametes, e.g., mules). - Reduced fitness (offspring are less likely to survive or reproduce successfully). Examples include hybrid inviability, hybrid sterility, and hybrid breakdown.

Answer 61

Hybrid Inviability Summary Definition: Hybrid inviability is a post-zygotic isolating mechanism where a hybrid organism formed from the mating of two different species fails to develop properly or survive to reproductive maturity. Cause: Genetic differences between the species result in incompatible genes, proteins, or developmental pathways, leading to issues in embryonic development. Outcome: The hybrid embryo may die early during development. If it survives birth, it may not be healthy enough to reach reproductive age. Example: A mule, resulting from a horse and donkey mating, often demonstrates reduced viability compared to its parent species.

Answer 62

Definition: Hybrid sterility is a postzygotic reproductive barrier where hybrids (offspring of two different species) are unable to produce viable gametes, rendering them infertile. Cause: Differences in chromosome number or structure between parent species prevent proper pairing and segregation of chromosomes during meiosis in the hybrid. Examples: Common examples include mules (horse × donkey) and ligers (lion × tiger). Evolutionary Role: Prevents gene flow between species, maintaining species boundaries and contributing to speciation. NCEA Relevance: Demonstrates how genetic variation and reproductive isolation mechanisms influence speciation and biodiversity.

Answer 63

Definition: A form of postzygotic reproductive isolation where the hybrid offspring of two different species are fertile, but their subsequent generations are inviable or sterile. Occurs in later generations: While the first-generation hybrids (F1) may appear healthy and fertile, problems arise in the second generation (F2) or beyond. Genetic incompatibility: This is due to the accumulation of genetic mismatches or incompatible gene interactions over generations. Prevents gene flow: Acts as a barrier to successful reproduction between species over time. Example: Seen in some plant species and animals, such as in certain rice strains where F2 hybrids show poor growth or sterility.

Answer 64

Definition: Divergent evolution occurs when two or more species share a common ancestor but accumulate differences over time, leading to the development of new species. Cause: It is driven by different selective pressures in distinct environments. Result: The resulting species become increasingly dissimilar in traits, even though they share an evolutionary origin. Example: The forelimbs of vertebrates such as bats (wings for flying), whales (flippers for swimming), and humans (arms for manipulating objects) illustrate divergent evolution. Evidence: Homologous structures, which are anatomical features inherited from a common ancestor but adapted for different functions, support divergent evolution.

Answer 65

Common Ancestor: Populations share a common ancestor but are exposed to different environmental pressures or geographic barriers. Isolation: Geographic (allopatric) or reproductive (sympatric) isolation prevents gene flow between populations. Variation: Genetic variation exists within populations due to mutations, independent assortment, and recombination during meiosis. Natural Selection: Different environmental pressures select for advantageous traits in each population, causing them to adapt to their respective environments. Accumulation of Differences: Over time, genetic differences accumulate due to natural selection and genetic drift. Speciation: The populations become so different that they can no longer interbreed, resulting in the formation of new species.

Answer 66

Common ancestry: Homologous structures arise from a common ancestor, indicating shared evolutionary origins. Divergent evolution: Over time, species that share a common ancestor may adapt to different environments, leading to variations in the structure, but the underlying bone structure remains similar. Inherited genetic information: The genetic code passed down from the common ancestor influences the development of homologous structures in offspring. Genetic mutations: Mutations in the genes that code for structural traits can lead to variations, though the basic structural elements remain the same across different species. Natural selection: Natural selection acts on these variations, shaping the function of the structures while preserving their homologous nature.

Answer 67

Convergent evolution occurs when different species that are not closely related independently evolve similar traits or features. This happens because they face similar environmental pressures or ecological niches. It results in analogous structures, which have similar functions but do not share a common ancestor. Examples include the wings of bats, birds, and insects, which all evolved for flight but come from different evolutionary lineages.

Answer 68

Different species, often from different evolutionary lineages, evolve similar traits or characteristics. This happens because they adapt to similar environmental pressures or ecological niches. The traits that evolve are not inherited from a common ancestor, but are the result of natural selection acting on each species independently. Examples include the wings of birds and bats or the streamlined body shape of dolphins and sharks. These traits arise due to the species facing similar challenges, like flying or swimming efficiently, leading to similar solutions despite different evolutionary origins.

Answer 69

Definition: Analogous structures are body parts that have a similar function but are not derived from a common ancestral structure. Convergent evolution: They arise through convergent evolution, where unrelated species independently evolve similar traits due to similar environmental pressures or ecological niches. Selection pressures: Species in similar environments may face similar selection pressures, such as the need to fly, swim, or climb, leading to the development of similar adaptations. No common ancestry: Unlike homologous structures, analogous structures do not share a common evolutionary origin. The similar features are the result of natural selection favoring similar solutions to environmental challenges. Examples: Wings of birds and insects, fins of dolphins and fish.

Answer 70

Mutualism: Species work together to benefit each other (e.g., pollination), causing adaptations that strengthen their relationship. Predation: Prey species evolve defenses (e.g., camouflage, toxins), while predators evolve better hunting strategies (e.g., speed, sensory adaptations). Competition: Competing species may evolve traits that allow them to better exploit resources, leading to adaptations like improved foraging behavior or territorial defense. Parasitism: Hosts may evolve stronger immune defenses, while parasites evolve mechanisms to bypass these defenses. Reciprocal adaptations: Species adapt in response to each other’s changes, driving evolutionary changes in both organisms over time.

Answer 71

* Gradualism: Proposes that evolution occurs slowly and steadily over long periods of time. Genetic changes accumulate gradually within populations. Fossil records show smooth, continuous changes. Often associated with Darwin’s theory of evolution by natural selection. * Punctuated Equilibrium: Suggests that species remain relatively unchanged for long periods (stasis). Evolution occurs in rapid bursts or sudden events, often in response to environmental changes. Fossil records show long periods of stability interrupted by brief periods of rapid change. Developed by paleontologists Niles Eldredge and Stephen Jay Gould.

Answer 72

Adaptive radiation refers to the process where a single ancestral species rapidly diversifies into a wide variety of forms to adapt to different environmental niches. This typically occurs when a species enters a new habitat or after a mass extinction event, with each new species evolving distinct traits that help them survive and thrive in different conditions. It is driven by natural selection and leads to high biodiversity in a relatively short period. Examples include the evolution of Darwin's finches on the Galápagos Islands, where different species evolved from a common ancestor to fill different ecological roles.

Answer 73

Geographic Isolation: Populations become physically separated by barriers (e.g., mountains, rivers, or oceans), preventing gene flow between them. Environmental Changes: New environments with different conditions (e.g., food sources, climate) create opportunities for organisms to adapt to new niches. Genetic Mutations: Random mutations in isolated populations can lead to genetic differences, which may provide advantages in the new environment. Natural Selection: Organisms with traits that are better suited to the new environment survive and reproduce more successfully, passing on those traits to future generations. Reduced Competition: With fewer species competing for resources in a new environment, organisms can diversify to exploit various ecological niches. Founder Effect: A small group of individuals from a population colonizes a new area, carrying only a subset of the original genetic variation, which may lead to rapid divergence in the new environment.