Topic 7 Flashcards
What is the genotype of an organism?
the genotype is the genetic constitution of an organism
meaning the specific set of alleles that it possesses.
For example, in humans, the genotype for blood type might be AA, AO, BB, BO, AB, or OO.
What is the phenotype of an organism?
the phenotype is the observable characteristics or traits of an organism,
which result from the expression of its genotype and interaction with the environment.
For example, height can be influenced by both genetic factors and environmental factors like nutrition.
True or False
A gene can have multiple alleles
True
A single gene can have multiple alleles.
For example, the gene controlling blood type in humans has three common alleles: I^A, I^B, and i.
What are dominant, recessive, and codominant alleles?
Dominant alleles are expressed in the phenotype even if only one copy is present (e.g., B for brown eyes).
Recessive alleles are only expressed when two copies are present (e.g., b for blue eyes).
Codominant alleles are both expressed in the phenotype when present together (e.g., I^A and I^B in AB blood type).
What does it mean for an organism to be homozygous or heterozygous at a specific locus?
Homozygous organisms have two identical alleles at a specific locus (e.g., BB or bb).
Heterozygous organisms have two different alleles at a specific locus (e.g., Bb).
How do you use genetic diagrams to predict outcomes in monohybrid crosses?
In monohybrid crosses, you track the inheritance of a single characteristic (e.g., flower color).
A Punnett square is often used to show the possible genotypes of offspring from two parents,
based on the dominant and recessive alleles they carry.
What is a dihybrid cross?
A dihybrid cross tracks the inheritance of two different characteristics (e.g., seed shape and color in peas).
It involves using a Punnett square to predict the combinations of alleles for both traits and their phenotypic ratios in the offspring.
what is codominance?
in codominance, both alleles are expressed equally in the phenotype.
For example, in cattle, if the red allele (R) and white allele (W) are codominant,
the heterozygous RW genotype would result in roan cattle (a mix of red and white hair).
What are sex-linked traits and how do they affect genetic crosses?
Sex-linked traits are associated with genes located on sex chromosomes (X or Y).
In humans, traits like red-green color blindness are X-linked.
Males (XY) are more likely to express X-linked recessive traits because they only have one X chromosome.
What is autosomal linkage and how does it affect inheritance patterns?
Sex-linked traits are associated with genes located on sex chromosomes (X or Y).
In humans, traits like red-green color blindness are X-linked.
Males (XY) are more likely to express X-linked recessive traits because they only have one X chromosome.
What is autosomal linkage and how does it affect inheritance patterns?
Autosomal linkage refers to genes located on the same chromosome (not sex chromosomes) that tend to be inherited together.
This reduces the variety of offspring genotypes compared to unlinked genes,
because linked genes do not assort independently.
what is epistasis?
Epistasis occurs when one gene masks or suppresses the expression of another gene.
For example, in mice, one gene determines if pigment will be produced, while another gene controls the pigment’s color.
If the first gene blocks pigment production, the mouse will be albino, regardless of the second gene’s alleles.
What is the purpose of the chi-squared test in genetic studies?
The chi-squared (X²) test is used to compare observed phenotypic ratios from a genetic cross with expected ratios.
This helps determine if any deviations from expected results are due to chance or other factors, like linkage or epistasis.
How do species exist in nature?
Species exist as one or more populations.
Each population consists of organisms of the same species living in a particular space and time, with the potential to interbreed.
For example, different populations of a bird species may be found in various regions, yet all belong to the same species.
Define a population in biological terms.
A population is a group of organisms of the same species occupying a particular space at a particular time, capable of interbreeding.
For example, a population of fish in a specific lake or a group of deer in a forest.
What is a gene pool?
A gene pool refers to the total collection of different alleles present in a population’s genetic makeup.
The gene pool contains all the possible alleles for every gene within the population.
What is allele frequency?
Allele frequency is the proportion of a specific allele within the gene pool of a population.
For example, if a population has two alleles (A and a) for a gene, and 70% of the alleles are A, the allele frequency of A is 0.7.
What does the Hardy-Weinberg principle state?
The Hardy-Weinberg principle is a mathematical model
that predicts allele frequencies in a population will remain constant from generation to generation,
assuming certain conditions are met, such as
no mutation, random mating, no gene flow, infinite population size, and no selection.
What conditions must be met for the Hardy-Weinberg principle to apply?
The conditions include:
- No mutations (allele frequencies are not altered by mutations).
- Random mating (individuals pair by chance, not by phenotype or genotype).
- No gene flow (no migration of individuals in or out of the population).
- Large population size (to minimize random changes in allele frequencies).
5.No natural selection (all genotypes must have equal reproductive success).
How do you calculate allele, genotype, and phenotype frequencies using the Hardy-Weinberg equation?
the Hardy-Weinberg equation is
p² + 2pq + q² = 1. Here:
p² represents the frequency of the homozygous dominant genotype.
2pq represents the frequency of the heterozygous genotype.
q² represents the frequency of the homozygous recessive genotype.
p is the frequency of the dominant allele, and q is the frequency of the recessive allele.
For example, if p = 0.7 and q = 0.3, then p² = 0.49, 2pq = 0.42, and q² = 0.09.
Why do individuals within a population of a species show a wide range of variation in phenotype?
Variation in phenotype is due to both genetic and environmental factors.
The primary source of genetic variation is mutation,
while meiosis and random fertilisation during sexual reproduction add further genetic variation.
Environmental factors such as diet, climate, and exposure to different conditions also influence phenotype.
How does meiosis contribute to genetic variation?
Meiosis introduces genetic variation through processes such as
crossing over (exchange of genetic material between homologous chromosomes) and independent assortment (random separation of chromosomes),
which produce unique combinations of alleles in gametes.
What role does random fertilisation play in genetic variation?
Random fertilisation combines the unique gametes from two parents,
resulting in offspring with a genetic makeup different from both parents.
This randomness further increases the genetic diversity within a population.
How does natural selection work?
Natural selection occurs when predation, disease, and competition for survival resources result in differential survival and reproduction.
Organisms with phenotypes that provide selective advantages (e.g., better camouflage or resistance to disease)
are more likely to survive, reproduce, and pass on favourable alleles to the next generation.
