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Biology > Inheritance, Variation and Evolution > Flashcards

Inheritance, Variation and Evolution Flashcards

1
Q

5 features of sexual reproduction

A
  • involves 2 parents
  • fusion of male and female gametes (in plants this is the pollen+egg)
  • gametes are formed by meiosis
  • this increases genetic variation
  • offspring inherit genetic information from both parents
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2
Q

5 features of asexual reproduction

A
  • involves 1 parent
  • cells divide by mitosis (clones)
  • no fusion of gametes
  • this decreases genetic variation of a population
  • genetically identical offspring
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3
Q

process of meiosis

A
  1. cell with 46 (23pairs, 2 sets) chromosones copies genetic information to make 96 chromosones (46pairs, 4 sets)
  2. the cell divides into 2, theres 2 sets of chromosones in each cell
  3. the chromosones then do not duplicate the chromosonesand split again
  4. producing 4 gametes each with 1 set of chromosones (23 chromosones)
  5. all four are genetically different and contain different mixtures of chromosones (this causes variation)
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4
Q

4 differences between mitosis and meiosis

A
  • mitosis requires 1 devision to get a daughter cell whereas meiosis requires 2 divisions
  • mitosis produces daughter cells with 46 chromosones (2 sets) whereas meiosis produces daughter cells with 23 (1 set)
  • mitosis produces 2 daughter cells whereas meiosis produces 4
  • mitosis daughter cells are clones whereas meiosis daughter cells aren’t genetically identical
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5
Q

when does mitosis occur? (3)

A
  • growth
  • repair
  • asexual reproduction
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6
Q

when does meiosis occur?

A

in the formation of gametes (sex cells)

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7
Q

what happens at fertilisation?

A
  1. ovaries releases an egg (ovum) with 23 chromosones
  2. testes releases sperm where each cell has 23 chromosones
  3. the nucleuses of the gametes are fused (the egg is fertilised by the sperm) to produce a zygote with 46 chromosones in 23 pairs
  4. (this mature into an embryo and then the number of cells increase by mitosis, and as the embryo develops, and the cells begin to differentiate (or specialise) )
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8
Q

4 advantages of sexual reproduction

A
  • Produces variation in the offspring
  • The species can adapt to new environments due to variation, which gives them a survival advantage
  • A disease is less likely to affect all the individuals in a population
  • Humans can speed up natural selection through selective breeding, which can increase food production
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9
Q

4 advantages of asexual reproduction

A
  • the population can increase rapidly when the conditions are favourable
  • only one parent is needed
  • it is more time and energy efficient as you don’t need a mate
  • it is faster than sexual reproduction
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10
Q

2 disadvantages of sexual reproduction

A
  • time and energy are needed to find a mate
  • it is not possible for an isolated individual
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11
Q

3 disadvantages of asexual reproduction

A
  • it does not lead to variation in a population
  • the species may only be suited to one habitat
  • disease may affect all the individuals in a population
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12
Q

examples of 3-4 organisms that reproduce both sexually and asexually?

A
  • fungi
  • malarial parasites
  • some plants- strawberry plants and daffodils
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13
Q

how do fungi reproduce both sexually and asexually?

A
  • Fungi reproduce sexually to generate variation
  • Fungi release spores by asexual reproduction
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14
Q

how do malarial parasites reproduce both sexually and asexually?

A
  • Malarial parasites reproduce sexually in the host mosquito
  • Malarial parasites reproduce asexually in the human host
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15
Q

how do some plants reproduce both sexually and asexually?

A
  • Plants use sexual reproduction to produce seeds
  • Plants such as strawberries reproduce asexually by sending out runners, or daffodils when their bulbs divide
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16
Q

what is a genome?

A

the entire genetic material of that organism

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17
Q

why has the studying of the human genome been important? -3 reasons

A
  • search for genes linked to different types of disease
  • understand inherited disorders and their treatment
  • trace human migration patterns from the past
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18
Q

describe the structure of DNA

A
  • DNA is a polymer made from four different nucleotides.
  • These are arranged in a repeating fashion.
  • Each nucleotide consists of a phosphate joint to a deoxyribose sugar joiny to one of the four different bases.
  • this nucleotides base then connects to a base of another nucleotide that fits
  • (one deoxyrybose sugar in a pair of nucleotides is attached to the phosphate of the next row/ pair of nucleotides and one phosphate of a pair is connected to the sugar of the next row)
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19
Q

what are the 4 different bases in DNA?

A
  • thymine, T
  • adenine, A
  • guanine, G
  • cytosine, C
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20
Q

what are the 4 possible combinations of bases?

A
  • A-T
  • C-G
  • G-C
  • T-A
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21
Q

explain the relationship between DNA bases, amino acids and proteins

A
  • A sequence of three bases is the code for a particular amino acid, (known as a triplet or the triplet code)
  • The order of the bases controls the order in which amino acids are assembled to produce a particular protein
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22
Q

describe protein synthesis

A
  1. template mRNA is made from the different order of bases in the DNA
  2. the template leaves the nucleus and bins to a ribosome in the cytoplasm
  3. carrier molecules (transfer RNSA or tRNA) attach amino acids to the template (mRNA) in order
  4. the amino acids are joined together in their specific order to make a specific protein molecule
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23
Q

how is protein folding important for it’s function?

A
  • The sequence of amino acids in the chain determines how the chain will fold up to make the protein, so different proteins have different three-dimensional shapes.
  • The three-dimensional shape of a protein determines its function.
  • This is because proteins form attachments and interact with many other molecules and structures inside organisms.
  • The shape of a protein determines what it can interact with, just like the shape of a key determines which locks it can operate.
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24
Q

what is mutation?

A

a change in a gene or chromosome or number of chromosones. It is a rare, random change in the genetic material and it can be inherited.

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25
Q

what can mutations lead to?

A
  • could cause different genes to be switched on or off, and this could create a different or faulty protein to be synthesised.
  • may change the activity of a protein, in a coding part of the DNA, or it might change how the genes are expressed if the change is in a non-coding section of DNA
  • These might result in phenotype changes or they might appear hidden, and be unnoticed.
  • Alternatively, they might result in a serious consequence, such as genetic disease such as cystic fibrosis.
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26
Q

what do non-coding parts of the DNA do?

A

they can switch genes on and off, so variations in these areas may affect gene expression, and if the correct protein is synthesised or not

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27
Q

how are characteristics controlled by one or more genes?

A
  • each gene has 2 copies called alleles
  • a capital letter shows a dominant allele which is always seen
  • a lower case letter shows a recessive allele and we need 2 copies (alleles) of it in a pair to be seen
  • for example, dominant= G for brown hair whereas recessive= g for ginger hair
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28
Q

define dominant alle

A

An allele that always expresses itself whether it is partnered by a recessive allele or by another like itself.

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29
Q

define recessive allele

A

Describes the variant of a gene for a particular characteristic which is masked or suppressed in the presence of the dominant variant. A recessive gene will remain dormant unless it is paired with another recessive gene.

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30
Q

define homozygous

A

This describes a genotype in which the two alleles for the characteristic are identical. (both recessive or both dominant)

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31
Q

define heterozygous

A

This describes a genotype in which the two alleles for a particular characteristic are different. (one recessive one dominant)

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32
Q

what is DNA?

A

A large and complex polymer, which is made up of two strands forming a double helix. DNA determines the characteristics of a living organism. With the exception of identical twins, each person’s DNA is unique.

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33
Q

define chromosones

A

The structure made of DNA that codes for all the characteristics of an organism. They are contained inside the cell’s
nucleus and are long threads of DNA, which are made up of many genes.

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34
Q

define gene

A

a small section of DNA on a chromosome, that code for a particular sequence of amino acids, to make a specific protein. It is the unit of heredity, and may be copied and passed on to the next generation.

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35
Q

define genotype

A

the combination of alleles an organism has in their DNA

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36
Q

define phenotype

A

how the genes/ genotype are expressed (characteristics). these can be influenced by the environment

37
Q

6 things to remember when drawing genetic crosses

A
  • with X and Y chromosones, neither is dominant or recessive
  • there’s a 50% chance of XX (female) being produced
  • there’s a 50% chance of XY (male) being produced
    *the 23rd pair of chromosones determines sex
  • mother has XX
  • father has XY
38
Q

2 examples of inherited disorders

A

cystic fibrosis and polydactyly

39
Q

2 social issues of genetic testing/ embryo screening

A
  • false positive- the individual could believe that they have inherited a genetic condition, when they have not
  • false negative- failed to detect a certain or faulty chromosome. these incorrect results can have an impact on the lives of individuals, such as planning the level of care needed for children with inherited disorders
40
Q

economic issue of genetic testing/ embryo screening

A
  • gene therapy is not always successful
41
Q

ethical issue of genetic testing/ embryo screening

A
  • gene therapy- some people disagree with gene alteration in people, as they believe it is unnatural
42
Q

how is sex determined?

A
  • Twenty two pairs are known as autosomes, and control characteristics, but the 23rd pair carries genes that determine sex - whether offspring are male or female:
  • males have two different sex chromosomes, X Y
  • females have two X chromosomes, XX
43
Q

what is variation?

A

Difference between individuals which can be genetic or environmental

44
Q

what causes variation?

A

a random mutation in an organism’s gene

45
Q

what is a mutation?

A

A random and spontaneous change in the structure of a gene, chromosome or number of chromosomes.

46
Q

what does mutation lead to?

A
  • can lead to variation within genes leads to different genotypes, and this can be seen by a different phenotype
  • but usually variants have no effect on the phenotype
47
Q

what is natural selection?

A

process where organisms that are better adapted to an environment will survive and have more offspring. This means their genes are passed on to the future generations. This process is fundamental to the process of
evolution and may result in the formation of a new species

48
Q

how is a new species formed?

A
  1. two populations are seperated by something geographical that acts as a barrier e.g. sea, river, mountain range
  2. in both populations, genetic mutations continue to occur- causing variation
  3. because the environments are different, different mutations are advantages in each population. survival of the fittest occurs- those with advantages survive and pass on their gene
  4. the two populations get so different they can’t reproduce with eachother and create fertile offspring- they become different species.
49
Q

define selective breeding

A

An artificial process in which organisms with desired characteristics are chosen as parents for the next generation.

50
Q

explain the process of selective breeding

A
  • Decide which characteristics are important enough to select.
  • Choose parents that show these characteristics from a mixed population.
  • They are bred together.
  • Choose the best offspring with the desired characteristics to produce the next generation.
  • Repeat the process continuously over many generations, until all offspring show the desired characteristics.
51
Q

3 desired characteristics in plants

A
  • disease resistance in food crops
  • wheat plants that produce lots of grain
  • large or unusual flowers
52
Q

3 desired characteristics in animals

A
  • animals that produce lots of milk or meat
  • chickens that lay large eggs
  • domestic dogs that have a gentle nature
53
Q

2 benefits of selective breeding

A
  • new varieties may be economically important, by producing more or better quality food
  • animals can be selected that cannot cause harm, for example cattle without horns
54
Q

3 risks of selective breeding

A
  • reduced genetic variation can lead to attack by specific insects or disease, which could be extremely destructive
  • rare disease genes can be unknowingly selected as part of a positive trait, leading to problems with specific organisms, eg a high percentage of Dalmatian dogs are deaf
  • can create physical problems in specific organisms, eg large dogs can have faulty hips due to not being formed correctly
55
Q

what is genetic engineering?

A

modifying the genome of an organism by introducing a gene from another organism to result in a desired characteristic

56
Q

how is genetic engineering carried out?

A
  1. selection of the desired characteristic
  2. the gene responsible for the characteristic is ‘cut out’ of the
    chromosome
  3. the gene is transferred and inserted into another organism
  4. replication of the modified organism.
57
Q

give an example of genetic engineering

A

Plant crops have been genetically engineered to be disease resistant or to produce bigger fruits.

58
Q

5 benefits of genetic engineering

A
  • Genetic modification is a faster and more efficient way of getting the same results as selective breeding.
  • Improve crop yields or crop quality, which is important in developing countries. This may help reduce hunger around the world.
  • Introduce herbicide resistance, which results in less herbicides being used, as weeds are quickly and selectively killed.
  • Insect and pest resistance can be developed and inserted into the plants. The plant produces toxins, which would discourage insects from eating the crop.
  • Sterile insects could be created such as a mosquito. They would breed, which would lead to infertile offspring. This may help with spread of diseases, such as malaria, dengue fever and the Zika virus.
59
Q

5 risks of genetic engineering

A
  • Transfer of the selected gene into other species. What benefits one plant may harm another.
  • Some people believe it is not ethical to interfere with nature in this way. Also, GM crop seeds are often more expensive and so people in developing countries cannot afford them.
  • GM crops could be harmful, for example toxins from the crops have been detected in some people’s blood.
  • GM crops could cause allergic reactions in people.
  • Pollen produced by the plants could be toxic and harm insects that transfer it between plants.
60
Q

explain the process of genetic engineering inc. enzymes and vectors

A
  • Enzymes are used to isolate the required gene, this gene is inserted into a vector, which is usually a bacterial plasmid or a virus.
  • The vector inserts the gene into required cells.
  • The genes are transferred to animal, plant or microorganism cells, during early development. This allows them to develop with the desired characteristics.
61
Q

plant cloning

describe the process of tissue culture

A
  1. tissue is removed from the tip of the parent plant
  2. tissue is placed on a medium containing growth hormones (e.g. agar)
  3. hundreds of clones can be made
62
Q

plant cloning

describe the process of taking cuttings

A
  1. cuttings are taken from a parent plant, each with a new bud on
  2. the cuttings are kept in moist conditions until they are ready to plant
  3. cloned plant is produced (genetically identical)
63
Q

state 2 methods of plant cloning

A

taking cuttings and tissue culture

64
Q

state 2 methods of animal cloning

A

embryo transplants and adult cell cloning

65
Q

3 advantages of taking cuttings

A
  • produced quickly
  • produced cheaply
  • simpler, older method
66
Q

4 advantages of tissue culture

A
  • quick
  • very little space needed
  • can be grown all year
  • preserves rare plants that are hard to reproduce naturally
67
Q

describe the process of adult cell cloning

A
  1. The nucleus is removed from an unfertilised egg cell.
  2. The nucleus from an adult body cell, such as a skin cell, is inserted into the egg cell.
  3. An electric shock stimulates the egg cell to divide to form an embryo.
  4. These embryo cells contain the same genetic information as the adult skin cell.
  5. When the embryo has developed into a ball of cells, it is inserted into the womb of an adult female to continue its development.
68
Q

describe the process of embryo transplants

A

hundreds of ideal offspring can be produced every year from the best bull and cow
1. sperm is taken from a bull from a high yield dairy herd
2. cow is artificially inseminated with sperm
3. zygotes develop into embryos in the cow and are then removed from the uterus
4. embryos are split into several smaller embryos each of which can grow into a new calf
5. embryos are placed in the uteruses of foster mothers

69
Q

what 3 things did darwin propose about his theory of natural selection?

A
  • individual organisms within a particular species show a wide range of variation for a characteristic
  • individuals with characteristics most suited to the environment are more likely to survive to breed successfully
  • the characteristics that have enabled these individuals to survive are then passed on to the next generation
70
Q

3 reasons why darwins theory was only gradually accepted

A
  • the theory challenged the idea that God made all animals and plants that live on Earth (creationism)
  • there was insufficient evidence when the theory was published to convince many scientists
  • the mechanism of inheritance and variation was not known until 50 years after the theory was published
71
Q

describe the work of Alfred Wallace

A
  • speciation- The formation of new and distinct species in the course of evolution.
  • After a variety of zoological discoveries Wallace proposed a theory of evolution, which matched Darwin’s unpublished ideas that he had kept secret for nearly 20 years. This encouraged Darwin to collect his scientific ideas and collaborate with Wallace. They published their scientific ideas jointly.
72
Q

describe the work of Lamarck and the problems with his theory

A
  • came before darwin
  • believed a characteristic which is used more and more by an organism becomes bigger and stronger, and one that is not used eventually disappears
  • and any feature of an organism that is improved through use is passed to its offspring
  • his theory implies that all organisms would gradually become complex, and simple organisms disappear.
  • simple organisms are still detected in all varieties of life, plus it is now known that mutations can create variation such as neck length
73
Q

describe the work of mendel

A
  • studied the inheritance of different characteristics in pea plants
  • One of Mendel’s observations was that the inheritance of each characteristic is determined by ‘units’ that are passed on to descendants unchanged.
74
Q

how has our understanding of genetics developed over time?

A
  • early 20th century- it was observed that chromosomes and Mendel’s ‘units’ behaved in similar ways. This led to the theory that the ‘units’, now called genes, were located on chromosomes.
  • mid-20th century- two scientists, James Watson and Francis Crick worked out the structure of DNA. By using data from other scientists Rosalind Franklin and Maurice Wilkins, they were able to build a model of DNA. They showed that bases occurred in pairs, and x-ray data showed that there were two chains wound into a double helix. This model was used to work out how genes code for proteins.
  • Many years of work from different scientists’ focusing on DNA, chromosomes and genes, has led us to the possibility of treating genetic conditions using gene therapy.
75
Q

why are there few traces of early life forms and how does this effect our understanding of how life began?

A
  • Because there are gaps in the fossil record because many early forms of life were soft-bodied, which means that they have left few traces behind. What traces there were may have been destroyed by geological activity.
  • This is why scientists cannot be certain about how life began.
76
Q

4 reasons species can become extinct

A
  • habitat destruction- deforestation, destruction of coral reefs
  • introduced species (predator, competetor or disease)- accidental from hitchhiking, intentional from pets or food crops
  • hunting and fishing- since human population has increased, incl. poaching for ivory and fur etc.
  • climate change- human activity like burning fossil fuels, produces too much CO2 causing greenhouse effect and global warming
77
Q

describe the 3 ways fossils can be formed

A
  • hard body parts, such as bones and shells, which do not decay easily or are replaced by minerals as they decay
  • parts of organisms that have not decayed because one or more of the conditions needed for decay are absent. For example, dead animals and plants can be preserved in
    amber, peat bogs, tar pits, or in ice
  • preserved traces of organisms, such as footprints, burrows and rootlet traces - these become covered by layers of sediment, which eventually become rock
78
Q

what can we learn from fossils?

A
  • supports Darwin’s theory of evolution, which states that simple life forms gradually evolved into more complex ones.
  • Evidence for early forms of life comes from fossils. By studying fossils, scientists can learn how much (or how little) organisms have changed as life developed on Earth.
79
Q

how do antibiotic- resistant strains of bacteria arise and spread?

A
  1. random mutations occur in the genes of individual bacterial cells
  2. some mutations protect the bacterial cell from the effects of the antibiotic
  3. bacteria without the mutation die or cannot reproduce when the antibiotic is present
  4. resistant bacteria can reproduce with less competition from normal bacterial strains
80
Q

give an example of an antibiotic-resistant bacteria

A

MRSA

81
Q

what is antibiotic-resistant bacteria an example/ evidence of?

A

evolution

82
Q

3 ways the emergence of antibiotic-resistant bacteria be reduced and controlled

A
  • doctors should not prescribe antibiotics inappropriately, such as for the treatment of non-serious infections
  • patients should always complete the full course of antibiotics to ensure all bacteria are killed and none survive to mutate and form resistant strains
  • the agricultural use of antibiotics should be restricted
83
Q

how are organisms named and classified in the linnaean system?

A
  • Living organisms are classified into groups depending on their structure and characteristics.
  • The classification of species allows the subdivision of living organisms into smaller and more specialised groups.
84
Q

what are the 7 divisions in the Linnaean system?

A
  • kingdom - animal, plants, fungi, protists prokaryotes
  • phylum - Chordata- have backbones, Arthropod- have jointed legs and an exoskeleton Annelids- segmented worms
  • class - mammals, birds, amphibians, fish, reptiles
  • order - carnivores, primates
  • family - canidae- dogs, felidae- cats
  • genus - felidae divided into things like panthera- lion and tiger
  • species - lion or tiger
85
Q

what acronym can you use to remember the 7 divisions of the Linnaean system?

A

Kids Prefer Candy Over Fresh Green Salad

86
Q

how have scientific advances led to the proposal of new models of classification?

A
  • The development of microscopes allowed cells to be examined in far more detail. Organelles within the individual cells could be distinguished and this allowed a more scientific approach of classification.
  • The development and study of biochemistry and the processes undertaken inside the cells, in some cases, have allowed any ambiguities within this classification system to be clarified.
  • The comparisons of DNA sequences have allowed the relationship of organisms to be explored further. In some cases, species that are more closely related may have fewer differences contained within the DNA sequences.
87
Q

what is the three-domain system and what is it divided into?

A
  • Classification systems have continued to be developed by other scientists, such as Carl Woese who developed the three-domain system. This is based on evidence now available from chemical analysis.
  • The updated system divides organisms into:
    Archaea (primitive bacteria usually living in extreme environments)
    Bacteria (true bacteria)
    Eukaryota (including protists, fungi, plants and animals)
88
Q

describe how evolutionary trees work

A
  • Evolutionary trees are a method used by scientists to represent the relationships between a set of organisms.
  • The tips of the tree often represent different species and where two branches join, this represents a common ancestor for those two species.
  • They can be created from current data such as DNA analysis and existing fossil data.

Biology (17 decks)

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