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Biology mod 6 Genetics, evolution and ecosystems > 6.1.2 Patterns of inheritance > Flashcards

6.1.2 Patterns of inheritance Flashcards

1
Q

Define genotype.

A

The alleles of a gene possessed by an individual.

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2
Q

Define phenotype

A

The observable characteristics of an organism which is influenced by its genotype.

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3
Q

Define gene

A

A length of DNA that codes for a single polypeptide or protein.

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4
Q

Define locus

A

The position of a gene on a chromosome.

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5
Q

What is co-dominance?

A

Where two alleles of the same gene are expressed in the phenotype at the same time.

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6
Q

Define allele

A

Form of a gene

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7
Q

Define dominant

A

An allele that when present will always express itself in the phenotype.

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8
Q

Define recessive

A

An allele that will only express itself when no dominant allele is present.

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9
Q

Define homozygous

A

The alleles of a gene are both the same.

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10
Q

Define heterozygous

A

The two alleles of a gene are different.

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11
Q

How do we express co-dominance?

A

The gene is symbolised as a capital letter and the alleles are represented by superscript letters.

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12
Q

Give a human example of co-dominance.

A

Blood groups.

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13
Q

What are the two types of linkage?

A

Sex-linkage
Autosomal linkage

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14
Q

Which sex chromosomes do women have?

A

XX

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15
Q

Which sex chromosomes do men have?

A

XY

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16
Q

What is sex linkage?

A

Some genes are found on a region of a sex chromosome (e.g X) that are not present on the other sex chromosomes (e.g Y).
As the inheritance of these genes is dependent on the sex of the individual, they are called sex-linked genes.

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17
Q

Which chromosome are sex linked genes usually on?

A

The X chromosome.

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18
Q

Why are males more likely to show sex-linked recessive conditions?

A

Sex-linked traits in humans appear more often in males than in females due to the presence of only one X chromosome in males. Females have two X chromosomes which means if one copy of the gene is mutated, there is a chance that the other copy will be normal thus ensuring a normal phenotype.

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19
Q

Why can only females be disease carriers?

A

Females have two X chromosomes so the presence of one affected X chromosome can be masked by another healthy one. Males only have one X chromosome so they would show the disease in their phenotype.

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20
Q

What is a carrier?

A

A person who has inherited a disease recessive allele however does not show the disease themselves. Their offspring have a 50% chance of acquiring the disease.

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21
Q

What is autosomal linkage?

A

When two or more genes on the same chromosome (non-sex chromosome) do not assort independently during meiosis and so stay together.

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22
Q

If an individual had the genotype FFGG how would it be written if there was autosomal linkage?

A

(FG)(FG).

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23
Q

What ratio would we expect in a usual F2 Dihybrid cross?

A

9:3:3:1

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24
Q

What is epistasis?

A

When the presence of one gene inhibits the expression in the phenotype of another gene.

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25
Q

During sexual reproduction, genetic variation is caused by what three processes?

A
  • Crossing over during prophase I
    -Independent assortment during metaphase I
    -Random fusion of gametes during fertilisation.
26
Q

What is crossing over?

A

When non-sister chromatids exchange alleles during meiosis I at the chiasma. The crossing over places stress on the DNA molecules and as a result this section of a chromatid may break and region with the chromatid from the other chromosome.
The swapping of alleles is significant as it can result in a new combination of alleles on the two choromses.

27
Q

What else other than process involved in sexual reproduction (meiosis) can cause variation between two individuals?

A

Mutations.

28
Q

What is independent assortment?

A

The production of different combinations of alleles in daughter cells due to the random alignment of homologous pairs along the equator of the spindle during metaphase I. The different combinations of chromosomes pair up and are pulled towards the equator of the spindle. Each pair can be arranged with either chrome on top. The chromosomes are then separated and pulled to different poles.

29
Q

What is the random fusion of gametes?

A

During fertilisation, any male gamete can fuse with any female gamete to form a zygote. This random fusion of gametes at fertilisation creates genetic variation between zygotes as each will have a unique combination of alleles.

30
Q

Phenotypic variation can either be _____ or ______.

A

Genetic
Environmental

31
Q

Variation in phenotypes based on ___ factors cannot be inherited by the organisms offspring.

A

Environmental.

32
Q

What are selection pressures?

A

Environmental factors which affect the chance of survival of an organism.

33
Q

What are the two types of selection?

A

Stabilizing
Directional

34
Q

What is stabilising selection?

A

Natural selection keeps allele frequencies relatively constant over generations.
This means things stay as they are unless their is a major chance in the environment. Individuals with alleles towards the middle of the range are more likely to survive.

35
Q

What is directional selection?

A

Natural selection that produces a gradual change in allele frequencies over several generations.

36
Q

When would directional selection occur?

A

When there has been a change in environment or a new allele has appeared advantageous.

37
Q

What is genetic drift?

A

When chance affects which individuals in a population survive, breed and pass on their alleles. For example, when a population is significantly small, chance can affect which alleles get passed on to the next generation. Overtime, some alleles will be lost or favoured purely by chance. This is less likely to have an affect on large populations as chance variations would even out due to natural selection.

38
Q

What is a genetic bottleneck?

A

Occurs when a previously large population suffers a dramatic fall in numbers. E.g a major environmental effect. The surviving individuals end up breeding and reproducing with close relatives which reduces genetic diversity.

39
Q

What is the founder effect?

A

When a small number of individuals in a large parent population start a new population with only s few alleles in the initial gene pool. Which alleles end up in the founding population is due to chance and so as a result, the changes in allele frequencies may occur in a different direction than the larger parent population

40
Q

What is interspecific variation?

A

Variation between species.

41
Q

What is intraspecific variation?

A

Variation within species

42
Q

What is discontinuous variation?

A

Qualitative differences in the phenotypes of individuals within a population.

43
Q

Give an example of discontinuous variation.

A

Blood groups

44
Q

Give some features of discontinuous variation.

A

-Distinct classes or categories.
-characteristics cannot be measured over a range.
-individuals cannot have features that fall between categories.

45
Q

Does discontinuous variation occur due to genetic, environmental factors or both?

A

Just genetic.

46
Q

Does continuous variation occur due to genetic, environmental factors or both?

A

Both genetic and environmental.

47
Q

Features of continous variation.

A

-No distinct classes or categories exist.
-Characteristics can be measured and fall within a range between two extremes.

48
Q

When does continuous variation occur?

A

When there are quantitative differences in the phenotypes of individuals in a population.

49
Q

What does the hardy weinberg principle state?

A

If certain conditions are met then the allele frequencies of a gene within a population will not change from one generation to the next.

50
Q

What conditions are needed for the hardy weinberg principle?

A

-Mating is random
-Large population
-No immigration or emigration
-No mutations
-No natural selection.

51
Q

Give the two hardy weinberg equations.

A

p^2 + q^2 + 2pq = 1
p + q = 1

52
Q

What is artificial selection?

A

The process by which humans choose organisms with desirable traits and selectively breed them together to enhance the expression of these traits over many generations.

53
Q

Explain the process of artificial selection via selective breeding.

A
  1. The population shows phenotypic variation - there are individuals with different phenotypes (i.e. different characteristics)
  2. A breeder (the person carrying out the artificial selection) selects an individual with the desired phenotype
  3. Another individual with the desired phenotype is selected. The two selected individuals should not be closely related to each other
  4. The two selected individuals are bred together
  5. The offspring produced reach maturity and are then tested for the desirable trait. Those that display the desired phenotype to the greatest degree are selected for further breeding
  6. The process continues for many generations: the best individuals from the offspring are chosen for breeding until all offspring display the desirable trait
54
Q

Give a commonly used example today of selective breeding.

A

Domestic dog breeding.

55
Q

Give some ethical considerations surrounding artificial selection/selective breeding.

A

Selective breeding can lead to ‘inbreeding’ which occurs when the ‘best’ animals or plants which are closely related to each other are bred together. This results in reduction in the gene pool (inbreeding depression). This means that there is a higher chance of an organism inheriting harmful genetic defects and organisms being vulnerable to new diseases.

56
Q

What are the two types of speciation?

A

Sympatric
Allopatric

57
Q

When does allopatric speciation occur?

A

when there is geographic isolation e.g a barrier separating the species such as a body of water or a motor way.

58
Q

Explain allopatric speciation.

A

The barrier separating the species creates two populations of the same species who are reproductively separated from each other so as a result no genetic exchange occurs. If there are sufficient selection pressures acting to change both of the gene pools then the populations will diverge and become separate species.

59
Q

Outline sympatric speciation.

A

Takes place with no geographical barrier. A group of organisms could be living in the same place but there must be two populations within the wider group and no gene flow occuring between them. Something must happen to split or separate the populations.

60
Q

Give some examples as to why sympatric speciation may occur.

A

populations are separated because they live in different environments within the same area.
E.g soil pH has a major effect on plant growth so a population growing in soil with a specific pH may flower at a different time to another population so there is genetic isolation of the two populations.

Populations are seperated because they have different behaviours. E.g differences in feeding.

61
Q

What is genetic isolation?

A

When two populations of the same species become reproductively isolated from each other.

62
Q

What is speciation?

A

The formation of new species from pre-existing species over time as a result of changes in gene pools.

Biology mod 6 Genetics, evolution and ecosystems (6 decks)

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