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Biology A Level > Inheritance And Evolution > Flashcards

Inheritance And Evolution Flashcards

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1
Q

Gene

A

A base sequence of DNA that codes for the amino acid sequence of a polypeptide which results inn a characteristic

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2
Q

Allele

A

One or more alternative versions of the same gene

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3
Q

Genotype

A

The genetic constitutions of an organism - the different alleles it has

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4
Q

Phenotype

A

The expression of the genetic constitution and its interaction with the environment - what characteristics an organism has as a result of its genes and the effects of the environment on them

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5
Q

Gene locus

A

The position on a chromosome where a particular gene is found

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6
Q

Dominant alleles of a gene

A

An allele whose characteristic appears in the phenotype even when there is only one copy

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7
Q

Recessive alleles of a gene

A

An allele whose characteristics only appears in the phenotype if two copies are present

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8
Q

Co dominant alleles of a gene

A

An allele whose characteristics appear together with another allele in the phenotype because neither allele is recessive

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9
Q

Multiple alleles

A

More than two alleles of a gene

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10
Q

Diploid

A

A cell with two of each type of chromosome

Homologous pairs of chromosomes

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11
Q

Haploid

A

A cell with only one of each type of chromosome

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12
Q

Heterozygous genotype

A

Two different alleles at the same gene locus on each of a pair of chromosome

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13
Q

Homozygous genotype

A

Two of the same alleles at the same gene locusts each of a pair of chromosomes

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14
Q

Monohybrid inheritance

A

The inheritance of a single characteristic controlled b one gene with two or more alleles

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15
Q

Dihybrid inheritance

A

The inheritance of two characteristics which are controlled by different genes

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16
Q

Sex linked characteristic

A

Alleles that code for the characteristics are located on the sex chromosome (X OR Y)

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17
Q

Autosomal chromosomes

A

A chromosome that is not a sex chromosome

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18
Q

Autosomal linkage

A

When two genes coding for different characteristics are located on the same chromosome and consequently are inherited together.

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19
Q

Epistasis

A

When the alleles of one gene mask the expression of alleles on another gene.

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20
Q

Dominant epistasis

A

Just one copy of the epistasis allele will block expression of the second gene

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21
Q

Recessive epistasis

A

Two copies of the epistasis allele are required to block expression of the second gene.

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22
Q

Dihybrid crosses with no linkage

A

Inheritance of two different characteristics controlled by two different genes found on two different chromosomes

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23
Q

In meiosis 1 homologous pairs segregate independently this mean that

A

Genes on different chromosomes are inherited independently

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24
Q

Epistasis

3

A

An allele of one epistasis gene masks (blocks)
The expression of a second gene

One characteristic controlled by two genes

Epistasis can be either recessive epistasis or dominant epistasis

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25
Q

Recessive epistasis

A

Only a homozygous recessive genotype on the epistatic gene masks the expression of the second gene.

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26
Q

Dominant epistasis

A

Occurs when the epistatic allele is dominant, the organism can be heteros or homozygous to show the effect

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27
Q

Mutation

A

Random changes in base sequences of genes to give new allele

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28
Q

Meiosis

A

Crossing over and independent segregation of homologous pairs

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29
Q

Homologous pairs form

A

Bivalents at the start of meiosis 1

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30
Q

Crossing over occurs

A

Sections of non sister chromatids are exchanged to give new combinations of alleles in the gametes. Chiasma are the points a which the crossing over occurs

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31
Q

During meiosis 1

A

Homologous pairs are separated

The homologous pairs segregate independently giving many combinations of maternal and paternal alleles in the gametes.

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32
Q

Random fusion of gametes

A

Any gamete from one parent is equally likely to fuse with any gamete from the other parent regardless of the allele combinations they contain.

33
Q

Autosomal genes

A

Yess carries on chromosome 1-22

34
Q

How many genes on X chromosome in humans

A

Roughly 2000

35
Q

Y chromosome

A

Much smaller

Carries only 78 genes

36
Q

In males the X chromosome

A

I inherited from ty mother therefore all males with a recessive sex linked condition must have a mother who is a carrier of the condition (or has the condition)

37
Q

All females receive an X chromosome from

A

Their father- if he has a recessive sex linked condition then the daughter will be a carrier of the condition (or have the condition)

38
Q

Males have only one

A

X chromosome and will have a recessive sex linked condition with just one recessive allele

39
Q

Females have two

A

X chromosomes and will only have a sex linked recessive condition if homozygous for the recessive allele

40
Q

Dihybrid crosses with no linkage

A

Inheritance of two different characteristics controlled by two different genes found on two different chromosomes

41
Q

In meiosis 1 homologous pairs segregate independently

A

This means that genes on different chromosomes are inherited independently

42
Q

Epistasis

3

A

An allele of one epistatic green masks the expression of a second gene

One characteristic controlled by two genes

Can either be recessive epistasis or dominant epistasis

43
Q

Linkage

A

Inheritance of genes located on the same autosomal chromosomes

44
Q

Chi squared test

A

Statistical test used to compare actual and expected results to determine whether the differences are due to chance or are significant

45
Q

Degrees of freedom

A

Number of categories - 1

46
Q

Population

A

A group of organisms of the same species living in a particular place at a particular time, the organisms are free to interbreed with one another

47
Q

Gene pool

A

The complete range of alleles present in a population

48
Q

Allele frequency

A

How often an allele occurs in a population expressed as a percentage

49
Q

Genotype frequency

A

How often a genotype appears in a population expressed as a percentage

50
Q

Hardy-Weinberg model can only be used if allele frequency doesn’t change over time, following conditions must apply
5

A

Large population- less likely for genetic drift
Mating is random
One allele does not confer an advantage so that natural selection will not occur
There are no emigrants or immigrants
No mutations occur

51
Q

Equation for allele frequency

A

P + q = 1

52
Q

Equation for genotype frequency

A

P^2 + 2pq + q^2 = 1

53
Q

P

A

Dominant allele

54
Q

Q

A

Recessive allele

55
Q

P^2

A

Homozygous dominant genotype

56
Q

2pq

A

Heterozygous genotype

57
Q

Q^2

A

Homozygous recessive genotype

58
Q

Calculating actual allele frequency

A

When alleles are co dominant and the heterozygous phenotype is distinguishable from the homozygous phenotype

59
Q

Intraspecific variation

A

Between members of a population and between membres of a species

60
Q

Interspecific variation

A

Between members of different species

61
Q

Causes of phenotypic variation

2

A

Genetic variation between individuals due to different individuals possessing different allele combinations

Environmental differences between individuals

62
Q

Causes of genetic variation

2

A

Gene mutations to create new alleles

Crossing over of non sister chromatids
of homologous pairs in meiosis 1

Independent segregation of homologous chromosomes in meiosis 1

Random fusion of gametes

63
Q

Evolution is

A

The change in allele frequency in a population over he course of many generations

64
Q

Two causes of evolution

A

Natural selection

Genetic drift- in small populations

65
Q

Natural selection

A

Changes allele frequency in populations over the course of many generations

66
Q

Natural selection

7

A
  • individuals subject to selection pressure such as competition, predation, disease
  • phenotypic variation due to genetic variation, different combinations of alleles
  • there is differential reproductive success
  • individuals with advantageous alleles have reproductive success
  • process repeated over many generations
  • frequency of advantageous alleles in gene pool increases
  • population becomes more adapted to its environment
67
Q

Stabilising selection

4

A

Occurs in a stable environment

Individuals with extremes of phenotypes have lower reproductive success

Mean phenotype remains unchanged but more of the population becomes closer to the mean

Standard deviation and range is reduced

68
Q

Directional selection

3

A

Occurs when the environment changes

Individuals with phenotype of one extreme have higher reproductive success

Mean phenotype in the population shifts towards the favoured extreme over many generations

69
Q

Disruptive selection

3

A

Occurs when the environment favours individual of both extreme

Individuals with phenotype of both extreme have increased reproductive success

After many generations it may result in two different breeding populations- speciation

70
Q

Genetic drift

A

The random changes in frequency due to chance rather than natural section

71
Q

Genetic drift process

4

A

Individuals in a population show variation in their phenotype

By chance those with one allele happen to have more offspring so more of the population carry the allele

By chance the process is repeated, those with the allele produce more offspring and the frequency of the allele increases in the population

If enough differences inn allele frequency build up over many generations genetic drift can lead to speciation

72
Q

Genetic drift is. More evident in small populations because

A

Chance differences are less likely to cancel each other out. In a small population,small populations have a bigger effect
Genetic drift increases the genetic diversity of a population

73
Q

Speciation

A

The development of a new species from an existing species

74
Q

A population becomes a new species when

A

It’s members can no longer interbreed with and produce fertile offspring with the original population

75
Q

Two forms of speciation

A

Allopatric and sympatric

76
Q

Allopatric speciation

A

Occurs when two populations become physically separated and there is no interbreeding / gene flow between the populations

77
Q

Allopatric speciation process

6

A

A sub group becomes geographically isolated by physical barrier

Isolated population experiences different environmental conditions an directional selection will occur changing allele frequency

Different random mutations will occur in isolated and original population

Genetic drift will occur changing allele frequency in isolated population

After many generations, individuals from the isolated populations allele frequency wil be so different that they willl no longer be able to interbreed to produce fertile offspring with the original population

So many differences in gene pool that the two populations are reproductively isolated

78
Q

Sympatric speciation

A

When two populations are still occupying the same habitat but a change has occurred to stop them interbreeding with one another

Two populations become reproductively isolated and stop interbreeding

79
Q

Mechanisms of reproductive isolation

Sympatric speciation

3

A

Seasonal changes= due to a mutation some plants may flower at a different time of the year , they can therefore only interbreed with plants flowering at the same time

Mechanical changes= gene mutations which lead to changes in size and functioning of the genitalia making mating between two sub groups physically impossible

Behavioural changes= a sub group may develop. A different courtship ritual that only attracts mates within the sub group

Biology A Level (18 decks)

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