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Green > 6.1.2: Patterns of Inheritance > Flashcards

6.1.2: Patterns of Inheritance Flashcards

1
Q

Give an environmental factor that contributes to phenotypic variation

A

Diet in animals

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2
Q

Give a genetic factor that contributes to phenotypic variation

A

Etiolation in plants

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3
Q

How does sexual reproduction lead to genetic variation within a species (2 reasons) ?

A

During meiosis crossing over and independent assortment occurs. Also, due to fusion of gametes at fertilisation

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4
Q

How are alleles produced for monogenic inheritance ?

A

Sexual reproduction and meiosis

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5
Q

What is codominance?

A

Neither allele is recessive and both are dominant so isn’t switched off and is always expressed

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6
Q

What is dihybrid inheritance ?

A

2 genes on seperate chromosomes

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7
Q

Where are the genes carried on for dihybrid inheritance ?

A

Autosomes

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8
Q

Who observed dihybrid inheritance ?

A

Mendel who crossed F2 generations by self fertilisation

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9
Q

What is a classic mendelion ratio ?

A

9:3:3:1

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10
Q

What will be observed if both parents are heterozygous for both genes in a dihybrid cross? What are the exceptions?

A

9:3:3:1 ratio will be observed UNLESS there is autosomal linkage, epistasis or crossing over in meiosis

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11
Q

What are cases of multiple alleles ?

A

A type of codominance but there are 3 or more alleles in the gene pool. There is a monogenic phenotype (phenotype controlled by 1 gene)

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12
Q

Give an example of multiple alleles

A

Blood group type which uses the ABO system

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13
Q

Give an example of codominance

A

Gene in cattle for coat colour

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14
Q

Give an example of monogenic inheritance

A

Seed colour and shape

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15
Q

When is a gene sex linked ?

A

If it is carried on the x chromosome

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16
Q

What are 1-22 pairs of chromosomes called ?

A

Autosomes

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17
Q

Describe the XX chromosomes

A

Female, chromosomes similar in shape and size

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18
Q

Describe the XY chromosomes

A

Male,Y chromosome is genetically empty so contains no genes

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19
Q

What causes colour blindness ?

A

Recessive allele found on the X chromosome

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20
Q

What is the blood disease haemophilia an example of ?

A

Sex linkage ( a recessive + sex linked allele)

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21
Q

What are the effects of a large gene pool

A

Introduces more heterozygosity

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22
Q

What are the effects of a reduced gene pool with a recessive allele ?

A

Increases homozygosity

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23
Q

What causes normal blood clotting ?

A

A cascade of reactions which produces fibrin

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24
Q

What causes a lack of blood clotting - haemophilia ?

A

Missing factor needed for a cascade of reactions so no fibrin made

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25
Q

Why is haemophilia rare and how is it treated?

A

Small falls can cause early death so less likely to be passed on. Treated with blood transfusions.

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26
Q

How can crossing over be identified ?

A

When a ratio of 9:3:3:1 is expected but a 3:1 ratio is observed.

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27
Q

Describe what happens during crossing over

A

Non sister chromatids of homologous pair overlap, chromatids break and sections of chromatids and alleles are swapped

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28
Q

What hold a chromosome together ?

A

Chiasmata and centromere

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29
Q

What happens if the chiasmata break in a chromosome?

A

They can be repaired wrong creating crossing over due to them being linked in the first place

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30
Q

What is autosomal linkage ?

A

2 genes located on the same chromosome pair so alleles for genes are inherited together

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31
Q

Give an example of autosomal linkage

A

Body colour and wing length of a fly

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32
Q

What is epistasis ?

A

2 separate genes on different chromosomes

1 gene codes for something with a dominant and recessive allele(hypostatic gene)

Other gene can mask the expression of the first gene (epistatic gene)

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33
Q

What is recessive epistasis ?

A

Epistatic gene is homozygous recessive to prevent the expression of the hypostatic gene creating a recessive epistatic effect

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34
Q

What is dominant epistasis ?

A

Epistatic gene requires atleast one dominant allele to prevent the expression of the hypostatic gene creating a dominant epistatic effect

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35
Q

How can phenotypic ratios be observed to indicate epistasis ?

A

Breed parents that are both heterozygous for 2 genes. Offspring phenotypic ratios indicate type of epistasis occurring

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36
Q

What does a 9:3:3:1 phenotypic ratio indicate

A

2 independent genes so no epistasis

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37
Q

What does a 9:3:4 phenotypic ratio indicate ?

A

Recessive epistasis

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38
Q

What does a 12:3:1 phenotypic ratio indicate ?

A

Dominant epistasis

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39
Q

What does a 13:3 phenotypic ratio indicate ?

A

Dominant epistasis

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40
Q

What is the chi squared test used for ?

A

A statistical test to determine the significance of the difference between observed and expected results

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41
Q

What is a null hypothesis ?

A

No significant difference between expected and observed results

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42
Q

What are degrees of freedom ?

A

Number of categories - 1

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43
Q

What do you compare the chi squared value to ?

A

5% or 0.05 column in critical values table

44
Q

What does a chi squared value LESS than critical value indicate ?

A

It is insignificantly different statistically (95% confident)

45
Q

What does a chi squared value LARGER than critical value indicate ?

A

It is significantly different statistically

46
Q

What is continuous variation ?

A

A characteristic with continuous values

47
Q

Give 3 examples of continuous variation measures ?

A
  • Height
  • Mass
  • Hand span
48
Q
A
49
Q

Give 2 ways continuous data can be represented ?

A
  • Histogram
  • Line graph
50
Q

What causes continuous variation ?

A

Genes and the environment (polygenic)

51
Q

How many genes are involved in continuous variation ?

A

Many polygenic genes involved

52
Q

What is discontinuous variation ?

A

A characteristic with categorical or discrete values

53
Q

Give 2 examples of discontinuous variation measures

A
  • Blood group type
  • Attached/ detached earlobe
54
Q

Give 1 way discontinuous variation can be represented

A

Bar chart

55
Q

What causes discontinuous variation ?

A

Genetics

56
Q

How many genes are involved in discontinuous variation ?

A

One or 2 genes involved

57
Q

Define selection and what it shows

A

Shows how traits of organisms show variation within populations

58
Q

Give the 3 types of natural selection

A
  • Stabilising selection
  • Directional selection
  • Disruptive selection
59
Q

When does stabilising selection occur ?

A

When there is no change in environment

60
Q

Explain stabilising selection

A
  • Average/modal trait is positively selected for
  • Extreme traits are negatively selected
  • Results in a reduction in frequency of extreme alleles ( standard deviation) and increase in average alleles
61
Q

Give an example of stabilising selection

A

Babies with average birth rates are more likely to survive and reproduce than under/overweight babies - and can pass on alleles

62
Q

What can disruptive selection ultimately lead to ?

A

Speciation

63
Q

Explain disruptive selection

A
  • Individuals with alleles coding for extreme traits are more likely to survive and pass on alleles
  • Allele frequency shifts
  • Extreme alleles are positively selected for and the average alleles are selected against
64
Q

Give an example of disruptive selection

A

Finches observed by Darwin

65
Q

When does directional selection occur ?

A

When there is a change in environment and the most common phenotype is no longer the most advantageous and the modal trait changes

66
Q

Explain directional selection

A
  • Organisms with more extreme phenotypes are positively selected for
  • Allele frequency shifts towards extreme phenotype as evolution occurs
67
Q

Give an example of directional selection

A

Peppered moths during industrial revolution

68
Q

Describe genetic drift

A

Random changes in allele frequency within a population between generations

69
Q

What does continuous genetic drift result in ?

A

Evolution

70
Q

How does population size impact allele frequency ?

A

Smaller the population the bigger the impact of allele frequency changes have proportionally as there are less alleles present in the gene pool

71
Q

Define mutation

A

Random changes in DNA code which can change allele frequency

72
Q

Give 4 factors affecting the evolution of a species

A
  • Mutation
  • Gene flow
  • Sexual selection
  • Natural selection
73
Q

Describe gene flow

A

Movement of alleles between population

74
Q

Give an example of gene flow

A

Movement of alleles between populations

75
Q

Describe sexual selection

A

Leads to an increase in the frequency of alleles which code for characteristics that improve mating success

76
Q

Describe natural selection

A

Leads to an increase in individuals with alleles that improve chances of survival. Reproduction rates and alleles coding for characteristics increases

77
Q

Define evolution

A

Changes in allele frequencies in the gene pool over time

78
Q

Define population

A

Groups of organisms of the same species in the same habitat

79
Q

Describe the founder effect

A
  • Few individuals from existing population relocate to an isolated area resulting in a small population breeding together and therefore a small gene pool
80
Q

Give 2 consequences of the founder effect to populations

A
  • Less genetic variation within following generations
  • Frequency of rare alleles will be higher in new population so impact natural selection more
81
Q

Describe when genetic bottleneck occurs

A

When events that cause large reductions in population size, leaving only a few individuals left occur

82
Q

Give 4 effects of genetic bottleneck that affect populations

A
  • Gene pool and genetic diversity reduced
  • Genetic diseases within populations more likely to be passed on
  • Issues with inbreeding and reduced fertility

HOWEVER

  • Beneficial mutations will have greater impacts and lead to quicker development of new species
83
Q

When is the hardy weinberg principle used?

A

Used to calculate allele frequency in populations

84
Q

Why is the hardy weinberg principle hard to apply ?

A

Frequency of alleles in populations will not change between generations if factors normally affecting evolution aren’t influencing the population

85
Q

What does p^2 in the hardy weinberg principle represent ?

A

Frequency of AA individuals

86
Q

What does 2PQ in the hardy weinberg principle represent ?

A

Frequency of Aa individuals

87
Q

What does q^2 in the hardy weinberg principle represent ?

A

Frequency of aa individuals

88
Q

What do you always work out first with the hardy weinberg principle ?

A

q^2

89
Q

What are the 2 types of isolating mechanism ?

A

Geographical mechanism - allopatric speciation
Reproductive mechanism - sympatric speciation

90
Q

What us allopatric speciation

A
  • Speciation within DIFFERENT habitats
  • Geographic isolation which separates the original population into 2 so they are unable to reproduce
  • Environments differ so populations accumulate different beneficial mutations
  • Results in founder effect and genetic drift which enhances the differences
  • 2 populations become so genetically different they are unable to interbreed to produce fertile offspring
  • Classified as 2 different species
91
Q

What must exist for allopatric speciation to occur ?

A

Genetic variation within the gene pool of the original species

92
Q

What proves allopatric speciation ?

A

Contemporary evidence such as DNA sequencing and Darwin’s beak evidence

93
Q

What is sympatric speciation ?

A
  • Speciation within the SAME habitat
  • Individuals within the same species are unable to reproduce
  • Due to random mutation which impacts reproductive behavior so there is no gene flow between populations
  • Due to members of 2 different species breeding to produce fertile offspring. New species has different number of chromosomes to parents so can’t interbreed with members of parent population. Gene flow is stopped. Hybrid individual is reproductively isolated
  • DNA overtimes becomes so different the organism can’t interbreed to produce fertile offspring so is classified as a separate species
94
Q

Define artificial selection

A

When humans select plants/animals with favorable characteristics in a population and breed them together

95
Q

Explain the animal example of artificial selection

A

Modern dairy cattle
- Female with very high milk yield selected and bred with male whose mother has high milk yield
- Offspring with highest milk yield selected and bred together
- Continued over several generations until very high milk yield cow produced

96
Q

Explain plant example of artificial selection

A

Bread wheat
- Wheat plants with high wheat yield selected and bred together
- Offspring with highest yields bred together
- Continued over several generations to produce plant with very high wheat yield

97
Q

Give 2 issues with artificial selection

A
  • Similar alleles bred together which reduces number of alleles in gene pool
  • If new disease introduced, there is less chance alleles are present that could offer resistance to population
98
Q

What is it important to maintain when carrying out artificial selection ?

A

Maintain resources of genetic material for use in the future by preserving the original ‘wild type’ organisms that haven’t undergone artificial selections

99
Q

What are the ethical considerations of artificial selection ?

A

It can exaggerate traits which can lead to health problems in organisms

e.g. Pedigree dogs such as pugs which have flat faces that lead to breathing problems

100
Q

What does pure breeding suggest

A

Homozygosity

101
Q

What do populations which have undergone natural selection look like ?

A

Individuals within population show wide range of variation in phenotype due to genetic and environmental factors

102
Q

When does speciation occur ?

A

When original population of the same species becomes reproductively isolated and can’t breed together. Barrier to successful interbreeding

103
Q

Define prezygotic barriers ?

A

Prevent fertilisation and formation of zygote

104
Q

Give an example of a prezygotic barrier

A

Temporal separation between frogs with different mating seasons

105
Q

Define postzygotic barriers

A

Reduce reproductive potential of offspring often due to hybridization. Barrier to successful interbreeding

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