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Year 13 Biology > 6.2 - Genetic Inheritance > Flashcards

6.2 - Genetic Inheritance Flashcards

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1
Q

How is variation caused?

A

Genetic variation:
Sexual reproduction
Mutations

Environmental variation:
Any variation caused by anything other than genetic differences
E.g. scars, direction roots grown in response to sunlight, water etc.

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2
Q

What is most variation caused by a combination of?

A

A combination of genetic and environmental factors

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3
Q

Phenotype def

A

Appearance of a characteristic

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4
Q

Phenotype def

A

Appearance of a characteristic

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5
Q

Genotype def

A

The genetic makeup of an organism

- influences phenotype

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6
Q

Monogenic def

A

Determined by a single gene

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7
Q

Gene locus def

A

Determined by a single gene

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8
Q

Heterozygous def

A

Having different alleles at the same gene locus on a pair of homologous chromosomes
E.g. Bb

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9
Q

Homozygous def

A

Having identical alleles at the same gene locus on a pair of homologous chromosomes
E.g. BB, bb

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10
Q

True-bred def

A

Homozygous (dominant or recessive)

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11
Q

Recessive def

A

Masked by dominant alleles (little letter)

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12
Q

F1 def

A

First generation of offspring (to original parents)

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13
Q

F2 def

A

Second generation (offspring of F2)

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14
Q

Two forms of variation

A

Continuous

Discontinuous

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15
Q

Continuous variation info

A
  • no defined categories/distinct groups
  • there is a range - any value possible
  • caused by more than one gene (polygenic) and, often, the environment
  • the greater the no. of gene loci contributing to characteristic, greater range in variation
  • quantitative
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16
Q

Discontinuous variation info

A
  • discrete categories - no intermediates, e.gl eye colour
  • usually caused by one gene (monogenic)
  • genes at diff loci interwct to influence one charcteristic and cause discontinuois variation (epistasis)
  • no environmental effects cause it
  • qualitative
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17
Q

How to test the genotype of a plant

A

Test cross with a homozygous recessive, e.g. tt for short plants
If ant offspring are small then the plant is heterozygous (dominant), Tt
T is tall - dominant

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18
Q

What does dihybrid inheritance involve?

A

Looks at the simultaneous inheritance of two characteristics (controlled by different gene loci)
E.g. seed colour and seed shape

The inheritance of one does not affect the other

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19
Q

What are the three blood groups?

A

A
B
O

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20
Q

What are the 4 blood group phenotypes and genotypes

A

AB
Bo
Ao
oo

O is recessive to A and B
B is recessive to A, but dominant to O

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21
Q

What letter is usually used for blood groups in punnet squares

A

I

Stands for immunoglobulin

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22
Q

Chromosomes for different genders

A

Male: XY
Female: XX

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23
Q

Male chromosome info

A

Chromosomes are not fully homologous
Y chromosome lacks many of the genes that code for characteristics on the X chromosome
Males can be neither homozygous or heterzygous for these genes
This makes males more susceptible to genetic diseases (In top portions of X and Y chromsomes)

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24
Q

Two diseases caused by sex-linked genes

A

Haemophilia

Colour blindness

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25
Q

Haemophilia info

A

Gene causing haemophilia found in X chromosome but not the Y

Functional allele: Xh
Faulty allele:

Female carriers (heterozygous) do not have the disease

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26
Q

Colour blindness info

A

Gene causing red-green colour blindness is found on tye X chromosomes but not the Y

Functional allele: XB
Faulty allele: Xb

Female carriers (heterzygous) do not have the disease

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27
Q

Tortoiseshell cats info

A

A gene for cat coat is sex-linked
The two alleles are:
Orange - C^O
Black - C^B

The two alleles are both dominant - they are co-dominant

When both black and orange alleles are present, coat colour is called tortoishell.

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28
Q

What is autosomal linkage?

A

When 2 or more genes on the same chromosome are inherited together
- they do not undergo independent assortment

  • autosomes are the non-sex chromsomes
29
Q

What are autsosomes?

A

The non-sex chromosomes

30
Q

Ratio of dominant and recessive, etc. (not sure about rest) in dihybrid crosses

A

9:3:3:1

31
Q

Epistasis def

A

An interaction of non-linked genes (on different chromosomes) where one masks the expression of the other.

Epistasis reduces the number of phenotypes in the F2 generation and so reduces variation.

32
Q

Key terms and info for Epistasis

A

Epistasis reduces the number of phenotypes in the F2 generation and so reduces variation.

The alleles that are masking the effect of the alleles of the other gene are called epistatic alleles

The alleles whose effect is being masked are called the hypostatic alleles

33
Q

What are epistatic alleles

A

The alleles that are masking the effect of the alleles of the other genes

34
Q

What is recessive Epistasis?

A

Where the homozygous recessive alleles of a gene locus 1 are epistatic (prevent the expression of) to both alleles on gene locus 2 (hypostatic)

35
Q

What is a “true bred” gene?

A

A gene that contains homozygous alleles

36
Q

Dominant epistatis def

A

Where the dominant alleles of gene locus 1 are epistatic (prevent the expression of) to both alleles on gene locus 2 (hypostatic)

37
Q

Epistasis by complementary gene action

A

The genes can work together

38
Q

Ratios to look out for in genetic inheritance

A

• 3:1 phenotypic ratio for 2 genes/traits ‐ autosomal linked and no crossing over will have occurred
• A NON 9:3:3:1 phenotypic ratio showing 4 phenotypes for 2 genes/traits ‐ autosomal linked and crossing over will have occured
> The further apart the gene loci for the linked genes, the more likely crossing over is and the higher the number of recombinant phenotypes
• Any phenotypic ratio where there is a distinct male/female difference ‐ sex linkage
• Any modification of a 9:3:3:1 phenotypic ratio will show epistasis
> 9:3:4 recessive epistasis
> 12:3:1, 13:1 dominant epistasis
> 9:7 or 9:3:4 epistasis by complementary gene action
• 9:3:3:1 ratio ‐ generally dihybrid inheritance of non linked genes

39
Q

Go to textbook to revise topic from start

A
40
Q

What does a ratio of 3:1 show in inheritance

A

Shows ratio for 2 genes/traits

- autosomal linked and no crossing over occurs

41
Q

What 9:3:3:1 ratio shows

A

Shows 4 phenotypes for 2 traits/genes

  • autosomal linked and crossing over will have occurred
  • further apart the gene loci for linked genes, more likely crossing over is and higher number of recombinant phenotypes
42
Q

What does any phenotypic ratio where there is a distinct male/female difference show

A

Sex linkage inheritance, e.g. genetic diseases like haemophilia more common in men

43
Q

What a modification of a 9:3:3:1 phenotypic ratio shows

A

Shows Epistasis

9: 3:4 - recessive Epistasis
12: 3:1, or 13:3 - dominant Epistasis
9: 7 or 9:3:4 - Epistasis by complementary gene action

44
Q

What a 9:3:3:1 ratio also shows

A

Generally dihybrid inheritance of non-linked genes

45
Q

What is Hardy-Weinberg pricniple

A

A principle that is used to predict allele frequencies within a population

46
Q

When can Hardy-Weinberg principle be applied?

A
  • large population
  • random mating
  • no selective advantage for genotype
  • no gene mutation, migration or genetic drift
47
Q

Hardy-Weinberg equations

A

p + q = 1

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

48
Q

Two types of selection/natural selection

A

Stabilising selection

Directional selection

49
Q

Stabilising selection info

A

Occurs when organisms’ environment doesn’t change
Favours intermediate phenotypes (Goldilocks, over extremes)
Reduces variation in a population
E.g. animals with very short/long fur selected against in constant temps, compared to animals with medium length fur
- higher frequency of alleles for mid length fur

50
Q

Directional stabilisation info

A

Occurs when environment changes
Favours a new (extreme) phenotype
Causes a change in population mean phenotype
- e.g. climate change - temp decreases.
- animals with longer fur more likely to survive, breed and pass on allele for long fur
- over time allele for long fur becomes more frequent in population

51
Q

Genetic drift def

A

Random changes in allele frequency in small populations

52
Q

Genetic drift info

A

Happens in small populations (with a gene pool)
Chance mutations that are neither beneficial/harmful cause change in frequency of alleles
The population alleles can ‘drift’ from original

  • only happens in small populations because each individual forms a larger proportion of gene pool and therefore has a greater effect on the gene pool.
    It is also easier to ‘lose’ a gene from a small gene pool
53
Q

2 types of genetic drift

A

Genetic bottleneck

Founder effect

54
Q

Genetic bottleneck info

A

An event, e.g. flood, rapidly reduces the number of a population
Some alleles lost from population at random
Genetic variation reduced - genetic drift

55
Q

Founder effect

A

A small number of individuals from an original larger population establish a new population
Some alleles lost from population at random (these could be advantageous)
Genetic variation reduced - genetic drift
Could lead to inbreeding - due to reduced alleles in gene pool
Also could lead to more homozygous recessive reproduction - more genetic diseases etc.

56
Q

Speciation def

A

The splitting of a population of a species into 2 isolated populations that over time undergo genetic changes which result in reproductive isolation and therefore the formation of 2 different species.

57
Q

How does speciation occur?

A

Via isolation

58
Q

Two isolating mechanisms that cause speciation

A

Geographical isolation

Reproductive isolation

59
Q

Two types of speciation

A

Allopathic - geographical isolation

Sympatric- reproductive isolation

60
Q

Geographical isolation info (allopatric)

A

Populations are physically separated, e.g. by water, mountains, fences, etc.
Barrier prevents gene flow between populations
Genetic changes occur is species
- caused by genetic drift, mutations or natural selection
The populations become genetically so different
- they can no longer interbreed to produce fertile offspring (reproductively isolated)
- new species have been formed

61
Q

Reproductive isolation info (sympatric)

A

Several things can lead to individuals in a population becoming reproductively isolated:
- behavioural changes e.g. changes to sleep patterns, courtship behaviours, etc.
- Biological changes e.g. size differences, genitalia differences
- genetic changes e.g. change in chromosome number prevents zygote viability
Once populations can no longer interbreed to produce fertile offspring (reproductive isolation)
- new species has been formed

62
Q

Explain why a collection of small islands remote from a mainland provides optimal conditions for speciation.
(2 Marks)

A
  • geographical isolation (don’t accept allopatric)
  • different species on different islands have different selection pressures
  • species on islands can only reproduce with organisms/species on the same island
  • small populations/gene pools
63
Q

Suggest how different isolating mechanisms allowed tame dogs to evolve separately from wolves.
(3 Marks)

A

Geographic:
- wolves avoid human settlements

Behavioural:
- differences in courtship/pheromones

Mechanical:
- idea of different size of wolves and some small dogs

Gamete incompatibility:
- possibility of different chromosome number

Seasonal/temporal:
- Different breeding seasons/times

64
Q

Artificial selection def

A

Selective breeding of organisms in order to produce desired phenotypes in an organism
- often to benefit humans
Humans chose parents with desired phenotypes and therefore desired alleles
- interbreed them to produce offspring with higher frequency of these phenotypes
Repeated over many generations

65
Q

Stages of artificial selection - simple

A

Male and female with desired characteristic chosen
Male and female interbred
Best offspring selected and interbred
This is repeated over many generations

66
Q

Examples of selective breeding/artificial selection in animals and plants

A

Animals:
- highest yield of milk, meat

Plants:
- highest yield of crops,

67
Q

Problems with natural selection/selective breeding

A
  • Inbreeding

- Ethical considerations of selective breeding

68
Q

Artificial selection problems - inbreeding info

A
69
Q

Artificial selection problems - ethical considerations info

A

Year 13 Biology (19 decks)

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