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LGS A-Level OCR Biology > Unit 6 - Patterns of Inheritance > Flashcards

Unit 6 - Patterns of Inheritance Flashcards

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1
Q

Genotype

A

Allele combinations possessed by an organism leading to specific phenotypes

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2
Q

Discontinuous variation

A 
Qualitative differences 
Clearly distinguishable categories (categorical)
Monogenic inheritance 
One/two genes 
An allele has a large effect
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3
Q

Continuous variation

A 
Quantitative differences
Phenotypic diff have a wide range of variation in a pop. (sig affected by environment)
Each allele has a small effect 
Polygenic inheritance 
Large number of diff genes involved
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4
Q

Monogenic inheritance

A

One gene w/ 2 or more alleles

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5
Q

Monohybrid cross

A

1 gene, 2 alleles (r and d)

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6
Q

Drawing genetic crosses

A

Parental genotype
Parental phenotype
Parental gametes
F1 ratio for genotype then phenotypes

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7
Q

Codominant inheritance

A

Involves more than one dominant allele

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8
Q

Multiple alleles genetic crosses

A

1 trait
1 gene
>2 alleles

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9
Q

Example of multiple allele genetic cross

A

Blood group
I A
I B
I O

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10
Q

3 ways genetic variation arises from sexual reproduction

A

IA of homologous chromosomes (M1)
Crossing over
IA of sister chromatids (M2)

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11
Q

23rd pair of chromosomes

A

Only pair that varies in shape and size
X - v. large and doesn’t carry genes involved in sexual development
Y - V. small, no genetic info, but carries gene that causes formation of male embryos

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12
Q

Sex linked genes

A

Characteristics determined by genes carried on X and Y

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13
Q

Why do sex-linked genes affect males

A

Y is much smaller so only has one copy of the gene, if recessive allele is found on X but no D allele on Y, male will express the recessive trait (usually condition)
Most females will have a D allele present on the 2nd X chromosome so are either normal or a carrier

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14
Q

Examples of sex-linked conditions

A

Haemophilia - blood clots v. slowly due to a lack of protein blood clotting factor
Red-green colour blindness

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15
Q

Dihybrid cross

A

Used to show inheritance of 2 diff characteristics, 2 genes at diff loci, >2 alleles on each

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16
Q

Expected results of a heterozygous dihybrid cross

A

9:3:3:1

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17
Q

Why may the actual ratio vary from expected

A

Fertilisation is random

If there is no crossing over, alleles for 2 characteristics will be inherited together if on same chromosome

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18
Q

Autosome

A

Any chromosome that is not a sex chromosome

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19
Q

Autosomal linkage

A

2 separate genes are found on the same autosome
Represented by diff letters
Linked genes are inherited together so offspring usually show same combination as parents (certain gametes are more common)

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20
Q

W/ no crossing over in autosomal linkage

A

Gametes stay in parental comb. and offspring show 3:1 phenotypic ratio

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21
Q

What may prevent linked genes from being inherited together

A

If they’re separated by chiasmata

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22
Q

W/ crossing over in autosomal linkage

A

Genotypic and phenotypic ratios are variable
Parental types > cross-over type
Proportion depends on how often cross overs ocurred between two loci

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23
Q

Recombinant offspring

A

Offspring w/ a diff combination of alleles to either parent

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24
Q

Closer genes are located on a chromosome …

A

Less likely to be separated during crossing over –> fewer recombinant offspring

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25
Q

Recombination frequency

A

Measure of amont of crossing over occured in meoisis - indicating level of linkage
Also used to map genes loci ; 1% = distance of 1 map unit on chromosome

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26
Q

Calculating recombinant frequency

A

No of recombinant offspring/ total no. of offspring

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27
Q

50% recombination frequency

A

No linkage, separate chromosomes

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28
Q

<50% recombination frequency

A

Gene linkage and IA has been hindered
Signifies autosomal linkage
Linked genes are inherited together
Crossing over produces few recombinant offspring

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29
Q

Homozygous

A

Has identical alleles on both chromosome

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30
Q

H0 in chi squared

A

There is no sig. difference between expected and observed values

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31
Q

Degrees of freedom in chi squared

A

No. of categories - 1

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32
Q

Epistasis

A

Interaction of genes at diff loci
Genes masking the expression of other genes (not alleles)
Gene regulaion is a example w. reg . genes controlling structural genes

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33
Q

When can epistasis be seen

A

Multistep reactions

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34
Q

Hypostatic

A

Gene affected by another gene

Cause the phenotype

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35
Q

Epistatic gene

A

Gene that affects the expression of another gene; can happen as a result of dominant or recessive alleles

36
Q

Epistatic alleles

A

Another pair of alleles found at diff loci

37
Q

Antagonistic epistasis

A

Dominant and recessive epistasis

38
Q

Dominant epistasis

A

If there are ANY dominant alleles present in the epistatic alleles, masks expression of hypostatic alleles

39
Q

Phenotypic ratio in a heterozygous dihybid cross w/ dominant epistasis

A

12:3:1

40
Q

Recessive epistasis

A

Occurs when a pair of homozygous recessive alleles at one gene locus masks the expression of the hypostatic allele at a 2nd locus

41
Q

Phenotypic ratio in a heterozygous dihybrid cross w/ recessive epistasis

A

9:3:4

42
Q

Bivalent

A

Homologous pair of chromosomes

43
Q

Chiasmata

A

Point representing where homologous touch and exchange genetic info

44
Q

Gene pool

A

Total no.of genes and their alleles in a particular population

45
Q

Assumptions of the Hardy-Weinberg Principle

A

Pop is v. large (reduced effect of genetic drift)
Mating within pop. is random - no selective breeding
No selective advantage for any genotype coded for by that allele
No mutation
No migration

Gene pool is stable

46
Q

Hardy Weinberg principle

A

A is dominant, p = freq. of A
a is recessive, q = freq. of a
p + q = 1
p^2 + 2pq + q^2 = 1

47
Q

When to use p + q = 1

A

When given allele frequency

48
Q

When to use p^2 + 2pq +q^2

A

When given phenotypes

49
Q

Evolution

A

Changes in allele frequencies over time leading to changes in species

50
Q

What can affect allele frequencies

A

Mutations - new advantageous alleles will remain in pop
Natural selection
Effects of small population
Genetic drift
Artificial selection and selective breeding

51
Q

Selection

A

Increase in allele frequency

52
Q

Stabilising selection

A

Selection pressure toward the centre increases no. of individuals at the modal values
Extreme values are selected against and lost

53
Q

Types of selection

A

Stabilising
Directional
Disruptive

54
Q

Directional selection

A

Selection pressure towards one extreme moves the mode in this direction
Extreme value is advantageous; more likely to survive and reproduce

55
Q

Disruptive selection

A

Selection pressure toward the extremes creates two modal values
Intermediae values selcted against - lose those alleles
Creates two distnct populations
e.g. Darwin’s finches

56
Q

Genetic drift

A

Random events causing changes in allele frequencies
Effects are greatly increased in small pop or small gene pools
Alleles in new generation will therefore be the genes of the ‘lucky’ individuals and not necessarily healthier individuals

57
Q

Polymorphic

A

Genes w/ > 1 allele

58
Q

Effects of small populations

A

Founder effect and genetic bottleneck reduce genetic diversity by creating small populations

59
Q

Founder effect

A

Occurs when a small group of migrants that aren’t genetically representative of the pop. from which they came from, establish in a new area
New population is v. small w/ an increase in inbreeding and relatively low genetic variation

60
Q

Why does inbreeding cause genetic diseases

A

Increases impact of recessive alleles and most genetic diseases are caused by recessive alleles

61
Q

Genetic Bottleneck

A

Big events that cause drastic reduction in a parent pop leaving a surviving pop w/ v. low genetic diversity (unless they mutate)

62
Q

Events that may cause genetic bottleneck

A

Overhunting to the point of extinction
Habitat destruction
Natural disasters

63
Q

Process leading to Genetic Bottleneck

A 
Orig population
Large no. die 
Reduced population (some alleles lost)
Reproduction 
New population w/ low genetic diversity
64
Q

Order of conservation

A

Habitat
Population
Genes

65
Q

Artifical selection and selective breeding

A

Humans use animal and plant breding to selectively develop particular phenotypic ratios by choosing spp individuals
Occurs over several generations

66
Q

Agent of selection in natural selection

A

Environment

67
Q

Agent of selection in artifiicial selection

A

Human

68
Q

Effect of allele frequencies in selection

A

Changes for both natural and artificial

69
Q

Effect of evolution due to natural selection

A

Drives it

70
Q

Effect of evolution due to artificial selection

A

Drives it then slows it down

71
Q

Speed of natural selection

A

Slow

72
Q

Speed of artifical selection

A

Fast

73
Q

Ethical considerations w artificial selection and selective breeding

A

Health problems; certain traits may be exaggerated
Reduction of genetic diversity - more susceptible to genetic diseases caused by r alleles, potentially useful alleles for the future lost

74
Q

Speciation

A

Formation of new and distinct species through the course of evolution

75
Q

Factors that may cause directional selection

A

Predation
Habitat changes
Competition

76
Q

Environments that cause directional selection

A

Slowly changing environmental conditions in one direction

77
Q

‘Ingredients’ for speciation

A 
Existing genetically varying poulation 
Isolation: geographical or reproductive 
Time 
Different selective pressures
Large change in allele frequencies
78
Q

Why do you need diff selective pressures for speciation

A

Changes allele frequencies in diff directions

79
Q

Allopatric speciation

A

Geographically isolated

Gene pool is physically separated so the sep pop can then evolve independently of each other

80
Q

What causes changes in allele frequency in allopatric speciation

A

Accumulation of diff mutations forms separate gene pools
Different biotic/ abiotic factors
Differential reproductive successes

81
Q

Sympatric speciation

A

Reproductively isolated
Organisms inhabiting same area separated into 2 or more groups due to changes in alelles and phenotypes preventing them from successfully breeeding together

82
Q

Examples of things causing reproductive isolation

A 
Seasonal changes (Different flowering seasons)
Mechanical changes (Changes in genitalia)
Behavioural changes (Diff courtship rituals)
83
Q

How does the presence of epistatic alleles inhibit the expression of the hypostatic allele

A

Epistatic allele codes for repressor protein/ TF
Product of epistatic allele binds to promoter of hypostatic allele
Product stops transcription or inhibits enzyme action of enzyme encoded by A

84
Q

Causes of variation in continuous variables e.g. height

A

Environment
Age
Polygenic

85
Q

Result of speciation

A

Gene flow restricted

Leads to diff specialisation

LGS A-Level OCR Biology (42 decks)

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