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Biology > -Patterns of inheritance > Flashcards

-Patterns of inheritance Flashcards

1
Q

What is the definition of an allele?

A

version of a gene

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2
Q

What is the definition of a genotype?

A

The combination of alleles an organism has.

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3
Q

What is the definition of a phenotype?

A

The characteristics displayed by an organism.

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4
Q

What do mutations and sexual reproduction lead to?

A

Variation

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5
Q

What 3 ways does sexual reproduction lead to variation?

A

Crossing over
Independent assortment/segregation of chromosomes
Random fertilisation

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6
Q

How does the environment cause variation?

A

Phenotypic variation can be affected by the environment.
By diet, climate, lifestyle, light, nutrients

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7
Q

What is etoilation?

A

Where plants grow abnormally long and spindly due to not enough light

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8
Q

What is chlorosis?

A

Plants do not produce enough chlorophyll. Due to a lack of magnesium.

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9
Q

What is the difference between inter and intra specific variation?

A

Interspecific is variation between different species.
Intraspecific is the differences between organisms of the same species.

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10
Q

What is continuous variation?

A

It is quantitative, any feature that can be measured. Controlled by both genes and the environment. EG height.

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11
Q

What is discontinuous variation?

A

It is qualitative, any feature that can’t be measured.
Controlled by genes.
Eg blood group

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12
Q

What is the definition of a gene?

A

Sequence of nucleotide bases that code for a protein (polypeptides)

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13
Q

What is the locus of a gene?

A

The position of a gene on a chromosome.

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14
Q

What is monogenic inheritance?

A

The inheritance of a characteristic controlled by a single gene.

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15
Q

What ratio do we expect from a heterozygous monohybrid cross?

A

3:1

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16
Q

How do you find out if an organism with a dominant phenotype, eg tongue roller homozygous TT or heterozygous Tt?

A

Do a back cross.
Cross organism with a double recessive type tt.
If TT then all offspring will have dominant phenotype.
If Tt at least 1 offspring will have recessive phenotype.

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17
Q

What is codominance?

A

Where both alleles are expressed and neither one is recessive. eg sickle-cell

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18
Q

Do the snap dragon genetic cross diagram for understanding and practice.

A

…

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19
Q

What is multiple allele inheritance?

A

When a gene has more than two alleles that exist at a particular locus. However all affect the same characteristic/feature.
Only two can be present in an individual at any one time (only two homozygous chromosomes)
There is usually a dominance heirarchy.

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20
Q

What is an example of multiple allele inheritance?

A

Human ABO blood groups.
Four groups (phenotypes) A, B, AB, O

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21
Q

Write out the possible combinations of alleles to form different phenotypes and genotypes of human blood groups.

A

…

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22
Q

What is dihybrid inheritance?

A

The inheritance of two characteristics controlled by different genes. The classic example is Mendel’s peas.

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23
Q

What was Mendel’s experiment on dihybrid inheritance in peas?

A

He did a monohybrid cross of both pea colour and shape, then he decided to look at how they were inherited together.
There are 4 possible combinations of characteristics (round yellow, round green, wrinkled yellow, wrinkled green)
He had found that round was dominant to wrinkled and yellow dominant to green. The F1 generation were all heterozygous for both characteristics and when crossed together there was a 9:3:3:1 ratio.

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24
Q

What is the heterozygous cross predicted ratio for dihybrid inheritance?

A

9:3:3:1

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25
Q

What is a sex linked chromosome?

A

Any gene with the loci on the X or Y chromosome is said to be sex linked.

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26
Q

What is the difference between the size of the X and Y chromosomes and what does this mean?

A

The X chromosome is much longer than the Y and so there is no homologous portion of the Y chromosome for many genes.
The Y is very small and so controls very few features.

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27
Q

Why do characteristics controlled by recessive alleles on the X chromosomes appear more frequently in males?

A

There is only one X chromosome and so only one recessive allele is needed for the recessive characteristic to be expressed.

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28
Q

What are examples of sex-linked genetic disorders?

A

Haemophilia
Colour blindness
Duchenne muscular dystrophy

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29
Q

What is haemophilia A?

A

Unable to clot blood fast enough
One of the genes on the non-homologous region of the X chromosome codes for a non-clotting protein called factor 8.
A mutated form of the allele codes for non-functioning factor 8.

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30
Q

What is an autosome?

A

An autosome is a chromosome that is not a sex chromosome.

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31
Q

What word do we use to describe genes that are on the same chromosome?

A

Linked.

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32
Q

Are linked genes free to undergo independent assortment?

A

NO

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33
Q

What is independent assortment?

A

The organisation of homologous chromosomes when they line up in metaphase 1 is independent of any other pair.

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34
Q

What happens to a phenotypic ratio if two genes are autosomally linked?

A

It is not a 9:3:3:1 like a dihybrid cross.
It is more like a 3:1.

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35
Q

What happens during crossing over to linked genes?

A

The closer the genes are the less likely they are to get separated.
The further they are apart the more likely it is that recombinant genes will form.

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36
Q

What is a recombinant?

A

They are new combinations of phenotypes that prove that linkage is not complete. They are produced in prophase 1 of meiosis.

37
Q

What is epistasis?

A

The interaction of different genes where the gene at one locus masks the expression of another gene at the second locus.
(Baldness masks widow’s peak hairline or if there is no melanin in mouse hair it masks the colour of the mouse hair)
The alleles at the first locus are epistatic to those at the second locus.
The alleles at the second locus are hypostatic to those at the first locus.

38
Q

Is epistasis an inheritance or an interaction?

A

It is an INTERACTION.
If an exam question asks about an interaction then it is epistasis but if it asks about inheritance it cannot be epistasis.

39
Q

Is epistasis dominant or recessive?

A

It can be EITHER.

40
Q

What is dominant epistasis?

A

A dominant allele at one gene locus masks the expression of alleles at a second gene locus.

41
Q

What is the predicted ratio for dominant epistasis?

A

12:3:1 or 13:3

42
Q

What is recessive epistasis?

A

Two recessive alleles at one gene locus masks the expression at another gene locus.

43
Q

What is the expected ratio for recessive epistasis?

A

9:3:4

44
Q

Why do we use the chi-squared test?

A

It measures the size between the observed and expected results.
It helps us to determine whether the differences are significant or not.
It is used to test the null-hypothesis.

45
Q

What is a null-hypothesis?

A

No significant difference between what we expect and observe. (differences are due to chance)

46
Q

What is the chi-squared equation?

A

look up

47
Q

Look through the worked example of the chi-squared test on GC

A

…

48
Q

What is population genetics?

A

The investigation of how allele frequencies change over time in a population.

49
Q

What is the gene pool?

A

The sum total of all alleles of all genes in a population at any given time.

50
Q

What is allele frequency?

A

The relative frequency of a particular allele in a gene pool.

51
Q

What does evolution mean in terms of alleles?

A

It involves the long-term change of allele frequencies of a population.

52
Q

What 5 key factors affect evolution?

A

Mutation.
Sexual selection
Immigration/emigration
Genetic drift
Natural selection

53
Q

What does the distribution of the different variants of traits in a population take shape of in a graph?

A

A bell shaped curve. Known as the normal distrbution.

54
Q

What is a selection pressure?

A

Eg predation, disease and competition.

55
Q

What are the 3 types of selection?

A

Stabilising.
Directional
Disruptive

56
Q

What is directional selection?

A

A type of natural selection that occurs when an environmental change favours a new phenotype and so results in the change in the population mean.

57
Q

What is the founder effect?

A

When a small sample of the original population establishes in a new area; it’s gene pool is not as diverse as that of the parent population.

58
Q

What is a genetic bottleneck?

A

A sharp reduction in size of a population due to environmental catastrophies such as earthquakes, floods, diseases, or human activities such as habitat destruction, overhunting or genocide, which reduces genetic diversity. As the population expands it is less genetically diverse than before.

59
Q

What is stabilising selection?

A

Natural selection leading to constancy within a population. Intermediated phenotypes are favoured and extreme phenotypes selected against. Alleles for extreme phenotypes may be removed from the population. Stabilising selection reduces genetic variation within a population.
It normally happens when the organism’s environment remains unchanged.

60
Q

Look at what different selection pressures do to a normal distribution graph.

A

…

61
Q

What is disruptive selection?

A

When both extremes are favoured for over intermediate values.
Average phenotypes are selected against and extreme selected for.
The population divides into two distinct groups.

62
Q

What is genetic drift?

A

It says that characteristics are passed on by chance rather than due to factors that affect the individual’s ability to survive and reproduce.
Individuals show variation within their population in their genotypes.
By chance one allele is passed on more than others.
So the number of individuals with the alleles increases.
If by chance the same allele is passed on more often again and again it can lead to evolution as the allele becomes more common in the population.

63
Q

Does genetic drift generally have a greater effect in smaller or larger populations?

A

It usually has a bigger effect in small populations as chance has a greater influence.
In larger populations any chance factors are evened out.

64
Q

When can genetic drift arise because of smaller populations?

A

Can arise after genetic bottleneck or as a result of the founder effect.

65
Q

Summarise genetic bottleneck.

A

Original population -> Large numbers die -> Reduced population, some alleles are lost from original population -> Reproduction ->New population, genetic diversity greatly reduced.

66
Q

What is the founder effect?

A

A new population establishes from a larger parent population and the new population is likely to have a loss in genetic variation.
Eg migrating humans that aren’t representative of parent population.
It is a special type of genetic drift

67
Q

Is the frequency of an allele related to whether it codes for a dominant or recessive characteristic?

A

NO, it can change over time in response to changing conditions.

68
Q

What does the Hardy-Weinberg principal model?

A

It models the mathematical relationship between the frequencies of alleles and genotypes in a theoretical population that is stable and not evolving.

69
Q

What factors affect allele frequencies in a population (and therefore genetic diversity)?

A

Population size
Mutation rate
Migration
Natural selection (directional, disruptive, stabilising)
Changes to the environment - eg adverse causing genetic bottleneck
Isolation of population (founder effect)
Nom-random mating
Genetic drift

70
Q

What does the Hardy-Weinberg principle state?

A

Allele and genotype frequencies in a population will stay the same in absence of evolutionary selection pressures.

71
Q

What is the Hardy-Weinberg principle formula?

A

p+q=1

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

72
Q

What is artificial selection?

A

Humans select 2 organisms from a species who have desirable characteristics and breed them together.
Select offspring who display the desirable characteristics.
Repeat over many generations.

73
Q

How do you breed cattle to make a high yield herd?

A

Breed together the females with high milk yield and the men whose mother had a high yield.
Repeat.

74
Q

What are other characteristics to consider when breeding cattle for high milk yield?

A

Milk quality.
Lactation period ) how long they lactate for.
Large udders
Calm temperament
Easy calvings
Fertility

75
Q

What are the problems with selective breeding?

A

Can cause health problems. Certain traits are exaggerated.
Reduces genetic diversity and gene pool
Potentially useful alleles for the future are lost.
Inbreeding depression - inbreeding increases likelihood of individuals possessing 2 recessive alleles so lowers chance of survival.
Increased susceptibility of certain diseases.
Characteristics that are desirable to humans can be associated with features that are harmful for the animal.
Selective breeding doesn’t increase the rate of mutation.

76
Q

What are common problems in boxers caused by artificial selection?

A

Cancer and heart disease

77
Q

What are common problems in German Shepherds caused by artificial selection?

A

Heart disease, cancer, lack of digestive enzymes, skin infection.

78
Q

What are common problems in cocker spaniels caused by artificial selection?

A

Inflammation of ear, glaucoma

79
Q

What are common problems in bulldogs caused by artificial selection?

A

Breathing, hip and joint problems

80
Q

What are common problems in dalmatians caused by artificial selection?

A

Deafness, heart disease, skin conditions

81
Q

What is a species?

A

A group of organisms that can interbreed to produce fertile offspring.

82
Q

What is speciation?

A

The development of a new species.

83
Q

Why does speciation occur and what does it lead to?

A

Occurs when populations of the same species become reproductively isolated. Changes in allele frequencies lead to changes in phenotypes. They can no longer breed to produce fertile offspring.

84
Q

How does geographical isolation cause speciation?

A

The gene pools are separated and there is no interbreeding with the two groups.
Variation occurs due to mutation and different selection pressures. Leads to changes in allele frequencies.
After many generations the two groups become so different that they cannot intertbreed to produce fertile offspring.

85
Q

What is allopatric speciation?

A

Populations are separated from each other geographically.
Allele frequencies change so much over time in the two groups that they cannot breed to produce fertile offspring.

86
Q

What is sympatric speciation?

A

They don’t have to be geographically isolated to become reproductively isolated.
Random mutations can lead to reproductive isolation.
It is rarer than allopatric speciation.

87
Q

What methods can sympatric speciation occur from?

A

Changes in alleles and phenotype of two populations prevent them from successfully breeding with each other.
Seasonal/temporal changes - different flowering or mating seasons.
Mechanical changes - changes in genitalia prevent successful mating
Behavioural changes - different rituals.

88
Q

Does sympatric speciation occur more in plants or animals?

A

Plants

Biology (21 decks)

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