Variation and Inheritance Flashcards Preview

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Flashcards in Variation and Inheritance Deck (74):
1

Define chlorosis.

When the leaves of a plant look pale because the cells are not producing the normal amount of chlorophyll and so the plant does not produce enough food

2

What environmental factors affect the phenotype of a plant?

- Lack of light
- Mineral deficiencies
- Virus infections

3

What is a source of genetic variation?

- Random fertilisation
- Independent assortment
- Crossing over
- Mutations

4

Define genotype.

The combination of alleles an organism inherits for a characteristic

5

Define phenotype.

The observable characteristics of an organism that are often aff teed by the environment

6

Define dominant allele.

The version of a gene that will always be expressed if present

7

Define recessive allele

The version of a gene only expressed if two copies of the allele same recessive allele are present

8

Define homozygous

When there are two identical allele for a characteristic

9

Define heterozygous

When there are two different alleles present for a characteristic, and the dominant one is expressed

10

Define continuous variation

A characteristic that can take any value in a range, there are many genes for a characteristic

11

Define discontinuous variation.

A characteristic that can only occur in specific values, there are one or two genes for a characteristic

12

Define monogenic inheritance.

The inheritance of a single gene

13

What does a homozygous genetic cross result in?

100% heterozygous genotype

14

What does a heterozygous genetic cross result in?

50% heterozygous genotype = dominant phenotype
25% recessive genotype = recessive phenotype
25% dominant genotype = dominant phenotype

15

Define codominance.

When two different alleles for a gene are equally dominant and thus both alleles will be expressed in the phenotype of the organism present

16

How do you set up a genetic cross for codominant alleles?

Capital letter with a superscript

17

What will a homozygous genetic cross of codominant alleles result in?

100 % heterozygous genotype = 100% codominant phenotype

18

What will a heterozygous codominant genetic cross result in?

50% heterozygous genotype - 50% codominant genotype ab
25% homozygous dominant genotype a - 25% genotype a
25% homozygous dominant genotype b - 25% genotype b

19

Define multiple alleles.

Genes that have more than two versions e.g. Tall, intermediate and short vs tall and short

20

How many alleles of any gene can be present in an individual?

2, one from each parent

21

What does the immunoglobulin gene code for?

The different antigens in a RBC

22

What are sex linked chromosomes?

Characteristics carried on the sex chromosomes

23

Does the chromosome carry less genes? And if so then why?

Yes because it is smaller

24

What is haemophilia?

When the patients blood clots very slowly due to a lack in Factor VIII

25

What happens if a male inherits the recessive haemophiliac gene?

They will have the disorder as they cannot have the corresponding dominant allele on their Y chromosome

26

Define a carrier

An individual that has the gene for a genetic condition but does not necessarily express it

27

What is a dyhybrid cross?

Shows the inheritance of two different characteristics caused by two genes which may be located on different pairs of homologous chromosomes

28

What is the ratio commonly found in a F2 dihybrid cross

9:3:3:1

29

Why may the ratio differ?

- the fertilisation of gametes is a random process, small sample = skewed results
- the genes being studied are both on the same chromosome thus if no crossing over occurs the alleles for the two characteristics will always be inherited together

30

Define autosomal linkage.

When the genes that are linked are in non-sex chromosomes

31

Recombination frequency equation

Number of recombinant offspring / Total number of offspring

32

What percentage suggests gene linkage?

50 or more

33

Define epistasis.

The interaction of genes at different loci

34

What results in epistasis occurring?

Continuous and multiple genes

35

Define hypostatic.

A gene that is affected by another gene

36

Define epistatic

A gene that affects the expression of another gene

37

What is recessive epistasis?

If the presence of two recessive alleles results in the lack of an enzyme

38

What is dominant epistasis?

When a dominant allele results in a gene having an effect on another gene by coding for an enzyme which modifies one of the precursor molecules in the pathway

39

Define population genetics

The investigation of how allele frequencies within populations changes over time

40

Define gene pool

The sum of the total gene sin a population at any given time

41

Define allele frequency

The relative frequency of a particular allele in a population

42

Calculation allele frequency

P+Q=1

43

What is the Hardy-Weinberg principle.

In a stable population with no disturbing factors, the allele frequencies will remain constant from one generation to the next and the will be no evolution

44

What is the Hardy-Weinberg equation?

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

45

What assumption is made by the Hardy-Weinberg principle?

A theoretical breeding population of diploid organisms that is large and isolated
Random mating
No mutations
No selection pressures

46

What factors lead to changes in allele frequency?

- Mutation
- Sexual selection
- Gene flow
- Genetic drift
- Natural selection

47

Which populations cannot adapt to change as easily?

Small populations with limited genetic diversity

48

Which factors affect the size of populations?

Density dependent factors
Density independent factors

49

Define density dependent factors.

Dependent on population size and competition, predation, parasitism, and communicable disease

50

Define density independent factors.

Affect all populations of all sizes
- Climate change
- Natural disasters
- Seasonal change
- Human activities

51

What are population bottlenecks?

Large reductions in population size over t least one generation

52

What is a pro and con of a genetic bottleneck?

Pro: a beneficial mutation will have a much greater impact and lead to the quicker development of new species
Con: the gene pool is greatly reduced and the effects will be seen in future generations

53

What is the founder effect?

The occurrence of a small population due to he establishment of new colonies by a few individuals

54

What is the effect of rare alleles in a small population?

They will become more frequent and have a much bigger impact on natural selection in the population

55

What is a normal distribution?

The bell shaped curved which forms form the distribution of different variants

56

What is stabilising selection?

The norm or average is selected for - increase in frequency of alleles
The extremes are selected against - decrees in frequency of alleles

57

What is directional selection?

When there is a change is the environment and the normal phenotype is no longer advantageous

It is therefore selected against and the allele frequency shifts to the more extreme phenotypes, resulting in evolution

58

What is disruptive selection?

When the extremes are selected for and the norm is selected against

59

Define speciation

The formation of new species through the process of evolution

60

Define allopatric speciation

The more common form of speciation when some members of a species are separated from the rest by some physical barrier

61

What causes allopatric speciation?

Different environment
Different election pressures
Different physical adaptations
.. Founder effect -> genetic drift

62

Define sympatric speciation

When members of two different species interbreed to produce fertile offspring
It may have a different number of chromosomes to the parents and so not breed with those species
= stop in gene flow + causes reproductive isolation of hybrid species

63

What cause sympatric speciation?

Disruptive selection
Mating preferences
Behaving real differences
= reproductive isolation, and although they live in the same habitat gene flow will still interfere with the process of speciation

64

What is a prezygotic reproductive barrier?

A barrier preventing fertilisation and the formation of a zygote

65

What is a postzygotic reproductive barrier?

A reduction in the viability or reproductive potential of an offspring

66

Define polymorphic

Display more than one distinct phenotype for most characteristics

67

What is the wild type allele?

The allele coding for the most common characteristic

68

What are mutants?

Alleles arising from mutations

69

What is artificial selection?

Instead of changes in the environment leading to survival of the fittest, the selection pressure for breeding plants with desirable characteristics is applied.

70

Define inbreeding

The breeding of closely related individuals

71

What are the problems caused by inbreeding?

It limits the gene pool which reduces genetic diversity and thus the ability of an organism to evolve and adapt to changes in its environment

Genetic disorders arise due to the accumulation of recessive of alleles when inbreeding occurs = less biologically fit organisms

72

What are seed banks?

Banks that keep samples of seeds of different species of plants

73

What are gene banks?

Store biological samples, other than seeds

74

What is outbreeding?

The breeding of unrelated or distant plants species - reduces the occurrence of homozygous recessive and increases the potential of plant species to adapt to changes in the environment