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Biology A2 > Variation and Inheritance > Flashcards

Variation and Inheritance Flashcards

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1
Q

Define chlorosis.

A

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

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2
Q

What environmental factors affect the phenotype of a plant?

A
  • Lack of light
  • Mineral deficiencies
  • Virus infections
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3
Q

What is a source of genetic variation?

A
  • Random fertilisation
  • Independent assortment
  • Crossing over
  • Mutations
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4
Q

Define genotype.

A

The combination of alleles an organism inherits for a characteristic

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5
Q

Define phenotype.

A

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

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6
Q

Define dominant allele.

A

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

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7
Q

Define recessive allele

A

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

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8
Q

Define homozygous

A

When there are two identical allele for a characteristic

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9
Q

Define heterozygous

A

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

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10
Q

Define continuous variation

A

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

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11
Q

Define discontinuous variation.

A

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

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12
Q

Define monogenic inheritance.

A

The inheritance of a single gene

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13
Q

What does a homozygous genetic cross result in?

A

100% heterozygous genotype

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14
Q

What does a heterozygous genetic cross result in?

A

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

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15
Q

Define codominance.

A

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

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16
Q

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

A

Capital letter with a superscript

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17
Q

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

A

100 % heterozygous genotype = 100% codominant phenotype

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18
Q

What will a heterozygous codominant genetic cross result in?

A

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

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19
Q

Define multiple alleles.

A

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

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20
Q

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

A

2, one from each parent

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21
Q

What does the immunoglobulin gene code for?

A

The different antigens in a RBC

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22
Q

What are sex linked chromosomes?

A

Characteristics carried on the sex chromosomes

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23
Q

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

A

Yes because it is smaller

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24
Q

What is haemophilia?

A

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

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25
Q

What happens if a male inherits the recessive haemophiliac gene?

A

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

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26
Q

Define a carrier

A

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

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27
Q

What is a dyhybrid cross?

A

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

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28
Q

What is the ratio commonly found in a F2 dihybrid cross

A

9:3:3:1

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29
Q

Why may the ratio differ?

A
  • 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
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30
Q

Define autosomal linkage.

A

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

31
Q

Recombination frequency equation

A

Number of recombinant offspring / Total number of offspring

32
Q

What percentage suggests gene linkage?

A

50 or more

33
Q

Define epistasis.

A

The interaction of genes at different loci

34
Q

What results in epistasis occurring?

A

Continuous and multiple genes

35
Q

Define hypostatic.

A

A gene that is affected by another gene

36
Q

Define epistatic

A

A gene that affects the expression of another gene

37
Q

What is recessive epistasis?

A

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

38
Q

What is dominant epistasis?

A

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
Q

Define population genetics

A

The investigation of how allele frequencies within populations changes over time

40
Q

Define gene pool

A

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

41
Q

Define allele frequency

A

The relative frequency of a particular allele in a population

42
Q

Calculation allele frequency

A

P+Q=1

43
Q

What is the Hardy-Weinberg principle.

A

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
Q

What is the Hardy-Weinberg equation?

A

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

45
Q

What assumption is made by the Hardy-Weinberg principle?

A

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

46
Q

What factors lead to changes in allele frequency?

A
  • Mutation
  • Sexual selection
  • Gene flow
  • Genetic drift
  • Natural selection
47
Q

Which populations cannot adapt to change as easily?

A

Small populations with limited genetic diversity

48
Q

Which factors affect the size of populations?

A

Density dependent factors

Density independent factors

49
Q

Define density dependent factors.

A

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

50
Q

Define density independent factors.

A

Affect all populations of all sizes

  • Climate change
  • Natural disasters
  • Seasonal change
  • Human activities
51
Q

What are population bottlenecks?

A

Large reductions in population size over t least one generation

52
Q

What is a pro and con of a genetic bottleneck?

A

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
Q

What is the founder effect?

A

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

54
Q

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

A

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

55
Q

What is a normal distribution?

A

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

56
Q

What is stabilising selection?

A

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

57
Q

What is directional selection?

A

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
Q

What is disruptive selection?

A

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

59
Q

Define speciation

A

The formation of new species through the process of evolution

60
Q

Define allopatric speciation

A

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

61
Q

What causes allopatric speciation?

A

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

62
Q

Define sympatric speciation

A

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
Q

What cause sympatric speciation?

A

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
Q

What is a prezygotic reproductive barrier?

A

A barrier preventing fertilisation and the formation of a zygote

65
Q

What is a postzygotic reproductive barrier?

A

A reduction in the viability or reproductive potential of an offspring

66
Q

Define polymorphic

A

Display more than one distinct phenotype for most characteristics

67
Q

What is the wild type allele?

A

The allele coding for the most common characteristic

68
Q

What are mutants?

A

Alleles arising from mutations

69
Q

What is artificial selection?

A

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

70
Q

Define inbreeding

A

The breeding of closely related individuals

71
Q

What are the problems caused by inbreeding?

A

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
Q

What are seed banks?

A

Banks that keep samples of seeds of different species of plants

73
Q

What are gene banks?

A

Store biological samples, other than seeds

74
Q

What is outbreeding?

A

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

Biology A2 (2 decks)

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