Inheritance and selection Flashcards

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1
Q

What is meant by genotype?

A

The genetic make up of an organism that describes all the alleles that the organism contains, i.e. Bb

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2
Q

What is meant by phenotype?

A

The observable characteristics of an organism. It is the result of the interaction between the expression of the genotype and the environment.

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3
Q

What is a gene?

A

A section of DNA that is a sequence of nucleotide bases, that codes for a single characteristic of an organism.

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4
Q

What is an allele?

A

One of the different forms of the gene.

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5
Q

What is meant by the gene locus?

A

The position of the gene on the chromosome.

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6
Q

What are homologous chromosomes?

A

A pair of chromosomes that an individual possesses, one from the mother, one from the father.

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7
Q

What is meant by the term homozygous?

A

Both alleles from both chromosomes are the same.

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8
Q

What is meant by the term heterozygous?

A

The alleles on the two different chromosomes are different.

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9
Q

What is an individual with two dominant alleles called?

A

Homozygous dominant.

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10
Q

What is an individual with two recessive alleles called?

A

Homozygous recessive.

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11
Q

What is meant by ‘dominant allele’?

A

An allele that will always be expressed in the phenotype of the individual.

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12
Q

What is meant by ‘recessive allele’?

A

An allele that will not be expressed in the phenotype of the individual if a dominant allele is present in the genotype.

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13
Q

What is meant by the F1 generation?

A

The first set of offspring from the genetic cross.

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14
Q

What is meant by the F2 generation?

A

The offspring of the crossing of the F1 generation.

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15
Q

How many pairs of chromosomes do humans have?

A

23

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16
Q

What are the human sex chromosomes/gametes?

A
Females = XX
Males = XY
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17
Q

What does the term sex-linked refer to?

A

Any gene that is carried on either the X or Y chromosome is said to be sex-linked.

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18
Q

What is the effect of the Y chromosome on sex linked disorders?

A

The Y chromosome is shorter than the X chromosome, so if the gene is carried on the X chromosome, the male wont have 2 alleles for it and only one due to the length.

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19
Q

Why will characteristics controlled by a recessive allele often occur more frequently in males?

A

Because a male will only need one recessive allele rather than two to be expressed as there is no dominant allele on the other chromosome.

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20
Q

What is an example of a sex-linked disorder?

A

Haemophilia (caused by a recessive allele).

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21
Q

What is a carrier?

A

When an individual possesses the particular allele without expressing it in the phenotype.

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22
Q

What is the family tree diagram called?

A

A pedigree chart.

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23
Q

What is a male represented by in a Pedigree Chart?

A

A square.

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24
Q

What is a female represented by in a Pedigree Chart?

A

A circle.

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25
Q

What does shading mean in a Pedigree Chart?

A

Presence of a characteristic.

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26
Q

What does a dot mean in a Pedigree Chart?

A

Carrying.

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27
Q

What is co-dominance?

A

In which both alleles are equally dominant and therefore will both be expressed in the phenotype.

28
Q

What are multiple alleles?

A

When there are more than 2 alleles of a gene, of which only two may be present at the loci of an individuals homologous chromosomes.

29
Q

Snap dragons can have red or white alleles. They are co-dominant. What colour will a heterozygous individual be?

A

Pink.

30
Q

What do the alleles for blood groups code for?

A

The production of different antigens on the surface membrane of red blood cells.

31
Q

In terms of blood groups, what do alleles I(A), I(B) and I(O) do?

A

I(a) produces antigens A on the surface membrane of red blood cells
I(B) produces antigens B on the surface membrane of red blood cells
I(O) produces neither of the antigens
I(A)I(B) produces both A and B antigens on the surface membrane of red blood cells.

32
Q

In terms of blood groups, which alleles are dominant?

A

A and B are co-dominant , and both are dominant over O.

33
Q

What is meant by a dominance hierarchy?

A

A chart showing each allele being dominant to all those below in the table, and recessive to all those above it.

34
Q

What is the gene pool?

A

Gene pool refers to all of the alleles of all of the genes of all of the individuals in a population at any one time.

35
Q

What is the allelic frequency?

A

The number times and allele occurs within the gene pool.

36
Q

If there is 10,000 people in a population, why will there be 20,000 alleles in the gene pool of a non-sex linked gene? Although we have the alleles in every cell of our body, we only count for one cell.

A

Because we have homologous pairs of chromosomes and therefore have two alleles for each gene, one from each parent.

37
Q

What is it important to consider when looking at heterozygous combinations?

A

There are 2 different arrangements, e.g. Bb and bB, as you could inherit the dominant allele from either parent or vice versa.

38
Q

How many different combinations of genotype are there for a two allele gene?

A

4

39
Q

What numbers can allelic frequency be between?

A

0 and 1.0

40
Q

What does the Hardy-Weinberg principle do?

A

It provides a mathematical equation that can be used to calculate the frequencies of the alleles of a particular gene in a population.

41
Q

What does the Hardy-Weingberg principle predict?

A

The proportion of dominant and recessive alleles of any gene in a population remains the same from one generation to the next.

42
Q

What conditions must be met in order for the Hardy-Weinberg assumption to be realistic? (5 points)

A

No mutations arise
The population is isolated so there is no flow of alleles into or out of the population
There is no selection so that all alleles are equally likely to be passed on to the next generation
The population is large
Mating with the population is random.

43
Q

What is the Hardy Weinberg equation?

A

p(squared) + 2pq + q(squared) = 1

44
Q

What is p in the Hardy Weinberg equation?

A

The frequency of the dominant allele.

45
Q

What is q in the Hardy Weinberg equation?

A

The frequency of the recessive allele.

46
Q

What is p(squared) in the Hardy Weinberg equation?

A

The frequency of the homozygous dominant genotype.

47
Q

What is q(squared) in the Hardy Weinberg equation?

A

The frequency of the homozygous recessive genotype.

48
Q

What is 2pq in the Hardy Weinberg equation?

A

The frequency of the heterozygous genotype.

49
Q

Why is 2pq used in the Hardy Weinberg equation?

A

Because there is two variations of the heterozygous genotype.

50
Q

Why must p+q = 1.0 in the Hardy Weinberg equation?

A

Because there are only 2 alleles so the frequency of one plus the other must be 1.0 (100%)

51
Q

Why must p(squared) + 2pq + q(squared) = 1.0 in the Hardy Weinberg equation?

A

Because AA+Aa+aA+aa = 1.0 because there are 4 variations of the all combinations.

52
Q

What is meant by selection?

A

The process by which organisms that are better adapted to their environment survive and breed, while those that are less well adapted fail to do so.

53
Q

What is directional selection?

A

When selection favours individuals that vary in one direction from the mean of the population, which changes the characteristics of the population.

54
Q

What is stabilising selection?

A

Selection favours average individuals and preserves the characteristics of a population.

55
Q

What kind of curve do you get on a graph that plots variation?

A

A normal distribution curve.

56
Q

Over time, what happens to the mean in directional selection and why?

A

The mean will move in the direction of the individuals with the advantageous alleles because they will possess a phenotype more suited to the new conditions, making them more likely to survive and breed. They therefore contribute more offspring to the next generation than other individuals, of which will possess the advantageous alleles and phenotypes.

57
Q

What is an example of directional selection from AS?

A

Antibiotic resistance.

58
Q

Over time, what happens to the individuals in stabilising selection and why? What will happen to the mean?

A

Individuals straying far from either side of the mean tend to be eliminated because if environmental conditions remain constant, individuals at the extremes will never be at an advantage. The mean will remain the same.

59
Q

What is speciation?

A

Speciation is the evolution of new species from existing species.

60
Q

What is a species?

A

A group of individuals that share similar genes and are capable of breeding with one another to produce fertile offspring. In other words, they belong to the same gene pool.

61
Q

What is natural selection?

A

The concept ‘survival of the fittest’. Organisms with the desirable trait will survive, reproduce, and pass on their advantageous alleles to their offspring.

62
Q

What is evolution?

A

A change in the genetics and hence characteristics of living organisms over time.

63
Q

Explain speciation.

A

There is geographical isolation of members of the original population so when insert what happened to cause geographical isolation, the insert species became separated. This creates separate gene pools and there is no interbreeding between the populations. There are different selective pressures in different areas due to different environmental conditions, so each of the insert the separated populations will have different selective pressures. Mutations between the separated populations will cause variation within the isolated populations. There is differential survival in the new populations as some individuals are better adapted to the environment. Those individuals with the advantageous alleles will survive, reproduce, and pass on their alleles to their offspring. This leads to a change in allelic frequency. Over time, the isolated populations will become so genetically different that they are unable to breed and produce fertile offspring; they are different species’.

64
Q

What is meant by geographical isolation?

A

Geographical isolation occurs when a physical barrier prevents two populations from breeding with one another. Such barriers include oceans, rivers, mountain ranges and deserts.

65
Q

How long would speciation take?

A

Thousands of years.