3.7 Genetics , populations , evolution and ecosystems (A- level only)

Question 1

what is a genotype?

Answer 1

The genetic constitution of an organism.

Question 2

What is a phenotype?

Answer 2

The expression of the genes and its interaction with the environment.

Question 3

What is a homozygous allele?

Answer 3

A pair of homologous chromosomes carrying the same alleles for a single gene.

Question 4

What is a heterozygous allele?

Answer 4

A pair of homologous chromosomes carrying two different alleles for a single gene.

Question 5

What is a recessive allele?

Answer 5

An allele only expressed if no dominant allele is present .

Question 6

What is a dominant allele?

Answer 6

An allele that will always be expressed in the phenotype.

Question 7

What is multiple alleles?

Answer 7

More than two alleles for a single gene.

Question 8

What is sex - linkage ?

Answer 8

A gene whose locus is on the X chromosome.

Question 9

What is autosomal linkage?

Answer 9

Genes that are located on the same chromosome ( not the sex - chromosomes).

Question 10

What is epistasis?

Answer 10

When one gene modifies or masks the expression of a different gene at a different locus.

Question 11

What is monohybrid inheritance?

Answer 11

Genetic inheritance cross of a characteristic determined by one gene.

Question 12

What is dihybrid inheritance?

Answer 12

Genetic inheritance cross for a characteristic determined by two genes .

Question 13

What is co dominance ?

Answer 13

Both alleles are equally dominant and expressed in the phenotype.

Question 14

What is gene pool?

Answer 14

All the alleles of all genes within a population at one time.

Question 15

What is population ?

Answer 15

All the individuals of one species in one area at one time.

Question 16

What is allele frequency ?

Answer 16

The proportion of an allele within the gene pool.

Question 17

What is the Hardy - Weinberg principle ?

Answer 17

The mathematical model which can be used to predict the allele frequencies within a population.

Question 18

What is the accuracy / conditions of the hardy - weinberg principle?

Answer 18

It assumes that there will be no change in the allele frequency between generations within a population , so it’s not perfectly accurate.

Question 19

What are the assumptions of the hardy - weinberg principle ?

Answer 19

• No migration to introduce or removal of alleles from the population.
• No mutations to create new alleles
• No selection favouring particular alleles.
• Mating is random ( no inbreeding)
• The population is large

Question 20

What is the hardy - weinberg equation?

Answer 20

p^2 + 2pq + p^2 = 1
p^2 = frequency of homozygous dominant genotype.
2pq = frequency of heterozygous genotype.
q^2 = frequency of homozygous recessive genotype.

p+q= 1
p = frequency of dominant allele
q = frequency of recessive allele

Question 21

What causes variation within a population of species ?

Answer 21

• main source is mutation
• meiosis (crossing over and independent segregation)
• random fertilisation

Question 22

What are the three types of selection?

Answer 22

• Stabilising
• Directional
• Disruptive

Question 23

What is disruptive selection ?

Answer 23

• Individuals which contain the alleles coding for either extreme trait are more likely to survive and pass on their alleles.
• Allele frequency changes and more individuals possess the allele for the extreme trait.
• middling trait allele becomes less frequent
• continued disruptive selection can ultimately lead to speciation

Question 24

What is speciation ?

Answer 24

Speciation is the process that results in the creation of new species

Question 25

How does speciation happen?

Answer 25

•One original population of the same species becomes reproductively isolated.
•This means that there are now two populations of the same species but they cannot breed together.
• Results in the accumulation of differences in their gene pool

Question 26

What are the two ways that populations can become reproductively isolated ?

Answer 26

• Allopatric speciation
- Geographical barrier
• Sympatric speciation
- Changes in the reproduction mechanisms

Question 27

What is sympatric speciation?

Answer 27

Populations can become reproductively isolated due to differences in their behaviour

Question 28

How can sympatric speciation occur?

Answer 28

• Due to random mutation which could impact reproductive behaviour such as may cause to perform different courtship behaviour
• Due to this , individuals will not reproduce together so no gene flow between the two groups within the population
• Overtime these reproductively isolated populations will accumulate different mutations to the extent that their DNA is so different they can’t interbreed therefore classed as two different species

Question 29

What is genetic drift?

Answer 29

This is the change in the allele frequency within a population between generations.

Question 30

What can result in evolution?

Answer 30

• Continuous , substantial genetic drift can result in evolution
• the smaller the population is the bigger the impact allele frequency have and this is why evolution occurs more rapidly in smaller populations