6.1.2

Question 1

What is codominance?

Answer 1

Codominance is when two different alleles occur for a gene - both being equally dominant. This means that both alleles are expressed in the phenotype of the organism if present.

Question 2

What is incomplete dominance?

Answer 2

Incomplete dominance is when two different alleles occur for a gene, but are only partially expressed in the phenotype. E.g. a white plant and a red plant being crossed to form a pink plant.

Question 3

What are sex-linked characteristics?

Answer 3

Sex-linked characteristics are those that are determined by genes carried on the sex chromosomes.

Question 4

In humans, what sex chromosome is larger?

Answer 4

X chromosome

Question 5

What does the X chromosome being larger mean for sex-linked characteristics?

Answer 5

There are some genes in the X chromosome that males only have one copy of, meaning that if a gene is present in the X chromosome, it will be expressed whether dominant or recessive, if the Y chromosome does not have that gene.

Question 6

Give an example of a sex-linked genetic disorder

Answer 6

Haemophilia

Question 7

What is a dihybrid cross used for?

Answer 7

It is used to show the inheritance of two different characteristics, caused by two genes, which may be located on different pairs of homologous chromosomes.

Question 8

What is an autosome?

Answer 8

Non-sex chromosome

Question 9

What is autosomal linkage?

Answer 9

When two genes are linked by being on the same chromosome

Question 10

If two genes are very far apart on the same chromosome, are they weakly or strongly linked?

Answer 10

Weakly

Question 11

How does autosomal linkage affect independent assortment?

Answer 11

There is no independent assortment, as the linked genes are inherited as one unit

Question 12

What is the only way autosomal linked genes can be separated?

Answer 12

Crossing over

Question 13

What are recombinant offspring?

Answer 13

Offspring that are produced by crossing over

Question 14

What is recombination frequency?

Answer 14

A measure of the amount of crossing over that has happened in meiosis

Question 15

How is recombination frequency calculated?

Answer 15

Number of recombinant offspring/total offspring

Question 16

What does a recombination frequency of 50% indicate?

Answer 16

There is no linkage and the genes are on separate chromosomes

Question 17

What does a recombination frequency of <50% indicate?

Answer 17

There is gene linkage and the independent assortment has been hindered

Question 18

What statistical test can be carried out to determine whether the observed frequencies are significantly different to the expected values?

Answer 18

Chi-squared

Question 19

What is epistasis?

Answer 19

Epistasis is the interaction of genes at different loci

Question 20

What is dominant epistasis?

Answer 20

Dominant epistasis is when a dominant allele results in a gene having an effect on another gene, masking said gene

Question 21

What is a gene pool?

Answer 21

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

Question 22

What is the allele frequency?

Answer 22

The relative frequency of a particular allele in a population

Question 23

What is the Hardy-Weinberg principle?

Answer 23

It states that in a stable population with no disturbing factors, the allele frequencies will remain constant from one generation to the next and there will be no evolution

Question 24

What conditions are required for the Hardy-Weinberg principle to hold true?

Answer 24

• No mutations
• No immigration/emigration
• No selection
• Mating is random
• The population is large

Question 25

How can the Hardy-Weinberg principle be expressed?

Answer 25

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

Question 26

What factors affect evolution?

Answer 26

Mutation
Sexual selection
Gene flow
Genetic drift
Natural selection

Question 27

What is gene flow?

Answer 27

The movement of alleles between populations. This is caused by immigration and emigration

Question 28

What is genetic drift?

Answer 28

A change in allele frequency due to the random nature of mutation

Question 29

What is the founder effect?

Answer 29

When a few individuals of a species colonise a new area, their offspring initially experience a loss in genetic variation, and rare alleles can become much more common in the population

Question 30

What is the bottleneck effect?

Answer 30

When a major disaster of event kills or a large number of the population, so only few individuals survive.

Question 31

What is stabilising selection?

Answer 31

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

Question 32

What is directional selection?

Answer 32

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

Question 33

What is disruptive selection?

Answer 33

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

Question 34

What is speciation?

Answer 34

Formation of new species through the process of evolution

Question 35

What events lead to speciation?

Answer 35

Members of a population become isolated and no longer interbreed with the rest of the population, resulting in no gene flow.
Alleles within the groups continue to undergo random mutations. Environments of each group may be different or change.
The accumulation of mutation and changes in allele frequencies over many generations lead to changes in phenotype

Question 36

What is allopatric speciation?

Answer 36

Allopatric speciation is the more common form of speciation and happens when some members of a population are separated from the rest of the group by a physical barrier, so they are geographically isolated.

Question 37

What is sympatric speciation?

Answer 37

Sympatric speciation occurs within the population that share the same habitat. It is reproductive speciation

Question 38

What is artificial selection?

Answer 38

The selection for breeding of plants or animals with desirable characteristics by farmers or breeders.

Question 39

What is inbreeding?

Answer 39

The breeding of closely related individuals.