6.1.2 Patterns of Inheritance

Question 1

Define phenotype.

Answer 1

The expression of an organism’s genetic constitution e.g. low metabolism, combined with its interaction with the environment e.g. diet.

Question 2

How can meiosis bring about genetic variation?

Answer 2

● Random arrangement of chromosomes during lining up.

● Crossing over of chromatids before the first division.

Question 3

How does random fertilisation bring about genetic

variation?

Answer 3

Gametes are haploid cells, meaning they only contain half of a person’s DNA. As this is determined by meiosis, every gamete contains different DNA. Therefore the same two individuals can produce genetically different offspring.

Question 4

Define monogenic inheritance.

Answer 4

Where one phenotypic characteristic is controlled by a single gene.

Question 5

Define dihybrid inheritance.

Answer 5

Where two phenotypic characteristics are determined by two different genes present on two different chromosomes at the same time.

Question 6

What is meant by sex-linkage?

Answer 6

Where an allele is located on one of the sex chromosomes, meaning its expression depends on the sex of the individual.

Question 7

What is meant by multiple alleles?

Answer 7

A gene with more than two alleles.

Question 8

What is meant by codominant alleles?

Answer 8

Two dominant alleles that both contribute to the phenotype, either by showing a blend of both characteristics, or the characteristics appearing together.

Question 9

What is meant by autosomal linkage?

Answer 9

Where two or more genes are located on the same (non-sex) chromosome. In this case, only one homologous pair is needed for all four alleles to be present. For genes that aren’t linked, two homologous pairs are needed.

Question 10

What is meant by epistasis?

Answer 10

Where two non-linked genes interact, with one gene either masking or suppressing the other gene.

Question 11

What is the chi-squared test?

Answer 11

A statistical test to find out whether the difference between observed and expected data is due to chance or a real effect. Can be used to compare expected phenotypic ratios with observed ratios.

Question 12

How is a chi-squared test performed?

Answer 12

The formula results in a number, which is then compared to a critical value (for the corresponding degrees of freedom). If the number is greater than or equal to the critical value, we conclude there is no significant difference and the results occured due to chance.

Question 13

How can the number of genes coding for a

characteristic influence variation?

Answer 13

● Discontinuous variation= characteristic determined by one gene (monogenic inheritance)
● Continuous variation= characteristic determined by more than one gene (polygenic inheritance)

Question 14

What is stabilising selection?

Answer 14

Occurs when environmental conditions stay the same. Individuals closest to the mean are favoured, and any new characteristics are selected against. Results in low diversity.

Question 15

What is directional selection?

Answer 15

Occurs when environmental conditions change. Individuals with phenotypes suited to the new conditions will survive and pass on their genes. Over time the mean of the population will move towards these characteristics.

Question 16

What is genetic drift?

Answer 16

A change in a population’s allele frequencies that occurs due to chance rather than selective pressures. In other words, it is caused by ‘sampling error’ during reproduction.

Question 17

What is meant by a genetic bottleneck?

Answer 17

Where a catastrophic event dramatically reduces the size of a population, thereby decreasing the variety of alleles in the gene pool and causing large changes in allele frequencies.

Question 18

What is meant by the founder effect?

Answer 18

When a small number of individuals become isolated, forming a new population with a limited gene pool, with allele frequencies not reflective of the original population.

Question 19

What is the Hardy-Weinberg principle?

Answer 19

Allows us to estimate the frequency of alleles in a population, as well as if allele frequency is changing over time.

Question 20

Explain the Hardy-Weinberg equation for calculating

allele frequency.

Answer 20

The frequencies of each allele for a characteristic must add up to 1.0. The equation is therefore; p + q = 1
Where p= frequency of the dominant allele, and q= frequency of the recessive allele.

Question 21

Explain the Hardy-Weinberg equation for calculating

genotype frequency.

Answer 21

The frequencies of each genotype for a characteristics must add up to 1.0. The equation is therefore; p2 + 2pq + q2 = 1
Where p2= frequency of homozygous dominant, 2pq= frequency of heterozygous, and q2= frequency of homozygous recessive.

Question 22

Define speciation.

Answer 22

Where a population is split and isolated, there are different selective pressures on the two groups. If the genetic makeup changes to the extent the two groups can not longer interbreed, they have become separate
species.

Question 23

What is meant by allopatric speciation?

Answer 23

Speciation resulting from a physical barrier e.g. river, mountain range. The environments occupied by the two groups are different, and therefore different alleles are favoured.

Question 24

What is meant by sympatric speciation?

Answer 24

Speciation resulting from a non-physical barrier e.g. a mutation that no longer allows two organisms to produce fertile offspring. Any changes in anatomy or behaviour may also prevent breeding.

Question 25

What is artificial selection?

Answer 25

Humans choose particular organisms to breed together in order to produce a desired characteristic in the offspring.

Question 26

Give examples of artificial selection in plants and

animals.

Answer 26

● Plants= seeds used from plants that produce larger fruit and vegetables.
● Animals= cows with higher milk yield are chosen and selectively bred.

Question 27

Why is it important to keep a resource of genetic

material when selective breeding?

Answer 27

Allows any traits that were accidentally bred out to be reintroduced, or to revert back to a point before any negative traits were introduced.

Question 28

Give some ethical issues around the use of artificial

selection.

Answer 28

● Anatomical changes in animals e.g. respiratory issues in pugs.
● Higher susceptibility to disease in both plants and animals.