genetics, populations and evolution

Question 1

What is a gene?

Answer 1

A sequence of DNA bases that codes for a protein (polypeptide).

Question 2

What is an allele?

Answer 2

A different version of a gene caused by a difference in base sequence.

Question 3

What is a genotype?

Answer 3

The genetic constitution (alleles) of an organism.

Question 4

What is a phenotype?

Answer 4

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

Question 5

What is a dominant allele?

Answer 5

An allele whose trait appears in the phenotype even with only one copy present.

Question 6

What is a recessive allele?

Answer 6

An allele whose trait only appears in the phenotype if two copies are present.

Question 7

What are codominant alleles?

Answer 7

Two alleles that are both expressed in the phenotype.

Question 8

What is a locus?

Answer 8

The fixed position of a gene on a chromosome.

Question 9

What is a homozygote?

Answer 9

An organism with two identical alleles at a gene locus.

Question 10

What is a heterozygote?

Answer 10

An organism with two different alleles at a gene locus.

Question 11

What is a carrier?

Answer 11

A person who carries a recessive allele but does not express it in the phenotype.

Question 12

What is a monohybrid cross?

Answer 12

A genetic cross involving one gene with two alleles.

Question 13

What is a dihybrid cross?

Answer 13

A genetic cross involving two genes. The typical F2 phenotypic ratio is 9:3:3:1.

Question 14

Why might actual ratios deviate from expected ratios in a dihybrid cross?

Answer 14

Due to sex linkage, autosomal linkage, or epistasis.

Question 15

How does the ABO blood group system work genetically?

Answer 15

It involves 3 alleles: IA, IB (codominant), and IO (recessive).

Question 16

What is sex linkage?

Answer 16

When a gene is located on a sex chromosome, often the X chromosome.

Question 17

Why are males more likely to express X-linked recessive traits?

Answer 17

Males have only one X chromosome, so recessive alleles are always expressed.

Question 18

What is autosomal linkage?

Answer 18

When genes are on the same autosome and are inherited together unless separated by crossing over.

Question 19

What is epistasis?

Answer 19

When one gene masks or suppresses the expression of another gene.

Question 20

Example of epistasis?

Answer 20

Baldness gene masking the gene for widow’s peak — baldness is epistatic.

Question 21

What is the chi-squared test used for in genetics?

Answer 21

To determine whether observed results significantly differ from expected ratios.

Question 22

What is the null hypothesis in a chi-squared test?

Answer 22

There is no significant difference between observed and expected values.

Question 23

How do you calculate degrees of freedom in chi-squared tests?

Answer 23

Number of categories - 1.

Question 24

When do you reject the null hypothesis in chi-squared tests?

Answer 24

When the chi-squared value is greater than or equal to the critical value.

Question 25

What is the gene pool?

Answer 25

The complete set of alleles in a population.

Question 26

What is allele frequency?

Answer 26

The proportion of a particular allele in a population, usually given as a percentage.

Question 27

What are the Hardy-Weinberg equations?

Answer 27

Allele frequency: p + q = 1 Genotype frequency: p² + 2pq + q² = 1

Question 28

What conditions must be met for Hardy-Weinberg to apply?

Answer 28

No mutations, large population, random mating, no selection, no migration.

Question 29

What causes genetic variation?

Answer 29

Mutation, crossing over, independent assortment, random fertilisation.

Question 30

What causes phenotypic variation?

Answer 30

Genetic factors, environmental factors, or a combination of both.

Question 31

What is natural selection?

Answer 31

The process where individuals with advantageous traits survive and reproduce, passing on their alleles.

Question 32

What is stabilising selection?

Answer 32

Favours average phenotypes, reducing variation. Occurs in stable environments.

Question 33

What is directional selection?

Answer 33

Favours one extreme phenotype. Occurs during environmental change.

Question 34

What is disruptive selection?

Answer 34

Favours both extremes over the average. Leads to increased variation.

Question 35

What is speciation?

Answer 35

The formation of new species due to reproductive isolation.

Question 36

What is allopatric speciation?

Answer 36

Speciation due to geographic isolation and different selection pressures.

Question 37

What is sympatric speciation?

Answer 37

Speciation without geographic isolation, due to random mutations.

Question 38

What is seasonal isolation?

Answer 38

When organisms breed at different times of the year.

Question 39

What is mechanical isolation?

Answer 39

Mating is prevented by incompatible reproductive organs.

Question 40

What is behavioural isolation?

Answer 40

Differences in courtship behaviours prevent mating.

Question 41

What is genetic drift?

Answer 41

A change in allele frequencies due to random chance, not selection.

Question 42

In which populations does genetic drift have the greatest effect?

Answer 42

Small populations.

Question 43

What are the consequences of genetic drift?

Answer 43

Loss of genetic variation, fixation or loss of alleles.