Genetics and Inheritance

Question 1

Suggest three causes of genetic variation (3)

Answer 1

1. Mutation
2. Crossing over
3. Independent segregation
4. Random fusion of gametes

Question 2

What is meant by a genome? (1)

Answer 2

1. DNA in a cell/organism
2. Genetic material/code in a cell/organism
3. Total number of DNA bases in a cell

Question 3

What is a gene pool? (1)

Answer 3

1. All the alleles in a population

Question 4

How do multiple alleles of a gene arise? (2)

Answer 4

1. Mutations
2. Which are different / at different positions in the gene

Question 5

In genetic crosses, the observed phenotypic ratios obtained in the offspring are often not the same as the expected ratios. Suggest two reasons why. (2)

Answer 5

1. Small sample size
2. Fusion of gametes is random
3. Crossing over
4. Epistasis
5. Lethal genotypes

Question 6

What is meant by a recessive allele? (1)

Answer 6

1. Only expressed in the homozygote

Question 7

What does Hardy Weinberg’s equation predict? (3)

Answer 7

1. The frequency of alleles
2. Will stay constant over generations
3. Providing no mutation/no selection/mating at random/no migration

Question 8

Define gene linkage (1)

Answer 8

1. Genes/loci on same chromosome

Question 9

Define epistasis (1)

Answer 9

1. The allele of one gene affects or masks the expression of another in the phenotype

Question 10

Describe why observed phenotypes don’t match expected values (3)

Answer 10

1. Random fusion of gametes
2. Small sample
3. Selection advantage

Question 11

Define codominance (1)

Answer 11

1. Both alleles expressed in the phenotype

Question 12

Rules for Dominant alleles (3)

Answer 12

1. Affected offspring MUST have at least one affected parent
2. Unaffected parents ONLY have unaffected offspring
3. If both parents are affected and have an unaffected offspring

Question 13

Rules for recessive alleles (1)

Answer 13

1. Unaffected parents can have an affected offspring

Question 14

Male offspring are more likely than females to show recessive sex-linked characteristics. Explain why.(2)

Answer 14

1. Recessive allele always expressed in males
2. Females need two recessive alleles / be heterozygous

Question 15

Expected offspring phenotype ratios from heterozygous parents:
1. Monohybrid
2. Dihybrid
3. Epistasis
4. Autosomal linkage

Answer 15

1. 3:1
2. 9:3:3:1
3. 9:4:3 or 15:1
4. 3:1 (no other pattern other than 4 phenotypes with recombination of alleles)

Question 16

What is meant by the term phenotype? (2)

Answer 16

1. Expression due to genetic constitution
2. Due to interaction with environment

Question 17

Explain how a single base substitution causes a change in the structure of a polypeptide (3)

Answer 17

1. Change in sequence of amino acid/ primary structure
2. Change in hydrogen/ionic/disulphide bonds
3. Alters tertiary structure

Question 18

State the Hardy-Weinberg equation that is for the frequency of the genotype/phenotype (1)

Answer 18

P2 + 2Pq + q2 = 1

Question 19

State the Hardy-Weinberg equation that is for the frequency of the allele (1)

Answer 19

P + q = 1

Question 20

Sex link rules (to prove a characteristic is not sex linked) for dads and daughters (2)

Answer 20

1. If daughter is affected, father is not
2. AND it is a recessive disease

Question 21

Sex link rules (to prove a characteristic is not sex linked) for mothers and sons (2)

Answer 21

1. If son is affected, mum is not
2. AND it is a dominant disease