Module 7- Inheritance

Question 1

Define gene

Answer 1

Sequence of DNA nucleotide bases

Question 2

Define allele

Answer 2

Altnernative form of a gene

Question 3

Define recessive allele

Answer 3

The allele determines a characteristic only if no dominant allele is present

Question 4

Define dihybrid

Answer 4

Inheritance of 2 genes

Question 5

Define monohybrid

Answer 5

Inheritance of 1 gene

Question 6

Define dominant allele

Answer 6

This allele determines the development of a characteristic, even if one copy is present

Question 7

Define a homozygous chromosome

Answer 7

A pair of chromosomes that have the same alleles of a gene

Question 8

Define a heterozygous chromosome

Answer 8

A pair of chromosomes that have different alleles of a gene

Question 9

Define gametes

Answer 9

An egg cell or a sperm cell

Question 10

Define genotype

Answer 10

The alleles present in an organism

Question 11

Define phenotype

Answer 11

The physical appearance of an individual

Question 12

Define multiple gametes

Answer 12

A gene that has many different forms e.g. blood group

Question 13

Define condominance

Answer 13

When both alleles are expressed equally

Question 14

2 marks

Males are more likely than females to show a phenotype produced by a recessive allele carried on the X chromosome. Explain why.

Sex-linked genes

Answer 14

1. Males have only one allele
2. Females need two recessive alleles

Question 15

2 marks

Explain what is meant by the term phenotype

Answer 15

1.Characteristic due to genetic genotype /alleles
2.Characteristic due to environment

Question 16

2 marks

The actual % of heterozygous is likely to be lower in future generations. Explain why

Answer 16

• Affected individuals usually do not reproduce
• Die during childhood
• Do not pass on allele
• Genetic screening

Question 17

1 mark

In fruit flies, the genes for body colour and wing length are linked. Explain what this means

Answer 17

Genes on the same chromosome

Question 18

2 marks

In fruit flies, males have the sex chromosomes XY and the females have XX. In fruit flies, a gene for eye colour is carried on the X chromosome. The allele for red eyes, R, is dominant to the allele for white eyes, r.
Male fruit flies are more likely than female fruit flies to have white eyes. Explain why.

Answer 18

1. Males have only one allele
2. Females need two recessive alleles

Question 19

3 marks

In fruit flies, the genes for body colour and for wing development are not on the sex chromosomes. The allele for grey body colour, G, is dominant to the allele for black body colour, g. The allele for long wings, L, is dominant to the allele for short wings, l.
A geneticist carried out a cross between fruit flies with grey bodies and long wings (heterozygous for both genes) and fruit flies with black bodies and short wings.
Grey body and long wings- 223
Black body and short wings- 218
Explain the results.

Answer 19

1. The 2 genes are linked (autosomal linkage)
2. No cossing over (crossing over less likely to occcur if linked genes are close together)
3. No Gl and no gL gametes produced

Question 20

2 marks

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

Answer 20

1. Small sample size
2. Random fertilisation
3. Linked Genes
4. Epistasis
5. Lethal genotypes

Question 21

A student investigated the monohybrid inheritance of eye shape in fruit flies. Two fruit flies with bar (narrow) eyes were crossed. Of the offspring, 1538 had bar eyes and 462 had round (normal) eyes.
Using suitable symbols, give the genotypes of the parents. Explain your answer.

Answer 21

1. Bb / suitable equivalent
2. Both parents have bar eyes, but have some offspring with round eyes, so parents must be carriers of recessive allele for round eyes

Question 22

Define genes locus

Answer 22

Location of a gene on a chromosome