7- Inheritance =)

Question 1

Explain what is meant by the term phenotype. (2)

Answer 1

• expression/ characteristic ∵ genotype
• & the environment

Question 2

Suggest two reasons why observed ratios are often not the same as expected ratios. (2)

Answer 2

1. random fertilisation of gametes
2. small sample size
3. linked genes
4. epistasis
5. lethal genotypes

lethal- fatal

Question 3

Explain what is meant by codominant alleles. (1)

Answer 3

both expressed in phenotype

Question 4

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. (2)

Answer 4

• males only have 1 allele
• females need 2 recessive alleles

Question 5

Mutation is one cause of genetic variation in organisms.
Give two other causes of genetic variation. (2)

Answer 5

1. crossing over
2. random fusion of gametes
3. independent assortment

Question 6

What is a gene pool? (1)

Answer 6

all the alleles in a pop

Question 7

Several years later, scientists repeated their study on this population. They found that the frequency of the recessive allele had decreased.
(A statistical test showed that the difference between the two frequencies of the t allele was significant at the P = 0.05 level.
Use the terms probability and chance to help explain what this means. (2)

Answer 7

• there is a probability of 0.05
• that diff in freq are due to chance

Question 8

In fruit flies, the genes for body colour and wing length are linked. Explain what this means. (1)

Answer 8

Genes on the same chromosome