3.7.1 Inheritance

Question 1

Define phenotype. (2)

Answer 1

1. Expression of genetic constitution of an
   organism/genotype;
2. And its interaction with the environment;

Question 2

Define genotype. (1)

Answer 2

1. The genetic constitution of an organism;

Question 3

If a gene is sex-linked on the X chromosome, why
is the phenotype more common in XY organisms?
(2)

Answer 3

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

Question 4

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

Answer 4

1. Crossing over;
2. Independent segregation/assortment (of
   homologous chromosomes);
3. Random fertilisation;

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/fertilisation of gametes is
   random;
3. Linked Genes;
4. Epistasis;
5. Lethal genotypes;

Question 6

Name the relationship between two alleles when
both alleles appear in the phenotype (1)

Answer 6

Co-dominance

Question 7

Name the type of gene interaction when one gene
affected the expression of another (1)

Answer 7

epistasis

Question 8

Explain what it means when two genes are linked
(1)

Answer 8

on same chromosome.

Question 9

Which statistical test could the scientist use to
determine whether his observed results were
significantly different from the expected results?
Give the reason for your choice of statistical test.
(2)

Answer 9

1. Chi squared test;
2. Categorical data.