Inheritance

In most species of plants and animals, the cell that is formed as a result of fertilisation is diploid and contains homologous chromosomes.

Explain why the cell that is formed as a result of fertilisation is a diploid cell and contains homologous chromosomes.

State the name of the stage in meiosis when reduction division occurs and explain a reason for your choice.

stage in meiosis ______

reason ______

Identify the stages of meiosis shown in Fig. 4.1 and Fig. 4.2.

Fig. 4.1 ______

Fig. 4.2 ______

The cells formed at the end of meiosis in a Lilium pollen mother cell each have 12 chromosomes.

State the number of sister chromatids found in a Lilium pollen mother cell at the start of meiosis.

______

Explain why the enzymes coded for by the lac operon are described as inducible enzymes.

An investigation into the induction and action of the lac operon was carried out using the bacterium, Escherichia coli, grown in a growth medium containing glucose.

When the bacteria had used all the glucose, an excess of lactose was added to the growth medium. The activity of $\beta$-galactosidase was measured from this time ($0\ \text{min}$), as shown in Fig. 3.1.

With reference to the lac operon, explain the shape of the curve in Fig. 3.1.

Huntington’s disease is an inherited genetic disease.

Using Huntington’s disease as an example, outline the relationship between genes, proteins and phenotype.

Retinitis pigmentosa is an inherited genetic disease that causes loss of vision.

The inheritance of a rare form of retinitis pigmentosa in a family is shown in Fig. 2.1.

Scientists concluded that the inheritance of this rare form of retinitis pigmentosa is linked to the Y chromosome.

Using evidence shown in Fig. 2.1, explain why the scientists reached this conclusion.

Incontinentia pigmenti is a disease that affects the skin, hair and central nervous system.

The disease is caused by a dominant allele on the X chromosome.

Construct a genetic diagram to determine the expected offspring for a healthy father and a heterozygous mother with incontinentia pigmenti.

State the expected phenotypic ratio of the offspring.

Use the symbols:
$X^A$ = allele for incontinentia pigmenti
$X^a$ = normal allele

offspring genotypes

offspring phenotypes

expected ratio = ______

Some diseases are caused by mutations in regulatory genes.

Suggest how a mutation in a regulatory gene that codes for a repressor protein could cause a disease.

List all the possible genotypes of a guinea pig with short black fur.

A test cross could be used to determine the genotype of a female guinea pig with short black fur.

Describe the phenotype of the male guinea pig that could be used to carry out this test cross.

A black guinea pig with long fur that was homozygous at both loci was crossed with a chocolate guinea pig with short fur that was homozygous at both loci. The F1 offspring of this cross had short black fur. F1 offspring were mated together to produce the F2 offspring.

Complete the Punnett square to:

• show the cross between the F1 offspring
• predict the F2 offspring genotypes.
  You should include the gametes in your answer.

State the ratio of F2 offspring phenotypes. You should include a key to link phenotypes to genotypes.

ratio of F2 offspring phenotypes: ______

Some genes in guinea pigs are structural genes and some are regulatory genes.

Describe the difference between a structural gene and a regulatory gene.

Explain the terms gene, genotype and phenotype.

gene = ______
genotype = ______
phenotype = ______

A monohybrid genetic cross can be carried out to produce an F1 and an F2 generation.

• Outline how a monohybrid genetic cross is carried out.
• State the expected percentage of each of the different offspring genotypes in the F2 generation.

Assume that the inheritance pattern is for autosomal dominant and recessive alleles.

List all the possible genotypes of a guinea pig with short black fur.

A test cross could be used to determine the genotype of a female guinea pig with short black fur.

Describe the phenotype of the male guinea pig that could be used to carry out this test cross.

A black guinea pig with long fur that was homozygous at both loci was crossed with a chocolate guinea pig with short fur that was homozygous at both loci. The $F_1$ offspring of this cross had short black fur. $F_1$ offspring were mated together to produce the $F_2$ offspring.

Complete the Punnett square to:
• show the cross between the $F_1$ offspring
• predict the $F_2$ offspring genotypes.
You should include the gametes in your answer.

State the ratio of $F_2$ offspring phenotypes. You should include a key to link phenotypes to genotypes.

ratio of $F_2$ offspring phenotypes: ______

Some genes in guinea pigs are structural genes and some are regulatory genes.

Describe the difference between a structural gene and a regulatory gene.