Reproduction & Inheritance (Edexcel A (SNAB) AS Biology)

The following diagram shows events that may occur in the oviduct of a female mammal.

Identify process R.

(1)

Describe the events that occur during process R.

(4)

(1)

Explain the importance of process T with reference to the diagram in part (a).

(2)

A liver cell of the house mouse (Mus musculus) contains 24 chromosomes.(i)

Which of the following best describes the chromosome number in the gametes? 

During meiosis, the nucleus of the original parent cell undergoes two rounds of division.

The following diagram shows microscope images of cells undergoing one of these rounds of division. Note that the images in the diagram are in no particular order.

Identify the round of division that these cells are going through.

(1)

Give one visible reason for your answer at part (i).

(1)

The diagram below shows a pair of chromosomes during meiosis.

Name the process that is illustrated in the diagram.

(1)

Describe the purpose of the letters in the diagram.

(1)

The following image shows the gametes containing the chromosomes shown at part (b) at the end of meiosis. 

Complete diagrams II to IV to show the appearance of the chromosomes in each gamete. Use both letters and shading. Diagram I has been completed for you.

Describe and explain the events that occur during meiosis that contribute to genetic variation within a species.

Factor VIII is a coagulating agent that plays an important role in blood clotting and is coded for by the F8 gene. There are abnormal alleles of this gene that lead to blood clotting abnormalities. A person that inherits these abnormal alleles will suffer from haemophilia. The F8 gene is an example of a sex-linked gene.

Describe what is meant by the term 'sex-linked gene'.

The F8 gene is found on the X chromosome. Individuals that are heterozygous for this gene are known as carriers; they will not suffer from haemophilia but their offspring may.

The diagram below shows the sex chromosomes of a male individual. 

Explain why this individual will not be a carrier of haemophilia.

The pedigree diagram below shows the pattern of inheritance of haemophilia. 

The following alleles are possible:

• X^H - normal female
• X^h - abnormal female
• Y^H - normal male
• Y^h - abnormal male

State the genotypes of individuals 1, 2 and 3.

(3)

Using an example from the pedigree diagram, deduce and explain the type of allele that causes haemophilia.

(2)

Haemophilia in male offspring will always be inherited from their mother.

Explain why it is impossible for male offspring to inherit haemophilia from their father.

A group of scientists carried out a study looking at the relationship between the number of crossing over events taking place during meiosis and the distance between the crossing over events and the centromere in male trout (a species of fish). Some of their results are shown in the graph below.

(i)

What can be concluded from the graph? 

The scientists found that some of the genes in the species of fish mentioned at part (a) were linked.

State what is meant by the term 'autosomal linkage'.

(2)

Explain the possible effect of this on genetic variation in this species of fish.

(2)

The graph shows the change in the mass of DNA over time in a cell.

(i)

Which of the following is the best description of the graph at part X? 

The cell is preparing to undergo a type of cell division at point Y on the graph at part (c).

Identify the type of cell division.

(1)

Use the information in the graph and give a reason for your answer at part (i).

(1)