On Fig. 2.1, show one homologous pair by circling two chromosomes.
Fig. 2.2 displays the banding pattern for chromosome pair 11 of Mus musculus. This banding pattern is produced by staining.
Explain why chromosomes, such as those in Fig. 2.2, are called a homologous pair.
State how many chromosomes are found in M. musculus spermatozoa.
M. musculus forms gametes by meiosis. These gametes are genetically dissimilar. Gametes fuse randomly at fertilisation.
Explain why meiosis matters in the life cycle of M. musculus, other than making genetically different gametes.
Explain how the random fusion of gametes causes rare, recessive alleles to be expressed.
A mutation that makes mice coats look woolly is found in a gene on chromosome 11. The mutation produces a very shortened polypeptide product. Mice showing the woolly coat phenotype have longer fur than mice with normal coats.
Explain how a base substitution mutation can produce a very shortened polypeptide product.
The inheritance of the woolly coat characteristic was studied. Draw a genetic diagram to illustrate a cross between two heterozygous parents with normal coats. Use A and a as the alleles. Show parental genotypes, gametes, offspring genotypes and offspring phenotypes.