Question

question number 5 please

Activ Micro chror Data-based questions: Comparing the chromosomes or and humans Figure 6 shows all of the types of chromosome in mice and in humans. Numbers and colours are used to indicate sections of mouse chromosomes that are homologous to sections of human chromosomes. Mouse and human genetic similarities Mouse chromosomes Human chromosomes A Figure 6 Chromosomes 1 Deduce the number of types of chromosomes in mice and in humans. 2 Idestify the two human chromosome types that are most similai to mouse chromosomes. 3 Identify mouse chromosomes which contain sections that are not homologous to human chromosomes. 4 Suggest reasons for the many similarities between the mouse and human genomes. [2] 5 Deduce how chromosomes have mutated during the evolution of animals such as mice and humans. Comparing the genome sizes

Answer 1

Although the size of the mouse genome is approximately the same and it contains nearly identical sets of genes, there has been a much longer time period over which changes have had a chance to accumulate—approximately 100 million years versus 5 million years. It may also be that rodents have significantly higher mutation rates than humans; in this case the great divergence of the human and mouse genomes would be dominated by a high rate of sequence change in the rodent lineage.

Mutation has led to extensive sequence divergence between humans and mice at all sites that are not under selection—such as the nucleotide sequences of introns. Indeed, human-mouse-sequence comparisons are much more informative of the functional constraints on genes than are human-chimpanzee comparisons.

According to rough estimates, a total of about 180 break-and-rejoin events have occurred in the human and mouse lineages since these two species last shared a common ancestor. In the process, although the number of chromosomes is similar in the two species (23 per haploid genome in the human versus 20 in the mouse), their overall structures differ greatly.

Nonetheless, even after the extensive genomic shuffling, there are many large blocks of DNA in which the gene order is the same in the human and the mouse. These regions of conserved gene order in chromosomes are referred to as synteny blocks.