Types of DNA sequence

Question 1

what happens if DNA is denatured?

Answer 1

reassociates as a duplex at a rate dependent on the proportion of unique and repeat sequences present

Question 2

distribution of genes

Answer 2

heterochromatic and centromeric regions are non coding
highest gene density is in subtelomeric regions

chromosomes 19 and 22 are gene rich
4 and 18 are gene poor

Question 3

size of genes

Answer 3

small genes with single exons to genes with up to 79 exons (e.g dystrophin, 2.5 Mb of genome)

Question 4

what gene has many exons?

Answer 4

dystrophin has 79 exons, occupies 2.5 Mb of the genome

Question 5

unique single-copy genes

Answer 5

most human genes code for polypeptides involved in or carry out a variety of cellular functions

e.g. enzymes, hormones, receptors, and structural and regulatory proteins

Question 6

multigene families

Answer 6

many genes have similar functions, having arisen through gene duplication events with evolutionary divergence making up multigene families

some found physically close in clusters, some are widely dispersed throughout the genome on different chromosomes

Question 7

example of multigene families found physically close in clusters

Answer 7

alpha and beta globin gene clusters on chromosomes 16 and 11

Question 8

example of multigene families found dispersed throughout the genome

Answer 8

HOX homeobox gene family

Question 9

2 types of multigene families

Answer 9

classic gene families - high degree of sequence homeology

gene superfamilies - limited sequence homeology but are functionally related, similar structural domains

Question 10

classic gene families

Answer 10

high degree of sequence homeology

Question 11

examples of classic gene families

Answer 11

copies of genes coding for various ribosomal RNAs clustered as tandem arrays as the nucleolar organising regions on short arms of 5 acrocentric chromosomes

different transfer RNA gene families dispersed in clusters throughout genome

Question 12

gene superfamilies

Answer 12

limited sequence homeology but functionally related, similar structural domains

Question 13

examples of gene superfamilies

Answer 13

HLA (human leukocyte antigen) genes on chromosome 6 and T cell receptor genes (structural homology with immunoglobin Ig genes)

derived from duplication of a precursor gene

Question 14

pseudogenes

Answer 14

genes closely resembling known structural genes which are not functionally expressed

Question 15

how did pseudogenes arise?

Answer 15

by genes undergoing duplication events rendered sient through acquisition of mutations in coding or regulatory elements

insertion of complementary DNA sequences produced by reverse transcriptase on naturally occuring mRNA transcript lacking promoter sequences needed for expression