Genomes and Their Evolution

Page
8

Unequal crossing over during prophase I of meiosis can result in one chromosome with a deletion and another with a duplication of a particular region

Transposable elements can provide sites for crossover between nonsister chromatids

Slide 59

Fig. 21-12

Transposable

element

Gene

Nonsister

chromatids

Crossover

Incorrect pairing

of two homologs

during meiosis

and

Slide 60

Evolution of Genes with Related Functions: The Human Globin Genes

The genes encoding the various globin proteins evolved from one common ancestral globin gene, which duplicated and diverged about 450–500 million years ago

After the duplication events, differences between the genes in the globin family arose from the accumulation of mutations

Slide 61

Fig. 21-13

Ancestral globin gene

Duplication of

ancestral gene

Mutation in

both copies

Transposition to

different chromosomes

Further duplications

and mutations

-Globin gene family

on chromosome 16

-Globin gene family

on chromosome 11

Evolutionary time







2

1















2

1









G

A





Slide 62

Subsequent duplications of these genes and random mutations gave rise to the present globin genes, which code for oxygen-binding proteins

The similarity in the amino acid sequences of the various globin proteins supports this model of gene duplication and mutation

Slide 63

Table 21-2

Slide 64

Evolution of Genes with Novel Functions

The copies of some duplicated genes have diverged so much in evolution that the functions of their encoded proteins are now very different

For example the lysozyme gene was duplicated and evolved into the α-lactalbumin gene in mammals

Lysozyme is an enzyme that helps protect animals against bacterial infection

α-lactalbumin is a nonenzymatic protein that plays a role in milk production in mammals

Slide 65

Rearrangements of Parts of Genes: Exon Duplication and Exon Shuffling

The duplication or repositioning of exons has contributed to genome evolution