Chromosomes In Evolution

How is DNA packed into chromosomes?

In a hierarchical way:

• DNA doubel helix coiled around histone octamers

• About 165 nucleotides weap around a single octamer (wrapping 2.85 times)

• These “beads” are separated by 500 nt long spacer sequence

• Histone beads pack into 30 nm fibres

• Fibres are tied up into scaffolds

• Condensed scaffolds make up the macroscopic form of chromosome

What are chromosomes carriers of?

DNA/genes

Can DNA and chromosome be studied?

Yes, they can be studied in the laboratory

How many pairs of chromosomes do humans have?

23 pairs (22 autosomal pairs and 1 set of sex chromosomes: female XX, male XY)

What are the comparisons of chromosomes?

• All apes have 48 chromosomes

• Humans have 46 chromosomes

• Chromosome bands between human and chimpanzee are 99% the same

• Translocation of two ape chromosomes formed human chromosome 2

• Pericentric inversion chromosome 4 between humans and chimpanzees

• Karyotypes among great apes differs by inversions

• All mammals share identical X-chromosome banding

• Humans share bands with: 99+% chimpanzee, 99+% gorilla, 95% african green monkey, 35+% domestic cat, 7% mice

What does chromosomal evidence support?

Close relationship between humans and chimpanzees