A3.1 Diversity of organism (year 6)

Question 1

Evaluate the evidence for the hypothesis that chromosome 2 in humans arose from the fusion of chromosomes 12 and 13 with a shared primate ancestor

Answer 1

Modern humans have 46 chromosomes whereas chimpanzees have 48. If we shared a common ancestor with them, what happened to the chromosome number?

• in terms of shape, the 2 non-human acrocentric (centromere is at 1 end) chromosomes when placed end to end have a similar leength to the human chromosome.
• the position of the satellite DNA in the human chromosome corresponds to the position of the centromere in the non-human chromosome 13
• in terms of banding patterns, the long arm of chromosome 12 matches the short arm of human choromosome 2, and the long arm of chromosome 13 matches the banding patterns of the human chromosome.
• there are telemores in the centre of the human chromosome although telomeres are usually found at the tips of chromosomes.

Question 2

current and potential future uses of whole genome sequencing

Answer 2

• increasing speed and decreasing costs
• current: research into evolutionary r/s
• future: personalized medicine

Question 3

Explain the difficulties with the biological species concept

Answer 3

One of the major assumptions of the concept of a species is that all members of a species have a common lineage and come from a series of common ancestors (tree of life concept)

however:
- bacteria reproduce asexually using binary fission = horizontal gene transfer
- some insects reproduce without needing the male called PARTHENOGENESIS
- some plants use VEGETATIVE PROPOGATION and reproduce without the male
- genes can also transfer from bacteria to archaea, viruses to eukaryotes, bacteria to eukaryotes etc. = we could be a mosaic of genes from both human and non-human sources
- there are also “jumping genes” that travel in plasmids from one bacterium to another, resulting in identical genes in several very different species

this challenges the idea of a common ancestry with other members of a species.

Question 4

Is cross-breeding between closely related species likely to produce fertile offspring?

Answer 4

only if parent chromosome numbers are the same - if they are different the offspring is infertile

Question 5

What are DNA barcodes used for?

Answer 5

DNA barcode is a short sequence of DNA inside an organisms cells that can be used to quickly identify the species.

the barcode is matched against a specific sequence to a known seequence stored in a genetic libtary