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Karyotyping
The karyotype is the number, size and shape of chromosomes in a cell during metaphase.
- Human karyotype is 22 pairs of autosomal chromosomes and 1 sex chromosome pair.
- Species that appear similar can have very different karyotypes. Male human karyotype is below.
Chromosome painting is a method used to identify and differentiate the chromosomes since many chromosomes have similar sizes.
- Fluorescent in-situ hybridization (FISH) is a technique in which fluorescent probes that are specific for each chromosome are hybridized to the chromosomes so they can be identified.
- Can detect abnormal numbers of chromosomes (e.g. disorders like Down's Syndrome are caused by having an extra chromosome).
- Can detect deletions or duplications of chromosomal regions.
- Can be used to determine how species are evolutionarily related. Example: FISH probes for chromosome 16 in tree shrews label one arm on chromosome 10 in humans. The probes also appear to bind to the chromosomes in the same order in each species. So somewhere during evolution, chromosome 16 from tree shrews became part of chromosome 10 in humans.
Practice: Species Number of Chromosomes
You are studying the genome of two species of penguins that live in the same region of Antarctica. You determine that each of the penguin species have about the same number of genes encoded in their DNA. You have also determined that one species of penguin has 16 autosomal chromosomes and 2 sex chromosomes. Given this information, what is the best estimate for the number of chromosomes in the second penguin species?