lecture 25: Human genetic variation

bio 302 exam 4 material

simple tandem repeats (STR)

a site where a small number of base pairs are repeated

• abundant in the human genome [one every 2 kb]

• very polymorphic [many alleles in the population]

polymorphism

a site with a short sequence of bases repeated at a spot on the chromosome

• each chromosome has from 1-10 copies of the short sequence at that site

• can be homozygous or heterozygous

Polymerase Chain Reaction (PCR)

a pre-defined DNA sequence in the genome that has been amplified by repeated cycles of DNA synthesis using two primers that hybridize the ends of the target DNA

• in each cycle the amount of target DNA is doubled

• after 30 cycles the sequence is easily visible

melting of DNA

this is the first step of a PCR cycle at 95 degrees C

separation of the two DNA strands [denaturing]

• recall: the dna strands are held together by weak H bonds

denature

when a macromolecule loses its shape due to exposure to heat or chemicals

new strand synthesis

this is the third and final step of PCR cycle at 72 degrees C

• dna polymerase was isolated from Taq bacterium

Taq bacterium

(Thermus aquaticus) a bacterium that lives at hydrothermal vents on the sea floor where the water temp can be as high as 200 degrees C

heterozygous

individuals are often (homozygous/heterozygous) at an STR locus

CODIS (Combined DNA Index System)

database used by the FBI that holds 1.3 million crime samples

mitochondrial DNA

after fertilization, when the sperm and the egg fuse, the mitochondria from the sperm are destroyed

• all the mitochondria in the offspring are inherited from the mother]

• genes in the _____ show non-mendelian inheritance patterns

uniparental inheritance

genes in mtDNA show non-Mendelian inheritance patterns since mitochondrial DNA is only from the mother

• only mother’s pass on this disease

• doesn’t undergo recombination

mitochondrial eve

estimated how long ago the woman with ancestral mtDNA that gave rise to all existing mtDNA molecules around today

Y-chromosome

present in only males and doesn’t recombine with the X chromosome

• mutations that arise in one male will be passed on to his sons

• uniparental inheritance in male lineage

haplotype

groups of people that have been geographically isolated on the planet have common patterns of DNA changes for their SNPs, Y-chromosomes, and mtDNA

• can tell what part of the planet a person’s ancestors came from by examining their DNA and comparing it to samples from living populations