Chapter 4: Human Genetic Diversity: Mutation and Polymorphism

Reference Genome

the sequence of DNA that is expected for a species (must be constantly updated)

Locus/Loci

position on a chromosome

ranges between large span of nucleotides and single nucleotides

Allele

forms of a gene (dominant or recessive)

Mutation

change in nucleotide(s) within DNA

Polymorphism

two or more variants of a gene at a specific locus within a population, each occurring at a frequency of at least 1% in the population

humans are ____% genetically identical to each other

99.5

humans are ____% genetically identical to chimpanzees

>99%

mutation vs polymorphism

• polymorphism: variation that occurs in greater than 1% of population

• mutation: variation that occurs in less than 1% of population

chromosomal mutations affect

entire chromosome

• ex: trisomy 21 (down syndrome)

regional or sub-chromosomal mutations affect

portion of chromosome

gene mutation affect

only individual gene

copy number variants

a type of genetic variation where a section of DNA is present in different numbers of copies compared to what is typical

Inversion Polymorphism

a type of genetic variation in which a segment of a chromosome breaks off, flips around, and reinserts in the opposite orientation.

• balanced: not missing a gene

• unbalanced: missing a gene (sometimes not viable if affecting germline)

germline mutation

mutation that occurs in gametes can be passed to offspring

somatic mutations

a mutation that occurs in somatic (body) cells and are not passed on

spontaneous mutation

a type of gene mutation that is

induced mutation

a type of gene mutation that is caused by (or induced by) mutagens

• e.g., UV light, polymerases

How can gene mutations be corrected?

proofreading by DNA polymerases

Spontaneous gene mutations can occur via

depurination

demethylation

deamination

methylation of CPG islands (

• spontaneous deamination fo 5-methylcytosine to thymidine in CPG islands results in C to T or G to A mutation—may not be recognized by repair machinery

• accounts for about 30% of single nucleotide substitutions

induced mutations

uv light or ionizing radiation, chemicals, etc

rate of mutation

some specific mutations occur more often that others