genetic variation

any two unrelated people are ___% identical at the level of DNA

99

allele

one of (at least) a pair of genes occupying a specific location on a chromosome (locus) that control the same trait

homozygous

having the same allele for the same trait on both members of a chromosome pair

heterozygous

having different alleles for the same trait on both members of a chromosome pair

genotype

-set of alleles that determines the expression of a particular characteristic or trait

-entire set of genes in an organism

phenotype

expression of a particular characteristic or trait

punnett square

diagram that is used to predict the genotypic outcome of a particular genetic cross or breeding experiment

polymoprhism

having multiple phenotypes in the same population of species (multiple forms of the same allele occurring at the same loci)

mutation

change in DNA sequence

germline cell mutation

can be transmitted from one generation to the next

somatic cell mutation

cannot be transmitted

can lead to cancer cell formation

types of small scale mutations

single gene, deletions/insertions

single gene mutations

base-pair substitution or point mutation, in which one base pair is replaced by another

single gene mutations typically result in a ______

silent substitution

missense mutation

produce a change in a single amino acid

nonsense mutation

produce one of the three stop codons, results in premature termination of the polypeptide chain

deletion/insertion mutation

results in extra or missing amino acids in a protein

example of deletion mutation

3-bp in cystic fibrosis

frameshift mutation

deletion or insertion that is not in a multiple of 3

duplications or amplifications

repeated increase in the number of copies of DNA in a cell

promoter mutation

decreases affinity of RNA polymerase for a promoter site

splice-site mutations

occur at intron/exon boundaries

gain-of-function mutation

produce new or excess protein products

loss-of-function mutation

reduces or eliminates protein product

dominant negative mutations

produces abnormal protein product that interferes with normal protein produced

spontaneous mutations

arise naturally during DNA replication

induced mutations

attributed to environmental causes (mutagens)

mutagens

agents that cause induced mutations

nonionizing radiation

can move electrons from inner to outer orbits within an atom --> atom becomes unstable

UV radiation

type of nonionizing radiation that causes formation of covalent bonds between adjacent pyrimidine bases

pyrimidine dimers

formed by UV radiation where adjacent pyrimidine bases (thymine or cytosine) bond abnormally, leading to physical distortion and potential mutations

___ genes are more likely to experience mutations

large

DNA mutation hotspots

certain nucleotide sequences are more susceptible to spontaneous mutations

example of mutation hotspot

-80% of cytosine-guanine dinucleotides are methylated

-methyl group is attached to the cytosine base

-can easily lose amino group and become a thymine

most common group of single-gene diseases

genetic disorders of human hemoglobin

hemoglobin genes

two normal beta genes, four normal alpha genes

hemoglobinopathies

result from mutations in genes that control expression of hemoglobin protein, producing abnormal hemoglobins and anemia

sickle cell disease

homozygous recessive

beta-globin missense mutation

valine substitued for glutamic acid at position 6

anemia, tissue infarctions, infections

heterozygous advantage of sickle cell

resistant to malarial infection

population genetics

Study of allele frequency distribution and change under the influence of evolutionary processes

4 causes of genetic variation

mutations

natural selection

genetic drift

gene flow

gene frequency

number of individuals with a given genotype/gene divided by the total number of individuals in the population

Hardy-Weinberg Principle

principle that allele frequencies in a population will remain constant unless one or more disturbing factors cause the frequencies to change

natural selection

-increases population frequency of favorable mutations

-decreases frequency of variants that are unfavorable for a given environment

genetic drift

random evolutionary process that produces larger changes in gene frequencies in smaller population

founder effect

occurs when a few individuals become isolated from a larger population and form a new population whose gene pool composition is not reflective of that of the original population

bottleneck effect

Genetic drift resulting from the reduction of a population as a result of a chance event such that the surviving population is no longer genetically representative of the original population

gene flow

occurs when populations exchange migrants who mate with one another