Genotype

An organism's genetic makeup

Phenotype

The physical expression of an organism's genotype

(genotype + environment)

Number of Human Chromosomes

and

Number of the Human Sex Chromosome (X or Y)

Incomplete Dominance or Codominance

The blending of two alleles into a new allele instead of one dominating the other (a white flower mating with a red flower to produce a pink flower)

Polygenetic Inheritance

Multiple genes affecting one trait i.e skin or hair color

Does environment affect phenotype?

Yes

Example: the growth form of pea plants depends on soil acidity

Epistasis

A polygenic trait where alleles at one locus are influenced by those at another locus

Ex: mice coat color (B_ = black, bb= brown, but C_ = pigment, cc = no pigment (white, regardless of B allele)

B_:bb:cc = 9:3:4; the 2 loci behave with independent assortment

Pleiotropy

A single gene influences the expression of multiple traits

Ex: a single gene controls the length of multiple legs (4 pairs of 2) in spiders

Pedigree

A family genotypic/genetic history

Used for tracking of observable traits esp. genetic disease

Square = male, circle = female; shading = affected by studied phenotype (expresses desired trait), no shading = not affected, 1/2 shading = infer carrier if trait is recessive, heterozygote or incomplete dominance if dominant

Cystic Fibrosis

Present in 1/2500 of pop. (1/25 of pop. are carriers)

Normal airway lining: Cl ions leave the cell through an ion channel; water follows through osmosis and moist, thin mucus allows cilia to beat and sweep away foreign particles

CF-affected lining: mucus thickens, inhibiting beating of cilia; propensity for respiratory problems, infection increases

Huntington's Disease

Nervous system degeneration esp. loss of fine motor skills

Single locus dominant (heterozygote =/= carrier)

Symptoms do not appear until 35-45y old

Hemophilia

Decreases efficacy of blood clotting (treatable w/ clotting factor 8)

Sex-linked recessive on X

European royal families: high rate of occurrence due to intermarriage, but only among men (any women w/ the allele are carriers [heterozygotes])

Type I Diabetes

Autoimmune destruction of pancreatic insulin-producing Beta cells causing cessation of insulin production

Likely polygenic due to difficulties w/ analyzing pedigrees, inheritance patterns

Likely has an environmental component as well (identical twins have a ~50% risk of both having Diabetes instead of 100% due to identical genotypes)

Leads to aneuploidy (n-1 or n+1 gamete chromosomes)

1st cell division: When chromosomes pair, they do not seperate properly

2nd cell division: tetrads do not seperate properly

Excess copy of chromosome 21

Phenotype: Distinctive facial features, possible learning disabilities

Excess copy of chromosome 13

Affected individuals likely will not survive to adulthood

Excess copy/copies of X in males

XXY, XXXY, XXXXY

Phenotype: Sterile male

X0 in females (only one copy of X)

Phenotype: sterile female, impeded physiosexual maturity

One X is inactivated so the female does not produce twice the gene product as the male

Inactive X condenses into a Barr Body

 Inactivation is random with respect to cell lines (one gamete line might have inactive X1, other might have inactive X2)

Alternate means of sex determination in grasshoppers

Female: XX

M: X (but diploid for all other chromosomes)

Alternate means of sex determination in bees and butterflies

Female: ZW

Male: ZZ

Alternate means of sex determination in bees, ants, wasps

Female: Diploid

Male: Haploid (eggs are not fertilized by queen)

Genes on the same chromosome assort in different patterns that do not follow 'normal' ratios for genotypic and phenotypic distribution

Genes cross over during meiosis, forming new gamete chromosome combinations

Recombinant fraction ('original' genotypes/total genotypes) increases as genes move farther apart

(0.5 ~ same chromsome, 0 = very close genes or the same gene [pleiotropy])