Friday March 26, 1999
Announcements:

Lecture notes:

Genes: units of instructions for producing or influencing a specific trait.

Locus: each gene has its own "location" on a chromosome.

Alleles: gene pairs (one on each homologous chromosome)

Genotype: the information on the gene(s)

Phenotype: how these genes are expressed in the individual.

Homozygous: both alleles of a gene locus are the same.

Heterozygous: the alleles of a gene locus differ.

Dominant allele: this allele will mask the effect of a recessive allele if it is present.
Standard - A = dominant allele a = recessive allele

Autosomal gene: a gene on one of the 22 pairs of chromosomes that do not determine gender.

Sex-linked or X-linked gene: the gene is on the X chromosome.

F₁ generation: F = filial meaning offspring. F₁ is the 1^st generation.

F₂ generation: 2^nd generation.

Piebald - white streak of hair.

Achondroplasia - type of dwarfism.

Huntington's disease

Cystic Fibrosis

Sickle cell anemia

Tay Sachs Disease

Galactosemia

PKU

Albinism

Hemophilia

Color blindness

Duchenne Muscular Dystrophy

Lesch-Nyhan Syndrome

Deletions, duplications, inversions, and translocations on chromosomes affect genotype and thus phenotype.

Nondisjunction (one type of translocation) is the failure of 1 or more chromosomes to separate during meiosis. This can occur at either Anaphase I or Anaphase II. Either way the result is an individual with an abnormal chromosome number.

Example: Trisomy 21 - Down syndrome

Genotype - xxx (or more)
Phenotype - female
no unusual secondary sex characteristics
sometimes same mental retardation
Usually fertlie

Genotype - XXY
phenotype - male
underdeveloped genitals
usually sterile
enlarged breasts
mental retardation

Genotype - xo
phenotype - female
short
web neck
tiny non-functional ovaries
no secondary sex characteristics
no metal retardation

Genotype - xyy
phenotype - male
taller than average
extensive acne
mental retardation
generally fertile

Incomplete dominance: on allele cannot mask the presence of the other (example: red and white snapdragons mate, the
heterozygous individuals are pink)

Codominance: expression of both alleles (example: blood groups)

Variable expressivity: the genotype can be expressed in the phenotype in a variety of ways. (example: polydactyly)

Mulitfactorial Inheritance: many gene pairs combine to produce a trait (example: eye color)