Sec 11.2, Complex Patterns of Inheritance Main idea: Complex inheritance of traits does not follow inheritance patterns described by Mendel.

Incomplete Dominance With incomplete dominance there is a phenotype in between the homozygous phenotypes. Example: Red, white, and pink flowers.

Codominance Heterozygous combination that expresses both traits at the same time. Example: sickle cell anemia/disease Affects red blood cell’s ability to carry oxygen. Cells block circulation in small blood vessels. Heterozygotes have both normal cells and sickle cells.

Multiple Alleles Some traits are controlled by more than 2 alleles. Ex. Blood groups in humans; multiple alleles and codominance. IA = A IB = B i = O

Multiple Alleles Coat color of rabbits is another example; there is a hierarchy of dominance. There 4 alleles for coat color C, cch, ch, and c Chinchilla: cchcch cchch cchc Albino: cc Full Color: CC Ccch Cch Cc Himalayan:chch chc,

Sex Determination 22 pairs of human chromosomes are autosomes. 23rd pair are sex chromosomes. Sex chromosomes determine gender (male/female). Males are XY Females are XX

Sex-linked Traits Traits controlled by genes on the X chromosomes (from mother) are one type of sex- linked traits. Males are affected by recessive alleles more often than females.

Red green color blindness is an X-linked recessive trait. Hemophilia is a sex-linked disorder that causes delayed blood clotting.

Polygenic Traits Controlled by 2 or more genes. Lots of phenotypes Examples: skin color, height, eye color, fingerprints

Environmental Influences The environment may also affect a trait. Example: Heart disease Several factors in the environment influence gene expression. Example: Temperature, light, nutrition, hormones, and infectious agents

Sec. 11.3, Chromosomes and Human Heredity Main Idea—Chromosomes can be studied using karyotypes.

Karyotype studies: Pairs of homologous chromosomes are arranged in decreasing size.

Karyotype Chromosomes are stained during metaphase and used to make a karyotype. The 22 autosome pairs (non-sex chromosomes) are matched together. The 23rd pair (sex chromosomes) are matched together.

Nondisjunction This occurs when chromosomes fail to separate properly during cell division. Resulting cell will not have the correct number of chromosomes.

Problems caused by nondisjuction: Monosomy—when a cell has only one copy of a particular chromosome Trisomy—when a cell has 3 copies of a particular chromosome

Example: Down Syndrome Condition also known as Trisomy 21 (3 copies of chromosome 21). Results in short stature, heart defects, and mental disability.