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.