12 2 12 3 Complex Inheritance of Human

12. 2 & 12. 3 Complex Inheritance of Human Traits

Codominance With codominance, a cross between organisms with two different phenotypes produces offspring with a third phenotype in which both of the parental traits appear together. .

Codominance Examples

Multiple Alleles Control: 1. blood type: IA, IB, i IA and IB are codominant Table on page 331 It is important that one know his/her blood type Blood transfers Parentage

Polygenic Inheritance controlled by two or more genes (Aa x Bb x Cc) found on same or different chromosomes Ex. Stem length in plants, skin color

Skin Color Controlled by 3 -4 pairs of genes Genes are controlled by the production of melanin (a chemical that adds brown color to the skin; the darker a person is the more melanin one has)

Non-Disjunction Failure of the chromosomes to separate during meiosis. This may result in offspring either having too many chromosomes or not enough

Down’s Syndrome Extra 21 st chromosome Trisomy 21 Karyotype

Monosomy X Female missing a chromosome X Turner’s syndrome

Klinefelter’s Syndrome Male with extra chromosome (XXY)

Genetic Disorders Causes errors in the genetic material Sickle Cell Anemia – red blood cells have a sickle shape instead of an oval. Found in African Americans Mostly or dark – skinned people. Cells clog blood vessels causing pain and early death

Sickle Cell Normal Blood Cell

Environment can play a major role in genetics 1. Internal factors – Hormones Horn Size 2. External factors—Arctic Fox Temperature Nutrition Light Chemicals Infectious agents