Notes # 8: Chapter 14 Mendel and the Gene Idea

I. General Genetics Terms A) Trait: characteristic that can be inherited B) Allele: Alternate forms of a gene C) Dominant allele: priority over other alleles / Fully expressed D) Recessive allele: Only fully expressed if no dominants.

E) Genotype: genetic makeup Represented by letters F) Phenotype: How genotype is expressed. G) Homozygous: Identical alleles for a gene H) Heterozygous: Different alleles

II. Punnett Squares Determine possible outcomes for offspring A) Test cross: Unknown x homozygous recessive B) Monohybrid cross: One trait. 1) P generation: Parental generation – “true breeding” homozygous 2) F1: First (filial) generation – hybrid / heterozygous 3) F2: Phenotype ratio is always 3:1, dominant: recessive

C) Dihybrid Cross: 2 traits 1) P: homo dom x homo recessive 2) F1: All heterozygous 3) F2: 9:3:3:1 (dom: rec/dom: dom/rec: rec)

III. Dominance A) Complete dominance: Can’t tell difference between heterozygote and homozygous dominant phenotypes C) Incomplete dominance: Blending of dominant and recessive D) Codominance: both alleles are dominant. No blending. Both traits are present. Blood types

IV. Mendel’s Rules of Inheritance Three Principles of Genetics A) Law of Dominance: Dominant trait masks recessive in a heterozygote B) Law of segregation: 1) Two alleles for same trait go into different gametes (sex cells) 2) defines allele 3) get one set of alleles from each parent 4)there’s a dominant and recessive

C) Law of Independent Assortment pairs of alleles segregate into gametes independently (Not all the alleles from mom stick together nor from dad.)

V. Patterns of Inheritance A) Linked genes: stay together during assortment B) Sex linked traits on sex chromosome Ex: color blindness