Genetics Review Lecture
Introduction
- Resources for biology review, including GIFs, study tips video, and "Stroll Through the Playlist".
- Focus on genetic problems: Mendelian and non-Mendelian crosses, pedigrees.
- Five preliminary points before starting.
Preliminary Points
- Tools Needed: A sheet of paper and writing utensil.
- Vocabulary: Assumes prior knowledge of genetic terms.
- Symbols: Focus on concepts, not symbols (e.g. superscripts, different letters).
- Probability: Punnett squares show probability, not certainty.
- Complexity of Genetics: Includes polygenic traits, pleiotropy, epistasis, and epigenetics.
Mendelian Genetics
One-Trait (Monohybrid) Crosses
- Example: Guinea pigs with allele "H" for hair.
- Genotypes: HH, Hh, hh.
- Cross hairless guinea pig (hh) with heterozygous (Hh).
- Resulting genotype ratio: 1:1 (Hh: hh).
- Phenotype ratio: 1:1 (hair: hairless).
Two-Trait (Dihybrid) Crosses
- Example: Cats with traits for hair and love of sinks (fictional).
- Heterozygous genotype: HhSs.
- Cross HhSs with HhSs using a 16 square box.
- Gamete combinations using FOIL: HS, Hs, hS, hs.
- Resulting phenotype ratio: 9:3:3:1 for heterozygous two-trait cross.
Non-Mendelian Genetics
Incomplete Dominance
- Intermediate phenotype (e.g., pink snapdragons from RR and rr).
- Genotype ratio from two pink snapdragons (Rr): 1 RR: 2 Rr: 1 rr.
- Phenotype ratio: 1 red: 2 pink: 1 white.
Codominance
- Both traits expressed fully (e.g., BW for black and white speckled chickens).
- Genotype ratio from cross of black (BB) and speckled (BW) chickens: 1:1.
- Phenotype ratio: 1:1 (black: speckled).
Multiple Alleles
- Example: Blood types A, B, AB, O.
- Heterozygous Type B x Heterozygous Type A: 25% chance of Type O offspring.
Sex-Linked Traits
- Traits often on X chromosome (e.g., hemophilia).
- Male with disorder: XhY.
- Female with disorder: XhXh.
- Male children inherit X from mother, Y from father.
- Example cross: hemophilia male (XhY) x homozygous dominant female (XHXH) = 0% chance of disorder.
Pedigrees
- Track traits using shaded (recessive) and unshaded (dominant) shapes.
- Circles = females, Squares = males.
- Autosomal recessive traits: shaded shapes must be "ee".
- Determine genotypes by starting with shaded shapes.
- Example of deducing non-sex-linked trait from pedigree analysis.
Conclusion
- Recommended resources and further practice.
- Importance of understanding genetics and its applications.
"Stay Curious!" - Amoeba Sisters