(182) Mega Genetics Review: Mendelian and non-Mendelian Genetics

Overview of Genetics Review

• The video reviews various topics in genetics including Mendelian crosses, non-Mendelian traits, and pedigrees.

• It serves as a complementary resource to "Stroll Through the Playlist" with a focus on general genetic problems.

Five Important Points Before Starting

1. Materials Needed: A sheet of paper for problem-solving.

2. Genetic Vocabulary: Assumes prior knowledge of genetic terms.

3. Symbol Variance: Different representations exist for alleles; focus on concepts.

4. Probability Understanding: Punnett squares indicate probabilities, not certainties.

5. Complexity of Genetics: Many traits can be polygenic or pleiotropic and influenced by epistatic relationships or epigenetics.

Mendelian Genetics

One-Trait Cross (Monohybrid Cross)

• Allele Representation: H represents hair; Hh (heterozygous), HH (homozygous dominant), hh (homozygous recessive).

• Example Problem: Cross a hairless guinea pig (hh) with a heterozygous guinea pig (Hh).

  • Genotype Ratio: 2 Hh: 2 hh (1:1)

  • Phenotype Ratio: 2 with hair: 2 hairless (1:1)

Two-Trait Cross (Dihybrid Cross)

• Example with Cats: Genotype of heterozygous cat for both traits is HhSs.

• FOIL Method for gametes: HS, Hs, hS, hs.

• Phenotype Ratio for HhSs x HhSs: 9:3:3:1.

Non-Mendelian Genetics

Incomplete Dominance

• Example with Snapdragons: RR (red), rr (white), Rr (pink).

• Genotype Ratio from Two Pink Snapdragons: 1 RR: 2 Rr: 1 rr.

• Phenotype Ratio: 1 red: 2 pink: 1 white.

Codominance

• Example with Chickens: BB (black), WW (white), BW (speckled).

• Genotype Ratio from Black and Speckled Cross: 2 BB: 2 BW (1:1).

• Phenotype Ratio: 2 black: 2 speckled (1:1).

Multiple Alleles

• Example with Blood Types: A, B, AB, O.

• Example Problem: Heterozygous type B and heterozygous type A parents; 25% chance offspring will be type O.

Sex-Linked Traits

• Example with Hemophilia: Males represented as XhY (affected) and females can be XhXh (affected) or XHXh (carriers).

• Crossing Example: Male with hemophilia (XhY) and homozygous dominant female (XHXH) have a 0% chance of having a child with hemophilia.

Pedigrees

• Used to track traits across generations; shaded shapes indicate traits of interest.

• Example: Determine genotypes in pedigrees for autosomal recessive traits using the letter "e".

• Concepts: Shaded shapes (ee); inference needed for non-shaded genotypes.

Conclusion

• Encouragement to practice more problems; check out full content videos for additional review.

• Importance of understanding genetics in real-world contexts.