Mega Genetics Review: Mendelian and non-Mendelian Genetics

Overview of Genetic Concepts

• The video aims to review how to tackle general genetic problems, covering both Mendelian and non-Mendelian traits.

• Topics include:

  • Mendelian one-trait and two-trait crosses (monohybrid and dihybrid)

  • Non-Mendelian traits (incomplete dominance, codominance, multiple alleles, and sex-linked traits)

  • Pedigrees

Pre-Video Preparation

• Five Important Points:

  1. Materials Needed: Have paper and a pen/pencil ready for exercises.

  2. Genetic Vocabulary: Familiarity with specific genetic terms is assumed.

  3. Symbol Variation: Symbols may vary in textbooks; focus on concepts rather than symbols.

  4. Understanding Probabilities: Genetic problems yield probabilities, not certainties; actual results may vary.

  5. Complexity of Genetics: Genetics can be complex beyond simple traits, with concepts such as:

     • Polygenic traits: Multiple genes control one trait.

     • Pleiotropic traits: One gene influences multiple traits.

     • Epistasis: A gene's expression can be affected by another gene.

     • Epigenetics: Factors affecting gene expression that are not part of the DNA sequence.

Mendelian Genetics

Mendelian One-Trait Cross (Monohybrid Cross)

• Example with Guinea Pigs:

  • Dominant allele (H) = Hair

  • Genotypes:

    • Homozygous dominant: HH

    • Heterozygous: Hh

    • Homozygous recessive: hh

  • Cross Example: Hairless guinea pig (hh) crossed with heterozygous (Hh).

  • Results:

    • Genotype Ratio: 2 Hh : 2 hh (or 1:1)

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

Mendelian Two-Trait Cross (Dihybrid Cross)

• Example with Cats:

  • Fictional trait: Cat loves sinks (S = loves sinks, s = does not love sinks)

  • Heterozygous genotype for both traits: HhSs

  • Dihybrid Punnett Square: 16 squares.

  • Gamete Combinations: HS, Hs, hS, hs (applying FOIL method).

  • Phenotype Ratio: 9:3:3:1 for heterozygous crosses.

Non-Mendelian Genetics

Incomplete Dominance

• Traits: Intermediate phenotype.

• Example with Snapdragons:

  • RR = red, rr = white, Rr = pink (intermediate).

  • Crossing Pink Snapdragons:

    • Genotype Ratio: 1 RR : 2 Rr : 1 rr.

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

Codominance

• Example with Chickens:

  • BB = black, WW = white, BW = black and white speckled.

  • Crossing Black Chicken and Black/White Speckled Chicken:

    • Genotype Ratio: 2 BB : 2 BW (1:1).

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

Multiple Alleles

• Example with Blood Types:

  • Blood types: A, B, AB, O.

  • Common notation: alleles written as exponents on letter I.

  • Cross: Heterozygous type B crossed with heterozygous type A results in 25% chance of type O offspring.

Sex-Linked Traits

• Typically located on X chromosome.

• Example with Hemophilia:

  • Genotype for Male with Hemophilia: XhY.

  • Female Genotypes: Only XhXh exhibits hemophilia; XHXh does not.

  • Cross: Male with hemophilia and homozygous dominant female --> 0% chance of child having hemophilia.

  • Male inherits X from mother, Y from father.

Pedigrees

• Used to track inheritance of traits.

• Shaded shapes represent individuals with the trait of interest; circles = females, squares = males.

• Heredity Example - Autosomal Recessive Trait:

  • Shaded shapes (ee) represent individuals with the trait.

  • Begin with shaded genotypes to deduce others.

• Consideration for whether a trait is sex-linked or autosomal based on patterns seen in the pedigree.

Conclusion

• Genetics is complex; continual practice and deeper content exploration are encouraged.

• Links to real-life examples provided in the video details emphasize the relevance of understanding genetics.