Patterns of Inheritance

Patterns of Inheritance

  • Focus on different inheritance patterns as discussed in Chapter 9 of genetics.

Mendel’s Dihybrid Crosses

  • Explored questions regarding whether traits are inherited independently.

  • Initial Hypothesis: Dependent Assortment

    • Actual data did not support this hypothesis.

  • Proposed Hypothesis: Independent Assortment

    • Data supported this hypothesis.

Mendel’s Law of Independent Assortment

  • Stated that each pair of alleles segregates independently during gamete formation.

Extensions of Mendel

  • Incomplete Dominance:

    • Example: Snapdragons; Red (RR) x White (rr) = Pink (Rr).

    • Generations:

    • Parental Generation: RR x rr

    • F₁ Generation: All pink (Rr)

    • F₂ Generation: Phenotypic ratio 1:2:1 (1 red: 2 pink: 1 white); Genotypic ratio 1:2:1.

  • Codominance:

    • Example: Red x White = both colors expressed (e.g., rhododendron with red and white flowers).

Multiple Alleles and Blood Types

  • Blood type inheritance exhibits multiple alleles and codominance.

  • Genotypes for Blood Groups:

    • Type A: AA or AO

    • Type B: BB or BO

    • Type AB: AB

    • Type O: OO

  • Carbohydrates on Red Blood Cells:

    • Carbohydrate A triggers Anti-B antibodies and vice-versa.

    • Group AB has none, while Type O is neutral (no reaction).

Pleiotropy and Polygenic Inheritance

  • Pleiotropy:

    • Single gene affects multiple traits (Example: albinism).

  • Polygenic Inheritance:

    • Multiple genes influence one trait, e.g., skin color, resulting in a continuous range (light, medium, dark).

    • Results in varied phenotypes such as multiple shades of skin tone based on combined alleles.

Nature vs. Nurture

  • Environmental influences on phenotypic traits.

Epigenetic Inheritance

  • Traits are transmitted not only via DNA sequences but also through gene expression modifications (chemical changes).

Studying Inheritance Patterns

  • Use of pedigree charts to track traits and inheritance through generations.

Types of Inheritance

  • Single-Gene Disorders:

    • Less common as most traits are polygenic.

  • Autosomal Dominant:

    • Traits appear in every generation equally in males and females (e.g., Huntington's Disease).

  • Autosomal Recessive:

    • Traits can skip generations; heterozygotes are carriers (e.g., Tay-Sachs).

  • X-Linked Inheritance:

    • Seen more in males due to single X chromosome acting as a determining factor (e.g., Duchenne muscular dystrophy, Hemophilia).

Male Sex Determination in Humans

  • SRY gene's role in male secondary sexual traits emergence.

  • Sex determination is multifactorial considering chromosomes, genes, and secondary sexual characteristics.

  • Disorders of sex development (DSD) can lead to various developmental outcomes and gender identity variances, illustrating complexities beyond biological definitions.