Copy of Genetics Part 2

Punnett Square Basics

  • Two-factor crosses: Requires 16 squares in a Punnett square. Each parent gives one allele from each gene pair.

  • Parent genotypes examples:

    • AaBb: can pass AB, Ab, aB, or ab

    • Aabb: can pass Ab or ab

    • aaBb: can pass aB or ab

    • AABB: can pass AB

Mendel's Experiments

  • Parent Genotypes and Alleles:

    • Round Yellow (RRYY) x Wrinkled Green (rryy)

    • Offspring combinations: RY, ry

    • Offspring genotype: RrYy (all Round and Yellow)

Dihybrid Cross Example

  • Round Yellow (RrYy) x Round Yellow (RrYy)

  • Offspring Genotypes:

    • 1/16 RRYY

    • 2/16 RRYy

    • 1/16 RRyy

    • 2/16 RrYY

    • 4/16 RrYy

    • 2/16 Rryy

    • 1/16 rrYY

    • 2/16 rrYy

    • 1/16 rryy

  • Ratios: 9/16 Round Yellow, 3/16 Round Green, 3/16 Wrinkled Yellow, 1/16 Wrinkled Green

Practice Problem

  • Right-handedness (R) is dominant over left (r); Tongue rolling (T) is dominant over non-rolling (t).

  • Cross: RRtt x RRTt

  • Outcomes: RRTt (8 Right-handed tongue rollers) and RRtt (8 Right-handed non-rollers)

Parent Genotypes for Cross

  • Woman: Right-handed and tongue roller (RrTt)

  • Man: Heterozygous right-handed and tongue roller (RrTt)

  • Expected offspring outcomes:

    • Genotypes: RRTT, RRTt, RrTT, RrTt, RRtt, Rrtt, rrTT, rrTt, rryy

    • Expected ratios: 9/16 Right-handed tongue rollers, 3/16 Right-handed non-rollers, 3/16 Left-handed tongue rollers, 1/16 Left-handed non-rollers

Mendel's Principles (Summary)

  • Traits come from genes.

  • Each gene can have different forms (alleles).

  • Some alleles are dominant, others are recessive.

  • Parents pass one allele from each trait to their young (segregation).

  • Alleles for one trait separate independently from others.

Exceptions to Mendel's Principles

  • Not all traits show simple dominance and recessiveness.

  • Many traits are affected by many genes.

Gene and Environment Interaction

  • Gene expression is influenced by environmental factors.

Incomplete Dominance

  • Traits may blend, e.g., red and white flowers can produce pink offspring.

  • Example: Red (RR), White (WW), Pink (RW)

Blood Types and Codominance

  • ABO blood types come from codominant alleles (IA, IB, i).

  • Possible genotypes:

    • Type A: IAIA, IAi

    • Type B: IBIB, IBi

    • Type AB: IAIB

    • Type O: ii

Blood Type Inheritance Example

  • Parents: IAi and IBi.

  • Possible offspring blood types: Type A, Type B, Type AB.

Rh Factor

  • Rh positive (R) is dominant over Rh negative (r).

  • Example: AB negative woman x O positive man. Possible genotypes:

    • Woman: IAIBrr

    • Man: IAiRr

Multiple Alleles in Traits

  • Some traits have multiple alleles (e.g., rabbit coat color has 4 different alleles).

  • Coat color hierarchy: C > cch > ch > c.