Applying Mendel's Principles in Genetics (PART 2)

Applying Mendel's Principles

• Objectives:
  • Explain the use of probability to predict traits.
  • Describe allele segregation when multiple genes are involved.
  • Describe Gregor Mendel's contribution to genetics.

Probability & Heredity

• Probability: The likelihood of an event occurring.
  • Example: Flipping a coin has two possible outcomes (heads or tails) with equal probability (50% for each).
  • Independent events: The outcome of one event doesn't affect the outcome of another. For three coin flips in a row, each flip has a 1/2 probability of landing heads up. The probability of all three flips landing heads up is 1/2 x 1/2 x 1/2 = 1/8
• The chance of a single coin flip is 1 in 2.

Probability & Heredity Using Segregation

• Segregation: Alleles segregate randomly during gamete formation, similar to a coin flip.
• Mendel's F₁ cross: Each F₁ plant has one green pod allele and one yellow pod allele.
• Gamete formation & probability: Half of the gametes produced by an F₁ plant will carry the yellow allele (g). To produce a plant with yellow pods (gg) needs two gametes carrying the g allele (1/2 x 1/2 = 1/4).

Probability & Heredity Using Segregation

• Homozygous: Organisms with two identical alleles for a gene are homozygous (GG or gg).
• Heterozygous: Organisms with two different alleles for a gene are heterozygous (Gg).
• Example: If an F₂ gamete has a 1/2 chance of carrying g, the probability of two F₂ gametes carrying the g allele is 1/2 x 1/2 = 1/4.

Probability & Heredity: Genotype/Phenotype

• Phenotype: Observable physical traits (like color or height).
• Genotype: Genetic makeup (combination of alleles).
• Example: In Mendel's pea plants, all plants with GG or Gg have the green pod phenotype despite different genotypes.
• Probabilities average out over a large number of offspring; smaller numbers may not show expected ratios.

Probability & Heredity: Punnett Squares

• Punnett Squares: Use mathematical probability to predict genotype and phenotype combinations in genetic crosses.
• Steps:
• Determine possible gamete alleles from parents.
• Arrange gametes on a square
• Combine gamete alleles in boxes to visualize possible offspring genotypes.

Independent Assortment

• Independent assortment: The segregation of one pair of alleles doesn't influence the segregation of another pair. The gene determining seed shape does not affect the gene for seed color.
• Monohybrid cross: Follows one gene.
• Dihybrid cross: Follows two genes.
• Example : Seeds The genes for seed shape (round/wrinkled) and seed color (yellow/green) are independently assorted.

The Two-Factor Cross: F₁ Generation

• The F₁ generation from crossing true-breeding plants with round yellow peas (RRYY) and wrinkled green peas (rryy) produces offspring with the heterozygous genotype RrYy. These plants all produce round, yellow peas.

The Two-Factor Cross: F₂ Generation

• Crossing F₁ generation plants produces F₂ generation plants.
• F₂ offspring showed combinations of phenotypes not present in the parents indicating independent segregation of alleles.
• The ratio of phenotypes was approximately 9:3:3:1.

Summary of Mendel's Principles

• Mendel's principles form the basis of modern genetics.
• Traits are inherited through genes.
• Some alleles are dominant (masking the effect of recessive). Others are recessive.
• Each organism inherits two copies of each gene, one from each parent. These genes segregate during gamete formation.
• Alleles for different genes segregate independently.
• Principles apply to organisms beyond plants. Morgan used the fruit fly, Drosophila melanogaster to further study inheritance.

Explore Mendel's principles of inheritance through probability and allele segregation. This quiz will help you understand how to predict traits using statistical methods and Gregor Mendel's significant contributions to genetics.