Probability

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Probability Genetics
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.A. Learning goals

• Explain the random process of chromosome
  segregation and distribution of alleles in
  gametes.
• Predict possible combinations of alleles in a
  zygote from the genetic makeup of the parents.

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B. Independent Assortment of Alleles

• Gametes (sperm and egg) will contain two alleles
  for each gene. They are divided randomly during
  meiosis.
• Sperm Egg
• Yy yy

Yy Yy
yy yy this random selection of
alleles occurs for23 pairs of chromosomes for
thousands of genes !!!
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Probability
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C. Punnett Square Terminology

• Homozygous Individuals with identical alleles
  Ex. RR, rr
• Heterozygous Individuals with different alleles
  ex. Rr
• Dominant always expresses the trait
• Rr, RR
• Recessive needs both recessive alleles to
  express the trait
• rr
• Phenotype physical characteristic
• Ex. White fur, blue eyes, green skin
• Genotype genetic makeup
• Ex. FF, Bb, or gg

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How to use Punnett Squares

• Choose a letter to represent the alleles in the
  cross.
• Write the genotypes of the parents.
• Determine the possible gametes (reproductive
  cells) that the parent can produce.
• Enter the possible gamete at the top and side of
  the Punnett square.

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D. Practice Ex. 1

• A plant that is homozygous recessive for short ,
  _tt___, is crossed with a plant that is
  homozygous for TT. How many offspring will be
  short?

T T
t t
Tt Tt Tt Tt
Answer O , all will be tall and heterozygous.
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Ex. 2

• The Rock has the heterozygous condition of
  rolling tongue, Rr and his wife has the
  heterozygous condition as well, Rr. They have
  four children. What is the ratio of rolling
  tongue among the offspring

T T
R r
Answer 31 of the offspring have rolling
tongue!
R r
RR Rr Rr rr
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Punnett Squares Monohybrid Dihybrid Crosses
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Punnett Squares
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Mendels Principles Summary

• The inheritance of biological characteristics are
  determined by genes.
• For two or more forms of a gene, dominance and
  recessive forms may exist.
• Most sexually reproductive organisms have two
  sets of genes that separate during gamete
  formation.
• Alleles segregate independently.