11-2

1
11-2 Probability and Punnett Squares
Sexual Reproduction and Genetics
Chapter 10

• Genetics and Probability
• How do geneticists use the principles of
  probability?
• Probability the likelihood that a particular
  event will occur
• The principles of probability can be used to
  predict the outcomes of genetic crosses.

2
Punnett Squares
Sexual Reproduction and Genetics
Chapter 10

• Punnett Squares a tool used to determine the
  combinations from a genetic cross
• Shows all possible combinations of gametes and
  likelihood each will occur

3
Setting up a Punnett Square
Sexual Reproduction and Genetics
Chapter 10

• Draw the punnett square size of your square
  depends on how many traits you are using (Ex. 1
  trait 4 boxes, 2 traits 16 boxes)
• Gametes produced by each parent are shown along
  the top and left side.
• Possible gene combinations for the offspring
  appear in the four boxes.

4
Mendels Experiment
Sexual Reproduction and Genetics
Chapter 10

• Gametes from the F1 generation parents are used
  to get the offspring for the F2 generation.
• Mendel only looked at one trait at a time in his
  first experiments
• Monohybrid cross a cross involving one trait

5
Probablility and Segregation

• One fourth (1/4) of the F2 plants have two
  alleles for tallness (TT).
• 2/4 or 1/2 have one allele for tall (T), and one
  for short (t).
• One fourth (1/4) of the F2 have two alleles for
  short (tt).

6
Sexual Reproduction and Genetics
Chapter 10
10.2 Mendelian Genetics
Mendels Law of Segregation

• Two alleles for each trait separate during
  meiosis.

• During fertilization, two alleles for that trait
  unite.

• Heterozygous organisms are called hybrids.

7
Sexual Reproduction and Genetics
Chapter 10
10.2 Mendelian Genetics
Monohybrid Cross

• A cross that involves hybrids for a single trait
  is called a monohybrid cross.

8
Sexual Reproduction and Genetics
Chapter 10
10.2 Mendelian Genetics
Dihybrid Cross

• The simultaneous inheritance of two or more
  traits in the same plant is a dihybrid cross.

• Dihybrids are heterozygous for both traits.

9
Sexual Reproduction and Genetics
Chapter 10
10.2 Mendelian Genetics
Law of Independent Assortment

• Random distribution of alleles occurs during
  gamete formation

• Genes on separate chromosomes sort independently
  during meiosis.

• Each allele combination is equally likely to
  occur.

• Law of independent assortment occurs during
  metaphase I of meiosis.

10
Sexual Reproduction and Genetics
Chapter 10
10.2 Mendelian Genetics
Punnett SquareDihybrid Cross

• Four types of alleles from the male gametes and
  four types of alleles from the female gametes can
  be produced.

• The resulting phenotypic ratio is 9331.

11
Sexual Reproduction and Genetics
Chapter 10
10.3 Gene Linkage and Polyploidy
Polyploidy