Probability and Punnett Squares

1
Probability and Punnett Squares

• Bio I
• Chapter 11.2

2
Genetics and Probability

• Probability is the likelihood that any particular
  outcome of an event will occur
• Example
• Event- bouncing a quarter
• Event outcome- quarter lands on heads

Event outcome
Question
Event
Heads
Heads or tails?
The bounce
3
Probability example (contd.)
Question
Event
Event outcome
Heads or tails?
Heads
The bounce
Probabilities
4
Genetics and probability

• How is probability associated with genetics?
• Much like the bouncing of a quarter, the
  segregation of alleles is completely random.
• Mendel realized this. He was then able to
  genetically explain the results of his crosses
  via probabilities.

5
Punnett Squares

• Terms to consider
• Homozygous -
• Heterozygous-
• Phenotype-
• Genotype-
• Punnett square
• Def Used to determine the probability of an
  offspring having a particular genotype
• Alleles are represented by upper (dominant) and
  lowercase (recessive) letters
• F Generation offspring of the original parents
• F Generation offspring of the F generation

2 identical alleles
2 different alleles for the same trait
Physical characteristics of an organism (ie blue
eyes)
Genetic make-up of an organism
1
2
2
6
Punnett Squares

• Lets do a punnett square
• Trait- skin of pea seeds (smooth or wrinkled)
• Alleles- S smooth and s wrinkled
• (dominant) (recessive)

Probabilities
SS
Ss
Smooth
Smooth
Ss
ss
Smooth
Wrinkled