Transcript Ertertewt ertwetr - Campbell County Schools

Probability and Punnett Squares
Chapter 11.2
Biology
Mr. Hines
Probability and Punnett Squares
After Mendall crossed the various pea plant
alleles, he had to count the offspring and
their traits.
He noticed that the numbers could be related
to the principles of Probability.
Probability – The likelyhood that a particular
event will occur.
If you flip a coin, the probability that you will
get heads is ½.
If you want to calculate the probability of
getting heads 3 times in a row, you would
perform this math
½ x ½ x ½ = 1/8
This means that you have a 1 in 8 chance of
flipping a coin 3 times and getting heads
all 3 times.
The principles of probability can be used to
predict the outcomes of genetic crosses.
A Punnett Square can be used to show how
the various crossed traits will combine to
form offspring.
A Punnett Square can also show the
probability of each outcome.
Important terms
Homozygous – organisms have 2 identical
alleles for a particular trait (TT for 2
dominant alleles or tt for 2 recessive
traits.)
Heterozygous - organisms that have 2
different alleles for the same trait (Tt –
one dominant and one recessive)
Phenotype – physical characteristics
Genotype – genetic characteristics
Example 1
Dogs with big feet and
small feet.
Genotype
FF
F = dominant Big feet
(capital letter)
f = recessive small feet
(lower case)
Ff
ff
Phenotype
Probability and segregation
Probability and segregation is best learned by
practicing with Punnet squares.
In this chapter, we will do monohybrid
crosses.
Monohybrid cross – a cross that deals only
with one trait (gene).
Example 2
Dogs with Large feet
F (dominant)
Dogs with small feet
f
(recessive)
Parents genotypes
Ff x Ff
Draw the phenotypes of both parents
Determine the probability of each trait after
crossing both parents.
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