Transcript Applying Mendel*s Principles Probability, Punnett

Applying Mendel’s Principles
Probability, Punnett Squares, &
Independent Assortment (Dihybrid Cross)
Section 11.2
Mendel’s Data
• Mendel’s pea plant data gave him a lot
of data to analyze
• He began observing patterns, for
example a cross of two heterozygous
parents for tallness always results in
approximately ¾ tall & ¼ short
• Concluded the principles of probability
could be used to explain the results of
his genetic crosses
Probability
• Probability: the likelihood that a particular event
will occur
• Using flipping a coin as an example:
– Two possible outcome
– The chance or probability is equal you will get
heads or tails and that probability is 1 out of 2 (
½ or 50%) for heads and 1 out of 2 (½ or
50%)for tails
– Each flip is independent
• Flip three times in a row – probability of getting
heads
– ½ X ½ X ½ = 1/8
– 1/8 chance of getting heads three times in a tow
• Past outcomes do not affect future ones
Probability & Punnett Squares
• Predicts averages:
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• Punnett squares use mathematical
probabilities to help predict
genotype and phenotype
combinations in genetic crosses
Independent Assortment
• After showing alleles for a trait segregate
during meiosis, Mendel began wondering if
the segregation of one pair affected the
segregation of another
• For example: does the gene that affects the
shape of the seed affect the gene for seed
color?
• He then began to follow two traits (two
genes) – these are called two-factor or
dihybrid crosses
Mendel’s Dihybrid Data & Conclusions
• Crossed parents that were heterozygous for
two traits
– Seed shape: R is dominant over wrinkled r
– Seed color: Y is dominant over green y
• So the parents were RrYy (round
yellow )
• The offspring resulted in:
– Round, yellow (RRYY & RrYy)
– Round, green (RRyy & Rryy)
– Wrinkled, yellow (rrYY & rrYy
– Wrinkled, green (rryy)
…continued
• Because allele combinations not found in
either parent were present in offspring, it
showed that alleles for seed shape
segregated separately from alleles for seed
color - & can result in new combinations
• These genes did not influence each other’s
inheritance
• Principle of independent assortment:
genes for different traits segregate
independently of each other during
meiosis (the formation of gametes)