BIO 201 Lecture Notes - Lecture 5: Lady Gaga, Thomas Hunt Morgan, Punnett Square

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7 Feb 2017
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Lecture 5
Gametes have genotypes
Haploids
An individual of genotype of AA produces 100% A gametes
An individual of genotype of aa produces 100% a gametes
An individual of genotype of Aa produces 50% a gamete and 50% A gamete
Punnett Square for a cross
Mendel developed two laws that described his results
Mendel’s first law states that the 2 copies of a gene segregate
o When any individual produces gametes, the 2 copies of a gene separate, so that each gamete
o Thus gametes from a parent with the RR genotype will all carry R; gametes from an rr parent
will all carry r; and the progeny derived from a cross between these parents will all be Rr
Gametes made by this Rr individual will be 50% R and 50% r
Mendel’s 1st law is the basis of “Particular
Inheritance”
Mendel’s second law states that copies of
different genes assort independently
o The law od “Independent Assortment”
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The Outcome of Independent Assortment
Each chromosome is inherited independently from
other chromosomes
o Among the A gametes, 50% are B and 50% are b
o Among the a gametes, 50% are B and 50% are b
Loci on separate chromosomes (and if they are far enough away from each other on the same
chromosome) are inherited independently of each other
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Statistical Independence
Mendel’s law of independent assortment is about statistical independence
When the probabilities of 2 events are independent of each other, the joint probability (the
probably that they will both occur) is the product of the 2 individual probabilities
If gender is independent of a student being a fan of Lady Gaga and we have:
o % males in the population = 50%
o % Lady Gaga fans in the population = 5%
o then the expected % of males, Lady Gaga fans in the population is (5%)*(50%)=2.5%
Because of this statistical independence, you can also calculate the ratios by multiplying the
rations of the individual traits
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