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Dihybrid Crosses. Mendel’s Peas. In addition to Mendel’s monohybrid cross experiments, he also studied the probability of inheriting 2 separate traits Example: Seed colour and seed shape Seeds can be green or yellow; they can also be wrinkled or smooth
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Mendel’s Peas • In addition to Mendel’s monohybrid cross experiments, he also studied the probability of inheriting 2 separate traits • Example: Seed colour and seed shape • Seeds can be green or yellow; they can also be wrinkled or smooth • What’s the probability of getting green, wrinkled seeds?
Consider the following: Yellow seeds = Y Green seeds = y Round seeds = R Wrinkled seeds = r If a pea plant is heterozygous for both traits, how many different sex cells can it produce? YyRr If 2 plants, heterozygous for both traits are crossed, what types of offspring are possible?
Two heterozygous plants are crossed:YyRr X YyRr Parent 1 Parent 2
Does inheriting yellow seeds, change the probability of the seeds being wrinkled? • NO! Traits are inherited independently from one another because alleles are on separate chromosomes. • One chromosome from each homologous pair is randomly assigned to each sex cell during meiosis. • This is known as the Law of Independent Assortment. • It’s like flipping a coin for every trait and chance has no memory: flipping ‘heads’ the first time, does not make it more likely that you will flip ‘tails’ the next time.
