Two Traits
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Mendel found that
traits that are not linked together will segregate into gametes independent
of any other traits. One could explain this by looking at the seed
color trait and the height trait. If each parent has two alleles for
each trait, then a pure bred Tall, Green seed plant would have the genotype
TTGG. We are assuming of course that tallness is dominant to
shortness, and Green seeds are dominant to Yellow seeds. A parent who
then is short and produces yellow seeds would have the genotype ttgg.
When crossed the offspring would all be heterozygous for both traits.
When these seeds are allowed to develop, mature and reproduce, the resulting
offspring from this cross would show the following phenotypes. 9 Tall, Green seeds 3 Tall Yellow Seeds 3 Short Green Seeds 1 Short Yellow seeds This demonstrated what is now called Mendel's Second Law, the Law of Independent Assortment. This states that two or more pairs of alleles segregate into gametes independent of one another. In other words, an individual that has a heterozygous genotype for both traits, TtGg, has the possibilities of having the following gametes TG, tg, Tg, tG. The tallness alleles will be in a gamete with one of the two seed color alleles. Which one does not matter because the will move or be taken into a gamete by chance. The important thing to remember her is that each gamete will have one of each type of alleles in it. We now know that meiosis is the process by which alleles are placed in gametes.
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