2. Mendel’s Law of Independent Assortment states that genes for different traits

Question

2. Mendel’s Law of Independent Assortment states that genes for different traits are inherited independently. For example, if a green, spotted, true-breeding (homozygous) organism is crossed with a blue, spotless, true-breeding organism, not all of the offspring will be green and spotted. This is a dihybrid cross. a. The table below shows the results for the F2 generation of a dihybrid cross. A green, spotted parent and a blue, spotless parent were initially crossed, and the F1 offspring were then crossed. How do these F2 results demonstrate the Law of Independent Assortment? Phenotype Number of Organisms Green, Spotted 281 Green, Spotless 93 Blue, Spotted 94 Blue, Spotless 32

Explanation / Answer

Answer:

We cross two true-breeding organisms: green, spotted organism (GGSS) and blue, spotless organism (ggss).

Because each parent is homozygous, the gametes made by the blue, spotless organism are gs, and the gametes made by the green, spotted organism are GS. This gives us F1 offspring that are GgSs.

Now, when we cross the F1 offsprings, we get the F2 offsprings in the following proportions (given in the question):

Parentals: GgSs x GgSs

F2: Green, Spotted = 281; Green, Spotless = 93; Blue, Spotted = 94; Blue, Spotless = 32

So, it gives a ratio of = 281 : 93 : 94 : 32, which is aprroximately 9 : 3 : 3 : 1.

This is exactly what we would expect to see if the F1 organism made four types of gametes with equal frequency: GS, Gs, gS, and gs, i.e, this is the result we'd predict if each gamete randomly got a G or g allele, and also randomly got an S or s allele in a separate event.

Thus, the above data demonstrates the law of independent assortment.

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