Question

A wild-type tomato plant (Plant 1) is homozygous dominant for three traits: solid leaves (MM), normal height (DD), and smooth skin (PP). Another tomato plant (Plant 2) is homozygous recessive for the same three traits: mottled leaves (mm), dwarf height (dd), and peach skin (pp). In a cross between these two plants (MMDDPP x mmddpp), all offspring in the F1 generation are wild type and heterozygous for all three traits (MmDdPp). Now suppose you perform a testcross on one of the F1 plants (MmDdPp x mmddpp). The F2 generation can include plants with these eight possible phenotypes: solid, normal, smooth solid, normal, peach solid, dwarf, smooth solid, dwarf, peach mottled, normal, smooth mottled, normal, peach mottled, dwarf, smooth mottled, dwarf, peach Assuming that the three genes undergo independent assortment, predict the phenotypic ratio of the offspring in the F2 generation.

Answer 1

There are 8 distinct phenotypes, each one has a 12,5% of appearance:

Since M=solid leaves D=normal height P= smooth skin.

Recessive traits can only be observed in homozygous recessive mmddpp.

1.MmDdPp: M=solid leaves D=normal height P= smooth skin.

2.MmDdpp M=solid leaves D=normal height pp= peach skin.

3.MmddPp M=solid leaves dd=dwarf height P= smooth skin.

4.Mmddpp M=solid leaves dd=dwarf height pp= peach skin.

5.mmDdPp mm=mottled leaves D=normal height P= smooth skin.

6.mmDdpp mm=mottled leaves D=normal height pp= peach skin.

7.mmddPp mm=mottled leaves dd=dwarf height P= smooth skin.

8.mmddpp mm=mottled leaves dd=dwarf height pp= peach skin.