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). Two plants. Plant 1 has solid leaves (two uppercase M), normal height (two uppercase D), and fruits with smooth skin (two uppercase P). Plant 2 has mottled leaves (two lowercase m), dwarf height (two lowercase d), and fruits with peach skin (two lowercase p). 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:________. Assuming that the three genes undergo-independent assortment, predict the phenotypic ratio of the offspring in the F2 generation.
a. solid, normal, smooth.
b. solid, normal, peach.
c. solid, dwarf, smooth.
d. solid, dwarf, peach.
e. mottled, normal, smooth.
f. mottled, normal, peach.
g. mottled, dwarf, smooth.
h. mottled, dwarf, peach.

Answer 1

Answer: In this type of cross between MmDdPp and mmddpp, the phenotypic ratios in the eight possible phenotypes are as follow; a. solid, normal, smooth = 1:8

b. solid, normal, peach = 1:8

c. solid, dwarf, smooth = 1:8

d. solid, dwarf, peach = 1:8

e. mottled, normal, smooth = 1:8

f. mottled, normal, peach = 1:8

g. mottled, dwarf, smooth = 1:8

h. mottled, dwarf, peach = 1:8

Explanation: The number of gametes that can be formed from a particular genotype is given as 2^n where n is the number of heterozygous loci. In the genotype MmDdPp, n = 3. Therefore, 8 gametes can be formed.

In genotype mmddpp, n = 0. Therefore, only one type of gamete can be formed.

Crossing the two genotype (MmDdPp and mmddpp) as shown in the attached image, 8 possible offsprings can be achieved. Phenotypes of these offspring had been stated earlier. The phenotypic frequency of each of these offspring is one out of eight (⅛).