Homework Assignment #1
Question 1
A corn breeder crosses a dent corn and sweet corn. SuSu X susu to produce
the F1 Susu genotype. The dent corn or normal
endosperm is completely dominant to the sugary (su) endosperm. He then
self-pollinates several F1 plants. He observes
the following results:
| Ear # |
Observed |
| Dent
Kernels |
Sugar
Kernels |
Ratio |
| 1 |
75 |
23 |
3.26:1 |
| 2 |
80 |
15 |
5.33:1 |
| 3 |
60 |
20 |
3.33:1 |
| 4 |
120 |
43 |
2.79:1 |
What is one possible explanation for the different ratios of dent:sugary
kernels among the four ears of corn?
Question 2
A purple flowered, brown pubescence soybean plant is crossed to a white
flowered, grey pubescence plant. The F1 plant
is self-pollinated to produce an F2 family. These
two loci are on separate chromosomes and there is complete dominance
gene action at each locus. There is no epistasis between these two traits.
Use a Punnett square and show the expected segregation ratio of the
F2 progeny.
Question 3
Purple kernel color is dominant to yellow in corn. Several anthocyanin
pigment genes influence the aleurone color of the corn kernel. In this
case, the cross is R1R1R2R2
x r1r1r2r2
to produce a dihybrid F1 plant. The R1
and R2 alleles are completely dominant to the
recessive alleles at each separate locus. Also, there is duplicate epistasis
interaction among the two loci. This means that a dominant allele at
either locus results in purple aleurone color. The R1
and R2 genes are not linked, but segregate independently.
Use a Punnett square to derive the expected ratio of purple to yellow
kernels in an F2 family.
Question4
Due to lethal genes in males, the ratio of male
to female human offspring is 49:51. This means
that 49% of live births are male and 51% are female
infants. Find the probability that a family of
only two children will consist of two girls. What
statistical principle is used when the sum of
male and female infants equals unity?
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