1. In a test cross, peas of an unknown genotype are crossed with peas of a known
ID: 23066 • Letter: 1
Question
1. In a test cross, peas of an unknown genotype are crossed with peas of a known genotype. In this example, smooth peas are the unknown and wrinkled peas are the known (rr). If half of the offspring from that cross are smooth and half are wrinkled, what is the genotype of the unknown plant?A. Incomplete dominance
B. Homozygous dominant: RR
C. Homozygous recessive: rr
D. Heterozygous: Rr
E. The genotype cannot be determined from the information given.
2. What fraction of offspring of the cross AaBb
Explanation / Answer
1. In a test cross, peas of an unknown genotype are crossed with peas of a known genotype. In this example, smooth peas are the unknown and wrinkled peas are the known (rr). If half of the offspring from that cross are smooth and half are wrinkled, what is the genotype of the unknown plant?
A. Incomplete dominance
B. Homozygous dominant: RR
C. Homozygous recessive: rr
D. Heterozygous: Rr
E. The genotype cannot be determined from the information given.
Rr x rr
Rr-------half are smooth
rr------------half are wrinkled
2. What fraction of offspring of the cross AaBb × AaBb is homozygous for all the dominant alleles, assuming that they are on different chromosomes?
C. 1/16
AaBb × AaBb
AABB---------1/16
3. The fact that a trait like height in humans varies over a wide range of values is due to
A. penetrance.
B. expressivity.
C. multiple alleles and the environmental influences on the expression of these genes.
D. epistasis.
E. discrete and qualitative genomic variation.
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