Download Monohybrid Crosses Worksheet Answers

Year 11 Genetics
Monohybrid Crosses Answers
1. In maize starchy is dominant to sugary. Two purebreeding plants were
crossed, one grown from a startchy seed and one from a sugary seed.
a. What is the phenotype of the F1 seeds? Starchy
b. These F1 seeds grew into mature plants and were allowed to
self fertilise. What is the expected ratio of starchy to sugary
seeds in the cobs on the F2 plants. 3:1
2. Mendel crossed pure breeding plants having green unripe pods with
pure breeding plants having yellow unripe pods. The F1 plants had
green pods. He allowed these to self fertilise and collected 580 F2
plants. How many of these would be expected to have green pods and
how many yellow pods? 435 green, 145 yellow
3. The allele causing cystic fibrosis in humans is recessive to the normal
allele. A man is heterozygous for the cystic fibrosis. Does he suffer
from the disease? No, but he is a carrier.
4. In guinea pigs, short hair is dominant to angora (or long hair). A
heterozygous animal was mated to a homozygous recessive.
a. What are the phenotypes of these animals? Short hair
(heterozygous) and Angora (homozygous recessive)
b. Using suitable symbols give their genotypes. H = short hair, h =
long hair. Hh is heterozygous, hh is homozygous recessive.
c. Draw out the genetic cross and state the proportion of their litter
are expected to be angora. 50%
5. ‘White forelock’, a patch of white hair at the front of the head, is a
dominant condition in humans. A woman with a white forelock married
a normal man and had a daughter with a white forelock. The daughter
also married a normal man. Using genetic crosses find the likelihood
that her first child will have a white forelock.
W = white forelock, w = no white forelock
6. Red Poll cattle are chestnut red. When crossed to White Shorthorn, the
calves have a mixture of red and white hairs and are called roan. Give
the possible phenotypes of the offspring of the following crosses and
the probability with which they will occur.
a. roan X roan , red (25%) white(25%) and roan (50%)
b. roan X white, roan (50%) and white (50%)
c. roan X red, red (50%) and roan (50%)
7. The ability to roll the tongue is a dominant trait in humans. A man and
a woman, both able to roll their tongues had four children. Some
children were able to roll their tongues and some were not. Draw out
the cross to show the genotypes of the parents and the offspring. How
many children would you expect to be able to roll their tongues? (75%)
T = tongue roller, t = non tongue roller
8. A budgerigar breeder bred together homozygous dark blue and
homozygous pale blue birds and obtained all mid-blue progeny. In an
attempt to obtain more mid-blue birds he bred the mid-blue birds with
each other. To his surprise the outcome was not as he expected. What
phenotypes will he have got by crossing the mid-blue birds and in what
proportions? (25% dark blue, 25% pale blue, 50% mid-blue) What
cross should he carry out to be sure that the offspring will all be midblue? dark blue X mid blue