Download Take Home Test 2. Mendelian Genetics: Monohybrid Crosses

Take Home Test 2. Mendelian Genetics: Monohybrid Crosses
Date: __________________________Name: _________________________________________
Lecture Time: ___________________Instructor: ______________________________________
Characters whose alleles behave in the predictable way discovered by Gregor Mendel are said to
be inherited in a Mendelian Fashion, or are said to be inherited according to the rules of Mendel.
In order to follow the rules Mendel discovered, alleles for the gene must be:
• present at only one locus in the genome (one copy per genome), and
• in a classic dominant/recessive relationship.
There may, of course, be more than two alleles for this character in the gene pool, but remember
any individual may only carry two alleles at any gene locus. In the following exercises, all the
traits are Mendelian in inheritance.
A. Monohybrid Crosses. A monohybrid cross involves only 1 gene. Plants can be true breeding
for this character, or not. If they are true breeding it means they are homozygous for the trait. If
they are not true breeding, they are heterozygous.
1. Let’s say you have a true breeding blue flower and a true breeding white flower. You do a cross
between them and discover that all the offspring have blue flowers.
a. What symbol would you use for the genotype of the blue flower?
_____ ­­
b. What symbol would you use for the genotype of the purple flower? _____
c. Show the F1 generation from a cross between the blue and purple flowers.
Draw the Punnett Square here:
Question
Answer
What percentage of the
offspring has blue flowers?
What percentage of the
offspring has purple flowers?
What percentage of the
offspring is heterozygous?
What percentage of the
offspring is homozygous?
d. Show the F2 generation of this experiment.
Draw the Punnett Square here:
Question
What percentage of the
offspring has blue flowers?
Answer
What percentage of the
offspring has purple flowers?
What percentage of the
offspring is heterozygous?
What percentage of the
offspring is homozygous?
What is the phenotypic ratio in
the F2 generation?
Take Home Test 2 Version 1 © Arkansas Scholastic Press 2009
2. Some fruit trees bloom early, and are subject to frost damage, others bloom late in the spring and
are therefore less likely to suffer any frost damage. In plums, this character is determined by a
single gene, and the early blooming allele is dominant over the late allele. You have learned that
you have an early blooming tree, and a late blooming tree in your garden, and that both trees are
homozygous for this condition.
a. How would you symbolize the genotype of the early blooming tree? ____
b. How would you symbolize the genotype of the late blooming tree? ____
c. Show the F1 generation from a cross between the early and late trees.
Draw the Punnett Square here:
Question
Answer
What percentage of the
offspring are early trees?
What percentage of the
offspring are late trees?
What percentage of the
offspring is heterozygous?
What percentage of the
offspring is homozygous?
d. Show the F2 generation of this experiment.
Draw the Punnett Square here:
Question
What percentage of the
offspring are early trees?
What percentage of the
offspring are late trees?
What percentage of the
offspring is heterozygous?
What percentage of the
offspring is homozygous?
What is the phenotypic ratio in
the F2 generation?
Take Home Test 2 Version 1 © Arkansas Scholastic Press 2009
Answer
3. Molecular biologists .have developed a strain of cotton that produces blue cotton instead of the
normal white kind. They did this by moving a blue pigment gene from the blueberry into the
cotton plant. The scientists named the blue allele “denim” because the funding for the project
was from the “blue jeans” industry. The denim allele is dominant over the normal white allele
for the color of the cotton fibers. Through normal cross pollination of this new plant with normal
cotton plants, then scientists were able to obtain a homozygous cotton plant that produces the
blue cotton.
a. What symbol would you use for the genotype of the homozygous denim cotton? ____
b. What symbol would you use for the genotype of the white cotton? ____
c. Show the F1 generation from a cross between the blue and white cotton.
Draw the Punnett Square here:
Question
Answer
What percentage of the
offspring has blue cotton?
What percentage of the
offspring has white cotton?
What percentage of the
offspring is heterozygous?
What percentage of the
offspring is homozygous?
d. Show the F2 generation of this experiment.
Draw the Punnett Square here:
Question
Answer
What percentage of the
offspring has blue cotton?
What percentage of the
offspring has white cotton?
What percentage of the
offspring is heterozygous?
What percentage of the
offspring is homozygous?
What is the phenotypic ratio in
the F2 generation?
Take Home Test 2 Version 1 © Arkansas Scholastic Press 2009
4. Now you have a true breeding tall and a true breeding dwarf apple tree. You do a cross between
them and discover that all the offspring are tall trees.
a. What symbol would you use for the genotype of the tall tree?
b. What symbol would you use for the genotype of the dwarf tree? ____
____
c. Show the F1 generation from a cross between the tall and dwarf trees.
Draw the Punnett Square here:
Question
Answer
What percentage of the
offspring are tall trees?
What percentage of the
offspring are dwarf trees?
What percentage of the
offspring is heterozygous?
What percentage of the
offspring is homozygous?
d. Show the F2 generation of this experiment.
Draw the Punnett Square here:
Question
What percentage of the
offspring has tall trees?
What percentage of the
offspring are dwarf trees?
What percentage of the
offspring is heterozygous?
What percentage of the
offspring is homozygous?
What is the phenotypic ratio in
the F2 generation?
Take Home Test 2 Version 1 © Arkansas Scholastic Press 2009
Answer