Biology
Lacks
Name___________________________________
Period ____________
Genetics In-Class Worksheet #1
On all problems, SHOW YOUR WORK. Show all crosses, using Punnett Squares. Use P to designate
your parents (or P1 and P2 for 2 generations of parents), F1 for your first generation of offspring, and F2 if
you have a second generation of offspring. Report all of the expected phenotypes of offspring using
fractions, ratios or percents.
Monohybrid Crosses
1. In humans, the gene for hanging earlobes (H) is dominant over the gene for attached earlobes (h). Show
what would happen if 2 heterozygous parents had children.
Yellow seeds are dominant in pea plants. Show a cross between a homozygous pea plant with yellow
seeds and a pea plant with green seeds. Then, for a second generation, cross one of the F1 offspring back
with its yellow parent. Report both generations of offspring using 2 Punnett Squares.
2.
3. In humans, the gene for Polydactyly (having 6 fingers) is dominant (P), and the gene for having 5 fingers
is recessive (p). Show a cross between a person who has 5 fingers and a person who is homozygous for
Polydactyly. (*Make sure your capital and lowercase p’s are distinguishable.) Then show a second
generation cross between one of the F1 children and a person with 5 fingers.
4. Huntington’s Disease is a dominant disorder that affects the brain. Show how 2 parents who both have
Huntington’s Disease could produce normal children.
Lethal Dominance
5. Achondroplasia is a genetic disorder that causes dwarfism. The gene for Achondroplasia is dominant (A).
The recessive form of the gene (a) codes for normal height. If a person receives two genes for the disorder
(homozygous dominant), the condition is lethal and the baby will die before birth. If a person is
heterozygous, they will exhibit dwarfism.
Show a cross between two people who are both dwarfs due to Achondroplasia and report their possible
offspring.
If the above couple gave birth to a living child, what is the chance that is it a dwarf? ___________________
CHALLENGE (Optional, for extra credit)
6. Tay Sachs is a recessive disorder which causes degeneration of the brain in children, and death by the age
of five. John is a normal adult. His brother died from Tay Sachs at a young age. John knows that his
mother’s mother was completely normal (not a carrier of Tay Sachs). Show a cross between John’s
grandparents and then show a cross between John’s parents. (Show 2 Punnett Squares.) Use L for normal
lipid degradation, and l for Tay Sachs.