Name:
Date:
Worksheet on Simple Dominance and the Monohybrid Cross
Every individual has 2 copies of each gene, one from each parent. In Simple Dominance we are
looking at one gene with two types of expression or alleles.
Genotype is the 2 alleles the individual has (2n or diploid). A capital letter (D) represents the
dominant allele. It shows. A Lower case letter (d) represents the recessive allele. It
hides.Homozygous means both alleles are the same: DD or dd .Heterozygous mean the alleles
are different: Dd
Gametes are eggs and sperm, they only gave 1 allele (n)
Phenotype is the way the individual looks or how the gene expresses itself (Tall, short, yellow,
green, etc.) You can see the phenotype but you can’t see the genotype you have to deduce it or
it has to be given.
P= parents
F1= first generation (kids)
F2= 2nd generation (grandkids)
How to do a problem: Let: Identify the alleles.
Given: Write down the parents genotype (Or whatever you’ve been given) write down the
cross. Identify the gametes.
Find: Write down what you are asked to find
Punnet Square: Set up Punnet square and solve.
Answer: put your answer in a box.
Example: In sunflowers tall is dominant over dwarf. If a sunflower, homozygous for tall, is
crossed with one homozygous for dwarf, what will be the appearance (Phenotype) of the F1
and F2 generations.
Let: T= tall and t= dwarf
Given: P cross = TT x tt
F1 cross = Tt x Tt
x T t
T TT Tt
t Tt tt
x T T
t Tt Tt
t Tt Tt
Find: F1 and F2 Phenotype
F1 = 100% tall
F2 = 3 Tall : 1 dwarf
Name:
Date:
Practise:
1. Alexia has two short haired Persian cats. In Persians long hair is recessive and short hair is
dominant. She mates them and the female has a litter of 8 kittens, six had short hair and 2 had
long hair. What was the genotype of the parents? What was the genotype of the kittens?
Let:
Given:
Find:
Punnets:
2. Brian Scott thought he would try Mendel’s experiment with sunflowers. In sunflowers Tall is
dominant over dwarf. What is the height of the offspring in the three following crosses? Tt x tt
TT x Tt
Tt x tt
Let:
Given:
Find:
Punnets:
3. Nick has decided to go into dairy farming. He wants a cow that produces lots of milk but has
no horns. Polled means hornless and is dominant in Ayrshire’s (these are good milkers) and
horned is recessive. A certain Polled bull is bred to three different cows.
cow A is horned and produces a polled calf
cow B is horned and produces a horned calf
cow C is polled and produces a horned calf
Let:
Given:
Find:
Punnets: