Download Genetics Problems 2

Pre-AP Biology
Name___________________
Advanced Genetics Topics &Problems
Prd._____Date____________
1. Dihybrid Punnett Squares
These are Punnett Squares used to solve genetics problems involving two traits in an
organism.
Step 1: Find the genotypes of the parents
Step 2: Figure out which combinations of genes will be in the gametes of each parent,
put those into a Punnett Square
Step 3: Fill in the Punnett Square—make sure each offspring has 4 genes (2 for each
trait)
Step 4: Figure out ratios of phenotype and genotype in the offspring
Solve:
Cross a plant that is heterozygous for both tall and purple flowers with a plant that is
heterozygous for tall with white flowers. Use T for tall, t for short; P for purple, p for
white:
Phenotype Ratio:______________________
2. Incomplete Dominance
These occur when an organism exhibits a trait that is halfway between each of the
parents. For example, in snapdragons, a red flowered plant (CR CR) is crossed with a
white flowered plant (CW CW) and a pink flower is produced. Show the results from this
cross here:
Now, cross two pink flowered snapdragons here:
Genotype Ratio:____________________
Phenotype Ratio:____________________
3. Codominance
In these cases, neither gene dominates over the other and both genes will be expressed
in the phenotype of the offspring. For example, a Black-feathered chicken (BB) is
crossed with a White-feathered chicken (WW). The phenotype of the offspring shows
both black and white feathers ( a mottled grey appearance). Show this cross here:
Now, cross two mottled grey chickens here:
Genotype Ratio:
Phenotype Ratio:
4. Multiple Alleles
This occurs when an organism has more than two alleles for a trait. An example of this is
human blood types. There are 3 alleles for human blood types: IA, IB, and i. Both IA and IB
are dominant over i. Neither IA or IB dominates over the other so when both alleles are
present, the individual will show both traits and will have Type AB blood (Codominance).
Now try a problem: Cross a man who has Type AB blood (IA IB) with a woman who has
Type O blood (ii).
What blood types could their children have? _______________________
What blood types could not be seen in their children? ____________________