Simple or complete dominance
Skill 2: Predict the outcome of a simple genetic cross using a Punnett Square. (Complete practice problems below and check your answers before the checkpoint.)
Each person has two alleles, or variations, of a certain gene. You inherit one from your Mom and the other from your Dad. You could have two copies of the same allele or two different ones. For example, Mom could pass along an allele for having blue eyes, but Dad could give you an allele for brown. These alleles are located in your DNA, in the nucleus of your cells.
Each person has two alleles, or variations, of a certain gene. You inherit one from your Mom and the other from your Dad. You could have two copies of the same allele or two different ones. For example, Mom could pass along an allele for having blue eyes, but Dad could give you an allele for brown. These alleles are located in your DNA, in the nucleus of your cells.
When an individual is heterozygous, the dominant allele is the one which will show up in the offspring's phenotype. In this case, the offspring will have brown eyes, as shown in the Punnett square. This tells us that brown is dominant over blue, thus hiding it. (This problem DOES NOT match up to the one in your packet.)
When an individual is heterozygous, the dominant allele is the one which will show up in the offspring's phenotype. In this case, the offspring will have brown eyes, as shown in the Punnett square. This tells us that brown is dominant over blue, thus hiding it. (This problem DOES NOT match up to the one in your packet.)
For an introduction or refresher for completing Punnett squares, watch this video.
For an introduction or refresher for completing Punnett squares, watch this video.
How many letters are used in the key?
How many letters are used in the key?
When writing a Punnett square key, consider how many dominant alleles there are. An allele is considered dominant if it shows up in the heterozygous offspring. In the eye color example above, there is one dominant allele, which is brown. We choose the letter 'B' to represent the dominant allele.
When writing a Punnett square key, consider how many dominant alleles there are. An allele is considered dominant if it shows up in the heterozygous offspring. In the eye color example above, there is one dominant allele, which is brown. We choose the letter 'B' to represent the dominant allele.
B - (capital letter) represents dominant trait (brown)
B - (capital letter) represents dominant trait (brown)
b - (lowercase letter) represents recessive trait (blue)
b - (lowercase letter) represents recessive trait (blue)
Complete the page below in your packet, then ask for the answer key to check your work.
Complete the page below in your packet, then ask for the answer key to check your work.
Ask me for the answer key to be sure your work is correct.
Ask me for the answer key to be sure your work is correct.