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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, 3/4 of the offspring will have purple flowers, as shown in the Punnett square. The one in the upper left has the genotype "BB," which is two alleles for purple flowers. The two with green backgrounds have the genotype "Bb" and will also be purple. This tells us that purple is dominant over white, thus hiding it. The only offspring with white flowers is the one on the bottom right with the genotype "bb", which has two recessive alleles for white flowers.
When an individual is heterozygous, the dominant allele is the one which will show up in the offspring's phenotype. In this case, 3/4 of the offspring will have purple flowers, as shown in the Punnett square. The one in the upper left has the genotype "BB," which is two alleles for purple flowers. The two with green backgrounds have the genotype "Bb" and will also be purple. This tells us that purple is dominant over white, thus hiding it. The only offspring with white flowers is the one on the bottom right with the genotype "bb", which has two recessive alleles for white flowers.
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.
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