As you have read, if an allele is paired with another one just like it, the name for the pair is homozygous. If the allele is paired with a different type, the pair is called heterozygous. You have also learned about how some alleles are domi- nant and some are recessive. A Punnett square shows how the pairs will possi- bly match up. Making a prediction about how the offspring will look is usually simple. If the pair is heterozygous or homozygous dominant, the dominant trait will be expressed. If the pair is homozygous recessive, the recessive trait will be expressed. There are some alleles, however, that behave like normal dominant alleles when in a heterozygous pair, but are deadly in a homozygous pair. For example, the alleles that control fur color in wild mice are yellow and black. The yellow allele is dominant (Y) and the black is recessive (b). When a mating occurs and the alleles are paired together, the hairs have yellow and black bands. From a distance this makes the mouse appear brown or buff-colored. However, the allele for yellow fur color is what scientists call a 'lethal' or deadly allele. If it is paired with itself, the two alleles kill the baby mouse before it can be born. Fortunately there are not many genes of this type. Fill in the Punnett square below for a case in which two mice, each heterozy- gous for the dominant yellow allele, are mated. Then use the diagram to answer the following questions. 1. How many live offspring will have one dominant allele for yellow fur? 2. How many mice will die before birth? 3. How many brown mice will be born? 4. If you see a healthy living yellow mouse can you tell if it is heterozygous or homozygous? Explain your answer.
As you have read, if an allele is paired with another one just like it, the name for the pair is homozygous. If the allele is paired with a different type, the pair is called heterozygous. You have also learned about how some alleles are domi- nant and some are recessive. A Punnett square shows how the pairs will possi- bly match up. Making a prediction about how the offspring will look is usually simple. If the pair is heterozygous or homozygous dominant, the dominant trait will be expressed. If the pair is homozygous recessive, the recessive trait will be expressed. There are some alleles, however, that behave like normal dominant alleles when in a heterozygous pair, but are deadly in a homozygous pair. For example, the alleles that control fur color in wild mice are yellow and black. The yellow allele is dominant (Y) and the black is recessive (b). When a mating occurs and the alleles are paired together, the hairs have yellow and black bands. From a distance this makes the mouse appear brown or buff-colored. However, the allele for yellow fur color is what scientists call a 'lethal' or deadly allele. If it is paired with itself, the two alleles kill the baby mouse before it can be born. Fortunately there are not many genes of this type. Fill in the Punnett square below for a case in which two mice, each heterozy- gous for the dominant yellow allele, are mated. Then use the diagram to answer the following questions. 1. How many live offspring will have one dominant allele for yellow fur? 2. How many mice will die before birth? 3. How many brown mice will be born? 4. If you see a healthy living yellow mouse can you tell if it is heterozygous or homozygous? Explain your answer.
Chapter13: Patterns In Inherited Traits
Section: Chapter Questions
Problem 6GP: In sweet pea plant, an allele for purple flowers (P) is dominant when paired with a recessive allele...
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