In mice, black fur (B) is dominant over white fur (b). Which of the following is not the correct method to determine if a mouse with a dominant phenotype has a homozygous or heterozygous genotype?
Select one:
A mouse with a dominant phenotype should be crossed with a mouse with a recessive phenotype.
Test crosses need to be conducted on a mouse with a dominant phenotype to determine their genotype.
The black mouse should mate with white mice.
A mouse with a dominant phenotype should be crossed with any true breeding mouse.
4 years ago
Answered By Alisha E
We know that the mouse has a dominant phenotype, which means that it exhibits the black fur trait. If it is homozygous the genotype is BB and if it is heterozygous the genotype is Bb. We need to determine which of the following methods are incorrect.
(1) A mouse with a dominant phenotype should be crossed with a mouse with a recessive phenotype.
(2) Test crosses need to be conducted on a mouse with a dominant phenotype to determine their genotype.
(3) The black mouse should mate with white mice.
(4) A mouse with a dominant phenotype should be crossed with any true breeding mouse.
When we make a punnet square with a BB mouse and a bb (white) mouse we get that all of the offspring have a Bb genotype. When we make a punnet square with a Bb mouse and a bb mouse we get the following offspring: Bb x2 and bb x2. When we cross a bb mouse with a mouse with a dominant phenotype and an unknown genotype we call this a test cross. When we cross these mice we will get either all Bb offspring (all dominant) matching the first punnet square, letting us know that the unknown mouse is of a BB genotype, or we will get some bb (white) mice, letting us know that the unknown mouse is of a Bb genotype as this matches the second punnet square. Because of this, we know that (1) is correct because we need to cross the dominant phenotype mouse with a recessive mouse, (2) is correct because we need to conduct the test cross and (3) is correct because the test cross involves the black mouse mating with the white mouse. However, (4) is incorrect because we do not want to cross the unknown genotype mouse with just any true breeding mouse as if we were to cross it with a true breeding BB mouse, for example, all of the mice would be black and we would not know their genotypes, which would not allow us to figure our the genotype of the black mouse. The test cross must be conducted between a dominant phenotype, unknown genotype mouse and a homozygous recessive mouse.
4 years ago
Answered By Alisha E
We know that the mouse has a dominant phenotype, which means that it exhibits the black fur trait. If it is homozygous the genotype is BB and if it is heterozygous the genotype is Bb. We need to determine which of the following methods are incorrect.
(1) A mouse with a dominant phenotype should be crossed with a mouse with a recessive phenotype.
(2) Test crosses need to be conducted on a mouse with a dominant phenotype to determine their genotype.
(3) The black mouse should mate with white mice.
(4) A mouse with a dominant phenotype should be crossed with any true breeding mouse.
When we make a punnet square with a BB mouse and a bb (white) mouse we get that all of the offspring have a Bb genotype. When we make a punnet square with a Bb mouse and a bb mouse we get the following offspring: Bb x2 and bb x2. When we cross a bb mouse with a mouse with a dominant phenotype and an unknown genotype we call this a test cross. When we cross these mice we will get either all Bb offspring (all dominant) matching the first punnet square, letting us know that the unknown mouse is of a BB genotype, or we will get some bb (white) mice, letting us know that the unknown mouse is of a Bb genotype as this matches the second punnet square. Because of this, we know that (1) is correct because we need to cross the dominant phenotype mouse with a recessive mouse, (2) is correct because we need to conduct the test cross and (3) is correct because the test cross involves the black mouse mating with the white mouse. However, (4) is incorrect because we do not want to cross the unknown genotype mouse with just any true breeding mouse as if we were to cross it with a true breeding BB mouse, for example, all of the mice would be black and we would not know their genotypes, which would not allow us to figure our the genotype of the black mouse. The test cross must be conducted between a dominant phenotype, unknown genotype mouse and a homozygous recessive mouse.