Which of the following statements about crossing over is TRUE?
2 answers:
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Ok, so I wrote these out just to make it a little bit easier for you to understand what I am about to explain.
So for the first one you have two different traits that can be inherited- having freckles or having no freckles, F and f respectively. The dominant trait (or having freckles) is shown by the capital F, and is almost always expressed over the recessive trait, or the lowercase f. So, for example, if you have a genotype of Ff, the trait having freckles will show up instead of not having freckles. The only way that you could have the trait of no freckles show up is if there are two recessive alleles for having no freckles, or ff. In this case, you have two parents who are both heterozygous for the trait of having freckles, so in other words the mother has Ff and the father has Ff. Each parent passes down one allele to the offspring, so since you are breeding Ff and Ff, you should result in having the possible genotypes of FF, Ff, Ff, and ff. This means that there is a 25% chance that the offspring will be homozygous for having freckles, a 50% chance that the offspring will be heterozygous for having freckles and a 25% chance that they would be homozygous for having no freckles, or a 1:2:1 ratio.
Incomplete dominance is a little bit different that just a normal monohybrid cross. Instead of just the dominant gene showing up in a heterozygous genotype, both traits show up. So like the question says, if a homozygous red flower plant was crossed with a homozygous white flower plant, their offspring would not just be white or red, they would be pink because it is a mixture of white and red. So then if you crossed the heterozygous, or Rr plants, the result would be a 25% chance of getting a homozygous RR red plant, a 50% chance of getting a pink Rr plant, and a 25% chance of getting a white rr plant, or another 1:2:1 ratio.
Sorry for the wordy answer, but hopefully this helps you understand this a little better :)
So for the first one you have two different traits that can be inherited- having freckles or having no freckles, F and f respectively. The dominant trait (or having freckles) is shown by the capital F, and is almost always expressed over the recessive trait, or the lowercase f. So, for example, if you have a genotype of Ff, the trait having freckles will show up instead of not having freckles. The only way that you could have the trait of no freckles show up is if there are two recessive alleles for having no freckles, or ff. In this case, you have two parents who are both heterozygous for the trait of having freckles, so in other words the mother has Ff and the father has Ff. Each parent passes down one allele to the offspring, so since you are breeding Ff and Ff, you should result in having the possible genotypes of FF, Ff, Ff, and ff. This means that there is a 25% chance that the offspring will be homozygous for having freckles, a 50% chance that the offspring will be heterozygous for having freckles and a 25% chance that they would be homozygous for having no freckles, or a 1:2:1 ratio.
Incomplete dominance is a little bit different that just a normal monohybrid cross. Instead of just the dominant gene showing up in a heterozygous genotype, both traits show up. So like the question says, if a homozygous red flower plant was crossed with a homozygous white flower plant, their offspring would not just be white or red, they would be pink because it is a mixture of white and red. So then if you crossed the heterozygous, or Rr plants, the result would be a 25% chance of getting a homozygous RR red plant, a 50% chance of getting a pink Rr plant, and a 25% chance of getting a white rr plant, or another 1:2:1 ratio.
Sorry for the wordy answer, but hopefully this helps you understand this a little better :)