please answer these questins so that I can better understand linkage and genitic
ID: 58908 • Letter: P
Question
please answer these questins so that I can better understand linkage and genitic mapping
1. What does it mean when traits show genetic linkage? Clearly state how genetic linkage defies the concept of independent assortment. (1.5pts)
2. What does it mean when a trait is sex-linked? (1.5pts)
3. Explain why males will exhibit recessive traits that are linked to the X chromosome more often then females. (2.5pts)
4. Recombination frequency cannot exceed 50%. What are the two explanations for this? *Hint: consider distance possible between loci, and independent assortment. (2.0pts)
Explanation / Answer
1. Two genes are linked because tghey are situated close to eash other on the chromosome so that there are very low chance of any recombination between them. The more closely two genes are, the more linked will be both of them. That actually means that as those are situated very close to each other, wherever the piece of chromosome goes, these two genes will go (travel) as a single piece of chromosome. As these can no longer independently assort, because of their physical location (sort of stuck to each other), they will no longer abey the law of independent assortment.
2. Genes located on sex chromosomes are called sex-linked genes, as they will be specific to one gender. If a gene sits on the Y chromosome, that will only be shown up in males. One copy of the gene makes sense, as the Y chromosome remains as a singleton always. For the same reason: proceed to (3)
3. For the same reason, that is, as males have one copy of X chromosome, they can exhibit a recessive trait as there is no dominant allele.
4. Consider law of independent assortment. Consider two genes with genotype Aa, Bb (both on different chromosomes), and according to the law of assortment, all the four alleles - A, a, B, b can assort independently, forming AB, Ab, aB, aa type gamets, each with exactly 25% frequency. This can only happen if these two genes sit on two different chromosomes.
Consider the above case but this tyme these two genes are on a single chromosome. Now they are not independent of each other. In other words, a chromosome with the alleles aB in the same chromosome will only produce a gamete with aB genes, not ab, AB or Ab, unless a recombination happens and a part of the chromosome (having the allele a, for example) detaches and pairs with the homologous chromosome (containing allele b).
What if the two genes are on the same chromosome and still we find all the combinations of alleles in the gamets? Are they still be able to assort independently? This can only happen if the genes are so far from each other that they are almost vulnerable to recombination and assort (sort of) independently. What about percentages? we will get a recombination frequency of 50 %, which applies to genes assorting independently.
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