Which types of mutations are more likely to be harmful, a base change in the thi

Question

Which types of mutations are more likely to be harmful, a base change in the third position of a codon, or a base change in the first position of a codon? Why? Are all changes to the third position of a codon silent? Do all changes to the first position of a codon change the encoded amino acid?

You start with true-breeding tall plants with yellow seeds, and true-breeding short plants with green seeds. You do a cross and all of the F1 are tall with yellow seeds. What fraction of the plants will have yellow seeds in the F2? Does it matter if the two traits (height and seed color) are linked when you answer that question? What fraction of the plants will be tall with green seeds in the F2? Does it matter if the two traits (height and seed color) are linked when you answer that question? If the two traits are completely linked (no recombination occurs between the genetic loci controlling these traits) what fraction of the F2 will be short with yellow seeds? If the two traits are unlinked, what fraction of the F2 will be short with yellow seeds?

Is the degree of linkage simply a matter of how far apart two genetic loci are on a chromosome?

What is the maximum genetic distance two loci can be apart on a chromosome? At what genetic distance do they simply become unlinked?

Why is the error rate during DNA replication related to population size?

Explanation / Answer

Mutation at the third position is not as harmful as the mutation at the first position. As third position is considered as wobble position.

First position determine the type of amino acid coded by the codon.

As change in third position usually doesn't change the amino acid coded by the codon it only changes the codon.

This can be done by independent assortment of Mendel's law.

TTYY. X ttyy

TtYy

Tall and yellow seeds

TtYy X TtYy

TY -9

Ty-3

tY-3

ty-1

So in total 12 out of 16 will have yellow seeds.

Yes it does matter if the genes are linked. If theu linked then the ratio will change.

Only 3 out of 16 will be tall and green.

NoN it will not matter in this case. as they are of different plants.

Linkage is the distance between two genes in a chromosome.

If their recombination frequency is more than 50% then it means that they are not linked as crossing over takes place.

If they are on separate chromosome they assort independently with each other and thus recombination frequency is less than 50%.

If error rate will increase there will be more variation in the population and thus it will lead to evolution.

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