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Phenotypic Ratios

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What are the expected phenotypic ratios for a monohybrid cross?

For a dihybrid cross?

For a sex-linked trait?

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(Have added this information as an attachment as well so that you get colour!)

From the data that you have given, I should be able to offer you some guidance regarding phenotypic ratios from standard Mendelian crosses.

Monohybrid cross:

Let the gene for Curly hair, the dominant allele have the symbol C and the gene for straight hair have the symbol c.

Assuming a homozygous, pure breeding cross between a curly haired person and a straight haired person.

i.e. CC x cc.

Then in the first generation the F1 all of the children would have curly hair because, they would all have the genotype Cc.

If however both had been heterozygous

i.e Cc x Cc

then the following possibilities arise;

CC Cc Cc cc

In other words there would be a ratio of 3 times as many curly haired as straight haired offspring.

From the data that you have, this is often referred to as the backcross experiment you have a mating between the following genotypes

i.e. Cc x cc

This mating will give the following combinations

Cc Cc ...

See Also This Related BrainMass Solution

Determining phenotypic ratio using test crosses

A true-breeding red snapdragon was crossed to a true-breeding white snapdragon. The F1 progeny were pink. When F1 x F1 matings were made, the following F2 progeny were observed.

1850 red
670 pink
831 white

Total 3351

a. Using clearly defined genetic symbols, give the appropriate parental, F1 and F2 genotypes in order to explain the above results.

b. What phenotypic ratio would be expected from a testcross of an F1 snapdragon

c. Suppose the white phenotype is now lethal. What phenotypic ratio would be expected from a cross between F1 individuals?

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