7- If G=yellow seeds and g=green seeds, predict the genotypic and phenotypic rat

Question

7- If G=yellow seeds and g=green seeds, predict the genotypic and phenotypic ratios of a cross between a) two Gg individuals; b) a Gg and a gg. If cross 'a' gives you 2/3 offspring that are yellow and 1/3 that are green, what is the mode of inheritance and what is the genotype of the yellow offspring?

8- For four genes (all autosomal recessive), beginning with a AaBbCcdd x aabbCcDd cross, what is the probability of producing a child in the F1 with the A- bb C- dd phenotype?

9- For three autosomal dominant genes, what is the probability that a cross between two heterozygotes (i.e. AaBbCc x AaBbCc) will produce an offspring with the dominant trait for all genes?

Explanation / Answer

7. If G=yellow seeds and g=green seeds and cross take place between

Gg X Gg  

GG, Gg, Gg, gg   

  Phenotypic ratio 3:1 = GG, Gg, Gg :  gg

Genotypic ratio 1:2:1 = GG : Gg, Gg :  gg

2.if cross is between Gg and a gg

Gg X gg

Gg , Gg , gg , gg.

Phenotype ratio= 2:2 i.e 1:1= Gg , Gg : gg , gg.

Genotype ratio =2:2 i.e 1:1= Gg , Gg : gg , gg.

If cross 'a' gives you 2/3 offspring that are yellow and 1/3 that are green, what is the mode of inheritance and what is the genotype of the yellow offspring?

It shows that each of the two alleles is inherited independently from the other, with a 3:1 phenotypic ratio for each. And the genotype of yellow offspring will be GG, Gg, Gg.

8. For four genes (all autosomal recessive), beginning with an AaBbCcdd x aabbCcDd cross, what is the probability of producing a child in the F1 with the A- bb C- dd phenotype?

AaBbCcdd x aabbCcDd cross

probability of getting phenotype  A- bb C- dd which is Aa bb Cc dd .

Aa X aa results in Aa with p=1/2

Bb X bb results in bb with p=1/2

Cc X Cc results in Cc with p=1/4

dd X Dd reults in dd with p=1/2

now applying product rule

1/2x1/2x1/4x1/2=1/32

probability of producing a child in the F1 with the A- bb C- dd phenotype is 1/32

9- For three autosomal dominant genes, what is the probability that a cross between two heterozygotes (i.e. AaBbCc x AaBbCc) will produce an offspring with the dominant trait for all genes?

cross between heterozygotes AaBbCc x AaBbCc so probability of getting all dominant traits for all gene are

so the dominant traits obtained should be AABBCC

Aa x Aa result in AA with p=1/4

Bb x Bb result in BB with p=1.4

Cc x Cc result in CC with p=1/4

so by product rule

1/4 x 1/4 x 1/4 =1/64

so the probability of getting offspring with the dominant trait for all genes is 1/64

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