Inheritance of color blindness Red-green color blindness is...

Inheritance of color blindness Red-green color blindness is due to a recessive allele of the gene OPN1MW with a locus on the X-chromosome (X-linked). Generation 1 Generation 2 The couple in generation 2 is planning to have children. Individuals with red-green colorblindness are shaded in the pedigree above. 1) What is the probability that their first child will be colorblind if it is a boy? 1/2 2) What is the probability that their first child will be colorblind if it is a girl? 3) If we assume instead that the shading in the pedigree above is tracking the "blue-yellow color blindness" associated with the gene OPN1SW with a locus on chromosome 7, the probability of the couple in generation 2 having a color blind son is

Transcript

00:01 This question regarding the red -green colorblind is a recessive x -linked.

00:11 So look at the pedigree and figure out the chance of the couple in second generation produce a first child with a colorblind if it's a boy.

00:21 So let's say if it's x -linked recessive, this means that the first generation male must be a recessive x lower or y.

00:28 This is the recessive, show recessive phenotype.

00:31 Male has only one x chromosome.

00:33 Amazon.

00:33 Female x, at least one copy of dominant allele shows normal phenotype.

00:39 We have no idea about the second.

00:41 Now, if you looked at the second generation female, she is phenotypically normal, so she inherits a x capital r from the mother.

00:50 And she has no choice but to inherit the x lower r from the father, because the other x of this woman comes from her father, which has x lower r only.

01:03 So the woman is a heterozygous.

01:05 Now the second generation male show phenotype, so recessive phenotype.

01:11 That means this male must have x lower r y genotype.

01:16 Male only has one x chromosome, the allele decide its phenotype.

01:20 So from there we know that we have a cross between the heterozygous female and x lower r y male.

01:28 So let's do the pendant square.

01:30 The parents, the two alleles separate from each other.

01:42 X capital r and x lower r separate from each other.

01:46 And x lower r and y from father.

01:50 So then in f1 generation, you put the two alleles back.

02:00 So you can see the top one has two x chromosomes, female.

02:03 The bottom, male, one y chromosome.

02:06 So the first question says that what is the probability that the first child will be colorblind if it's a boy? so let's look at the bottom.

02:14 So if it's a boy, you have two possible genomes...

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