A boy with Klinefelter syndrome (47, XXY) is born to a mother who is phenotypically normal and a

step 1 In order to answer this question, let's talk about inheritance. Is that considered the following

A boy with Klinefelter syndrome (47, XXY) is born to a...

A boy with Klinefelter syndrome $(47, \mathrm{XXY})$ is born to a mother who is phenotypically normal and a father who has the X-linked skin condition called anhidrotic ectodermal dysplasia. The mother's skin is completely normal with no signs of the skin abnormality. In contrast, her son has patches of normal skin and patches of abnormal skin. (a) Which parent contributed the abnormal gamete? (b) Using the appropriate genetic terminology, describe the meiotic mistake that occurred. Be sure to indicate in which division the mistake occurred. (c) Using the appropriate genetic terminology, explain the son's skin phenotype.

A boy with Klinefelter syndrome $(47, \mathrm{XXY})$ is born to a mother who is phenotypically normal and a father who has the X-linked skin condition called anhidrotic ectodermal dysplasia. The mother's skin is completely normal with no signs of the skin abnormality. In contrast, her son has patches of normal skin and patches of abnormal skin.
(a) Which parent contributed the abnormal gamete?
(b) Using the appropriate genetic terminology, describe the meiotic mistake that occurred. Be sure to indicate in which division the mistake occurred.
(c) Using the appropriate genetic terminology, explain the son's skin phenotype.

Key Concepts

Nondisjunction

Nondisjunction is the failure of homologous chromosomes or sister chromatids to separate properly during cell division. In the context of Klinefelter syndrome, nondisjunction during maternal meiosis (most commonly during meiosis I) leads to an egg carrying two X chromosomes instead of one. When this abnormal egg is fertilized by a normal sperm that provides a Y chromosome (or an X in other cases), the resulting zygote has an extra sex chromosome, resulting in the 47,XXY karyotype found in Klinefelter syndrome.

X-linked Inheritance

X-linked inheritance refers to the pattern by which genes on the X chromosome are transmitted and expressed. In males, who have only one X chromosome, a mutant allele on that chromosome will be expressed. In this example, the father carries an X-linked disorder; his single X chromosome carries the abnormal allele. When he passes this X to his son, the son inherits it along with another X from his mother, contributing to the son’s mosaic phenotype of the skin condition.

X-Chromosome Inactivation (Lyonization)

X-chromosome inactivation, or Lyonization, is the process by which one of the two X chromosomes in females (or in males with an extra X chromosome as in Klinefelter syndrome) is randomly silenced in somatic cells. This results in mosaics where some cells express genes from one X and other cells express genes from the other. In the boy with Klinefelter syndrome, this random inactivation causes patches of skin cells to express the normal maternal allele and other patches to express the abnormal paternal allele, leading to the observed mosaic pattern of normal and abnormal skin.

Transcript

00:01 In order to answer this question, let's talk about inheritance.

00:04 Is that considered the following pedigris from human families containing a male with kleinefelter syndrome, a set of abnormality seeing xxy individuals, that are these three black individuals here, or black squares here, okay? in each amb refer to the codominant alleys of the x -link g6pd gene.

00:24 For example, those who are a have the following genotype.

00:29 This is for a, ab is for ab, mbb is for b.

00:37 Now, remember that females are xx and male are xy, okay? so in case, actually this is not like this.

00:47 As this is an x -linked trade, then it means that for females, this is going to be a, this is going to be a, this is going to be a, b, and this is going to be a, and this is going to be a b, and this is going to be.

01:08 Type b okay and for males you have only two possibilities normally okay this or this now let's see a normal myosis for example let's have the this genotype here with that is actually like this or well this genotype here okay so in this case during myosis 1 what normally happens is that one allele moves here and the second a little moves here this is myiosis 1 during myel myiosis 2 what happens is that you can see it in general that you duplicate this allele and you move one allele here and another all here.

01:46 So you have this and this, okay, and the same happens here.

01:53 So this is what normally happens, what normally happens, okay? this is myiosis 2.

01:59 What happens if you have a non -disch junction in myiosis 1? if you have a non -disch junction in myiosis 1, then you have that both alleles are going to move to be.

02:09 Here and you have zero here so you have here a zero zero and here you have this and this so practically the initial genotype is gonna be present in the now if a non -diction happens in myosis 2 then everything is gonna be normal until myiosis 1 where you have here this or this now the non -ish junction in myiosis 2 can occur either here or here so let's suppose that in this case it happens in both sides and you will have here this and here you will get zero or zero and y and y so practically this is a non -didgenital meiosis 2 so in resume you have to look at the initial genotype of the of the person and in an undone disjunction in myiosis 1 you're going to have the same genotype in the gamit okay that is that in this case is this because normally you have either the a or the y chromosome here in the gametes, not both.

03:19 If you find both of them in the genotype then it means that there was a non -dischensionaryosis one.

03:25 Now if you find one of these two adiles but repeated it means either two a alleles like in this case or two y alleles like in this case then it means that it was a non -dissolution in myiosis too.

03:39 Okay so let's use that to answer this question here.

03:44 The genotype for this mother is like this.

03:49 And the genotype for this father is like this.

03:52 And they have a son with kleenefelter syndrome who is a .b.

03:58 Remember that normally maize cannot be a .b.

04:02 But in case of kleenefelter syndrome, they can be a .b.

04:06 So in this case, this genotype is like this.

04:11 Okay? so also remember that a person inherits one allele from each parent.

04:16 So in this case, the y chromosome comes from which of these parents? and the answer is from the father because mothers don't have a y allel, a white chromosome.

04:26 Okay, so the white chromosome is coming from the father...

Please give Ace some feedback