Trisomy 21

[geneticdummy]

would a person with autosomic trisomy (with normal reproductive capabilities) passon the trisomy? could we compute this?

[sdekivit]

it's possible, but only in about 5 % of the cases. There are 3 forms of trisomy 21. To read more about it, check the following link:

http://www.altonweb.com/cs/downsyndrome ... court.html

[geneticdummy]

thanks for the reply but I am more interested with an elementary theoretical solution just like in computing for the probability of basic mendellian trait inheritance. Disregarding the age of the female with trisomy 21, how could we compute for the probability of passing it on to her child? I first throught of using the punnett square but punnett square is for alleles and trisomy 21 concerns three chromosomes.

In the same vein, what gametes would a person with klinefelter's produce?If he has xxy as his sex chromosomes, would he produce 2 sperm with an xx and y respectivley, or two with x and xy?

I know that trisomies are generallynot inherited unlike mendellian characteristics. I know that they were caused by nondisjunction for instance, but how about their offsprings if ever they were able to reproduce?

[Dr.Stein]

That's why individuals with trisomy or ND are usually sterile, to anticipate the further abnormality of their offspring's chromosome structure and/or number.

But theoretically, it is always okay to discuss the possibilities in this way so don't worry, as long as you will not count this theoretically thingy to apply on ratio or percentage of possibilites in their offspring. Well, it will be like this:

* For instance trisomy 21
Female (2n): 47,XX+21,
after meiosis: 24,X+21 .....(1)
if with ND can be: 24,X+21 .....(1) and 23,X (normal) .....(2)
There will be two possibilities of gamets produced.

Male (2n): 47,XY+21,
after meiosis: 24,X+21 .....(1) and 24,Y+21 .....(2)
if with ND can be: 24,X+21 .....(1) and 23,Y (normal) .....(3)
or 23,X (normal) .....(4) and 24,Y+21 .....(2)
There will be four possibilities of gamets produced.

If this female trisomy marry a normal male, so there will be 2x2=4 possibilities of chromosome formulas for their F1.

If this male trisomy marry a normal female, so there will be 4x1=4 possibilities of chromosome formulas for their F1.

If this female trisomy marry a trisomy male, so there will be 2x4=8 possibilities of chromosome formulas for their F1.

* Klinefelter's syndrome
Yes, there will be two possibilities of the segregation, so there will be four possibilities of gamets produced.
- 47,XXY ---> 24,XX .....(1) and 23,Y .....(2)
- 47,XXY ---> 23,X .....(3) and 24,XY .....(4)

If this individual marry a normal female, so there will be 4x1=4 possibilities of chromosome formulas for their F1.

Please correct me if you think there are mistakes on my explanation