Familial Down Syndrome results from the inheritance of a chromosome with the lon
ID: 167835 • Letter: F
Question
Familial Down Syndrome results from the inheritance of a chromosome with the long arm of chromosome 21 translocated onto chromosome 14. There is no phenotype associated with the translocation itself. What is a reasonable explanation for why there is no phenotype associated with the translocation? ________ Let's say a carrier of the translocated chromosome mates with a wildtype individual, what is the probability that a full-term child born from this couple will have Familial Down Syndrome? See diagram for details on the carrier and its expected gametes. Assume no additional mutations occur.Explanation / Answer
a.) Familial down syndrome
In normal cases every chromosome have 2 sets, so set will be normal and other translocated set will act as carrier for next generation. In another case if this is dominant (i.e. both set of chromosomes are defective) then it results are lethal and leads to spontaneous abortion. Thus, there is no phenotype associated as such.
B.) There are 6 possible gametes from the familial down syndrome carrier parent, among these
1.Only single 14 or single 21 chomosomes with normal wild type gametes will lead to a normal chlid.
2. Translocated 14/21 and normal 14 chromosomes combined with normal wildtype parent gametes will be lethal combination
3 Only translocated 14/21 and normal 21 Chromosomes combined with wildtype parent gamete will result into typical familial downsyndrome
4. Only translocated 14/21 with wildtype gamete will result into carrier.
Surviving child will either be normal or carrier or surffering from familial down syndrome. So probability of having familial down syndrome is 25% among these for combination.
All together there will be 12 combination of all gametes from wild type and down syndrome parents. Among all these 12 combination only one child born will have familial down syndrome as full term syndrome to such couple. Answer: So its probability is 8%
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