For the following crosses, determine as accurately as possible the genotypes of
ID: 170935 • Letter: F
Question
For the following crosses, determine as accurately as possible the genotypes of each parent, the parent in whom nondisjunction occurs, and whether nondisjunction takes place in the first or second meiotic division. Both color blindness and hemophilia, a blood-clotting disorder, are X-linked recessive traits. In each case, assume the parents have normal karyotypes (see the table given below).
Table Human Aneuploidiesand Frequenciesat Birth.
Part A - A man and a woman who each have wild-type phenotypes have a son with Klinefelter syndrome (XXY) who has hemophilia.
Part B - A man who is color blind and a woman who is wild type have a son with Jacob syndrome (XYY) who has hemophilia.
Part C - A color-blind man and a woman who is wild type have a daughter with Turner syndrome (XO) who has normal color vision and blood clotting.
d) The man is XcY, the woman has at least one X chromosome with the wild-type C allele (XcXC ), and the child is XCO. Nondisjunction must have occurred in the woman at meiosis I or II.
Part D - A man who is color blind and has hemophilia and a woman who is wild type have a daughter with triple X syndrome (XXX) who has hemophilia and normal color vision.
Aneuploidy Syndrome Frequency at Birth Syndrome Characteristics Autosomal Aneuploidy Trisomy 13 Patau syndrome 1 in 15,000 Mental retardation and developmental delay, possible deafness, major organ abnormalities, early death Trisomy 18 Edward syndrome 1 in 8000 Mental retardation and developmental delay, skull and facial abnormalities, early death Trisomy 21 Down syndrome 1 in 1500 Mental retardation and developmental delay, characteristic facial abnormalities, short stature, variable life span Sex-Chromosome Aneuploidy 47, XXY Klinefelter syndrome 1 in 1000 (males) Variable secondary sexual characteristics, infertility, frequent breast swelling; no impact on mental capacity 47, XYY Jacob syndrome 1 in 1000 (males) Tall stature common; possible reduction but not loss of fertility; no impact on mental capacity 47, XXX Triple X syndrome 1 in 1000 (females) Tall stature common; possible reduction of fertility; menstrual irregularity; no impact on mental capacity 45, XO Turner syndrome 1 in 5000 (females) No secondary sexual characteristics; infertility, short stature; webbed neck common; no impact on mental capacityExplanation / Answer
Part A - A man and a woman who each have wild-type phenotypes have a son with Klinefelter syndrome (XXY) who has hemophilia.
B)A man who is color blind and a woman who is wild type have a son with Jacob syndrome (XYY) who has hemophilia.
a) The man is XcY, the woman is XhXH, the child is XhYY, and nondisjunction must have occurred in the man during meiosis II.
Part C - A color-blind man and a woman who is wild type have a daughter with Turner syndrome (XO) who has normal color vision and blood clotting.
d) The man is XcY, the woman has at least one X chromosome with the wild-type C allele (XcXC ), and the child is XCO. Nondisjunction must have occurred in the woman at meiosis I or II.
Part D - A man who is color blind and has hemophilia and a woman who is wild type have a daughter with triple X syndrome (XXX) who has hemophilia and normal color vision.
b) The man is XHY, the woman is XhXH, the child is XHXhY, and nondisjunction occurred in the woman during meiosis II.