A baby was born exhibiting signs of Down Syndrome, which was confirmed by genetic testing showing three copies of chromosome 21. This was the mother’s second child. The first child has a normal karyotype, as do the parents. The mother was 42 at the time of child’s birth. The most probable explanation for the etiology of trisomy 21 is: A. The sperm had an extra chromosome 21 due to nondisjunction at meiosis I. B. The egg had an extra chromosome 21 due to nondisjunction at meiosis I. C. The gametes produced by older mothers cause aberrant mitosis in the developing fetus. D. There is nondisjunction during early mitosis.

Question

13-08-2019
Biology

contestada

A baby was born exhibiting signs of Down Syndrome, which was confirmed by genetic testing showing three copies of chromosome 21. This was the mother’s second child. The first child has a normal karyotype, as do the parents. The mother was 42 at the time of child’s birth. The most probable explanation for the etiology of trisomy 21 is: A. The sperm had an extra chromosome 21 due to nondisjunction at meiosis I. B. The egg had an extra chromosome 21 due to nondisjunction at meiosis I. C. The gametes produced by older mothers cause aberrant mitosis in the developing fetus. D. There is nondisjunction during early mitosis.

Respuesta :

Otras preguntas

Hose A can fill a bucket in 2 minutes and hose B can fill the same bucket in 3 minutes. How long would it take to fill the bucket if both hoses were used at the

The value of a stock on Monday morning was $16.92. It went up $1.19 on Monday and $0.45 on Tuesday. The value dropped by $1.92 on Wednesday and feel another $0.

__________ is associated with early hunting and gathering societies and with many Native American societies, in which everyday life was not separated from the e

Electrons have four important roles in biological systems: forming covalent bonds, transferring energy from the environment, forming free radicals, and which ot

Please help!! I need step by steps thank you!! 1. 8 more than 10 times a number is negative 56 2. For a field trip 5 students rode in cars and the rest filled n

Explain in words how to add the polynomial 5p^3+2p-1 and 2p^2+8p+6

if the parent function is y=1/x, describe the change in the equation y= -1/x-5 -10

Convert the given radian measure to a degree measure. 1.1π

5. Who was the most recent presidential candidate to use the self-announcement method?

PLEASE HELP I was really sure that this would be 13 but it's not and I have no clue on what to do.

dcortega89 dcortega89 · Answer 1 · 2019-08-16T19:57:42+02:00

Answer: The correct answer is B. The egg had an additional chromosome 21 due to non-disjunction in meiosis I.

Explanation: Trisomies (as the case of Down syndrome) are caused in most cases by non-disjunction in meiosis. Meiosis is the cell division for the formation of gametes (ovule or sperm, in females and males respectively). In anaphase I, each homologous chromosome is carried to the opposite poles of the dividing cell, with the help of the mitotic spindle. Thus, at the end of this division, each daughter cell is expected to have only one homologue of the 23 chromosomes of the set (in the case of humans, the basic set consists of 23 chromosomes, in homologous pairs, being 46 in total). Thus, the non-disjunction in this phase will cause the equilibrium of this set to be altered and each daughter cell may have more or less chromosomes that will follow the division cycle in meiosis II, altering the final endowment of chromosomes in each gamete formed. And although this non-disjunction can occur in both men and women, the effect of maternal age would consist of a degeneration or degradation of certain cellular factors necessary for the formation and functioning of the mitotic spindle, which is the most likely case of the question, by the mother's advanced age.