Two brothers have x‑linked red–green colorblind vision, and their parents have normal color vision. the first brother's karyotype is 47,xxy (klinefelter syndrome), and the second brother's karyotype is 46,xy. in which parent and in what cell division phase did the first brother's chromosomal nondisjunction occur? assume no recombination.

(a) in the father in meiosis i
(b) in either parent in somatic cell mitosis
(c) in the father in meiosis ii
(d) in the mother in meiosis ii
(e) in the mother in meiosis i

The correct answer is option C, that is, in the mother in meiosis II.

Explanation:

A nondisjunction in meiosis I produce all the aneuploid gametes, while nondisjunction at meiosis II produces 50 percent aneuploid gametes and the 50 percent normal gametes comprising haploid number of chromosomes.  

As it is mentioned that one of the brothers possess normal number of chromosomes (46), the mother encounters nondisjunction at meiosis II resulting in the formation of one n+1 gamete exhibiting two copies of X chromosome. Fertilization of this n+1 gamete with sperm results in the creation of zygote (47, XXY).  

g1

choices:

a. g2. b. g1. c. m

cell division has two checkpoints namely, g1

checkpoint and spindle assembly checkpoint. the checkpoint which determines if

division has properly occurred is the g1 checkpoint. at this point, is a damage

in the dna is detected or  the has not reach the optimum size, the cell is

stopped in g1 and is not allowed to proceed to further process.

source:

cells use diffusion to get substances in and out of themselves. that diffusion will occur across the cell membrane or the outer covering of the cell. because we are talking about the surface of the cell, surface area and volume are  important factors here. as a cell increases in size, its surface area and volume increase as well.  we call that the surface area to volume ratio (sa: vol).  but the catch is that  volume increases at a greater rate than surface  area. in other words, as a cell gets bigger, the sa: vol gets smaller. so a really small cell like bacteria is mostly cell membrane (surface) with very little contents (volume). a really big cell like an egg, is mostly insides with a super thin membrane. so what ends up happening is that the cell cannot efficiently diffuse all of the stuff it needs in/out to survive. therefore cell size is limited to about 100mm. so how do we make organisms bigger than 100mm? cells divide! by dividing and becoming multicellular, organisms are able to grow!   check out the diagrams i attached to see the effect of sa: vol. i hope this ! good luck!