Please help 1. Jim Bob, who is colorblind(an X-linked, recessive condition) is m
ID: 279247 • Letter: P
Question
Please help
1. Jim Bob, who is colorblind(an X-linked, recessive condition) is married to Betty, Sue, who has normal vision and is not a carrier for coloblindness. Complete a Punnett square for Jim Bob and Betty Sue and answer the following question
A. What is Jim Bob's genotype?
B. What is Betty Sue's genotype?
c. What is the phenotypic ratio of their potential offspring?
D. If one of their daughters marries a man with normal vision, what is the probability that they will have a son with normal vision?
2. In gernetic disorder such as Down syndrome, an individual has three copies of chromosome 21. Based on what you know about meiosis, explain how this can happen, include in your explaination the following terms: Anaphase 1, Gametes, Fertilization, Homologous, chromosome.
Explanation / Answer
1. A. Jim bob's genotype- X*Y
B. Betty Sue's genotype- XX
C. X*Y X XX
X*X X*X XY XY
DAUGHTERS WILL BE CARRIERS AND SONS WILL BE NORMAL.
BOTH THE DAUGHTERS WILL BE CARRIERS.
BOTH THE SONS WILL BE NORMAL.
D. X*X X XY
X*X X*Y XX XY
50% DAUGHTERS WILL BE CARRIERS
50% SONS WILL BE SUFFERERS.
2.
During both mitosis and meiosis, there is a phase where each chromosome pair in a cell is separated, so that each new cell can get a copy of every chromosome. However, sometimes during this process, a pair of chromosomes doesn’t separate evenly, which results in one of the new cells having an extra section of chromosome. This is called nondisjunction. With Down syndrome, various types of uneven chromosome separation result in a person having an extra copy (or partial copy) of chromosome 21.
Trisomy 21 is the most common form of Down syndrome, accounting for about 95% of cases.^11start superscript, 1, end superscript This type of Down syndrome is caused by uneven separation of chromosome 21 during the creation of sex cells (this can happen in either the sperm or the egg cell), which leads to a fertilized egg with three copies of chromosome 21 instead of two. When the fertilized egg is developed, it passes along the extra copy of chromosome 21 to every cell in the body.
The mosaic form of Down syndrome is much less common, accounting for about 1% of cases. In this form, the uneven separation of chromosome 21 happens shortly after an egg has been fertilized. The timing of this nondisjunction is important, because it leads to a person having some cells with the typical 46 chromosomes, and some cells with 47 (these cells have an extra copy of chromosome 21). Because only some cells have the extra chromosome, mosaic Down syndrome may have less prominent symptoms than trisomy 21.
In the remaining 4% of cases of Down syndrome, the extra genetic material is passed on to new cells in a slightly different way. Rather than failing to separate, translocation occurs when a portion of chromosome 21 breaks off during the replication process, and then attaches to another chromosome.^11start superscript, 1, end superscript So rather than getting a full extra chromosome, translocation results in cells with the typical 46 chromosome, plus a little extra chromosome 21. The genes contained in the extra portion of chromosome 21 can cause many of the symptoms of Down syndrome.