bio question?

Question

I need some help!

1. What physical features do homologous chromosomes have in common?
2. How do trisomies arise?
3. Why do trisomies of certain chromosomes seem to occur much more frequently than others?

Answer 1

The first step in reproduction is the creation of the reproductive cells or gametes. For women, the gametes are eggs. For men, the gametes are sperm. The egg and the sperm cells contain half of the total chromosome complement, that is, 23 chromosomes instead of 46 chromosomes. This reduction to 23 chromosomes is necessary so that when the egg and the sperm unite at conception, to create a baby, the proper number of chromosomes, 46, is restored in that child. The process of reducing the number of chromosomes from 46 chromosomes to 23 chromosomes in the reproductive cells is called meiosis.

Homologous chromosomes are a pair of chromosomes, one from each parent, which carry genes for the same traits, in the same order. In a karyotype, the members of a homologous pair look alike.
Sometimes there is a mistake in the sorting of the chromosomes during the production of the sperm or the egg. This is called non-disjunction. Non-disjunction can occur during meiosis I or meiosis II. An error in the proper segregation of the chromosomes during both meiosis I and II are pictured below. In meiosis I, the error occurs when the homologous pairs both travel into the same daughter cell. The result is two daughter cells that have two copies of the chromosome (called disomic cells) and two cells that are missing that chromosome (called nullisomic cells).

The term "trisomy" is used to describe the presence of three chromosomes, rather than the usual pair of chromosomes. " Trisomy 21 is also known as Down syndrome. Other examples of trisomy include trisomy 18 and trisomy 13. Again, trisomy 18 or trisomy 13 simply means there are three copies of the #18 chromosome (or of the #13 chromosome)

As for why these chromosomes are more likely to undergo non-disjunction, it is not really clear, but some specialistic studies do exist. Have a look at this paper:
http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?cmd=Retrieve&db=PubMed&list_uids=12012633&dopt=Abstract

Answer 2

1. Both members of a homologus pair are the same size and look the same. One member of each homologous pair came form the father's sperm and the other came from the mother's egg. Both members of a homologous pair have genes for the same traits. However, the chromosomes do not neccesarily have the same traits , or instructions on those genes.They have the same length and centromere position.

2. Trisomy occurs when an individual has three copies of a chromosome. This is called a chromosomal mutation.

3. Many times when trisomy occurs in a zygote it results in a miscarriage or still birth. Trisomy is the result of nondisjunction which occurs during meiosis I when both members of a homologous pair go into the same daughter cell, or during meiosis II when the sister chromatids fail to separate and both daughter chromosomes go into the same gamete.

Answer 3

bypass including your doorstep mom. do not enable anybody - no longer your "moms" and not in any respect anybody answering your question - turn this right into a case of who's your "authentic" mom vs your doorstep mom. it is an elementary case of who has been there for you and who has been supportive of you and who can help you to make your very particular day a delightful one quite than one crammed with conflict and guilt tripping. you'll ultimately - and larger advantageous prior to later - ought to confront your bio-mom about her guilt tripping and about generating any conflict surrounding your wedding ceremony. If she will't conform to get alongside and make your particular day a delightful one for anybody then her messages, calls, etc to you'll bypass ignored and she ought to plot on no longer attending. Sounds harsh because i did not take any time attempting to make certain on smooth words. you want to do a more beneficial advantageous interest than I did, yet i imagine you fairly want to have this communication including your bio-mom... if for no different reason than if she screws this up she will be placing the tone for any destiny relationship with you and your husband... and grandchildren... and... etc. She'll be making a call which will impact some thing else of her existence so she more beneficial advantageous make darn particular what's more beneficial major to her - recrimination and conflict or team spirit and cooperation.

Answer 4

You're doing the online karyotyping lab huh? at least search the internet yourself.

Answer 5

Here's a good website. it helped me last year on a project. hope it helps u.

Answer 6

1. code for same genes, just different alleles
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