Genetic Questions - please help!

[Miss_Me]

Hi, i have a few genetic questions i'm kinda stuck on. Its for an assignment. So is there anyone out there who could help..pleasee! All help is greatly appreciated!! Thanks in Advance!

Here goes:

(Q1) Why are most mutations in a diploid organism recessive??

(Q2) Why is a random mutation more likely to be deleterious rather than beneficial??

(Q3) Most mutations are deleterious, but are essential to the evolutanary process..Why?

(Q4) What evidence is there that states that Downs syndrom is a result of non-disjunction at oogenesis rather than spermatogenesis?

(Q5) Humans with aneuploid karyotypes occur but are non-viable. Why is this??

I know there are quite a few questions, but if you could answer any, it would be a great help.

Thanks guys!

[mith]

Try reading the rules of this forum.

[Miss_Me]

sorry. was my 1st post. did not read rules before posting, realised later



I have tried checking up textbooks, but can't really find what i'm looking for. Others books are very brief. Any help please?

thanks

[adamMV07]

i will help some..#3?
evolution is a process of adaption right?
so lets take for example TB, it has infected a small village they were given antibiotics and symptoms ceased...but over a few years symptoms came back then when given the drug it was no help this is because the antibiotic killed the TB cells that were lower resistance, while a few that were resistant stayed in the body and multiplied...these different strains of TB is a result of EVOLUTION they have adapted to a medicine...it is a struggle humans have been dealing with since the beginning a fight against microbes..but as medicine is being second handedly it gives more chance for the pathogen to MUTATE!

[chenwithasterisk]

(Q1) Why are most mutations in a diploid organism recessive??[/b]

this is because most mutant alleles are harmful in a constant environment,the existing alleles have already passed the test of natural selection.therefore the mutant alleles are likely to cause harmful effects on the individuals IF they are expressed. therefore,any individual whose mutation is dominant,they would be likely to be selected against by natural selection.

to professional:im assuming the environment is constant,however, in a changing environment,anything can not be certain. therefore would a domiant mutation be beneficial?

(Q2) Why is a random mutation more likely to be deleterious rather than beneficial??

if a beneficial mutation occurs, the organisms that have benefial mutations would be selected for by the selective forces.such as the mutation allows organism to have a higher tolerance range of temperature.therefore,these organisms are likely to survive,passing down the alleles to the gene pool.in contrast,a random mutation doesnt give individuals any selective advantage,thus in a large gene pool. if the organism dies,the mutation will not be passed down.

(Q5) Humans with aneuploid karyotypes occur but are non-viable. Why is this??

aneuploidy refers to certain chromosomes are represented in an usual number of chromosomes rather than 2.

a question to pro, down's sydrome is the usual number of chromosome 21. (3 sets instead of 2). however, people with down's syndrome IS fertile.therefore its incorrect to say,humans with aneuploid are non-viable.

p.s. viable occurs,because chromsomes dont come in pairs.therefore,meiotic dividsion cant occur. no gametes would be produced.
my question is:wether or not a human is infertile totally depends on X or Y chromosomes. it has nothing to do with autosomal chromosmoes.right?