is the allele of a person present on the same gene or two genes of two different chromosomes????

Answer 1

Two genes of two different HOMOLOGOUS chromosomes.

Here's a better explanation:

Take the gene for eye-colour. For the sake of keeping the explanation to the point and simple, let's say there are 4 eye-colours: black, brown, blue and green.

Now the gene (gene is located on a chromosome) that codes for eye-colour is present at only the given locus (position) on the given chromosome for every human being (again, not allowing exceptions to keep things simple). However, when we say that so-and-so gene is on so-and-so chromosome, we are only saying that it will be found on that chromosome in a given locus.

So when you are talking of eye-colour, for example, and when you say that gene for eye-colour is on chromosome no. 15 at so-and-so position, you are saying that it will be found there in every normal person.

Alleles are varied forms of same gene.

To go back to the example: we assumed 4 eye-colours: black, brown, blue and green. Now due to variations in the same gene (the gene present at the same position on chromosome 15 in all persons), there are 4 'versions' of this gene: Bk version makes the eye-colour black, Bn brown, Be Blue and Gn Green.

By now you should get 2 facts:

1. Eye-colour was coded by the same gene in every person.

2. Due to some variations in the gene (note that these are not mutations), they turned out to be of 4 kinds: black, brown, blue and green. These 'varied versions' of the same gene are known as the Alleles of that gene.

Since a gene can only normally occur only once in 1 chromosome, 1 chromosome will have either black OR brown OR blue OR green version of that gene.

And since humans are diploid organisms (organisms having 2 copies of same set of chromosomes), we have 2 chromosomes which means we have 2 genes coding for eye-colour which means we have 2 alleles. Remember that we have 2 of 4 alleles that we could have. If we were triploid, we'd have 3 alleles.

Answer 2

25000 genes would imply that each chromosome has about (average) 1083 gene each (this varies, some chromosome are much bigger than others). The point is that each member of a pair of chromosome has the same genes (different expression of them), so you have 2 versions of each of the 25000 genes. If you have an XXY, then, for starters, this is the only pair that was replaced by a trio (unless there are more trisomies in that individual), but one only has a maximum of 3 versions of the genes from the X/Y chromosome (and to be very specific about it, the Y chromosome is a dwarf compared with the X, there are far less genes in the Y than on the X chromosome). Look at this this way: a gene is like a recipe to make protein. If you have 2 cook books, by different authors, describing how to make the same pot pie, do you have twice as many recipes, or do you simply have two different sets of instructions on how to make dinner?

Answer 3

Alleles are VERSIONS of the same gene eg freckles or no freckles.......if a trait is controlled by only 1 gene, this gene will be in the SAME place on the SAME chromosome number. Remember we get 2 of every chromosome. All the chromosomes are numbered from 1 to 22 and the 23rd pair are the sex chromosomes ( which in males are not the same).

Say you want the gene for hair on your middle joint on your finger....this is in a particular place on a particular gene eg ( now this is completely made up) on chromosome pair number 12 and in the same point on that chromosome ( in both chromosomes).

Technically you only need the information from 1 allele for you to get a dominant trait!!! Usaually a recessive trait is the absence of something being produced eg pigment, proteins etc.......

I am going to point out that some genes will have several genes working together ( eg polygenes) and there is pleiotrophy ( which escapes me at present what it does!! but I know it involves several genes)....so in these cases you may have these different genes ( working towards the same thing) on different chromosomes!!!!!

Answer 4

Alleles are two or more alternative forms of a same gene or a same characteristic occupying the same position i.e locus on paired chromosomes.

Answer 5

Two genes on two different chromosomes. You receive one allele of each gene from your mother and one allele from your father.

Answer 6

LIKE CHROMOSOMES GENES ALSO OCCUR IN PA IRES CALLED ALLELES.THE TWO ALLELES ARE PRESENT ON THE SAME POSITIONS CALLED 'LOCUS' OF THE SISTER CHROMOTIDS.