Beginner Curious About Chromosomes

[Snare]

I'm curious as to the process of how eukaryotes combine and chromosomes.

 

For example, a human male gamete and a human female gamete combine. What exactly happens during this process? How are the chromosomes that are inherited determined, and are they the only determination?

[Powell]

The assortment of chromosomes that the zygote recieves from the two gametes is primarily generated in three main ways.

 

The first is chromosomal crossovers, during prophase I in meiosis, when homologous chromosomes are paired together, there are points along the chromosomes that make contact with the other pair. This point of contact is deemed the chiasmata, and can allow the exchange of genetic information between chromosomes, giving a new combination of alleles on each chromosome

 

Good Diagram: http://www.emc.maricopa.edu/faculty/farabee/BIOBK/Crossover.gif

 

The second is Indepenadant Assortment which occurs in Metaphase I when the chromosomes are lined up along the equator of the cell. As there is a 50:50 chance of which way round a pair of homologous chromosomes will be on this equator, when the cell divides there will be a 2^n (n being haploid number of chromosomes) possible combinations of paternally dirived and maternally derived chromsomes in the daughter cell.

 

The final factor that causes variation is the random fusion between gametes, i.e. which gametes are involved in fertilisation, as genetically they will all be different.

[Snare]

How does this relate to the square "gene tables" I've seen?

 

- - H - h - -

H- HH-Hh

- --------

h -hH-hh

[Cap'n Refsmmat]

Those gene tables show the different possible combinations of the mother and father's genes. Each parent has two copies of each gene, and "donates" only one copy to its offspring. So in your table above, if both parents have one dominant copy of the gene and one recessive copy of the gene, the offspring might receive two dominant copies, a dominant and a recessive copy, or two recessive copies.

[Imaginer1]

So you're a beginner to the forums?

well, me too. But you're lucky- I know quite a bit about chromosones. (Well, it's mostly your opinion) Ask me a question!