Biology.I'm, dyng save me!?

W

white*elephant*AfTeRmAtH

New member
I'm totally stuck! :-p Coudl you explain these to me?

How do sex linkage and crossing-over show that genes are found on chromosomes?

How can crossing-over between two alleles be used to map their locations and chromosomes?

Three genes (A, B, and C re on the same chromosome. However, only C and A are usually expressed together in the same phenotype. Explain this result and describe the relative positions of A, B, and C on the chromosome.

eep. Help greatly appreciated!
 
Okay where do we start...
Well sex-linked genes...Humans contain 46 chromosomes or 23 pairs of chromosomes, 22 pairs( 44 chromosomes) are autosomes, and the last pair is the "sexsome" or sex chromosomes, which is represented by X and Y, females contain XX and males contain XY, the Y is what makes men have male features and characteristics.
some sex-linked diseases which are mutations on the sex chromosomes can be found at specific locus (just a fancy term for location) on the chromosome, and crossing-over is in prophase, where the sister chromatids line up and under go crossing over. Suppose your mom has green eye colour, and your dad has brown eye colour, crossing over will mix these traits, either homozygous or heterozygous (the locus for eye colour are the same on both of the chromosomes) thus the random exchange of traits can be found on the chromosomes which are genes....:S im getting confused myself lol

To map the location of two alleles, if we can identity the locus of one gene for a specific allele then the other locus for the same gene is found on the other chromosome in the same locus.

Gene A and C which are usually expressed together means that they are linked together to express the same physical trait, A is dependent on C, example would be the gene that codes for fur colour in bears, one codes for brown the other codes for black, however there is also another gene which decides if the colour genes are coded at all..if the gene for colour expression is expressed, then black or brown can be expressed, however if this first gene that determines colour expression is not expressed, it will result in albino, which is no colour expression of black or brown...
i sometimes dont know if what im talking about is relevant to the question..but hope that somehow helps you
good luck :)
 
Just to add a little to the other guys good answer.
This is for the second part.

Crossing over helps map genes through linkage mapping. The distance between two genes that link up affects the frequency of crossing over. The further the linked genes are from each other, the more likely the non-sister chromatids between the linked genes would cross over. By measuring the frequency of crossing over between certain genes you can measure the the distance between them and map them.
 
Back
Top