Biology Genetics Health Science Technology
Biotech2k
Biotech2k

@Biotech2k1

13 tweets 13 reads Dec 26, 2022
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Linked Genes
Here we will look at gene linkages.
1/ The rules of Mendelian Genetics treats every gene as if it were on a separate chromosome. Every gene has a 50% chance of making it into any gamete.
1/ The rules of Mendelian Genetics treats every gene as if it were on a separate chromosome. Every g...
2/ If you have a gene for eye color with the alleles Blue Eyes and Green eyes, each gamete has an equal 50% chance of getting the blue eyes or green eyes allele.
3/ The truth is genes are on chromosomes and many genes can be on the same chromosome. This brings up the concept of gene linkage. One such example is the genes for Major Histocompatibility Complex (MHC) on Chromosome 6.
4/ These genes are linked and you inherit the whole group of them from the same chromosome. You get 1 chromosome 6 from mom and 1 from dad. You will have the exact same genes for each of these genes as your parents on that chromosome.
4/ These genes are linked and you inherit the whole group of them from the same chromosome. You get...
5/ These linked genes are called a haplotype. This means that group of genes are all inherited together. This leads us to the concept then of crossing over. This is a process during meiosis. This is where the sister chromatids line up and synapse.
5/ These linked genes are called a haplotype. This means that group of genes are all inherited toget...
6/ During this process, you can get the crossing over of parts of the chromosome for sister chromatids. This is where parts of mom's chromosome 1 might exchange segments of DNA with dad's chromosome 1.
7/ The rate and locations on chromosome for crossing over is different for each and every chromosome. Some chromosomes or segments of chromosome will allow a lot of exchange of DNA while others won't ever have crossing over.
8/ Because of this process, the distance between 2 genes plays a role in gene linkage. The distance between 2 genes is measured in centimorgans (cM). The process of crossing over is called recombination and its used to measure the distance between two different genes.
8/ Because of this process, the distance between 2 genes plays a role in gene linkage. The distance...
9/ By measuring the rate of recombination occurring between 2 genes determines the distance between those 2 genes in centimorgans. There is a whole chapter in transmission genetics on recombination with single crossing over, double crossing over and even more.
9/ By measuring the rate of recombination occurring between 2 genes determines the distance between...
8/ When the distance between 2 genes reaches a distance more than 50 cM, those 2 genes are considered to be treated as if they were on 2 different chromosomes. This is because a 50 cM distance equates to a 50% chance of recombination happening between those 2 genes.
9/ That 50% puts them equal to the 50% rule for independent assortment. This process of recombination and crossing over of DNA between 2 sister chromatids only happens in Meiosis. This does not occur during mitosis.
10/ This allows for increased variation in the species as it embraces more combinations of genetic information. The tracking of genes by the use of their recombination frequencies is a huge part of transmission genetics.

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