Sex linked genes are genes that are on the X or Y chromosomes so that when a bad version or mutated version of the gene on the X chromosome in a male there is not another x chromosome to compensate or mask the effect which is why sex linked traits often cause disorders more frequently in males. Genomic imprinting is when the expression of a certain gene is different depending on which gender of parent it was passed along from.
What is a Barr body?
In a female organism in each cell one of the X chromosomes is turned off, this repressed X is called the Barr body. This results in mutli-colored fur and such in many animals when that trait is sex-linked because then a certain color is expressed in certain cells while not in others because which X become the Barr body is randomized and not the same in every cell.
What are linked genes?
These are genes that are on the same chromosomes so they tend to defy the rule of independent inheritance and actually be inherited together during meiosis. When crossing over occurs some linked genes get separated, the farther apart the genes are on the chromosome the more likely they are to be recombined through crossing over.
Facts:
- Chromosome theory of inheritance stated that genes have a specific location on the chromosome (loci) and that chromosomes undergo independent assortment
- Some sex linked disorders include: Muscular dystrophy, hemophilia, and color blindness
- Genetic recombination is when offspring have combination of traits different from either parent
- A linkage map is a map of genes based on the recombination frequencies
- Non-disjunction causes organisms to have more than the normal number of chromosomes
This is a karyotype of a person with Down syndrome. This shows how trisomy in chromosome 21 is the difference that causes this particular disorder. The effects of this disease is: unique facial features, shorter, heart problems, more likely to get respiratory infections, and in severe causes mental retardation.
Summary:
Morgan established the theory of sex-linked genes some genes that were more likely to be expressed based on the sex of the organism. Some genes are located on the X and Y-chromosomes so they display a different type of inheritance patterns because in males they only have one copy of the genes located on the X chromosome. During crossing over genes recombine and give rise to offspring with different varieties of traits. The farther apart a gene is on the chromosome the more likely recombination will occur so the recombination frequencies are used to determine the distances between genes on a chromosome. Inaccurate divisions during meiosis give rise to organisms with abnormal number of chromosomes, which can in some cases have no effect while in other case be detrimental to the organism.
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