What causes alleles to become dominant or recessive?

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What causes alleles to become dominant or recessive?

Postby Rolo Beorn » Sep 14 2016 3:08 pm

What causes alleles to become dominant or recessive?
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Re: What causes alleles to become dominant or recessive?

Postby relaxin » Sep 14 2016 4:23 pm

For genes that code for pigment, such as brown eye vs blue eyes, black hair vs blonde, it can be determined easily which gene is dominant. Some genes located on X-chromosome affect male only, such as gene for color blindness, they are recessive. It is because female has two X-chromosomes, a normal gene on the other X-chromosome will compensate the function of the abnormal gene. For other genes, it is difficult to explain it in a few words. It all depends on the role of the abnormal gene plays in normal physiological function. For details, please read the article below.

http://genetics.thetech.org/ask/ask227
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Re: What causes alleles to become dominant or recessive?

Postby mchlbrmn » Sep 20 2016 3:03 am

In the simplest case:

A dominant gene may be a functional, wild type gene.

A recessive gene might be an inactive mutant gene.

The presence of the wild type, active, gene on the one chromosome may provide enough gene product for a normal phenotype, even if the other chromosome contains the mutant, nonfunctional gene.

This is the classical case. The biological effects of a mutation can vary from mutation to mutation.
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Re: What causes alleles to become dominant or recessive?

Postby relaxin » Sep 20 2016 4:05 pm

This may be true for dominant gene. But a recessive gene is not necessarily an inactive mutant gene. A recessive gene is one that gets trumped by a dominant one.

The genes located on X-chromosome can be dominant or recessive. The genes encoding coagulation factor VIII or IX are dominant one. But since male has only one X-chromosome, only male will get hemophilia with a mutant allele. Female will get hemophilia with two mutant alleles.

For hair color, the brown allele is dominant and blond allele is recessive. A person with a brown allele and a blond allele will have brown hair; a person with no brown allele will be blond.

Phenylketonuria is an autosomal recessive disorder, because the gene encoding phenylalanine hydroxylase is located on chromosome 12 and the disorder is manifested only when both alleles of the gene are mutated.
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