MadSci Network: Genetics

Re: Do all polar bears have recessive genes or is white their dominant color?

Date: Thu Feb 7 09:30:40 2002
Posted By: Gail Lutowski, Staff, Forest Resources, Mary Karhs Warnell Forest Education Center, Warnell Scholl of Forest Resources; University of Georgia
Area of science: Genetics
ID: 1008171726.Ge

Dear Matt:

Despite a good bit of research, I was unable to determine the exact 
mechanism for color determination in polar bears.  However, I would 
suspect that, because the vast majority of polar bears are white, white 
coats are a dominant trait in polar bears.  

I believe your question about recessive genes probably stemmed from 
learning about albinism, which is indeed a recessive trait.  However, 
polar bears, while white, are not albinos.  True albinos lack or have very 
little of a pigment called melanin.  Melanin is what colors hair, eyes and 
skin.  True albinos, because they lack melanin, typically have red or blue 
eyes and very pale hair and skin.  If you look at a polar bear, they have 
dark eyes and a dark nose indicating that they do indeed produce melanin.  
Of course, it is possible for a polar bear to be albino.  An albino polar 
bear would have pink or blue eyes and a pink nose. 

Now, just because a polar bear is an albino, it does not mean that ALL  
its genes are recessive.

Organisms, like bears, are composed of many, many genes which are located 
on chromosomes.  This collection of genes is termed the “genome.”  Each 
individual gene in the genome has several variants.  These variants are 
called alleles.  Some alleles are dominant and some are recessive. 
Every organism’s genome contains a mixture of both dominant and recessive 
alleles, depending on the gene in question. 

Remember that there are two copies of each gene in a cell because there 
are two copies of each chromosome in every cell.  An albino has 2 copies 
of the recessive allele for the gene that controls melanin production and, 
thus, determines the color of the bear.  

So, while an albino polar bear has 2 recessive alleles for the melanin 
gene, it still has a bunch of other genes that may have 2 dominant alleles 
(this is called homozygous dominant), 2 recessive alleles (homozygous 
recessive) or 1 dominant and 1 recessive allele (heterozygous), once 
again, depending on the gene in question.  

I hope that this has answered your question.  Good luck in your genetic 


Admin note:
As an aside, polar bears have white fur but black skin.  In fact, polar
bear skin has a remarkably high melanin content to protect it from the
light scattered by its white fur.

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