i am trying to figure out the difference between heterozygous and homozygous and what that means for breeding reptiles. i always see it listed with snakes and lizards.
explain genetics
- Thread starter yourmylunch
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Homozygous means 2 of the same gene. (homo=same)
Heterozygous means 2 different genes (hetero=different)
Hope that helps.
Heterozygous means 2 different genes (hetero=different)
Hope that helps.
Trying to put it as simple as possible..
From a practical point of view, you first want to determine what kind of trait you are dealing with. There are Dominant, Co-dominant, and recessive genes out there.
For dominant genes:
Heterozygous carriers (Aa) show the gene in the same way that homozygous (aa) would. Normal looking animals would never carry a gene for a dominant mutation.
For Co-dominant genes:
Heterozygous carries (Aa) are not normal looking, and show a less exaggerated form than the homozygous (aa) carrier would. When you gross two heterozygous carries, 25% of the resulting offspring would be homozygous carriers. For example, a pastel ball python is a heterozygous carrier of the pastel gene. A Super pastel is the result of breeding 2 pastel genes together and hitting those 25% odds.
For recessive genes:
Heterozygous (Aa) carriers look "normal" but do carry the gene. These offspring are produced when a homozygous animals is bred to a normal. If a homozygous/visible albino ball python is bred to a normal, all of the offspring will certainly by heterozygous carriers of the gene. Breeding two "hets" together gives you the same 25% odds of hitting the homozygous version in one of the babies as you would for getting a super version of a co-dominant gene.
For more info:
http://www.newenglandreptile.com/genetics_intro.html
And for questions:
www.ball-pythons.net
From a practical point of view, you first want to determine what kind of trait you are dealing with. There are Dominant, Co-dominant, and recessive genes out there.
For dominant genes:
Heterozygous carriers (Aa) show the gene in the same way that homozygous (aa) would. Normal looking animals would never carry a gene for a dominant mutation.
For Co-dominant genes:
Heterozygous carries (Aa) are not normal looking, and show a less exaggerated form than the homozygous (aa) carrier would. When you gross two heterozygous carries, 25% of the resulting offspring would be homozygous carriers. For example, a pastel ball python is a heterozygous carrier of the pastel gene. A Super pastel is the result of breeding 2 pastel genes together and hitting those 25% odds.
For recessive genes:
Heterozygous (Aa) carriers look "normal" but do carry the gene. These offspring are produced when a homozygous animals is bred to a normal. If a homozygous/visible albino ball python is bred to a normal, all of the offspring will certainly by heterozygous carriers of the gene. Breeding two "hets" together gives you the same 25% odds of hitting the homozygous version in one of the babies as you would for getting a super version of a co-dominant gene.
For more info:
http://www.newenglandreptile.com/genetics_intro.html
And for questions:
www.ball-pythons.net
that post pretty much covers it, but afew more things (i'm a geneticist, i couldn't resist)
If you request a pedigree, females and males will appear as circles and squares. A homozygous (Both the same alleles) individual will be all black. A heterozygous individual will be half black and half white. A non-showing, non-carrying individual will be all white.
The way to determine how a mating will turn out is called a punnett square. It works as follows. A dominant allele (gene variant) will be represent by a Capitalized letter. if one of these is present, it will be expressed, and that is the trait you will see. A recessive allele is represented by a lower case letter, and they must have two and no other alleles to be expressed. A punnett square looks like this:
R r
r rR rr
r rR rr
the top two letters (R r) are one individual, in this case a heterozygote. The two side letters (r
r)
are another individual, a homozygous recessive.
so, to get the probable offspring, you just take the letter on the side, and the letter on the top, and where they meet, write the two letters, like coordinates on a graph.
the part about codominance was slightly off. Codominance is not caused by a heterozygote, nor does being a heterozygote lower the phenotypic (observable) expression of the allele. Codominance and incomplete dominance are caused by two seperate dominant alleles with distinct phenotypes, like red and white coloration in a flower. This is usually caused by cross breeding. Incomplete dominance between red and white alleles will cause a red and white patterned flower, wg\hile codominance will create a pink flower. How alleles will work out together in co/incomplete dominance just has to be found out, and there are several modern selective breeding databases. Knowing the basics of these genetics will greatly help you when breeding to produce a specific trait. I hope I have been of service, and happy breeding.
If you request a pedigree, females and males will appear as circles and squares. A homozygous (Both the same alleles) individual will be all black. A heterozygous individual will be half black and half white. A non-showing, non-carrying individual will be all white.
The way to determine how a mating will turn out is called a punnett square. It works as follows. A dominant allele (gene variant) will be represent by a Capitalized letter. if one of these is present, it will be expressed, and that is the trait you will see. A recessive allele is represented by a lower case letter, and they must have two and no other alleles to be expressed. A punnett square looks like this:
R r
r rR rr
r rR rr
the top two letters (R r) are one individual, in this case a heterozygote. The two side letters (r
r)
are another individual, a homozygous recessive.
so, to get the probable offspring, you just take the letter on the side, and the letter on the top, and where they meet, write the two letters, like coordinates on a graph.
the part about codominance was slightly off. Codominance is not caused by a heterozygote, nor does being a heterozygote lower the phenotypic (observable) expression of the allele. Codominance and incomplete dominance are caused by two seperate dominant alleles with distinct phenotypes, like red and white coloration in a flower. This is usually caused by cross breeding. Incomplete dominance between red and white alleles will cause a red and white patterned flower, wg\hile codominance will create a pink flower. How alleles will work out together in co/incomplete dominance just has to be found out, and there are several modern selective breeding databases. Knowing the basics of these genetics will greatly help you when breeding to produce a specific trait. I hope I have been of service, and happy breeding.