aussie_cowgirl
Well-known member
In light of a lot of discussions and arguments regarding genetics I decided to do up a little info thread about it. Hopefully it's useful to some of you. If you have any further questions feel free to mail me.
Cattle have 30 pairs of chromosomes, of these 29 are called autosomes and the remaining pair are sex chromosomes (ie XX being female or XY being male). During breeding, one chromosome of each pair from each parent is passed onto the progeny. So half of the calf's genetics come from the mother, half from the father. If the calf is a female, it means it received an X chromosome from her mother and an X chromosome from her father. Alternatively, if it was a male, he would have received an X chromosome from his mother and a Y chromosome from his father.
DNA is like the instruction manual for an organism. Each gene is responsible for something different in the animal. In each animals DNA there are 2 possible versions (known as alleles) of the gene.
Which allele is expressed in the animal is determined by which allele is more dominant. Dominant alleles are expressed even when another different allele is present. For a recessive allele to be expressed, BOTH alleles present for the gene MUST be the recessive one.
If an animal has 2 matching alleles (whether it be dominant or recessive) it is none as homozygous (homo= same). If an animal carries 2 different alleles it is known as heterozygous (hetero= different).
Here are some artistic renditions I made in paint
*****there is an error, the black cow in the last image should be 'heterozygous black'*****
To add to this confusion there are 2 types of white alleles. The white allele belonging to the Charolais is actually a red allele with a 'masking gene'. And the white allele belonging to the shorthorn is a white gene. Seeing as the allele is actually red, the colour is recessive. But from a Charolais x you can get grey, smokey, dun etc colours. This is caused by the masking gene, or more commonly known as the diluting gene which is dominant. The white allele in a Shorthorn is co-dominant with red and black. So homozygous shorthorn will only be Red or white, and a heterozygous shorthorn will be a roan. When crossed with a black animal you often get a black/blue roan which means the calf is heterozygous and has received a black and a white allele.
As mentioned earlier there is a diluter gene that alters coat colour further which is a dominant allele. Yellow cattle are red with a diluter gene present. Mousey brown cattle/grey cattle are black with a diluter gene. There is variation within colours, from pale yellow-orange and mousey brown-silver-grey.
The allele for 'polling' in cattle is dominant to the allele for horns. I.e
1 Polled Bull(PP) x Horned Cow (hh)= 100% poll 0% horned
2 Polled Bull(Ph) x Horned Cow(hh)= 50% poll 50% horned
3 Polled Bull(Ph) x Polled Cow(Ph)= 75% poll 25% horned
4 Polled Bull(PP) x Polled Cow(PP)= 100% poll 0% horned
5 Polled Bull(PP) x Polled Cow(Ph)= 100% poll 0% horned
Edit (thanks Dun):In some bos indicus type cattle there are 2 genes controlling horns. Along with the regular horned/polled gene there is a gene called the African horn gene (Af; polled is An) (which appears on the sex genes. The Y chromosome doesn't carry a matching allele so in males, there is only one allele. Therefore they are more susceptible).
Homozygous (Af Af) cattle always have horns.
Heterozygous (Af An); females will be polled, males will be horned
Homozygous (An An) Always polled
How it works with the regular horn/poll gene
AfAfPP and AfAfPp Horned cow and Horned bull
AfAnPP and AfAnPp Polled cow or Horned bull
AnAnPP and AnAnPp Polled cow and Polled bull
AfAfpp, AfAnpp and AnAnpp Horned cow and Horned bull
Cattle have 30 pairs of chromosomes, of these 29 are called autosomes and the remaining pair are sex chromosomes (ie XX being female or XY being male). During breeding, one chromosome of each pair from each parent is passed onto the progeny. So half of the calf's genetics come from the mother, half from the father. If the calf is a female, it means it received an X chromosome from her mother and an X chromosome from her father. Alternatively, if it was a male, he would have received an X chromosome from his mother and a Y chromosome from his father.
DNA is like the instruction manual for an organism. Each gene is responsible for something different in the animal. In each animals DNA there are 2 possible versions (known as alleles) of the gene.
Which allele is expressed in the animal is determined by which allele is more dominant. Dominant alleles are expressed even when another different allele is present. For a recessive allele to be expressed, BOTH alleles present for the gene MUST be the recessive one.
If an animal has 2 matching alleles (whether it be dominant or recessive) it is none as homozygous (homo= same). If an animal carries 2 different alleles it is known as heterozygous (hetero= different).
Here are some artistic renditions I made in paint
*****there is an error, the black cow in the last image should be 'heterozygous black'*****
To add to this confusion there are 2 types of white alleles. The white allele belonging to the Charolais is actually a red allele with a 'masking gene'. And the white allele belonging to the shorthorn is a white gene. Seeing as the allele is actually red, the colour is recessive. But from a Charolais x you can get grey, smokey, dun etc colours. This is caused by the masking gene, or more commonly known as the diluting gene which is dominant. The white allele in a Shorthorn is co-dominant with red and black. So homozygous shorthorn will only be Red or white, and a heterozygous shorthorn will be a roan. When crossed with a black animal you often get a black/blue roan which means the calf is heterozygous and has received a black and a white allele.
As mentioned earlier there is a diluter gene that alters coat colour further which is a dominant allele. Yellow cattle are red with a diluter gene present. Mousey brown cattle/grey cattle are black with a diluter gene. There is variation within colours, from pale yellow-orange and mousey brown-silver-grey.
The allele for 'polling' in cattle is dominant to the allele for horns. I.e
1 Polled Bull(PP) x Horned Cow (hh)= 100% poll 0% horned
2 Polled Bull(Ph) x Horned Cow(hh)= 50% poll 50% horned
3 Polled Bull(Ph) x Polled Cow(Ph)= 75% poll 25% horned
4 Polled Bull(PP) x Polled Cow(PP)= 100% poll 0% horned
5 Polled Bull(PP) x Polled Cow(Ph)= 100% poll 0% horned
Edit (thanks Dun):In some bos indicus type cattle there are 2 genes controlling horns. Along with the regular horned/polled gene there is a gene called the African horn gene (Af; polled is An) (which appears on the sex genes. The Y chromosome doesn't carry a matching allele so in males, there is only one allele. Therefore they are more susceptible).
Homozygous (Af Af) cattle always have horns.
Heterozygous (Af An); females will be polled, males will be horned
Homozygous (An An) Always polled
How it works with the regular horn/poll gene
AfAfPP and AfAfPp Horned cow and Horned bull
AfAnPP and AfAnPp Polled cow or Horned bull
AnAnPP and AnAnPp Polled cow and Polled bull
AfAfpp, AfAnpp and AnAnpp Horned cow and Horned bull