A brief presentation to explain homozygous.

1. HOMOZYGOTIC
By Antonio Arbués Pérez 4ºA E.S.O.

2. First of all... What is homozygous?
A cell can be homozygous or heterozygous according to the alleles of the
gene that are present in both homologous chromosomes:
- If the alleles are identical: it is a homozygous (eg. AA or aa)
- If the alleles are different: it is a heterozygous (eg. Aa)
If it is a homozygous (identical alleles) it can be of two forms:
- Dominant, when the two identical alleles are both dominant (AA)
- Recesive, when the two identical alleles are both recessive (aa)

3. Genotype and phenotype in homozygous
Genotype is what is inside (eg. AA, Aa, aa)
Phenotype is what we see (eg. Blue eyes, brown hair)
Talking about homozygous:
If we cross one homozygous dominant with another homozygous
dominant, the result will always be the same, 100% of genotypic
ratio of having the same. And equal with the phenotype. And with
the recessive ones always happens the same. Lets see the punnet
square to understand this:
AA/AA A A aa/aa a a
A AA AA a aa aa
A AA AA a aa aa

4. More examples with homozygous
If we cross a homozygous dominant with a homozygous recessive, the result
will be a 100% of genotypic ratio of getting heterozygous. Punnet square:
AA/aa a a
A Aa Aa
A Aa Aa
If we cross a homozygous (it doesn't matter if it is dominant or recessive)
with a heterozygous, the result will be a genotypic ratio of 50% of getting
another identical homozygous and 50% of getting a heterozygous. Punnet
square:
AA/Aa A a aa/Aa A a
A AA Aa a Aa aa
A AA Aa a Aa aa

5. Bibliography
http://en.wikipedia.org/wiki/Zygosity
My notebook and the exercises
My head