Biology Basic Genetics

假設dominant 係B
recessive 係b

homozygous dominant: BB
homozygous recessive : bb
heterozygous dominant : Bb
heterozygous recessive :bb*

* 兩個b 係不同的gene~

There're NO such terms "heterozygous dominant" and "heterozygous recessive". "Heterozygous", "homozygous dominant" and "homozygous recessive" are used to describe the genotype of an organism.
genotype: genetic make-up of an individual
homozygous : a term describing organisms whose genotype contains 2 identical alleles for a particular characteristic.
heterozygous: a term describing organisms whose genotype contains 2 different alleles for a particular characteristic.
dominant allele: an allele that can express itself whether in homozygous or heterozygous condition.
recessive allele: an allele that can express itself ONLY in homozygous condition.
To distinguish an organism's genotype between homozygous dominant, homozygous recessive and heterozygous, interbreed the organism to be tested with another organism having recessive characters. (NEVER do that for human beings, study the pedigree instead.)
Let F and f be the dominant and recessive alleles respectively.
Genotype of heterozygous: Ff
Genotype of homozygous dominant: FF
Genotype of homozygous dominant: ff
In the first fillial generation,
1) if all individuals have the dominant character, the organism to be tested is homozygous dominant;
2) if 50% of the individuals have the dominant character while the remaining 50% have the recessive character, the organism to be tested is heterozygous;
3) if all individuals have the recessive character, the organism to be tested is homozygous recessive.