An organism can be homozygous dominant, if it carries two copies of the same dominant allele, or homozygous recessive, if it carries two copies of the same recessive allele. Heterozygous means that an organism has two different alleles of a gene.

vestigial wings

In a nutshell, the dimples gene gives information for the dimples trait. Allele D = dimples and allele d = no dimples. Suppose the gene for dimples is on chromosome #5. Remember that each person is diploid or has two sets of each type of the autosomal chromosomes (the non-sex chromosomes, types 1-22).

If the test cross results in any recessive offspring, then the parent organism is heterozygous for the allele in question. If the test cross results in only phenotypically dominant offspring, then the parent organism is homozygous dominant for the allele in question.

A person is said to be homozygous for a gene if they have two identical copies of the gene. Homozygous: You inherit the same version of the gene from each parent, so you have two matching genes. Heterozygous: You inherit a different version of a gene from each parent. They do not match.

Heterozygous refers to having inherited different forms of a particular gene from each parent. A heterozygous genotype stands in contrast to a homozygous genotype, where an individual inherits identical forms of a particular gene from each parent.

For Hh, the gametes can carry the H (dominant allele) or the h (recessive allele). For hh, the gametes can only carry h (the recessive allele). For both heterozygous individuals (Hh), the gametes can carry the H (dominant allele) or the h (recessive allele).

Green is the recessive form. If an individual is KK, then it is dark green or in its dominant form. “KK” is a homozygote for the dark green gene….

A simple example to illustrate genotype as distinct from phenotype is the flower colour in pea plants (see Gregor Mendel). There are three available genotypes, PP (homozygous dominant ), Pp (heterozygous), and pp (homozygous recessive).

The genotype of the purple-flowered plant is PP. Since white flowers are recessive, the only possible genotype for a white-flowered plant is pp. As you can see, all of the offspring in Mendel’s first cross had a genotype of Pp. That’s why all of the plants in the p first generation had purple flowers.

The two alleles representing the trait are identical (e.g. PP for purple color, pp for white color).

Compatible genotypes for marriage are: AA marries an AS. You’ll end up with kids with AA and AS which is good. But sometimes if you’re not lucky all the kids will be AS which limits their choice of partner. AS and AS should not marry, there is every chance of having a child with SS.

A woman with an AA genotype cannot give birth to an SS child even if she sleeps with the founder of Sickle cell”. The other kids are AS and AA.”