Hair color, height, and shoe size are further instances of genotype. Examples of Genotypes The color of one's eyes is determined by a gene. The allele in this case is either brown or blue, with one inherited from the mother and the other from the father. The brown allele (B) is dominant, whereas the blue allele (R) is recessive (b). Hairy skin also is due to a combination of genes and environmental factors. An individual may be genetically programmed to produce hair on their face, chest, and back, for example, while being born without any observable hair. This phenomenon is called "hairlessness". Hairlessness can be caused by certain diseases that affect the immune system, such as alopecia areata. Otherwise, hairlessness can be inherited as a dominant trait from one's parents. If one parent is bald while the other is not, then the offspring will also be bald since both alleles at each locus are identical (BB). If one parent is hairy while the other is not (RR), then the offspring will also be hairy since they do not get either allele at a locus where the other parent was hairy.
Genetic markers used in genetic testing include proteins, enzymes, hormones, etc. That is why genetics is considered to be the study of markers associated with the transmission of traits, including disease susceptibility genes. Genetic markers can be found in every part of your body: your blood, saliva, urine, sweat, tears, breast milk, and genital fluids are all samples taken for genetic tests.
Gene vs. allele: graph
|Determines||An organism’s genotype||An organism’s phenotype|
|Number per genus locus||One||Two|
|Various Types||Alleles||Paternal vs maternal Dominant vs recessive|
|Examples||Eye color, hair color, skin pigmentation||Blue eyes, brown hair, dark skin|
A homozygous dominant genotype is defined as an organism having two dominant alleles for a characteristic. In the case of eye color, this genotype is denoted by the letters BB. A heterozygous genotype is defined as an organism with one dominant allele and one recessive allele. In the case of eye color, this genotype is called BBx/xy. A homozygous recessive genotype is defined as an organism having two recessive alleles for a characteristic. In the case of eye color, this genotype is called xx/xx.
A heterozygous genotype can be either pure or hybrid. If one of the alleles is from one species and the other allele is from another species, then it is called a hybrid allele. For example, if one brown mouse breeds with another mouse that has white fur, then the offspring will have brown fur because they have both brown and white genes. This is because the brown gene is dominant to the white gene. If both parents are brown, then all their offspring will also be brown because they will all have the same brown allele at each locus (genetic marker) for brown eyes. On the other hand, if one brown mouse breeds with a white mouse, then the offspring will have only white fur because they will all have different alleles at each genetic marker for brown eyes. Some mice will have one brown allele and some mice will have two white alleles at each genetic marker for brown eyes.
Because each parent contributes one allele, the following combinations are possible: AA, Aa, and aa. Offspring with genotypes AA or Aa will have the dominant trait manifested phenotypically, whereas aa people would have the recessive trait expressed. People with the homozygous state of the gene (aa) do not survive; those with one copy of the gene (Aa) may or may not be affected.
In conclusion, sickle cell anemia is caused by a single mutation in both copies of the β-globin gene. The phenotype depends on which type of hemoglobin is missing or defective. People with two copies of the mutated gene never develop the disease; people with one normal copy of the gene and one mutated copy may or may not be affected.
In terms of genetic inheritance, sickle cell anemia is an autosomal-recessive disorder. This means that individuals who have two copies of the mutant gene will always exhibit the disease, while individuals who have one normal copy of the gene and one mutated copy may or may not be affected.
People of African descent are most likely to suffer from sickle cell anemia. This is because they inherit two defective genes for hemoglobin from their parents. In fact, among blacks in the United States, it is estimated that 0.4% have SCD. That's about 8 in every 1000 blacks!