A phenotype is an individual’s observable traits, such as height, eye colour, and blood type. The genetic contribution to the phenotype is called the genotype. Some traits are largely determined by the genotype, while other traits are largely determined by environmental factors.
What are Traits?
In genetics traits are features and characteristics that can be passed from one generation to another.
- Examples include skin colour, cleft chin, blood type, and height.
- Traits of dogs would include, length of tail, shape of ears and colour.
- Each of these factors can be passed genetically to another generation.
- Each trait has different forms of the same trait.
- For example, everyone has a nose, but the nose can have many different shapes.
- The different forms of the same trait are called alleles.
- Traits can also be dominant or recessive
- Each individual has two alleles for each gene, one coming from mom and the other from dad.
- A dominant gene can be expressed even if only one copy of the gene is present.
- A dominant trait can be homozygous which means it has two of the same alleles, or heterozygous which means it has two different alleles.
- A recessive trait will only be expressed if an individual homozygous recessive.
- Phenotype is the physical expression of a trait.
Most genes have two or more variations, called alleles. For example, the gene for hairline shape has two alleles – widow’s peak or straight. An individual may inherit two identical or two different alleles from their parents. When two different alleles are present they interact in specific ways. For the traits included in this activity, the alleles interact in what is called a dominant or a recessive manner. The traits due to dominant alleles are always observed, even when a recessive allele is present. Traits due to recessive alleles are only observed when two recessive alleles are present. For example, the allele for widow’s peak is dominant and the allele for straight hairline is recessive.
If an individual inherits:
- Two widow’s peak alleles (both dominant), their hairline will have a peak
- One widow’s peak allele (dominant) and one straight hairline allele (recessive), they will have a widow’s peak
- Two straight hairline alleles (recessive), their hairline will be straight.
If earlobes hang free, they are detached. If they attach directly to the side of the head, they are attached earlobes. Some scientists have reported that this trait is due to a single gene for which unattached earlobes is dominant and attached earlobes is recessive. Other scientists have reported that this trait is probably due to several genes. The size and appearance of the lobes are also inherited traits.
In 1940, the famous geneticist Alfred Sturtevant noted that about 70% of people of European ancestry are able to roll up the lateral edges of the tongue, while the remaining 30% were unable to do so. Tongue rolling ability may be due to a single gene with the ability to roll the tongue a dominant trait and the lack of tongue rolling ability a recessive trait. However, there is some question about the inheritance of tongue rolling. Recent studies have shown that around 30% of identical twins do not share the trait.
This trait is reportedly due to a single gene with a cleft chin dominant and a smooth chin recessive.
Dimples are reportedly due to a single gene with dimples dominant (people may exhibit a dimple on only one side of the face) and a lack of dimples recessive.
Some scientists have reported that handedness is due to a single gene with right handedness dominant and left handedness recessive. However, other scientists have reported that the interaction of two genes is responsible for this trait.
This trait is reportedly due to a single gene; the presence of freckles is dominant, the absence of freckles is recessive.
Naturally Curly Hair
Early geneticists reported that curly hair was dominant and straight hair was recessive. More recent scientists believe that more than one gene may be involved.
While allergic reactions are induced by things a person comes in contact with, such as dust, particular foods, and pollen, the tendency to have allergies is inherited. If a parent has allergies, there is a one in four (25%) chance that their child will also have allergy problems. This risk increases if both parents have allergies.
Fold your hands together by interlocking your fingers without thinking about it. Which thumb is on top – your left or your right? One study found that 55% of people place their left thumb on top, 45% place their right thumb on top and 1% have no preference. A study of identical twins concluded that hand clasping has at least some genetic component. However, other scientists have not found evidence that genetics plays a significant role in determining this trait.
Colour-blindness is due to a recessive allele located on the X chromosome. Women have two X chromosomes, one of which usually carries the allele for normal colour vision. Therefore, few women are colour-blind. Men only have one X chromosome, so if they carry the allele for colour-blindness, they will exhibit this trait. colour-blindness is seen more frequently in men than in women.
Hairline shape is reportedly due to a single gene with a widow’s peak dominant and a straight hairline recessive.