Traits like human height and skin color shows a wide range of phenotype, as opposed to just two of three. From the standpoints of genes and alleles, explain why is this so.
Thus a polygenic trait refers to a trait which is controlled by two or more than two genes.
Polygenic inheritence can explain the large variation in the phenotypes of the organisms.
As the trait is controlled by more than one gene, it leads to a wide variation between extreme phenotypes.
Some examples of polygenic inheritance are: human skin and eye color; height, weight.
Human skin color is a good example of polygenic (multiple gene) inheritance.
Assume that three dominant capital letter genes (A, B and C) control dark pigmentation because more melanin is produced. The recessive alleles of these three genes (a, b & c) control light pigmentation because lower amounts of melanin are produced. A genotype with all "dominant" capital genes (AABBCC) has the maximum amount of melanin and very dark skin.
AABBCC→ Very black (*****)
A genotype with all "recessive" small case genes (aabbcc) has the lowest amount of melanin and very light skin.
aabbcc→ pure white
Each "dominant" capital gene produces one unit of color, so that a wide range of intermediate skin colors are produced, depending on the number of "dominant" capital genes in the genotype. For example, a genotype with three "dominant" capital genes and three small case "recessive" genes (AaBbCc) has a medium amount of melanin and an intermediate skin color. This latter genotype would be characteristic of a mulatto.
AaBbCc→ Mulatto
The wide range of phenotypes observed in traits like human height and skin color can be attributed to the involvement of multiple genes and alleles. To understand why this is the case, let's break it down:
1. Genes: Genes are segments of DNA that contain the hereditary instructions for building and maintaining an organism. They are inherited from our parents and are responsible for various traits.
2. Alleles: Alleles are different versions or variants of a particular gene. They contribute to the diversity of traits within a population. For example, the gene responsible for eye color can have different alleles like blue, brown, green, etc.
Now, let's consider the specific examples:
1. Height: Height is influenced by multiple genes, each with different alleles. This is known as polygenic inheritance. Several genes contribute to the growth and development of bones, muscles, and other factors affecting height. The combination of different alleles across these genes leads to a wide range of heights in the population.
2. Skin color: Similar to height, skin color is a polygenic trait controlled by multiple genes and alleles. Genes associated with skin color production, such as those involved in producing melanin, come in various forms or alleles. The combination of different alleles across these genes determines the amount and type of melanin produced, resulting in different skin colors.
The presence of multiple genes and alleles influencing these traits allows for a broader range of phenotypes in the population. It's important to note that these traits are also influenced by environmental factors, such as nutrition or exposure to sunlight, which can further contribute to variations in phenotype.