Dominant traits occur when one copy of a gene overrides another, while recessive traits only appear if both copies of the gene are inherited. Gregor Mendel’s research on peas in the 19th century popularized the concept. Eye color is determined by genes in different alleles that interact with each other to create various colors.
A dominant trait is a genetic trait that occurs when only one copy of the gene is present, overriding another inherited gene that codes for a different version of the trait. Conversely, a recessive trait will only appear if an organism inherits one copy of the gene from both parents. Otherwise, the recessive will sit dormant and the dominant trait will take over. The idea of recessive and dominant traits was popularized by Gregor Mendel, who researched peas in the 19th century to better understand genetic inheritance.
The reproduction process begins with the generation of eggs and sperm. These cells are haploid, meaning they contain half of the genetic material needed to code for the organism. When the egg and sperm fuse, they create a diploid cell with all the necessary genetic material, and the cell begins to grow and divide, eventually turning into a baby. This genetic material is divided into chromosomes, with individual traits determined by genes at specific locations on the chromosome known as alleles.
When someone inherits both a dominant and a recessive allele, the recessive gene essentially stays turned off, allowing the dominant gene to take over. For example, if a child inherits the genes for brown and blue eyes, the blue gene will lie dormant, ensuring that the child’s eyes are brown. This makes brown eyes dominant. Thanks to Gregor Mendel’s shorthand, many people use uppercase and lowercase letters to distinguish between dominant and recessive traits, like this: B/b, for brown/blue eyes.
In some cases, people inherit two copies of the same allele, making them homozygous for that particular trait. People can also be heterozygous, having two different alleles for a particular gene. When someone is homozygous for a trait, that trait will manifest itself whether it is dominant or recessive, because there is no other genetic material to compete with it. When someone is heterozygous for a trait, the difference between dominant and recessive traits becomes more important, because the dominant trait is the one that will manifest.
In a simple example of how dominant traits work, someone might have two parents who are heterozygous for brown and blue eyes. There is a 25% chance that the child will inherit the bb allele, causing him to have blue eyes. There is a 50% chance that the child will inherit a B from one parent and an ab from the other, making the child brown-eyed, with the ability to pass blue eyes on to her child. Finally, the child could inherit a B from both parents, making the child homozygous for brown eyes.
Since there are more eye colors than brown and blue, it should come as no surprise to learn that eye color is actually determined by genes in different alleles that interact with each other to create colors like green, gray, and hazel in addition to brown and blue. .
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