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Gregor Mendel discovered that the genotype is an organism's genetic makeup. For example, all of your genes are what comprise your genotype. The expression of those genes is called your phenotype, your traits that result when the instructions in your genes are carried out. "Alleles are variations of a gene. We get one set of alleles (genes) from one parent and the other set of alleles from the other parent.
Some of the traits that we have are based on simple inheritance where one version of a gene (dominant allele) masks, or hides the expression of the other version of that gene (recessive allele).
In writing, we represented dominant and recessive alleles with letters that distinguish the different types of alleles. A capital letter is used to represent the dominant allele and a lower-case letter is used to represent the recessive allele (example: dominant gene = P; recessive gene = p)." For a recessive trait to appear the offspring must receive two recessive genes from the parents.
Genetic disorders are caused by a mutation of a gene on a strand of DNA. This can come from a parent who is a carrier of the recessive gene and doesn't know it, or it can come from a mutation during development of the embryo.
In sexual reproduction, an organism receives one copy of each gene from each parent. Each body cell then has two copies of every gene. A dominant gene is one that is expressed (shows in the individual) even if there is only one copy of that type in the cells. For a recessive trait to be expressed, both copies of the gene must be of that type. Some diseases/disorders are controlled by dominant genes (eg, Huntington's), and some by recessive genes (eg, hemophilia.) Since parents can carry a recessive gene for a disease and not be aware of it, they may have no idea that there are diseases they may pass on to their offspring.
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