Genetics+-+Mendelian

__** Gregor Mendel's Law of Dominance **__

The law... When an organism is hybrid for a pair of contrasting traits, only the dominant trait is expressed (or shows).

How it came to be... Mendel crossed a pure Tall pea plant with a pure Short pea plant ("P" generation). The expected result was Medium height. INSTEAD, all of the offspring were observed to be Tall (F1 generation).

When this F1 generation was crossed, the Short height was seen again! It had been masked in the F1 generation due to the Tall height being dominant.

__** The Language of Genetics **__

In order to understand and discuss genetics, one must speak the language. Here are some of the terms that will be used in class to discuss genetics.
 * //** Dominant **//- describes a trait or an allele that is expressed, or shows when at least one dominant allele is inherited. It masks, or overpowers, the recessive allele. Written as a capital letter.
 * //** Recessive **// - describes a trait or an allele that is expressed only when two recessive alleles for the same characteristic are inherited. Written as a lowercase letter.
 * //** Homozygous **// - describes the presence of possessing two of the same allele. AKA "pure"
 * **// Heterozygous //** - describes the presence of possessing two different alleles. AKA "hybrid"
 * //** Genotype **// - the entire genetic makeup of an organism. Also describes the combination of genes for one or more specific traits.
 * //** Phenotype **// - an organism's appearance or other detectable characteristic. Also, a physical description of an organism's genotype.
 * //** Allele **// - a "version" of a gene. One of the alternative forms of a gene.
 * //** Gene **// - a segment of DNA that codes for a specific hereditary trait.
 * //** Chromosomes **// - structures in the nucleus made of DNA. Humans have 46 in each of their body cells.