Heredity, Genetics, & Evolution

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Heredity, Genetics, & Evolution
Knowledge of genetic mechanisms came as a result of
careful laboratory experiments over the last century and a half

Hybrids Through Breeding

 For thousands of years farmers and herders have been selectively breeding their plants and animals in order to produce more productive hybrids.
 It was somewhat of a hit or miss process since the actual mechanisms governing inheritance were unknown.

Chicken Domesticated horses

Cracking the Code of Life:
Part 1 The instructions for a
human being

Genetic Principles Discovered by Mendel
 Gregor Mendel (1822-1884) laid down the basic principles of heredity.
 Crossed different strains of purebred plants and studied their progeny.
 Worked with common garden peas and considered only one trait at a time.
 His work illustrates the basic rules of inheritance.

Mendel's research was with plants, but the basic underlying principles of heredity also apply to people and other animals.
The mechanisms of heredity are essentially the same for all complex life forms.

Mendel’s Experiments
Mendel picked common garden pea plants for the focus of his research because they can be grown easily in large numbers and their reproduction can be manipulated.
Today, bacterium and fruit flies are generally used for lab testing because they reproduce multiple generations very rapidly.

Generational Changes
In cross-pollinating plants that either produce yellow or green peas exclusively, Mendel found that the first offspring generation (f1) always has yellow peas. \
However, the following generation (f2) consistently has a 3:1 ratio of yellow to green.

This ratio is the key to understanding the basic mechanisms of inheritance.

Three important conclusions:
 That the inheritance of each trait is determined by "units" or "factors" (now called genes) that are passed on to descendents unchanged.
 That an individual inherits one such unit from each parent for each trait.
 That a trait may not show up in an individual but can still be passed on to the next generation.

Homozygous and Heterozygous
 The parent plants were homozygous for pea color - they each had two identical forms (or alleles) of the gene: 2 yellows or 2 greens.
 The plants in the f1 generation were all heterozygous for pea color - they each had inherited two different alleles (one from each parent plant).

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Heredity, Genetics, & Evolution