MCAT Biology


MCAT Biology > Genetics


Gregor Mendel was a 19th century Austrian monk who determined the laws of inheritance through true breeding of peas and other plants at his monastery. True breeding refers to the fact that the offspring have the same traits as the parents.

MCAT Genetics - Mendel Pea Pods


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Genetic Crosses

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Sex Determination

In humans there are two kinds of chromosomes, sexual and autosomal. There are 22 pairs of autosomal chromosomes and only 1 pair of sexual ones.

Sex is determined by the father, as there is a 500 chance that either the X or Y will be passed down, while a mother always passes down an X. For example a Punnett square for human birth would be as follows.


MCAT Genetics - Pedigree Chart

The parental generation is often denoted by a "P" and is the row that stands for an organisms parents.

The F1 generation is called the filial generation on the MCAT represents the offspring. This row is usually found beneath the parents and contains all of the offspring that the parents have.

The F2 generation is also called a filial generation and represents the children of the children of the original parents. This is also called the grandchildren generation. The pedigree can go on for Fn and represents and can be expanded to eventually included every human that has ever lived if the genetic evidence was available.

Cytoplasmic Inheritance

A good example of a something that is passed on through cytoplasmic inheritance is the mitochondria. The mitochondria is a cellular organelle that along with mitochondrial DNA is inherited through the mother alone. Mitochondria came into the eukaryotic cell through the process of endosymbiosis. However, this organelle proved very advantageous to the cell and thus had to be passed on. This unique characteristic allows for the tracking of human evolution through genetic evidence and has led to many discoveries in anthropology.

Genetics Variation

See Genetics Variation

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