Thursday, Oct. 12 Genetics - Genetic Variations

Key Terms

Crossing over – The process in which DNA from the father and DNA from the mother are exchanged.

DNA replication – The process in which an extra copy of DNA is made

Epigenetics – The study of how the chemicals that are not part of the DNA sequence affect the expression of genes.

Genetic Recombination – The redistribution of genes during meiosis.

Mutation – A random change that occurs in the DNA of a cell.



There is a huge amount of genetic variation among species – just look at all the different types of dogs. Meiosis is the process in which one cell divides into four cells called gametes (sperm or egg cells). Gametes have half the number of chromosomes as the original cell, so they only carry some of the genetic information of the original cell.


Crossing Over

Genetic recombination is the redistribution of genes in a cell. It’s why gametes have different genetic information thatn the original cell. When DNA from the male parent and DNA from the female parent exchange parts of chromosomes, this is called crossing over and gametes get new combinations of genes – and an increased variety of traits in a population.


DNA Replication

Before meiosis, an extra copy of DNA is made. During DNA replication, the two strand of a DNA molecule separate from each other. Think of it as unzipping a zipper. The “teeth” of the zipper are nucleotides. There are four nucleotides:

Adenine (A)

Cytosine (C)

Guanine (G)

Thymine (T)

A & T pair up and G & C pair up.

A mutation is a random change that happens in the genetic material of a cell. It can be an accident in the replication process or an environment sources, such as radiation or chemical exposure. Mutations are them copied in the process of replication and the number of mutated cells grows. Cancer cells pass along mutated DNA in this way.


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