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Changes in Chromosome Number
Next Generation: HS.LS3.2 HS.LS3.2

Changes in Chromosome Number

Author: Nathan Lampson

This lesson will explore what types of events can change the number of chromosomes an individual has and the physical outcomes of having an abnormal number of chromosomes.

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Terms to Know
Down Syndrome

A genetic disorder in which the 21st pair of chromosomes have three chromosomes vs. the normal pair, this is called a trisomy.

Klinefelter Syndrome

A condition in which a person has an XXY chromosomal pattern; males that inherit this are often infertile, may develop breasts and other female secondary characteristics and possible mental retardation.


When chromosomes don’t separate during meiosis causing gametes to have abnormal numbers, Down syndrome is an example of this.

Turner Syndrome

A genetic condition in which an X chromosome is missing, if the child is not miscarried, the effects can range from non-life threatening to life threatening. People with Turner syndrome are female due to the presence of only an X chromosome, are almost universally infertile and typically have cardiovascular issues along with other organ system problems.

XYY Syndrome

A condition in which a male inherits an extra Y chromosome; XYY syndrome doesn’t express any cognitive or life threatening abnormalities, it just tends to make males taller than average.