Do Now

●Hand in your labs in the bin.

●What are karyotypes used for?

●What are three purposes that they serve?

Karyotypes

●A picture of all the chromosomes in an individual arranged in an order of descending size. The sex chromosomes are placed at the end.

Autosomes are “regular” chromosomes and we use numbers to identify them.

Sex chromosomes determine an individuals gender.

Healthy humans have 44 autosomes and 2 sex chromosomes

What can Karyotypes tell you?1. The gender of the individual.

Two X chromosomes (XX) the individual is FEMALE One X and one Y (XY) the individual is MALE.

2. The species the individual belongs too 23 chromosomes = human

3. If the individual has a chromosome disorder One pair for each numbered chromosome is healthy.

Labeling a Karyotype

●To label a karyotype correctly, first list the number of chromosomes found in the karyotype. Ex. 46

●Secondly, list the type of sex chromosomes found in the karyotype. Ex. XX

●Lastly, list the any abnormalities at the appropriate chromosome number.Normal Human Female: 46, XXNormal Human Male: 46, XY

What are abnormalities?

●Sometimes, during meiosis, things go wrong.

●The most common error is nondisjunction, which means “not coming apart”.

●If nondisjunction occurs , abnormal numbers of chromosomes may find their way into gametes, and a disorder of chromosome numbers may result.

Autosomal Chromosome Disorders

●Two copies of an autosomal chromosome fail to separate during meiosis, an individual may be born with THREE copies of a chromosome.

●This is known as a “Trisomy”●Trisomy 13, Trisomy 18, Trisomy 21.

Down Syndrome

●Most common, Trisomy 21 (down syndrome)

●1 in 800 babies born in U.S. with Trisomy 21.

●Mild to severe mental retardation

●Increased susceptibility to many diseases and a higher frequency of other birth defects.

Sex Chromosome Disorders

●Turner’s Syndrome (nondisjunction)○Female inherits only one X chromosome○Karyotype: 45, X○Women are sterile, sex organs do not develop

at puberty.●Klinefelter’s syndrome (nondisjunction)

○Males receive an extra X chromosome○Karyotype: 47, XXY○The extra X chromosome interferes with

meiosis and prevents ind. from reproducing.