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, XX Normal 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.