KaryotypesKaryotypes

What is a Karyotype?What is a Karyotype? A A karyotypekaryotype is an organized profile of a is an organized profile of a

person's chromosomes.person's chromosomes. In a In a karyotypekaryotype, chromosomes are arranged , chromosomes are arranged

and numbered by size, from largest to and numbered by size, from largest to smallest. This arrangement helps scientists smallest. This arrangement helps scientists quickly identify chromosomal alterations quickly identify chromosomal alterations that may result in a genetic disorder.that may result in a genetic disorder.

To make a To make a karyotypekaryotype, scientists take a , scientists take a picture of someone's chromosomes, cut picture of someone's chromosomes, cut them out and match them up using size, them out and match them up using size, banding pattern and centromere position as banding pattern and centromere position as guides.guides.

Sample Karyotypes:Sample Karyotypes:Female Male

Alterations in Chromosome Alterations in Chromosome NumberNumber

NondisjunctionNondisjunction occurs when either occurs when either homologues fail to separatehomologues fail to separate during during anaphase I of meiosis, or sister anaphase I of meiosis, or sister chromatids fail to separate during chromatids fail to separate during anaphase II. anaphase II.

The result is that one gamete has 2 The result is that one gamete has 2 copies of one chromosome and the copies of one chromosome and the other has no copy of that chromosome. other has no copy of that chromosome. (The other chromosomes are distributed (The other chromosomes are distributed normally.) normally.)

Alterations ContinuedAlterations Continued

If either of these gametes unites with If either of these gametes unites with another during fertilization, the result is another during fertilization, the result is aneuploidyaneuploidy (abnormal chromosome (abnormal chromosome number)number)– A A trisomictrisomic cell has one extra chromosome cell has one extra chromosome

example: trisomy 21 (Down Syndrome)example: trisomy 21 (Down Syndrome)

– A A monosomicmonosomic cell has one missing cell has one missing chromosomechromosome and is usually lethal except for and is usually lethal except for one known in humans: Turner's syndrome one known in humans: Turner's syndrome

Trisomy 21 (Down Trisomy 21 (Down Syndrome)Syndrome)

The result of an The result of an extra copy of extra copy of chromosome 21.chromosome 21.

Characteristic Characteristic facial features, facial features, short stature; heart short stature; heart defects, defects, susceptibility to susceptibility to respiratory disease, respiratory disease, shorter lifespan.shorter lifespan.

Trisomy 13 (Patau Trisomy 13 (Patau Syndrome)Syndrome)

Serious eye, brain, Serious eye, brain, circulatory defects circulatory defects as well as cleft as well as cleft palate. palate.

1:5000 live births. 1:5000 live births.

Children rarely live Children rarely live more than a few more than a few months.months.

Trisomy 18 (Edwards Trisomy 18 (Edwards Syndrome)Syndrome)

Almost every organ Almost every organ system affected.system affected.

1:10,000 live births. 1:10,000 live births.

Children with Children with Trisomy 18 generally Trisomy 18 generally do not live more do not live more than a few months.than a few months.

Additional AlterationsAdditional Alterations

Nondisjunction of the Sex Nondisjunction of the Sex Chromosomes (X and Y)Chromosomes (X and Y)

Can be fatal, but many Can be fatal, but many people have these karyotypes people have these karyotypes and are just fine!and are just fine!

Klinefelter Syndrome (XXY)Klinefelter Syndrome (XXY)

Type of trisomy.Type of trisomy. Male sex organs; Male sex organs;

unusually small unusually small testes, sterile. testes, sterile.

Breast enlargement Breast enlargement and other feminine and other feminine body characteristics. body characteristics.

Normal intelligence.Normal intelligence.

XYY MalesXYY Males

Individuals are Individuals are somewhat taller than somewhat taller than average and often average and often have below normal have below normal intelligence. intelligence.

At one time (~1970s), At one time (~1970s), it was thought that it was thought that these men were likely these men were likely to be criminally to be criminally aggressive, but this aggressive, but this hypothesis has been hypothesis has been disprovendisproven over time. over time.

Trisomy X (XXX)Trisomy X (XXX)

Effects Females. Effects Females. 1:1000 live births. 1:1000 live births. healthy and fertile.healthy and fertile. usually cannot be usually cannot be

distinguished from distinguished from normal female normal female except by except by karyotype.karyotype.

Monosomy X (Turner’s Monosomy X (Turner’s Syndrome)Syndrome)

1:5000 live births1:5000 live births The only viable The only viable

monosomymonosomy in humans in humans women with Turner's women with Turner's

have only 45 have only 45 chromosomes!!! XO chromosomes!!! XO

individuals are individuals are genetically female, genetically female, however, they do not however, they do not mature sexually during mature sexually during puberty and are sterile. puberty and are sterile.

Short stature and Short stature and normal intelligence. normal intelligence. (98% of these fetuses (98% of these fetuses die before birth)die before birth)