Karyotypes&

Genetic Disorders

Karyotypesan organized profile of a person’s homologous

chromosomes (somatic cells only)

Each pair is organized by size, banding patterns, and location of centromere

Centromere

Banding Pattern“Bands” are large segments of DNA **Remember what chromosomes are made up of

Exception: Position 23Chromosome Pair #23 determines sex

Only pair that might NOT match up…

WHY?

vs.

Female

23rd pair of chromosomes are homologous

Both chromosomes are “X” chromosomes

Male23rd pair of chromosomes are

NOT homologous

One chromosome is “X” and the other is a “Y” chromosome

Normal Karyotypes

Has 46 chromosomes for humansArranged in 23 pairs

Normal Karyotype

• Taken after DNA replication

DisjunctionNormal separation of Chromosomes and Chromatids during Meiosis I and Meiosis II

(Anaphase I & II)

NON-disjunctionNondisjunction during Meiosis I

Metaphase I Anaphase I Failure to separate

homologous pairs

NON-disjunctionNondisjunction during Meiosis II

Metaphase II

Anaphase II

Failure to separate

Chromatids

What does nondisjunction cause?Missing Chromosomes – Monomy

Embryo/Fetus will not surviveMeans 45 chromosomesException is this can occur on 23rd chromosome pair

Turner’s Syndrome (X-)

Extra Chromosomes – TrisomyMeans 47 chromosomes

– Down Syndrome (Trisomy 21)– Patau Syndrome (Trisomy 13)– Klinefelter’s Syndrome (XXY)– XYY Syndrome– And many more………….

Trisomy 21 – Down SyndromeExtra Chromosome 21

Trisomy 13 – Patau SyndromeExtra Chromosome 13

Symptoms can include•Cleft lip or palate •Close-set eyes -- eyes may actually fuse together into one •Decreased muscle tone •Extra fingers or toes•Hernias•Hole, split, or cleft in the iris•Low-set ears •Mental retardation•Scalp defects (absent skin) •Seizures •Single palmar crease •Skeletal (limb) abnormalities •Small eyes •Small head•Small lower jaw •Undescended testicle

Klinefelter’s Syndrome (XXY)Extra Sex Chromosome “X”

Turner’s Syndrome (X-)

XYY Syndrome

• XYY syndrome is characterized by an extra copy of the Y chromosome

• males with this condition may be taller than average

• This chromosomal change typically causes no unusual physical features

• Most males with XYY syndrome have normal sexual development and are able to father children

Jamie Lee Curtis• XY male with Androgen

Insensitivity Syndrome (AIS)

• resistant to androgens– the hormones

responsible for male sexual development

QUESTIONS???