Karyotypes & Genetic Disorders

Karyotypes an 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

Chromosome Pair #23 determines sex Only pair that might NOT match up… Exception: Position 23 Chromosome 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

Male 23rd pair of chromosomes are NOT homologous One chromosome is “X” and the other is a “Y” chromosome

Has 46 chromosomes for humans Normal Karyotypes Has 46 chromosomes for humans Arranged in 23 pairs

Normal Karyotype Taken after DNA replication

Disjunction Normal separation of Chromosomes and Chromatids during Meiosis I and Meiosis II (Anaphase I & II)

Failure to separate homologous pairs NON-disjunction Nondisjunction during Meiosis I Metaphase I Anaphase I Failure to separate homologous pairs

Failure to separate Chromatids NON-disjunction Nondisjunction during Meiosis II Metaphase II Failure to separate Chromatids Anaphase II

What does nondisjunction cause? Missing Chromosomes – Monomy Embryo/Fetus will not survive Means 45 chromosomes Exception is this can occur on 23rd chromosome pair Turner’s Syndrome (X-) Extra Chromosomes – Trisomy Means 47 chromosomes Down Syndrome (Trisomy 21) Patau Syndrome (Trisomy 13) Klinefelter’s Syndrome (XXY) XYY Syndrome And many more………….

Trisomy 21 – Down Syndrome Extra Chromosome 21

Trisomy 13 – Patau Syndrome Extra 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

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