Chromosomal Disorders

Non-disjunction During meiosis, chromosomes are supposed to be divided evenly and into gametes. During meiosis, chromosomes are supposed to be divided evenly and into gametes. Sometimes, however, they do not separate properly. Sometimes, however, they do not separate properly. This is called non-disjunction This is called non-disjunction

Non-disjunction can lead to an extra chromosome or a missing chromosome in the Non-disjunction can lead to an extra chromosome or a missing chromosome in the gamete. gamete.

Karyotype* A picture of an individual’s chromosomes A picture of an individual’s chromosomes Used to determine if the individual has the appropriate number of chromosomes. Used to determine if the individual has the appropriate number of chromosomes. In normal humans: In normal humans: 46 chromosomes or 23 pairs of chromosomes 46 chromosomes or 23 pairs of chromosomes Any change in this number causes abnormality in the individual. Any change in this number causes abnormality in the individual.

Male or female? Normal?

Down Syndrome aka Trisomy 21 Three copies of chromosome 21 Three copies of chromosome 21 Symptoms: Mental retardation, stunted growth, altered facial characteristics Symptoms: Mental retardation, stunted growth, altered facial characteristics Frequency: 1 out of 800 births Frequency: 1 out of 800 births

Male or female? Normal?

Turner’s Syndrome aka Monosomy X Only one sex chromosome (X) Only one sex chromosome (X) Symptoms: Shortness, broad chest, infertile, never goes through puberty, amenorrhea (no periods), webbed neck Symptoms: Shortness, broad chest, infertile, never goes through puberty, amenorrhea (no periods), webbed neck Frequency: 1 out of 2,500 females Frequency: 1 out of 2,500 females

Male or female? Normal?

Klinefelter’s Syndrome Two X chromosomes and a Y (XXY) Two X chromosomes and a Y (XXY) Symptoms: Sterility, possible breast development, small testicles Symptoms: Sterility, possible breast development, small testicles (some men show no outward symptoms) Frequency: 1 out of every 500 males Frequency: 1 out of every 500 males

Male or female? Normal?

XYY An X and two Y chromosomes (XYY) An X and two Y chromosomes (XYY) Symptoms: Usually not noticed; often causes increase in height, may cause learning disabilities Symptoms: Usually not noticed; often causes increase in height, may cause learning disabilities Frequency: 1 out of 1,000 males Frequency: 1 out of 1,000 males

Male or female? Normal?

Triple X Syndrome aka Trisomy X Three X chromosomes (XXX) Three X chromosomes (XXX) Symptoms: possible infertility, tall, small head, learning disabilities, delayed puberty, big distance between eyes, possible mental retardation Symptoms: possible infertility, tall, small head, learning disabilities, delayed puberty, big distance between eyes, possible mental retardation Frequency: 1 out of 1,000 females Frequency: 1 out of 1,000 females

Male or female? Normal?

Edward’s Syndrome aka Trisomy 18 Three copies of chromosome 18 Three copies of chromosome 18 Symptoms: mental retardation, small lower jaw, protruding chest, small, abnormally shaped head, heart problems Symptoms: mental retardation, small lower jaw, protruding chest, small, abnormally shaped head, heart problems Frequency: 1 out of 3,000 births Frequency: 1 out of 3,000 births

Male or female? Normal?

Patau Syndrome aka Trisomy 13 Three copies of chromosome 13 Three copies of chromosome 13 Symptoms: mental retardation, deafness, eye abnormalities, cleft lip, cleft palate, small head, eyes close to each other, polydactyly (extra fingers) Symptoms: mental retardation, deafness, eye abnormalities, cleft lip, cleft palate, small head, eyes close to each other, polydactyly (extra fingers) Frequency: 1 out of 5,000 births Frequency: 1 out of 5,000 births

Autosomal Disorders Found on the “other” chromosomes (#’s 1-22). Found on the “other” chromosomes (#’s 1-22). Examples: Examples: Albinism, Cystic Fibrosis, Sickle Cell Anemia, PKU, and Huntington’s Disease. Albinism, Cystic Fibrosis, Sickle Cell Anemia, PKU, and Huntington’s Disease.

Albinism Carried on chromosome #11. Carried on chromosome #11. Recessive allele: aa Recessive allele: aa Unable to produce pigmentation in hair & skin. Unable to produce pigmentation in hair & skin.

Albinism

Cystic Fibrosis Found on chromosome #7. Found on chromosome #7. Very common; Fatal. Very common; Fatal. Recessive: cc Recessive: cc Malfunction in cellular “pumps” causing buildup of liquid in lungs. Malfunction in cellular “pumps” causing buildup of liquid in lungs.

Cystic Fibrosis

Tay-Sachs Disease Recessive allele: tt; Fatal Recessive allele: tt; Fatal Common in Jewish families. Common in Jewish families. Rapid breakdown of nervous system. Rapid breakdown of nervous system.

Sickle Cell Anemia Recessive: ss Recessive: ss Blood disorder. Blood disorder. Connection with malaria. Common in people whose ancestry traces back to Africa. Connection with malaria. Common in people whose ancestry traces back to Africa.

Sickle Cell Anemia

PKU Recessive: pp. Recessive: pp. Causes severe mental retardation. Causes severe mental retardation. No phenylketonuria diet. No phenylketonuria diet.

Huntington Disease Carried on Dominant allele: #4, HH or Hh Carried on Dominant allele: #4, HH or Hh No symptoms until later in life - passed down to children. No symptoms until later in life - passed down to children. Lose control of muscles. Lose control of muscles. Nervous system breaks down. Nervous system breaks down.