BIOL 1010 Lecture Notes - Lecture 7: Xyy Syndrome, Neural Tube Defect, Triple X Syndrome
Human Genetics
October 14, 2014
The human karyotype consists of both autosomes and sex chromosomes. If a trait is
on one of the sex chromosomes it is sex-linked.
• 22 pairs of homologous chromosomes exactly in both male and female
karyotypes
• There are one pair of sex chromosomes in mammals
o XX- female
o XY- male
Classification of Genetic Disorders:
• Multifactorial
o Examples:
Congenital Malformations: cleft lip, heart defects, and neural tube
defects.
Incidence: 1/250-600 with ethnic variation
Cancers: multiple causes including genetic disposition
Incidence: >1/3 (exclusive of skin cancer)
Coronary Heart Disease: multiple causes including genetic
disposition. Incidence: variable but up to 1/15 in Western populations
• Chromosomal
o Examples:
Down Syndrome (Trisomy 21): additional Trisomy 21
Incidence: 1/800
3% of down syndrome cases is due to translocation of a part of
chromosome 21 onto another chromosome
XYY Syndrome: additional Y chromosome
Incidence: 1/1000 males
o Caused by nondisjunction during meiosis!
▪ Homologous chromosomes don’t separate in meiosis I
▪ Sister chromatids don’t separate in meiosis II
o Non-disjunction gives rise to:
▪ Monosomics – lack a single copy of a chromosome
▪ Trisomics – carry an additional copy of a chromosome
o Nondisjunction of Sex Chromosomes:
Klinefelter Syndrome (XXY): sterile male with female body. 1/1000
Turner’s Syndrome X: sterile female, short stature, immature sex
organs. 1/5000 births
XYY Syndrome: associated with behavioral difficulties; fertile (male).
1/1000
XXX Syndrome: associated with learning difficulties; fertile (female).
1/1000
find more resources at oneclass.com
find more resources at oneclass.com
Document Summary
The human karyotype consists of both autosomes and sex chromosomes. If a trait is on one of the sex chromosomes it is sex-linked: 22 pairs of homologous chromosomes exactly in both male and female karyotypes, there are one pair of sex chromosomes in mammals, xx- female, xy- male. Congenital malformations: cleft lip, heart defects, and neural tube defects. Coronary heart disease: multiple causes including genetic disposition. Incidence: variable but up to 1/15 in western populations: chromosomal, examples: 3% of down syndrome cases is due to translocation of a part of chromosome 21 onto another chromosome: caused by nondisjunction during meiosis! Klinefelter syndrome (xxy): sterile male with female body. Turner"s syndrome (cid:523)x(cid:524): sterile female, short stature, immature sex organs. Xyy syndrome: associated with behavioral difficulties; fertile (male). Xxx syndrome: associated with learning difficulties; fertile (female). Incidence: 1/2000 in caucasian populations (very rare in asians) Incidence: 1/3000 males (rare in females) (untington"s disease: autosomal dominant, late onset.
