Human Genetics – Studying Chromosomes & Diseases

Human Chromosomes In humans, there are 23 pairs of chromosomes autosome 22 autosome pairs Contain genes that code for normal, human traits Ex: eye color Chromosomes 1-22 sex chromosome 1 sex chromosome pair Chromosomes that determine sex Females = XX, Males = XY Chromosome 23 Total chromosomes = 46

How is sex determined? Eggs = 22 autosomes, 1 sex chromosome (X) Sperm = 22 autosomes, 1 sex chromosome (X or Y) So who determines the sex of the baby? The sperm determines the sex of the baby

Studying Human Chromosomes Karyotype A picture of the paired chromosomes, arranged in order from largest to smallest

Karyotypes, cont. Karyotypes can be obtained by: Blood samples Amniocentesis Cells in the fluid around the unborn baby are analyzed

Chromosomes fail to separate properly during meiosis (called nondisjunction) Results in too few or too many chromosomes in offspring Often fatal, but some exceptions

Trisomy- Extra Chromosome Autosomy- Missing Chromosome

Trisomy 21 – Downs Syndrome Tri = 3, so Trisomy 21 is 3 chromosome 21’s Mental impairment Upward-slanted eyes Slightly flattened facial features

Trisomy 18 – Edward’s Syndrome Most die before birth; those born die within 2 months Heart abnormalities Difficulty breathing Small in size

die within their first days or weeks of life Only 5-10 % of children with this condition live past their first year 1/20,000 heart defects brain abnormalities poorly developed eyes extra fingers and/or toes cleft palate weak muscle tone Trisomy 13 – Patau’s Syndrome

Klinefelter Syndrome Males with 2 X chromosomes (XXY) Male appearance Learning disabilities Some feminine traits (breasts, higher pitched voice) Sperm count is low Hormone injections can help

Turner’s Syndrome 98% spontaneous abortion Have single X but no other sex chromosome (XO) Female appearance Tend to be short Affects sexual development (no ovaries) Hormone injections help

Translocations A piece of a chromosome connects to a different chromosome

Whole-chromosome painting probes: Ch 10 (red) and 17 (green) Arrows: translocation chromosomes

Deleted Chromosomes Cri-du-chat Doctors most often identify cri-du-chat by the infant's cat-like cry. Other signs are microcephaly, poor muscle tone, and mental retardation.

Fragile X Syndrome Moderate to severe mental retardation Speech delay, short attention, hyperactivity Poor motor coordination and mouthing objects Poor socialization, temper tantrum Mood disorder (bipolar), schizophrenia

Microdeletion Syndromes Williams-Beuren Syndrome (WBS) 1/20,000 all populations Phenotype Dysmorphic facies Growth and mental retardation Distinctive personality Transient hypercalcemia Arterial disease “uniform” 1.5 MB deletion del(7)q11.23 Region flanked by duplicated genes---non- homologous recombination 17 genes including ELN, which encodes tropoelastin (point mutation causes AD supravalvular aortic stenosis)

45,XX,der(14;21)(q10;q10)

46,XX,t(4;15)(q2?1.3;q13)

46,XX,t(9;22)(q34;q11)

46,X,r(X)

ins(22;9)(q11;q13q34)

46,XY.ish del(15)(q11.2q11.2)(SNRPN-)

46,XX.ish del(22)(q11.2q11.2)(TUPLE1-)

46,X,del(X)(p21.1)

46,XX,del(4)(p15.2p16.?2)