karyotyping. karyotypes chromosomes are distinguished by their appearance –size –position of...
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Karyotyping
Karyotypes
• Chromosomes are distinguished by their appearance– size – position of centromere– pattern of bands (when stained)
• Karyotypes show us there are 2 of each type of chromosome
Karyotypes
• What is a karyotype?– Micrograph (picture) of chromosomes
entered into computer– Chromosomes electronically arranged
into pairs based on appearance (reference above)
– The resulting picture is a karyotype
Chromosome Pair 23:
Sex chromosome
Chromosome Pairs 1-22: Autosomes
Note: Exception to rule is chromosome pair 23 if the person is male (XY).
The Human Genome (I)• Consists of 23
pairs of chromosomes.
• Chromosomes 1 through 22 are called autosomes.
• The X and Y chromosomes are the sex chromosomes.
– Males are XY. – Females are XX.
KaryotypingAs a Laboratory Technique for Disease Diagnosis
• Typical human cells contain 23 pairs of chromosomes.
• Variations in the number or structure of human chromosomes can cause a variety of genetic disorders.
• Variations in the number of chromosomes within a cell are called aneuploidies.
Non-Disjunction• Incorrect separation of chromosomes or
chromatids in meiosis known as non-disjunction
• Most embryos arising from gametes with abnormal chromosome numbers abort spontaneously (are miscarried)
• Some combinations of abnormal chromosome number survive to birth or beyond
Down Syndrome
• Trisomy 21– 3 copies of
chromosome 21• Characteristics
– facial features– short stature – heart defects– mental disabilities
• Statistics– 1 in 800– f increases w/age
Autosomal Nondisjunction
Incidence of Down Syndrome
1010 2020 3030 4040 505000
100100
200200
300300
400400
Age of Mother (years)Age of Mother (years)
Num
ber p
er 1
000
Birt
hsN
umbe
r per
100
0 B
irths
Sex Chromosome Nondisjunction
**this table will be in the lab today to help you determine each karyotype
Genotype Gender Syndrome Physical Traits
XY Male None-normal
XXYXXYYXXXY
Male Klinefelter’s Syndrome
sterility, small testicles, breat enlargement
XYY Male XXY Syndrome normal male traits
XX Female None-normal
XO Female Turner Syndrome
sex organs don’t mature at adolescence, sterility, short stature
XXX Female Trisomy X tall stature, learning disabilities, limited fertility
Fetal TestingTest Benefit RiskAmniocentesis Diagnosis of:
•chromosome abnormalities•other defects
•discomfort•infection•miscarriage
Chorionic villus sampling
Diagnosis of:•chromosome abnormalities•genetic defects
•miscarriage•infection•newborn limb defects
Fetal blood sampling
Diagnosis of:•genetic or chromosome abnormality•fetal blood problems and O2 levels•medications to fetus before birth
•bleeding from sample site•infection•amniotic fluid leak•fetal death