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