1. Nondisjunction and Karyotypes

2. Nondisjunction = having too few or too many chromosomes
When chromosomes are not distributed correctly in meiosis

3. Results of nondisjunction after fertilization:
Normal = a diploid cell with 2 of each chromosome

4. Results of nondisjunction after fertilization:
Monosomy = a diploid cell is missing a chromosome in one chromosome pair
Example: Turner Syndrome
(One X chromosome)

5. Results of nondisjunction after fertilization:
Trisomy = a diploid cell has an extra chromosome in one chromosome pair
Examples: Down Syndrome
(Trisomy 21)
Klinefelter Syndrome
(XXY)

6. Human Karyotyping Two ways to obtain chromosomes from the fetus:
Amniocentesis = removing amniotic fluid that contains cells from the fetus from the amniotic sac which surrounds the fetus during development using a syringe
Chorionic villi sampling (CVS) = removing cells from the chorionic villi (fingerlike extensions of the placenta that grow in the mother’s uterus)

7. Karyotype = representation of chromosomes in metaphase of mitosis
Arranged in homologous pairs by size
22 pairs are autosomes
1 pair are the sex chromosomes
(XY male or XX female)
=23 pairs (46 chromosomes)
Looking for abnormalities –sets that do not have 2 chromosomes

8. Chromosome Pair Affected # of Total Chromosomes in a cell
Nondisjunction in Humans:
Chromosome Pair Affected
# of Total Chromosomes in a cell
Clinical Syndrome
Estimated Frequency at Birth
Symptoms
Trisomy of chromosome 21 47
Down Syndrome
1/700
Short, broad hands with a single crease across the palm, short stature, hyperflexibility of joints, mental retardation, small head with flattened face, slanting eyes, large tongue X 45
Turner Syndrome
1/2500 female births
Female that do not fully develop sexual characteristics, usually sterile, short stature, webbing of skin in the neck, hearing impairment, heart abnormalities
XXY
Klinefelter Syndrome
1/500 male births
Male with small testes, infertile, developed breasts, feminine-pitched voice, long legs
XXX
Triplo-X
Female with normal genitalia, limited fertility, slight mental retardation