1. Making and reading karyotypes
Chromosomes
Making and reading karyotypes

2. Homologous Chromosomes:
Members of a pair of chromosomes
Same size
Same shape (centromere location)
Same number and type of genes
One came from mother, one from father

3. Homologous Chromosomes:
Specific gene information may differ (ex = brown eyes from mom, blue eyes from dad)
Same banding pattern when stained and viewed under a microscope. Bands DO NOT indicate genes.

4. Types of Chromosomes:
Humans have 23 pairs of chromosomes. Chromosomes can be divided into 2 types.
Autosomes:
Members of chromosome pairs #1-22.
Sex Chromosomes:
Members of chromosome pair #23
Females = XX
Males = XY

5. Sex Chromosomes
ALL pairs are homologous in females because they have two X chromosomes
The sex chromosomes of males are NOT homologous, they have one X and one Y

6. Karyotype: A picture of an individual’s chromosomes
Can be done before or after birth
Cells are removed from the amniotic fluid or chorionic villi before birth, grown in a lab and forced to divide (chemically)
Chromosomes are BEST seen during mitosis b/c they are duplicated and condensed
Chromosome pairs are matched up (now done by computer, formerly by cutting up a micrograph and doing it by hand)

8. Spectral Karyotype

9. What a karyotype can tell you:
Gender
Diagnose chromosomal disorders due to
Extra chromosome (trisomy)
Missing chromosome (monosomy)
Broken chromosomes
Piece could be totally missing (deletion)
Piece of one chromosome fused to another (translocation)
Piece could be flipped around (inversion)

10. What can’t you tell from a karyotype:
The form of the genes on the chromosomes
CANNOT determine particular traits such as hair color or eye color
CANNOT determine single gene disorders such as cystic fibrosis, sickle cell anemia, dwarfism, or Tay Sachs disease

12. Amniocentesis: