Chromosomes

Making and reading karyotypes

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

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.

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

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

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)

Spectral Karyotype

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)

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

Amniocentesis: