1. How our genes are organized
chromosomes
How our genes are organized

2. Review of key terms:
Gene
Chromosome
Chromatid
Homologous chromosome

3. What are chromosomes?
All eukaryotic cells store genetic information in chromosomes.
Most eukaryotes have between 10 and 50 chromosomes in their body cells.
Human cells have 46 chromosomes
23 pairs

4. Structure of chromosomes
Complex of DNA and protein called chromatin
Condenses during cell division
DNA exists as a single, long, double-stranded fiber
Organized in coils
DNA is wrapped around proteins called histones

5. Sets of chromosomes
Homologous chromosomes: chromosomes that are similar in size, shape and genetic content
Each homolog (individual
chromosome) in a pair come
from one of the two parents

6. Chromosome replication (S phase)
Each condensed chromosome consists of 2 identical chromatids joined by a centromere.

7. Types of chromosomes
Autosomes: chromosomes that are not directly involved in determining the sex of an individual
Sex chromosomes: pair of chromosomes directly involved in determining the sex of an individual

8. Types of chromosomes Autosomes: 22 pairs Sex chromosomes: 1 pair
Referred to as X and Y chromosomes in humans

9. Karyotype: a snapshot of our chromosomes
Each of the 23 pairs of chromosomes consists of two homologous chromosomes
Arranged by size in
in descending order
A picture of the chromosomes is called a KARYOTYPE

10. Using a Karyotype
A karyotype allows a cytogeneticist or lab technician to examine the chromosomes and see if there is anything extra or missing or if the structure is different
Sometimes there is an obvious abnormality, but other times it takes very careful observation to spot something