How our genes are organized chromosomes How our genes are organized

Review of key terms: Gene Chromosome Chromatid Homologous chromosome

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

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

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

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

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

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

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

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