Chromosomes

DNA STORAGE STRUCTURE Eukaryotic cells have their DNA in structures called chromosomes stored in the nucleus.Eukaryotic cells have their DNA in structures called chromosomes stored in the nucleus. A cell’s chromosomes

Chromosome Structure Chromosomes:Chromosomes: –Contains a single DNA molecule. –Have the DNA wrapped around proteins called histones. Chromosome structure

Chromosome condensation Chromosomes condense only for cell reproduction.Chromosomes condense only for cell reproduction. Condensation:Condensation: –Twist –Become shorter –Become thicker –Become visible Chromosomes can be moved about cell easier.Chromosomes can be moved about cell easier. Chromosome condensation

Chromosome replication Before cells divide chromosomes replicate so each daughter cell has a complete set of DNA.Before cells divide chromosomes replicate so each daughter cell has a complete set of DNA. Each copy is called a chromatid.Each copy is called a chromatid. Sister chromatids are connected by a centromereSister chromatids are connected by a centromere

Chromosome pairs Chromosomes are arranged in pairs called homologous pairs.Chromosomes are arranged in pairs called homologous pairs. In humans one pair determines sex: sex chromosomes.In humans one pair determines sex: sex chromosomes. All other chromosomes are called autosomes.All other chromosomes are called autosomes.

Sex Chromosomes Either X or Y.Either X or Y. –XX creates female. –XY creates male. Sex Chromosomes

Haploid Vs Diploid Haploid: Having one of each chromosome. Sperm/ pollen and egg (gametes)Haploid: Having one of each chromosome. Sperm/ pollen and egg (gametes) Diploid: having a pair of chromosomes. All cells except gametes have pairs of chromosomes.Diploid: having a pair of chromosomes. All cells except gametes have pairs of chromosomes. Human sperm at the surface of an egg

Chromosome Numbers Each species has characteristic number of chromosomes.Each species has characteristic number of chromosomes. –Humans = 46 –Fruit flies = 8 –Crayfish = 200 –Chimpanzee = 48 Fruit fly chromosomes

White board review 1.When DNA replicates what are the copies of the chromosomes called? 2.What are the 2 types of chromosome pairs called? 3.What does haploid mean?