CHROMOSOMES

How is DNA stored? All of the DNA in one human cell is 3 meters long end to end! A single cell is microscopic – how does that much DNA fit??

Chromatin DNA is wrapped around proteins Molecule is more compact http://www.johnkyrk.com/chromosomestructure.html

Chromatin Chromatin can be loosely or tightly coiled Loose = active genes, lots of transcription Tight = less active genes, little transcription http://www.johnkyrk.com/chromosomestructure.html

Histones The proteins around which DNA is coiled to form chromatin. Grouped into units of eight histones (AKA octamer) Each unit of a histone octamer and its DNA is called a nucleosome.

Chromosomes A form of DNA storage Chromatin is coiled to make a chromatin fiber Fibers are looped and coiled to make dense tube-shaped structures

Chromatin vs. Chromosomes Chromatin is how DNA is stored for most of a cell’s life Need easy access to active genes for making proteins Chromosomes form just before a cell divides Easy to sort and separate when in compact units

Parts of a chromosome Centromere = specific genetic sequences marking the center of the chromosome Telomeres = specific genetic sequences marking the ends of the chromosome

How many do we have? What’s your guess?

How many do we have? Humans have 23 PAIRS of chromosomes (46 total)

How many do we have? Humans have 23 PAIRS of chromosomes (46 total) Mouse = 20 pairs Chicken = 39 pairs Tomato = 12 pairs

How many do we have? Humans have 23 PAIRS of chromosomes (46 total) Mouse = 20 pairs Chicken = 39 pairs Tomato = 12 pairs Do you think that having more chromosomes means you are a more complex organism? Why or why not?

Why pairs? Why is it that chromosomes can be paired together?

Why pairs? One chromosome from Mom and one from Dad!

Why pairs? One chromosome from Mom and one from Dad! Homologous chromosomes = chromosomes that share the same sets of genes but the genes may have different variations EX: these chromosomes both have the hair color gene but mom’s chromosome is for brown hair and dad’s chromosome is for blond hair.

Sex chromosomes X and Y Females have ________ Males have ________

Sex chromosomes X and Y Females have XX Males have XY

Chromosomes & Evolution http://www.pbs.org/wgbh/nova/education/evolution/human-chromosome-2.html

EXIT TASK What do you call the proteins around which DNA wraps itself to form chromatin and chromosomes?