Defined: Tightly coiled DNA Forms during cell division –New chromosomes created for new cells 2 Parts: –1) Chromatids: two identical parts of a chromosome –2) Centromere: Joins chromatids together

Chromosomes condense at the start of mitosis. DNA wraps around proteins (histones) that condense it. DNA double helix DNA and histones Chromatin Supercoiled DNA

Defined: Picture of an individuals chromosomes –Identify sex & chromosome defects Size of final pair identifies sex –Same size: XX = female –Different size: XY = male Normal human will have 46 chromosomes

Down Syndrome: What’s Wrong? Writing notation: –1 st : total chromosome # –2 nd : Sex chromosomes –3 rd : extra or missing Down Syndrome: 47, XY, +21

Turner’s Syndrome: What’s Wrong? Write the notation for Turner’s Syndrome. 45, X, -23 or 45, XO, -23

Patau’s Syndrome: What’s Wrong? Write the notation for Patau’s Syndrome. 47, XY, +13

Klinefelter’s Syndrome: What’s Wrong? Write the notation for Klinefelter’s Syndrome. 47, XXY, +23

Body cells are diploid; gametes are haploid. Fertilization between egg and sperm occurs in sexual reproduction. Diploid (2n) cells have two copies of every chromosome. –Body cells are diploid. –Half the chromosomes come from each parent.

Diploid Cells = Cells with the full set of chromosomes –Paired chromosomes Somatic (body, or non- sex) cells are diploid Created by mitosis Ex: Skin, Muscle, Nerve, Blood Cells

What is the human diploid chromosome number? Remember…Diploid = total number of chromosomes Answer = 46

What is the human somatic chromosome number? Remember…Somatic cells are non-sex cells… …Somatic cells are diploid… …Diploid cells have the full set of chromosomes Answer = 46

How many chromosomes are in brain cells? Remember…Brain cells are non-sex cells… …Somatic cells are non-sex cells… …Somatic cells are diploid… …Diploid cells have the full set of chromosomes Answer = 46

Haploid (n) cells have one copy of every chromosome. –Gametes are haploid. –Gametes have 22 autosomes and 1 sex chromosome.

Haploid Cells = Cells with ½ the total number of chromosomes Gametes (sex cells) are the only haploid cells –Ex: Sperm, Egg, Pollen Chromosome number is reduced by meiosis How do humans get 46 chromosomes? Haploid sperm cell (23) + Haploid egg cell (23) = Diploid zygote (46)

What is the human haploid chromosome number? Remember…Haploid = half number of chromosomes Answer = 23 chromosomes

What is the human gamete chromosome number? Remember…Gamete cells are sex cells… …Sex cells are haploid… …Haploid cells have ½ the set of chromosomes Answer = 23

How many chromosomes are in female egg cells? Remember…Egg cells are sex cells… …Sex cells are gametes… …Gamete cells are haploid… …Haploid cells have ½ the set of chromosomes Answer = 23

What is the diploid chromosome number? 42

What is the haploid chromosome number? 21

How many chromosomes would be in somatic cells? 42

How many chromosomes would be in brain cells? 42

How many chromosomes would be in gamete cells? 21

How many chromosomes would be in egg cells? 21

How many chromosomes would be in muscle cells? 42

How many chromosomes would be in sperm cells? 21

Is this a male or female rat? male

Quick Review Chromsomes are tightly coiled strands of DNA Diploid (somatic) cells contain the entire set of chromosomes Haploid (gametes) cells contain only ½ the total number of chromosomes