• 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

• 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

• Diploid Cells = Cells with the full set of chromosomes– Paired chromosomes

• Half of our chromosomes come from each parent (23 from each parent)

• Somatic (non-sex) cells are diploid

• Created by mitosis• Ex: Skin, Muscle, Nerve,

Blood Cells

Humans have 46 total chromosomes. What is the human diploid chromosome number?

Remember…Diploid = total number of chromosomes

Answer = 46

Humans have 46 total chromosomes. 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

Humans have 46 total chromosomes. 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 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)

Humans have 46 total chromosomes. What is the human haploid chromosome number?

Remember…Haploid = half number of chromosomes

Answer = 23 chromosomes

Humans have 46 total 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

Humans have 46 total chromosomes. 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

Down Syndrome: What’s Wrong?

• Writing notation:– 1st: total

chromosome #– 2nd: Sex

chromosomes– 3rd: 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

• 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