1. The Chromosome

2. Keypoint # 1: Each chromosome is a tightly coiled string of DNA
Each chromosome is made out of ONE long piece of DNA packed into a tight shape
Why coiled? Because each DNA strand can stretch out to 5 FEET LONG when unwinded.
Chromosomes are the unit of heredity, they need to be passed from one generation to the next

3. Chromosomes are found in two shapes
A chromosome can be two columns of DNA joined in the middle by a centromere to look like a big X (normal)
When it looks like a big X, the left and right are identical to each other (same genes)
A chromosome can be one column of DNA (after meiosis- we will get to this!)
same gene
Each of these are considered ONE chromosome

4. Keypoint #2: Genes are the sections of chromosomes that code for traits
Each chromosome has its own set of GENES
Genes = sections of DNA that code for traits
Traits = expressions of your genes in the body (like eye color, blood type, ear lobe size, etc)
brown hair gene
Type A blood gene

5. egg cell and sperm Cells
Keypoint #3: There are two categories of cells in the body: Somatic and Sex Cells
Somatic cells = BODY CELLS. All of the cells in your body other than sex cells.
Sex Cells (gametes) = sperm in males; egg cells in females
muscle cells
lung tissue cells
brain cells
egg cell and sperm Cells

6. Keypoint # 4: Somatic cells are Diploid and sex cells are Haploid
Diploid(2n)= 2 of each chromosome. All somatic cells are diploid.
D = double the # of chromosomes
Haploid (n) = 1 of each chromosome. All sex cells (gametes) are haploid
H = half the # of chromosomes

7. Chromosome Numbers Review
One set of chromosomes is represented by the letter n
Haploid Cells (gametes) = n chromosomes
Diploid Cells (somatic cells) = 2n chromosomes

8. In humans: There are 23 pairs of Chromosomes in every somatic cell
Every person gets a set of 23 chromosomes from each parent
23 from mom from dad = 46 total (DIPLOID)!
images showing all 23 pairs (46) are called Karyotypes

9. In humans: There is one set of 23 chromosomes in every sex cell
There are 23 chromosomes in a sperm cell (male gamete)
There are 23 chromosomes in an egg cell (female gamete)
Only 23 chromosomes in a cell = HAPLOID

10. Every pair of chromosomes is unique
Each pair of chromosomes has their own set of genes that are always on that # chromosome
ex: Chromosome #19 always has the gene for hair color (you have two #19- one from mom and one from dad)
The Special #23 pair: XX or XY
X and Y = Sex chromosomes
Y + X = male
X + X = female
male or female?

11. Guided Practice Each chromosome is made of ____(#) strand of ________
Chromosomes have sections called ________ that code for ________ which are expressions of genes

12. # of chromosomes in humans
Somatic Cells
Sex Cells (gametes)
What kind of cells?
# of chromosomes in humans
Haploid (n) or Diploid (2n)