1. Chromosomes

2. What is a Chromosome?
Chromosomes are rod-shaped structures made of DNA and proteins
DNA is a long, thin molecule that stores genetic information

3. When and how do chromosomes form?
Chromosomes form during cell division when the DNA is compacted
DNA wraps tightly around proteins called histones, which maintain the shape of the chromosome and assist in the tight packing of DNA.
DNA
Histone

4. Duplicated chromosome ½ of duplicated chromosome = chromatid
Chromosomes
Each half of a duplicated chromosome is identical to the other, and each half is called a chromatid.
The constricted area of each chromatid is the centromere, which holds the 2 chromatids together until separation during cell division.
The centromere is important in moving the chromosomes during cell division
The ends of each chromosome has a similar sequence those ends are called telomeres
Duplicated chromosome
½ of duplicated chromosome = chromatid

5. Prokaryotes Chromosomes are much simpler
DNA is made of only 1 chromosome, which is circular-shaped
Very compact in order to fit into the cell.

6. Eukaryotes
Each species has a characteristic chromosome number in each cell.
For Example:
Dog 78
Human 46
Gorilla 48
Cat 32
Fern
1,262

7. 2 Major Types of Chromosomes
Sex Chromosomes determine the gender of the organism
For humans they are X or Y:
Females =
Males =
2 of the 46 chromosomes are this type in humans
Autosomes consist of all the other chromosomes in an organism.
44 of the 46 are this type in humans
The 44 = 2 copies of the same 22 chromosomes; 1 came from the mom and 1 came from the dad. Therefore 22 autosomes came from mom and 22 came from dad.
Two copies of each autosome are called homologous chromosomes or homologues. They are the same size and shape and carry the genes for the same traits. XX XY

8. Homologous Chromosomes or Homologues
Two Copies of the same chromosome

9. Where as this gene might code for blue eyes
Homologues do not have identical coding but have the same genes that code for the same traits
For Example:
This gene might code for brown eyes (the trait being eye color)
Where as this gene might code for blue eyes

10. Karyotype
A Karyotype is a visual representation in an organized form of chromosomes in an organism.
Arranged by size of autosomes from longest to shortest, leaving the sex chromosomes last

11. Chromosomes
When a cell has two sets of chromosomes, it is diploid, which means the cell has both chromosomes for each homologous pair
Ex. All normal body cells (somatic cells) are diploid.
Commonly abbreviated as 2n.
For humans, the diploid number 46.
When a cell only has one set of the chromosomes, it is haploid, which means the cell only has one copy of each chromosome for each homologous pair.
Ex. Sperm and Egg cells (Gametes / Sex Cells)
Commonly abbreviated as n.
For humans, the haploid number is 23.

12. (For a normal healthy organism barring chromosomal disorders)
Diploid (2n)
Haploid (n)
Human
Fruit Fly
Garden Pea
????? 46 23 8 4 20 10 17
Will Not Happen
The Diploid number of chromosomes must be _____, but the haploid number can be _____ or ____
(For a normal healthy organism barring chromosomal disorders)
EVEN
EVEN
ODD

13. Why do the reproductive cells need to be haploid and not diploid?
Using Humans as the example if you had mom give 46 chromosomes and dad give 46 chromosomes then the baby would have 92 chromosomes which is not the correct number of chromosomes for a human. Therefore the reproductive cells must be half the number of the normal cells. 46 46 23 23 92 46