Cell Reproduction

1
Cell Reproduction

• Chapter 8

2
Chromosomes

• Chapter 8
• Section 1

3
DNA and Chromosomes

• DNA is a long, thin molecule that stores genetic
  information.
• Inside the nucleus, the DNA is coiled and packed
  into very compact structures called chromosomes.

Fruit Fly
Fruit Fly Chromosomes
4
Chromosomes

• In eukaryotes, the genetic information is passed
  from each generation of cells to another by a
  chromosome.
• Chromosomes are made up of DNA and proteins.
• The cells of every organisms has a specific
  number of chromosomes.
• How many chromosomes do humans have?
• 46 chromosomes

5
Chromosome Formation
Histone Proteins
6
Chromosomes and Chromatids

• Before cell division, each chromosome is
  replicated, or copied.
• Chromosomes consist of two identical sister
  chromatids.
• When the cell divides, the sister chromatics
  separate from each other.
• One chromatid goes to each side of the two new
  cells.

7
Chromatids

• Each pair of chromatids is attached at an area
  called the centromere.

8
Chromosome Numbers

• Each species has a characteristic number of
  chromosomes.
• Potatoes? 48 chromosomes
• Horse? 64 chromosomes
• Sand dollar? 52 chromosomes
• Dog? 78 chromosomes
• Cat?32 chromosomes
• Fruit fly? 8 chromosomes

9
Types of Chromosomes

• Sex chromosomes determine the sex of an organism
  and they may also carry genes for other
  characteristics.
• In humans, sex chromosomes are either X or Y.
• Humans have 46 chromosomes (or 23 pairs), 2 of
  these are sex chromosomes.
• Females normally have two X chromosomes
• Males normally have an X and Y chromosome
• All other chromosomes in organism are called
  autosomes.
• The other 44 chromosomes, or 22 pairs, are
  autosomes.

10

• Every cell of an organisms produced by sexual
  reproduction has two copies of each autosome.
• The organism receives on copy from each parent.
• The two copies of each autosome are called
  homologous chromosomes or homologues.
• Homologues are the same size, shape and carry
  genes from the same trait

11
Karyotype

• Photomicrograph of the chromosomes in a normal
  dividing cell found in a human