Bell Ringer

• What is karyotyping and how is it useful?

Nondisjunction

• The homologous chromosomes, or sister chromatids do not separate properly during cell division.

• This can happen during Meiosis 1 or Meiosis 2

Objectives

• By the end of today you should be able to- Know the difference between somatic cells and gametes- Identify the difference between a diploid cell and a

haploid cell.- Compare the processes of Mitosis and Meiosis

You have two types of cells in your body•Somatic Cells

-body cells- Make up most of your body tissues and organs

•Germ cells-Cells in your reproductive organs that develop into gametes (sex cells)

• Every species has a characteristic number of chromosomes per cell.

Examples: Humans= 46 chromosomes or 23 pairs Dog= 78 chromosomes or 39 pairs Husk Tomato= 24 chromosomes or 12 pairs

Chromosomes 1-22 make up your autosomes ( characteristics not related to your sex)

The 23rd pair of chromosomes are your sex chromosomes. (XX or XY)

Sexual Reproduction

• Involves the fusion of two gametes, resulting in offspring that are a genetic mixture of both parents.

• This fusion is called fertilization. The nuclei of the sperm and egg cell fuse together to form one nucleus.

• Since you are taking DNA from 2 cells and creating one you need half the amount of DNA

Diploid and Haploid Cells

• Diploid Cells- The cell has two copies of

each chromosome; one from the mother , and one from the father

- Body cells-represented as 2n

- Humans cells the diploid number is 46

• Haploid Cells-A cell has only one copy of

each chromosome

-Gametes (sex cells)

-Each human egg or sperm cell has 22 autosomes and 1 sex chromosome

Organism Diploid (2n) Haploid (n)Human 46 23

Chimpanzee 24

Elephant 56

Garden pea 14

Turkey 40

Polar Bear 74

Pineapple 25

Meiosis

• Germ cells in reproductive organs undergo the process of meiosis to form gametes.

• Meiosis is a form of nuclear division that divides a diploid cell into a haploid cell.

Objectives

- What is the difference between somatic cells and gametes

- Identify the difference between a diploid cell and a haploid cell.

- Compare the processes of Mitosis and Meiosis

Objectives

• Illustrate the process of meiosis 1 and describe what is happening

• Describe how crossing over can alter the composition of chromosomes

Meiosis l• Prophase l

-Chromatin Chromosomes-nuclear membrane breaks down-Homologous chromosomes pair up-Crossing over may occur

Meiosis l

• Metaphase l-Homologous chromosome pairs are randomly lined up along the middle-This mixes up the chromosomal combinations and helps create genetic diversity

Meiosis l continued

• Anaphase l-Paired homologous chromosomes separate-Sister chromatids stay together during meiosis l

Meiosis l

• Telophase l-Nuclear membrane forms again-Spindle fibers disassemble- Cell undergoes cytokinesis

End Result is two cells with unique combinations of 23 chromosomes

Objectives

• Illustrate the process of meiosis 1 and describe what is happening

• Describe how crossing over can alter the composition of chromosomes

Objectives

• Illustrate the process of meiosis and describe what is happening• Describe how nondisjunction can alter the number of chromosomes

in a cell• Distinguish between mitosis and meiosis.• Compare and contrast spermatogenesis with oogenesis.

There is no Interphase: Chromosomes do NOT duplicate

Meiosis ll

• Prophase ll-Nuclear membrane breaks downChromosomes condense-Centrioles move to opposite sides of cell-spindle fibers assemble

• Metaphase ll-Spindle fibers align the 23 chromosomes in the middle-Each chromosome still has 2 sister chromatids

Meiosis ll

• Anaphase ll-The sister chromatids are pulled apart to opposite sides of the cell

• Telophase ll-nuclear membranes reform-spindle fibers break apart-The cell undergoes cytokinesis

CytokinesisThe end result is four haploid cells with a combination of chromosomes

from both the mother and the father.

Spermatogenesis

Oogenesis

Nondisjunction- The homologous chromosomes, or sister chromatids do not separate properly during cell division.

Meiosis 1

Meiosis 2

Objectives

• Illustrate the process of meiosis and describe what is happening• Describe how nondisjunction can alter the number of chromosomes

in a cell• Distinguish between mitosis and meiosis.• Compare and contrast spermatogenesis with oogenesis.