Meiosis

Review

1. Put the above steps in order with the NUMBER and NAME of each step.

2. What is the name of this cell division?3. What type of reproduction is this?4. How many daughter cells are produced?5. How many cell divisions occur?

12 3

45

Important Vocabulary

• Chromosomes: tightly coiled DNA in nucleus

• Genes: Sections of chromosomes (DNA) that code for a specific protein which determines a specific trait

Homologous Chomosomes

• Homologous: same

• Homologous chromosomes: Chromosomes of the same length with the same gene types, but 1 is from the mother and 1 is from the father

• Humans have 23 homologous chromosome pairs

Think about it…

• What would happen if your Mom and Dad gave you a full set of 46 chromosomes?

• Are you made from sexual or asexual reproduction?

• How many chromosomes are you getting from your Mom? Dad?

Haploid

• Haploid: 1 set of chromosomes from one parent – Represented by the letter “n”– “n” for humans = 23 chromosomes

• We have 46 total and half come from each parent• We have a haploid number of chromosomes in egg and

sperm cells• MEMORY TRICK: Haploid = HALF

• Example: If an alligator has 50 total chromosomes, what is the HAPLOID number?

Diploid

• Diploid: 2 set of chromosomes, one set from each parent– Represented by the letter “2n”– “2n” for humans = 46 chromosomes

• We have 46 total chromosomes in our SOMATIC (body cells)• MEMORY TRICK: Diploid = DOUBLE

• Example: If a rat has 20 chromosomes in its sperm cell, how many chromosomes are in the body cell?

Types of Cells• Somatic Cells: “BODY CELLS” – Cells NOT for reproduction– Made by MITOSIS cell division (asexual

reproduction)– Are DIPLOID (2 set of chromosomes)

• Also known as “2n”

– Examples:• Animals: all tissues form non-sex organs (skin cells, liver

cells, tongue cells, etc.)• Plants: leaves, roots, stems, Tissues from non-sex organs!

• Gamete Cells: “SEX CELLS”– Cells specifically for reproduction– Made by MEIOSIS cell division (sexual

reproduction)– Are HAPLOID (1 set of chromosomes)• Also known as “n”

– Examples:• Animals: sperm (male) and egg (female)• Plants: pollen (male) and ovule (female)

Meiosis• Produces GAMETE CELLS (sex cells)• The whole reason for meiosis is for SEXUAL

REPRODUCTION to take place. • Gametes have a HAPLOID number of

chromosomes– so they can come together to form a new offspring.

• Meiosis occurs in all organisms with many cells:– Humans– Animals – Plants

Key Facts about Meiosis

• DNA REPLICATES before division• # of divisions: 2• # of daughter cells: 4• Daughter cells are NOT IDENTICAL (genetic

variation!)

Mitosis vs. Meiosis

Mitosis vs. Meiosis

Cell Type Gametes Cells Somatic Cells

Body or Sex Cells?

Made by what type of cell division (mitosis or meiosis)?

Haploid or Diploid?

Number of chromosomes (2n or n)?

# of chromosomes in humans?

Animal Examples

Plant Examples

Number of cell divisions?

Genetic stability or variation?

Type of reproduction (asexual or sexual)?

Steps to Sexual Reproduction Male Human Female Human(testes) (ovaries)

Gamete Gamete (sperm) (egg)

Fertilization

Zygote

Death

MEIOSIS MEIOSIS

MITOSIS

MITOSIS

Memory Trick

MITOSISM = MakesI = IdenticalT = TwinsOSIS

1 diploid parent 2 diploid daughter cells

MEIOSISM = MakesE = EggsIOS = SpermIS

1 diploid parent 4 haploid daughter cells

Think-Write-Pair-Share

1) Describe a pollen cell from a flower. For this particular flower, a pollen cell has 10 chromosomes. In your Response, use the following terms. For some terms, you may not use them because they do not apply to a pollen cell: 2n/n, haploid/diploid, gametes/somatic cell, mitosis or meiosis, sexual/asexual.

Think-Write-Pair-Share

2) Describe a skin cell from a human. In your response, use the following terms: 2n/n, haploid/diploid, 23 or 46 chromosomes, gametes/somatic cell, homologous chromosomes, mitosis/meiosis, sexual/asexual.

Let’s try it…

1) A diploid cell of a mouse contains 12 chromosomes. How many chromosomes will be found in a haploid cell of a mouse?

2) The diploid cell of a bird contains 16 chromosomes. How many chromosomes will be found in the sperm cell?