1. How many chromosomes would a sperm or an egg contain if either one resulted from the process of mitosis?

Interest Grabber

1. How many chromosomes would a sperm or an egg contain if either one resulted from the process of mitosis?

Interest Grabber

46 chromosomes

2. If a sperm containing 46 chromosomes fused with an egg containing 46 chromosomes, how many chromosomes would the resulting fertilized egg contain? Do you think this would create any problems in the developing embryo?

Interest Grabber

2. If a sperm containing 46 chromosomes fused with an egg containing 46 chromosomes, how many chromosomes would the resulting fertilized egg contain? Do you think this would create any problems in the developing embryo?

Interest Grabber

46 + 46 = 92; a developing embryo would not survive if it contained 92 chromosomes.

3. In order to produce a fertilized egg with the appropriate number of chromosomes (46), how many chromosomes should each sperm and egg have?

Interest Grabber

3. In order to produce a fertilized egg with the appropriate number of chromosomes (46), how many chromosomes should each sperm and egg have?

Interest Grabber

Sperm and egg should each have 23 chromosomes.

MEIOSIS10.1

Making gametes…

All living things…reproduce.

ASEXUAL REPRODUCTION

Bacteria reproduce using binary fission

Budding and regeneration are used by plants and animals to reproduce asexually (mitosis)

BINARY FISSION & MITOSIS

Produces cells that are identical copies of parent cells.

ADVANTAGES OF ASEXUAL REPRODUCTION

• Can make offspring faster

• Don’t need a partner

DISVANTAGES OF ASEXUAL REPRODUCTION

• All offspring are alike

• Species cannot adapt and change

• One disease can wipe out whole population

SEXUAL REPRODUCTION

Combines the genetic material from two parents (sperm and egg) so offspring are genetically different.

ADVANTAGES OF SEXUAL REPRODUCTION

• Allows for variation in population

• Individuals can be different

• Provides foundation for EVOLUTION

• Allow species to adapt to changes in their

environment

EGG + SPERM

If egg and sperm had same number of chromosomes as other body cells . . .

…baby would have too many chromosomes!

MEIOSIS is the way…to make cells with half the number of chromosomesfor sexual reproduction

DIPLOID & HAPLOIDMost cells have 2 copies of each chromosome

(one from mom; one from dad)These cells are diploid (2n) and are called:

Body cells (aka somatic cells) are diploid (2n)

HOMOLOGOUSCHROMOSOMES

HOMOLOGOUS CHROMOSOMES• Same size• Same shape• Carry genes for the same

trait• But are NOT identical! (Don’t have to have the

SAME CHOICES)

DIPLOID & HAPLOID

• Some cells have only one copy of each chromosome.

• These cells are haploid (1n)• All sperm and egg cells are haploid

MITOSIS

• Makes 2 cells genetically identical to parent cell and to each other

• Makes 2n cells• Makes somatic (body) cells• Used by organisms to:

– increase size of organism, – repair injuries, – replace worn out cells

MEIOSIS

• Makes 4 cells genetically different from parent cell & from each other

• Makes 1n cells• Makes germ cells or

gametes (sperm & egg)• Used for sexual

reproduction

WHAT MAKES MEIOSIS DIFFERENT ?

1. Synapsis and Crossing over during (PROPHASE I)

1. Segregation and Independent Assortment during (ANAPHASE I)

3. Skip Interphase II (NO Synthesis) CELL DIVIDES TWICE, BUT…

ONLY COPIES DNA ONCE

Homologous chromosomes pair up during Prophase I = Synapsis

This group of FOUR (4)chromatids is called aTetrad.

WHAT MAKES MEIOSIS DIFFERENT? #1

WHAT MAKES MEIOSIS DIFFERENT? #1

Exchange of DNA betweenhomologous pairs = crossing overduring Prophase I

Allows for shufflingof genetic material

CROSSING

OVER

• Allows for rearranging of DNA in different combinations

• After crossing over, chromatid arms are not identical anymore

WHAT MAKES MEIOSIS DIFFERENT? #1

Separation of homologous chromosomes during ANAPHASE I

• Segregation• Independent Assortment

Separates gene choices and allows shuffling of genetic material

WHAT MAKES MEIOSIS DIFFERENT? #2

SEGREGATION(Anaphase I)

WHAT MAKES MEIOSIS DIFFERENT? #2

SEGREGATION & CROSSING OVERtogether make even more combinations

WHAT MAKES MEIOSIS DIFFERENT? #2

INDEPENDENT ASSORTMENT

WHAT MAKES MEIOSIS DIFFERENT? #2

INDEPENDENT ASSORTMENT at ANAPHASE I

Lots of different combinations are possible!This is why you don’t look exactly like your brothers and sisters even though you share the same parents!

WHAT MAKES MEIOSIS DIFFERENT? #2

WHAT MAKES MEIOSIS DIFFERENT recap so far:

• Crossing over, independent assortment and segregation are all ways MEIOSIS results in genetic recombination

• So daughter cells are different from parents and from each other

Skip INTERPHASE II (No Synthesis)CELL DIVIDES TWICE, BUT … …ONLY COPIES ITS DNA ONCE

G1 G2S P M A T C

G1

MITOSIS:

MEIOSIS:

S G2 P M A T CP M A T C

( I )

( II )

WHAT MAKES MEIOSIS DIFFERENT? #3

Go to Section:

Meiosis I

Section 11-4

Figure 11-15 Meiosis

Go to Section:

Meiosis I

Section 11-4

Figure 11-15 Meiosis

Meiosis I

Go to Section:

Meiosis I

Section 11-4

Figure 11-15 Meiosis

Meiosis I

Go to Section:

Section 11-4

Figure 11-15 Meiosis

Meiosis I

Go to Section:

Section 11-4

Figure 11-15 Meiosis

Meiosis I

Go to Section:

Meiosis II

Meiosis I results in two haploid (N) daughter cells, each with half the number of chromosomes as the original.

Prophase II Metaphase II Anaphase II Telophase IIThe chromosomes line up in a similar way to the metaphase stage of mitosis.

The sister chromatids separate and move toward opposite ends of the cell.

Meiosis II results in four haploid (N) daughter cells.

Section 11-4

Figure 11-17 Meiosis II

Go to Section:

Meiosis II

Meiosis I results in two haploid (N) daughter cells, each with half the number of chromosomes as the original.

Prophase II Metaphase II Anaphase II Telophase IIThe chromosomes line up in a similar way to the metaphase stage of mitosis.

The sister chromatids separate and move toward opposite ends of the cell.

Meiosis II results in four haploid (N) daughter cells.

Section 11-4

Figure 11-17 Meiosis II

Go to Section:

Meiosis II

Meiosis I results in two haploid (N) daughter cells, each with half the number of chromosomes as the original.

Prophase II Metaphase II Anaphase II Telophase IIThe chromosomes line up in a similar way to the metaphase stage of mitosis.

The sister chromatids separate and move toward opposite ends of the cell.

Meiosis II results in four haploid (N) daughter cells.

Section 11-4

Figure 11-17 Meiosis II

Go to Section:

Meiosis II

Meiosis I results in two haploid (N) daughter cells, each with half the number of chromosomes as the original.

Prophase II Metaphase II Anaphase II Telophase IIThe chromosomes line up in a similar way to the metaphase stage of mitosis.

The sister chromatids separate and move toward opposite ends of the cell.

Meiosis II results in four haploid (N) daughter cells.

Section 11-4

Figure 11-17 Meiosis II

Go to Section:

Meiosis II

Meiosis I results in two haploid (N) daughter cells, each with half the number of chromosomes as the original.

Prophase II Metaphase II Anaphase II Telophase IIThe chromosomes line up in a similar way to the metaphase stage of mitosis.

The sister chromatids separate and move toward opposite ends of the cell.

Meiosis II results in four haploid (N) daughter cells.

Section 11-4

Figure 11-17 Meiosis II

Ways Meiosis is different:• Homologous pairs match up & trade DNA

(SYNAPSIS & CROSSING OVER) in PROPHASE I

• SEGREGATION

& INDEPENDENT ASSORTMENT in Anaphase I

create genetic recombination

• Skipping INTERPHASE II- • (Dividing TWICE but copying DNA once)

produces 1n cells