Sexual Reproduction and MeiosisChapter 4 Lesson 1

p.116-126

Cell DivisionMitosis• Body cells

Meiosis• Sex cells

– Sperm and Egg Cells

Meiosis• A special kind of cell division that end in four

cells with half the number of chromosomes.

• Creates sex cells (egg cells and sperm cells)

• The original cell has 46 chromosomes.

• The final four cells has 23 chromosomes each.

Sexual Reproduction• When two parents make one offspring.

• Two different sex cells combine to form an offspring.

• An egg is a female sex cell.

• A sperm is a male sex cell.

• Fertilization is the joining of an egg and a sperm.• A fertilized egg cell is called a zygote.

Chromosomes• Human cells have 46 chromosomes, or

23 pairs of chromosomes.

• 23 of our chromosomes come from our mom.

• 23 of our chromosomes come from our dad.

Chromosomes• Each pair of chromosomes have the

same type of information.

• One set from mom

• One set from dad

Mom Dad

Gene for Eye Color

Mom Dad

Gene for Eye Color

Mom Dad

Before DNA is replicated, copied during interphase.

Duplicated Chromosomes after interphase.

Dad

Gene for Eye Color

Homologous Pairs of chromosomes have genes for the same traits.

Mom

Mom Dad

These are still homologous pairs. Now they are just duplicated.

We have 23 homologous pairs.

Sexual Reproduction

• Body cells have a full set of chromosomes in homologous pairs.

• We call these cells diploid.

• Sex cells have half the number of chromosomes.

• They do not have homologous pairs.

• We call them haploid. (half)

• In meiosis, one diploid cell divides and makes four haploid cells.

• When fertilization occurs, the new cell, called a zygote, will have the normal number of cells.

Diploid (2N)

Haploid (N)

Haploid (N)

Different organisms have different numbers of chromosomes.

– How many homologous pairs does each species have?

Stages of Meiosis

Fig. 2.7 ©Scion Publishing Ltd

The stages of meiosis.

Meiosis is used only for the production of sperm and eggs.

It consists of two successive cell divisions, producing four daughter cells (although in oogenesis only one of these develops into a mature oocyte; the others form the polar bodies).

Meiosis has two main functions: to reduce the chromosome number in the gamete to 23, and to ensure that every gamete is genetically unique.

Growth and Development

• After fertilization a single celled zygote is formed.

• The zygote will go through mitosis and cell division to become an organism.

MITOSIS MEIOSIS

MEIOSIS I

Prophase IChromosome

replication

Homologouschromosomepair

Chromosomereplication

2n = 6

Parent cell

Prophase

Replicated chromosome

Metaphase Metaphase I

Anaphase ITelophase I

Haploid n = 3

Daughter cells ofmeiosis I

MEIOSIS II

Daughter cells of meiosis II

nnnn

2n2n

Daughter cellsof mitosis

AnaphaseTelophase

• Choose one color to be the maternal chromosome.

• Choose one color to be the paternal chromosome.

• Cut a maternal and paternal chromosome to both be 5cm long.

• Then, cut a maternal and paternal chromosome to be both 8cm long.

• Chromosome 1

• Chromosome 2

How many chromosomes does the cell have total?

• Chromosome 1

• Chromosome 2

Cell Division

Mitosis Meiosis