SEXUAL REPRODUCTION

Chapter 4 lesson 1

Part 1

Reproduction of Organisms

Why do living things reproduce?

Sexual Reproduction and Meiosis

• What is sexual reproduction, and why is it beneficial?

• What is the order of the phases of meiosis, and what happens during each phase?

• Why is meiosis important?

sexual reproduction

a type of reproduction in which the genetic materials from two different cells combine, producing an offspring.

Gamete•The cells that combines to form offspring

•A reproductive cell•A sex cell•Formed by meiosis•In most organisms meiosis produces 1 of 2 types of gametes

2 types of gametes

•Ova (singular-ovum) - female gametes; female sex cell(book calls them eggs)

•Sperm - male gametes; male sex cell

2 types of gametes

sperm

ovum

Where are gametes formed?

• Testes – male reproductive organs

• Ovaries – female reproductive organs

In reproductive organs

The female sex cell, an ovum, forms in an ovary.The male sex cell, a sperm, forms in the testis.

Fertilization

the formation of a zygote from the union of 2 gametes

The process when a sperm and an ovum join togther.

What is sexual reproduction? (cont.)

During a process called fertilization, an ovum cell and a sperm cell join together to create a zygote.

Zygote

The new cell that forms from fertilization

Diploid cells

• Organisms that reproduce sexually form somatic (body) cells and germ (gametes; sex) cells.

• In somatic cells of most organisms, similar chromosomes occur in pairs.

• Diploid cells are cells that have pairs of chromosomes.

Diploid cells

• Pairs of chromosomes that have genes for the same traits arranged in the same order are called homologous chromosomes.

• Because one chromosome is inherited from each parent, the chromosomes are not identical.

• Different organisms have different numbers of chromosomes.

Diploid cells

Homologous chromosomes

Haploid cellsHaploid cells are cells that have only one chromosome from each pair of chromosomes.

haploidfrom Greek haploeides, means “single”

Haploid vs Diploid

Normal human cells have 23 pairs of chromosomes which is a total of 46

chromosomes.

Human diploid number is 46

Human haploid number is 23

Diploid & Haploid Examples

Haploid Diploid

Honey bee 16 32

Crayfish 100 200

Rabbit 22 44

Watermelon 11 22

Corn 10 20