1. Sexual Reproduction and Meiosis
Ch. 4 Sect. 1

2. Sexual Reproduction
Is a type of reproduction in which the genetic materials from two different cells combine, producing an offspring.
Sex Cells – are the cells that combine during sexual reproduction.
Sex cells form in reproductive organs
Females- Eggs (form in ovaries)
Males- Sperm (form in testis)

3. Sexual Reproduction
Fertilized Egg
Zygote
Fertilization – a process where an egg cell and a sperm cell join. It produces a new cell
The new cell that forms from fertilization is called a zygote.

4. Diploid Cells Are cells that have pairs of chromosomes.
Are usually body cells (somatic cells)
Homologous chromosomes- pairs of chromosomes that have genes for the same traits arranged in the same order.
Humans have 23 pairs of homologous chromosomes.

5. Haploid Cells
Haploid cells are cells that have one chromosome from each pair.
Sex cells (gametes) are haploid cells.
Meiosis – one diploid cell divides and makes four haploid sex cells.
Meiosis occurs only during formation of sex cells.

7. Phases of Meiosis Anaphase 1 Anaphase 2 Telophase 1 Telophase 2
Involves 2 division of the nucleus and cytoplasm
End result is 4 haploid cells – with half the # of chromosomes as the original cell.
Meiosis 1: Prophase 1 Meiosis 2: Prophase 2
Metaphase Metaphase 2
Anaphase Anaphase 2
Telophase Telophase 2

10. Creates genetic variation by producing haploid cells.
When meiosis occurs, it maintains the correct diploid number of chromosomes.
Creates genetic variation by producing haploid cells.
Importance of Meiosis

12. Advantages of Sexual Reproduction
Genetic Variation – Different DNA means that each offspring has a different set of traits.
Genetic Variation can cause advantages and disadvantages depending upon the environment.
Selective Breeding- mating with organisms with the desirable traits.

13. Disadvantages of Sexual Reproduction
Takes time and energy
Organisms must grow and develop to produce sex cells.
Find a mate (expose to diseases, predators, harsh environmental conditions).
Fertilization cannot take place during pregnancy.