Sexual Reproduction and Meiosis Ch. 4 Sect. 1

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)

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.

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.

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.

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 1 Metaphase 2 Anaphase 1 Anaphase 2 Telophase 1 Telophase 2

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

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.

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.