How do organisms create offspring through sexual reproduction?

What is Sexual Reproduction? It involves the joining of two cells to begin the development of a new individual. These special cells are called: Sex Cells (Gametes)

What are the names of these sex cells? Egg cell (Female) Sperm Cell (Male) The joining of a sperm cell with an egg cell is called fertilization.

How many chromosomes do we have in our cells? We have 46 chromosomes in each our body cells. We can also say that we have 23 pairs of chromosomes Karyotype

Why do we have 2 of each chromosome? We get one chromosome from each parent Each pair of chromosomes are called: Homologous Chromosomes

Homologous Chromosomes: Gene Mom Dad Eye Color B G Part of a chromosome that codes for a trait B Hair Color R Have genes that code for the same trait, but may have different versions of that trait

How are chromatids different than homologous chromosomes? Chromatids are exact duplicates of each other Homologous chromosomes have genes that code for the same trait, but they may code for different versions of that trait

How many chromosomes do the offspring have after mitosis? 46X Mitosis 46X 46X

Do our sex cells have 46 chromosomes? NO!!!

What would happen if our sex cells did have 46 chromosomes? 92 + Offspring Egg Sperm The offspring would have 92 chromosomes

Sexual Reproduction: 23 23 46 + Offspring Egg A fertilized egg cell is called a Zygote Sperm Characteristics of Sexual Reproduction: 1) Is the creation of a new individual from parents. 2 2) Offspring are not genetically to the parents. identical

Sex Cells (Gametes) Sex Cells: SPERM and EGG Sex cells should have 1/2 the normal number of chromosomes

Chromosome Number Diploid cells: (2n) normal number of chromosomes (Body Cells) Haploid cells: (n) ½ the normal number of chromosomes (Sex Cells)

Diploid vs Haploid Movie Clips

Meiosis The process by which haploid (sex) cells are produced with half the number of chromosomes.

What is the end result of meiosis? 46X Meiosis 23X 23X 23X 23X

Where does meiosis occur? Gonads – Ovaries and Testis

Why is meiosis important? Maintains the number of chromosomes from generation to generation Provides genetic variation Only during fertilization (union of sperm and egg) is the full (diploid) set of chromosomes restored.

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