Reproduction

Essential Question: How do organisms reproduce more organisms like themselves? (or, Where do babies come from?) All organisms are made out of cells that have DNA and come from other cells DNA holds the specific instructions to build proteins which are essential for cell structure and function The types of proteins produced by cells determine the structure and function of the organism You are a human because the instructions in your DNA allowed your cells to build the proteins necessary for the growth and development of a human organism

What is reproduction? Reproduction is basically the creation of a new organism by the passing of DNA from a parent organism to its offspring All living things reproduce

How is DNA passed from parents to offspring? Asexual Reproduction is when the DNA comes from one parent. All bacteria reproduce this way (binary fission) Sexual Reproduction is when the DNA comes from 2 parents - almost all animals and plants reproduce this way Sexual Reproduction involves the creation of special cells, called sex cells, in order to pass the DNA to the offspring

Where do sex cells come from? All cells come from other cells Eukaryotic cells that go through the process of mitosis make EXACT copies of themselves (one skin cell divides to form two identical skin cells, etc.) Sex cells (sperm and egg cells) are different from all other cells in the body because they have half as many chromosomes Human body cells have 46 chromosomes, but sex cells have only 23 So if a normal human body cell with 46 chromosomes goes through mitosis, it will produce two body cells just like it that have 46 chromosomes Since your original cell had 46, all the body cells that have been produced since have 46 chromosomes Where do sex cells with half that number (23) come from?

NOTES - Meiosis & Gamete Formation Each organism has many different types of chromosomes. All body cells in sexually reproducing organisms have two of each type of chromosome, one of each type from each parent. Homologous chromosomes

How are sex cells created from body cells? In order to reproduce, cells must be created that have only one of each type of chromosome Mitosis cannot do this because mitosis creates exact copies of the original cell

Diploid Cell – a body cell with a full set of chromosomes (two of each type)

Haploid Cell – a sex cell with a half set of chromosomes (one of each type) 2n → n If a body cell of a sexually reproducing organism has 20 chromosomes, then the sex cell will have 10 chromosomes A human body cell has 46 chromosomes, so a human sex cell has 23 chromosomes

Gamete – a haploid sex cell (sperm in males, egg in females) Gamete = Sex Cell = Haploid Cell = Sperm or Egg Cell

Meiosis – a type of cell division that produces haploid gametes

Human Sex Determination What does Calvin’s mother mean when she says “It’s your fault we didn’t have a sweet little girl! Your stupid chromosome!! Not mine!!