DevelopmentDevelopmentUnit 4-4 Notes

Mr. Hefti – Pulaski Biology

Step 1 – Meiosis in gonadsStep 1 – Meiosis in gonads

Gametogenesis

◦Oogenesis egg / ovaries

◦Spermatogenesis sperm / testes

Step 2 – Fertilization Step 2 – Fertilization Joining of egg and spermResults in zygote (that makes more cells

by mitosis)◦Equation:

1N + 1N 1N + 1N ￫ ￫ 2N2N

Occurs where?◦Internal mammals, reptiles, birds◦External fish, amphibians

Cells split apart side-by-sideMitosis!Each cell has full DNA code to become any

type of cell!All identical cells at this point (it’s now an

embryo)!

Step 3 – CleavageStep 3 – Cleavage

Step 4 – DifferentiationStep 4 – DifferentiationCells specialize based on what they are going to become

Contain full DNA code - only use portion needed for that type of cell◦Compare DNA code to recipe book

Step 5 – DevelopmentStep 5 – Development

Unique DNA code of each organism controls structure and function

Occurs where?◦Internal for mammals (except marsupials and monotremes)

◦External for birds, reptiles, fish, and amphibians Inside eggs, but outside mother’s body