In meiosis, the nucleus divides to form 4 daughter nuclei. Meiosis allows for differences in inherited characteristics.

Interphase similar to mitosis. chromosomes are replicated  chromatids subsequent phases differ

Prophase I

Members of homologous pair do not have identical DNA One from each parent

Crossing over occurs early in Prophase I genetic recombination an average of 1-3 “crossovers” per pair

Metaphase I Pairs are not arranged maternal vs. paternal

independent assortment

Anaphase I In humans, there are roughly 8 million possible combinations per gamete. When gametes fuse, that’s about 64 trillion combinations.

Meiosis II

Cancer Neoplasms (tumors) benign or malignant Malignancy (cancer) fast growing not encapsulated can metastasize

Loss of Cell Cycle Control

Growth factors (and their receptors) Mechanisms ( )

Oncogenes 1. may code for growth factors or their receptors HER-2, ras called proto-oncogenes when they function normally

Loss of “Brakes”

Tumor suppressor genes p53

Carcinogens chemicals radiation viruses are mutagens

Viruses and Cancer Human Papilloma Virus (HPV) Hepatitis Herpes

Fig. 06.