In meiosis, the nucleus divides to form 4 daughter nuclei.

Meiosis allows for differences in inherited characteristics.

Interphase similar to mitosis.chromosomes are replicated chromatidssubsequent phases differ

Prophase I

Members of homologous pair do not have identical DNAOne from each parent

Crossing overoccurs early in Prophase Igenetic recombinationan average of 1-3 “crossovers” per pair

Metaphase I

Pairs are not arranged maternal vs. paternal

independent assortment

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

Meiosis II

CancerNeoplasms (tumors)

benign or malignantMalignancy (cancer)

fast growingnot encapsulatedcan metastasize

Loss of Cell Cycle Control

Growth factors (and their receptors)

Mechanisms (11.18-21)

Oncogenes1. may code for growth factors or their receptors

HER-2, ras called proto-oncogenes when they function normally

Loss of “Brakes”

Tumor suppressor genesp53

Carcinogenschemicalsradiation virusesare mutagens

Viruses and Cancer

Human Papilloma Virus (HPV)

Hepatitis

Herpes

Fig. 06.