Cell Division

Cell Division In eukaryotes: Mitosis: Division of somatic (body) cells Growth and repair In prokaryotes Binary Fission: Asexual Reproduction of Unicellular organisms

The Cell Cycle The goal of mitosis is to create two daughter cells identical to the parent cell In order to do this, genetic material must first be duplicated (in DNA replication) and then evenly divided into the two new cells.

Cell Cycle Interphase contains: – G1: normal routine, cell growth – S: DNA copied – G2: prepares to divide Repeating cycle of cell growth and division Most cells spend over 90% of life in interphase (in between divisions).

The Cell Cycle Mitosis: nucleus divides Cytokinesis: cytoplasm divides

Cell Cycle Checkpoints Points where cell cycle is paused Don’t want all cells dividing unless there is a need for growth and repair. Cancer: uncontrolled growth of cells – Occurs because of mutations in genes for proteins that are supposed tell the cell to stop dividing – Something that causes mutations is a mutagen aka. carcinogen

Chromosomes Each chromosome has many genes (segment of DNA that codes for one protein)

Chromosomes All organisms of the same species have the same number of chromosomes. – Humans have 46 chromosomes – Horses have 64 – Some plants have hundreds (more doesn’t mean greater complexity) For the number to stay the same in new cells when cell divides, must be copied first.

Homologous Chromosomes Our body cells are Diploid. – We get 23 chromosomes from mom and 23 from dad. – Each of our chromosomes from mom have a homologous match from dad that has the same: Size Shape Genetic content – Sex cells are haploid Only pass on 1 copy of each of our 23 chromosomes

Homologous Chromosomes

Duplicating Cell Structures Centrioles Spindle fibers Sister Chromatids C B

Duplicating Cell Structures Sister Chromatids: Identical copies of chromosome held together at the centromere. Centrioles: anchor spindle fibers Spindle Fibers: pull chromosomes to ends of cell not the same as homologous chromosomes!!!

Interphase Longest phase where normal cell processes occur. If cell is going to divide, chromosomes are copied. Chromosomes are invisible under a light microscope.

Prophase Chromosomes coil up and become visible. Nucleus breaks down Spindles attach to chromatids

Metaphase Chromsomes line up in the middle (metaphase plate).

Anaphase Identical chromatids pulled to opposite ends of the cell.

Telophase Two new nuclei re-form.

Cytokinesis Cytoplasm divides. In plants, cell plate forms. In animals, cleavage furrow forms.

Results of Mitosis (Asexual Reproduction) 1.2 identical daughter cells are formed 2.Cells are diploid 3.Makes somatic (body) cells 4.Cells have 46 chromosomes

Dividing Water Lily Cell

So What's the Big Idea? Mitosis is the process of dividing to create two genetically identical daughter cells from the parent cell. Why? Growth/repair

MINI-POP QUIZ! What stage are they in?

Warm Up 10/18 What is cancer? What is the purpose of cell cycle “checkpoints”? Name three factors that can increase the rate of cancer.

Meiosis GOAL #1: Make cells for sexual reproduction called gametes Haploid = half the normal number of chromosomes – If gametes had 46 chromosomes, when they combined during fertilization, new cell would have ________. – Zygote = fertilized egg (diploid) GOAL #2: Create genetic variation – Mix up mom and dad’s genes to get new combinations

Meiosis Animation

Meiosis Two cycles of PMAT – The first division separates homologous pairs – The second division separates sister chromatids

Genetic Variation 2. Independent Assortment Each gamete gets some of mom’s and some of dad’s chromosomes 1. Crossing Over Homologous chromosomes switch genes. Produces unique chromosomes.

What’s the advantage of meiosis? Daphnia: What's the point?

Shuffling the Deck Meiosis and sexual reproduction make new gene combinations – Think: do you look just like one of your parents? More genetic variation among individuals of a population means some members will be able to survive in changing or difficult conditions.

Meiosis Recap

Oogenesis and Spermatogenesis Oogenesis: production of eggs aka ova – Creates 1 functional egg and 3 polar bodies Spermatogenesis: production of sperm – Creates 4 functional sperm

Results of Meiosis 1.4 different daughter cells are created 2.Cells are haploid – 23 chromosomes 3.Makes gametes – sperm (4) and egg (1)

Asexual vs. Sexual Reproduction Asexual – 1 parent – Offspring are clones – Types: Binary fission, budding Sexual – Two parents form haploid gametes – Fertilization produces diploid offspring – Offspring have traits from both parents

Advantages and Disadvantages Asexual – Produce many offspring quickly – DNA does not vary between individuals Sexual – Individuals get different combinations of genes – Genetic diversity provides variation needed for evolution