Mitosis and Meiosis Books Today you will make a meiosis book. The front cover will just have the title and your name. Pages 1-2 Vocabulary Page 3 Chromosome Structure Page 4 Mitosis Table of Contents Page 5 Interphase Page 6-10 Phases of Mitosis and Cytokinesis Page 11 Meiosis Table of Contents Page 12 Interphase Page 11-20 on Phases of Meiosis Page 21 Cytokinesis Page 22 Compare Mitosis and Meiosis

Meiosis Cell division where one diploid cell (2n) produces four haploid (n) cells called sex cells or gametes These cells have half the number of chromosomes as a body cell of a parent

Meiosis vocabulary What is a gamete? Male and female sex cells; the sperm and egg What is the male gamete? Sperm; has 23 chromosomes What is the female gamete? Egg; has 23 chromosomes

Meiosis vocabulary… What is a zygote? A fertilized egg – has a diploid number (2n) of chromosomes What is sexual reproduction? The pattern of reproduction that involves the production and fusion of haploid sex cells What is a diploid cell? Cell containing two of each kind of chromosome from the parent

Meiosis vocabulary… What is a haploid cell? Cell containing one of each kind of chromosome from the parent What is an allele? Gene form for each variation of a trait of an organism. Example: gene for height can express tall or short Homologous chromosomes: Pairs of like chromosomes even though the alleles may be different – so they are not identical chromosomes – sibling variation

Coils up into chromosomes Duplicates itself Coils up into chromosomes Chromatin

Interphase—period of cell growth and development DNA replication (copying) occurs during Interphase During Interphase the cell also grows, carries out normal cell activities, replicates all other organelles The cell spends most of its life cycle in Interphase

Phases of Mitosis Prophase Metaphase Anaphase Telophase

Prophase Chromosomes coil up Nuclear envelope disappears Spindle fibers form

Metaphase—(Middle) Chromosomes line up in middle of cell Spindle fibers connect to chromosomes

Anaphase—(Apart) Chromosome copies divide Spindle fibers pull chromosomes to opposite poles

Telophase—(Two) Chromosomes uncoil Nuclear envelopes form 2 new nuclei are formed Spindle fibers disappear

Cytokinesis — the division of the rest of the cell (cytoplasm and organelles) after the nucleus divides In animal cells the cytoplasm pinches in In plant cells a cell plate forms After mitosis and cytokinesis, the cell returns to Interphase to continue to grow and perform regular cell activities

The Phases of Meiosis Interphase Meiosis I Meiosis II Prophase I Crossing Over Metaphase I Anaphase I Telophase I Meiosis II Prophase II Metaphase II Anaphase II Telophase II

Interphase Carries out metabolic activities of the cell Replicates its chromosomes Precedes meiosis 1

Prophase I Chromosomes coil up and spindle form Homologous chromosomes pair up and a four-part structure called a tetrad forms

During prophase I… Tightly wound tetrads get so close to one another that the genetic material from one homologous pair exchanges with the other creating new combinations of alleles in the genetic code Nuclear membrane disappears Nucleolus disappears

What is crossing over? Exchange of genetic material by non-sister chromatids during prophase I Results in new combinations of alleles

Metaphase I Tetrads line up at the equator Homologous chromosomes are lined up in pairs along the midline or equator of the cell Spindle fibers attach to the centromere on each pair The pairs are not attached to each other

Anaphase I Homologous chromosomes are separated and pulled to opposite poles of the cell The centromeres do not split during this phase Each new cell receives only one chromosome from each homologous pair

Telophase I Spindle breaks down Chromosomes uncoil Cytoplasm divided in 2 Each cell has half the genetic information from the original cell Chromosomes are still doubled containing two sister chromatid Nuclear membrane reforms Two diploid daughter cells formed

Meiosis II Is there an interphase in Meiosis II? No. Chromosomes do not replicate The cells go directly from meiosis I to meiosis II

Prophase II Spindle forms in each of the two new cells Chromosomes are still coiled as sister chromatids Nuclear membrane disappears Nucleolus disappears

Metaphase II Chromosomes line up at the equator of the cell Spindle fibers attach to the centromeres

Anaphase II Centromeres split Spindle fibers pull separated chromatids to opposite poles of the cell

Telophase II Spindle fibers disappear Chromosomes uncoil Nuclear membrane reforms Nucleolus reforms Cytoplasm divides Each cell now has half the chromosomes that its parents had Four daughter haploid cells are formed

What are the two divisions of meiosis? Meiosis I and Meiosis II Meiosis I When homologous chromosomes come together and separate Meiosis II The division that results in 4 daughter cells, each with half the chromosomes present in the original cell

What is genetic recombination? Genetic variation due to crossing over and random assortment How many ways can the chromosomes line up? 2

How do you find the total number of different kinds of sperm and egg that can be produced? Take the number of pairs and place it as the exponent with a base of 2 Example: in humans there are 23 pairs of chromosomes For sperm: 223 = over 8 billion For egg: 223 = over 8 billion

What is the total when fertilization occurs? 223 * 223 = 70 trillion zygotes are possible