Tuesday January 29th, 2019 Interphase Prophase Metaphase Anaphase Do Now List the stage of mitosis the following onion cells are in: Interphase Prophase Metaphase Anaphase Telophase

Interphase: 4, 5, 6, 8, 11, 12, 13, 14, 16, 19, 20, & 22 Prophase: 2, 15 & 21 Metaphase: 1, 10, & 17 Anaphase: 7 & 18 Telophase: 3 & 9

The cell division of love (and diversity) <3 Meiosis The cell division of love (and diversity) <3 EQ: How does the sorting and recombination of genes in sexual reproduction result in variety of gene combinations?

Homologous Chromosomes vs. Sister Chromatids two chromosomes (one from your father, one from your mother) that have the same genes, length, & appearance Divided during meiosis I Sister Chromatids: halves of the same chromosome The duplicated sides that remain attached at the centromere Divided during meiosis II sister chromatids sister chromatids Label your diagram in your notes

Chromosomes Autosomes: chromosomes that contain genes for characteristics NOT directly related to the sex of an organism Chromosome pairs 1-22 in humans Sex Chromosomes: directly control the development of sexual characteristics Pair 23 – in mammals, the X and Y chromosomes determine gender Female = X X Male = X Y

Sex Chromosomes The X chromosome is the larger sex chromosome Also contains genes that have nothing to do with sexual characteristics The Y chromosome is the smallest chromosome Carries the fewest genes The genes on this chromosome direct the development of testes and other male traits

Karyotype

Types of Cells Somatic Cells: (body cells) Gametes: (sex cells) Contain normal number of chromosomes (46) Diploid (2 sets of each) Ex. skin cells, liver cells Mitosis Gametes: (sex cells) Contain half the number of chromosomes (23) Haploid (1 set of each) Ex. eggs (female) and sperm (male) Meiosis

Gametes (Sex Cells) Somatic Cells (Body Cells)

Gametes are haploids, Which means? Sex cells have half the chromosomes as somatic cells. Think/Pair/Share How do you think they get to have half the number of chromosomes?

Benefits of Sexual Reproduction Sexual Reproduction- two gametes fuse during fertilization and the offspring are a genetic mixture of both parents Benefits of Sexual Reproduction Allows genetic variation- differences in appearances that offspring show from their parents. Ability to adapt to environmental changes

Fertilization is the fusion of an egg and sperm Fertilization is the fusion of an egg and sperm - restores correct chromosome number Somatic cells Meiosis Fertilization Gametes

Steps of Meiosis Interphase I Meiosis I Prophase I : Crossing Over G1, S, G2 Cell growth and DNA rep. Meiosis I Prophase I : Crossing Over Metaphase I: Independent assortment Anaphase I Telophase I Meiosis II Prophase II Metaphase II Anaphase II Telophase II Students are not writing this page down.

Stop and Think What happens FIRST in both mitosis & meiosis? Interphase What happens during interphase?

Meiosis I – Overview DNA rep during interphase

Meiosis 1 Main points: Interphase occurs = DNA replication Crossing over occurs = exchange of genetic material Homologous chromosomes separate Results in 2 diploid daughter cells

Prophase I Homologous chromosomes pair up Nuclear membrane breaks down Crossing over occurs – exchanging of segments Creates new combinations

Metaphase I Homologous chromosomes align along the cell equator or middle of the cell each side has a chromosome from each parent Independent assortment occurs – random alignments of homologous chromosomes Adds to genetic variation

Independent Assortment

Anaphase I The paired chromosomes split and move towards opposite poles sister chromatids are still attached

Telophase I Spindle fibers fall apart Nuclear membrane reforms 2 nuclei

Cytokinesis Two diploid cells are produced How many chromosomes are in a diploid cell? 46 What is cytokinesis? Division of cell’s cytoplasm to create two new cells

Meiosis II No DNA rep

Meiosis II Main Points: No interphase = no DNA replication Sister chromatids separate Results in 4 genetically different, haploid gametes (n)

Prophase II Centrioles more to opposites sides Nuclear envelope breaks down

Metaphase II Spindle fibers align chromosomes along the metaphase plate (middle)

Anaphase II Sister chromatids are pulled apart towards opposite sides of the cell by centrioles

Telophase II Spindle fibers fall apart Nuclear membrane forms

Cytokinesis Produces 4 haploid gametes Each gamete is genetically unique What is cytokinesis? Division of the cells cytoplasm to create two new cells

Putting it all together… meiosis  fertilization  mitosis + development gametes 46 23 46 23 46 46 46 46 46 23 meiosis 46 46 egg 46 46 23 zygote fertilization mitosis & development mitosis sperm

The value of meiosis 1 Consistency over time meiosis keeps chromosome number same from generation to generation Mom from Mom Consider the greater variation with 23 pairs of chromosomes = mixing and matching Dad offspring from Dad

new gametes made by offspring The value of meiosis 2 Change over time meiosis introduces genetic variation gametes of offspring do not have same genes as gametes from parents new combinations of traits new gametes made by offspring Consider the greater variation with 23 pairs of chromosomes = mixing and matching from Dad variation from Mom offspring

Meiosis Results – reduction division Four haploid daughter cells called gametes Eggs Sperm Each cell is unique from one another (and parent) ***Move to before sexual reproduction Why is it called a reduction division? 1 cell divides into 4 cells The 4 new cells have a reduced number of chromosomes (haploid = half)

The whole Process

Gummy Worm Lab Use the lab instructions as well as the diagram in the book and the diagram in your notes to model the process of Meiosis using the candy provided to you. This is an explorative lab. You are responsible for reading and checking yourself as you go. Reminder: Nuclear Envelope – String Spindle Fibers – String Candy (Twizzler) Centrioles – M&Ms Chromosomes – Gummy Worms Centromere – Tooth Pick Cell – Paper Towel

Exit ticket Clear desk of everything except DO NOW and something to write with

Mitosis and meiosis are processes involved in cellular reproduction Mitosis and meiosis are processes involved in cellular reproduction. Which of the following describes and event that results from mitosis but NOT meiosis? A. two stages of cell division B. replication of cellular genetic material C. daughter cells that are identical to the parent cell D. four daughter cells that are produced from each parent cell

2. Which type of reproduction leads to increased genetic variation on a population? A. Parthenogenesis B. asexual reproduction C. Sexual reproduction D. Vegetative reproduction

The diagram below shows homologous chromosomes during prophase I of meiosis. Which of the following correctly describes the process being illustrated? A. mutation in which the DNA content of the gene is altered B. segregation of sister chromatids C. condensation and segregation of alleles D. crossing-over in which alleles are exchanged

The diagram shows a cellular process that occurs in organisms The diagram shows a cellular process that occurs in organisms. What is the name of this process?  A. meiosis B. mitosis C. endocytosis D. phagocytosis