Semester 1, Day 7

Meiosis

Agenda Study for Virus Quiz Turn in Virus Homework (18.1 and 18.2) Virus Quiz Lecture and Activity for Meiosis Practice Meiosis Reading/Work Time for Meiosis Review Meiosis Questions

Study Reasons why viruses are non-living Parts of a virus Diagram of virus cycles Steps of virus cycles

Homework to Turn In Cornell Notes: Section 18.1, 18.2 Questions:

Section Assessment 18.1: #1-6 Section Assessment 18.2: #1-6 Chapter 18 Assessment: #1-17, 19-26

Quiz Viruses

Reproduction & Genetic Material Production of Offspring

Asexual: 1 parent, genetically identical offspring Prokaryotic organisms, some plants

Sexual: 2 parents (1/2 DNA from each), genetically different offspring

“Not”

Fertilization

Sperm (Male) Ovum (Female)Zygote (Fertilized Ovum)

First cell of

an organis

mGametes: sex cells

Reproduction & Genetic Material Recall: DNA = genetic information

Image Source: www.riversideonline.com

DNA doesn’t

naturally occur like

this!

Chromosome: coiled

DNA

Reproduction & Genetic Material Unduplicated vs. Duplicated Chromosomes

Image Source: histology.kasralainy.edu.eg

Chromosomes Genes: Portion of DNA

that codes for a protein

Homologous Chromosomes: a pair of

chromosomes of the same length,

same centromere position, and carry

genes that control the same traits.

One chromosome from each parent

makes a pair.

Chromosome Number: Humans have

23 homologous pairs

Different

Genes

From Mom

From Dad

Same centromere

position

Genes that control a trait (ex.

eye color)

Same Length

23pair

sx

2 chromosome

s=

46chromosom

es1 pair

Chromosomes Karyotype: number & visual appearance of chromosomes in

an organism

Sex Chromosomes:-23rd “pair”-Female: X X-Male: X Y

Image Source: www.biotechnologyonline.gov.au

Chromosomes What would happen if human gametes each had 46

chromosomes?

Therefore… Gametes must have half (23) of the chromosomes!

Fertilization

Zygote

Can’t be

human!

46 46 92

MaleFemale

Fertilization

Zygote

Human!

23 23 46

MaleFemale

Chromosomes Let’s represent the # of chromosomes in a

gamete for ANY organism as “n”.

Fertilization

Zygote

n n 2nMale

Female

All Sexual Reproductio

n

“Haploid” = nGk. Haplos = Single “Diploid” = n

Gk. Diplos = Double

Chromosomes You receive one chromosome for every homologous pair from each

parent.

Child (2n)

Mom (2n) Dad (2n)

Pass on “n” Pass on “n”

Make your own chromosomes You have 4 small, 4 medium, and 4 large

chromosomes Decorate 2 small, 2 medium, and 2 large for MOM

All should be identical Example: polka dots

Decorate 2 small, 2 medium, and 2 large for DAD All should be identical Example: stripes

Meiosis Mom and Dad are both “2n”. How do they

make gametes of “n”?

2n 2nMom Dad

nn

Ovum Sperm

2n

Child

Fertilization

Process? Process?Process? = MEIOSIS• Cell division that

halves the chromosome number. Creates gametes for sexual reproduction.

Meiosis

MeiosisInterpha

se

Gap

1

Synt

hesis

Gap

2

Meiosis IPr

opha

se I

Met

apha

se

IAn

apha

se

ITe

loph

ase

I

Meiosis II

Prop

hase

II

Met

apha

se

IIAn

apha

se

IITe

loph

ase

II

PMAT I PMAT II

Meiosis Meiosis I: 1st Cell Division Meiosis II: 2nd Cell Division

Meiosis I Meiosis II

Body Cell2n

(Diploid)n

(Haploid)

n(Haploid)

Gametes

(become sperm

or ovum)

Meiosis Interphase (before division):

preparing for cell division G1 Phase (Gap 1)

Cell is growing Normal functions Prepping for DNA duplication

S Phase (Synthesis) DNA is copied Single chromatids Sister

chromatids G2 Phase (Gap 2)

Cell continues growing Prepping for cell division

Ignore other organelles for

nowDNA is

uncondensed (not in

chromosomes) and is called

chromatin

Gap 1

Synthesis

Gap 2

Your Body Cell (2n)Single Chromatids

Your Body Cell (2n)Sister Chromatids

Act this out with our chromosomes

Meiosis Meiosis I: 1 cell 2 cells

Prophase I Chromatin condenses into

chromosomes Homologous chromosomes pair

up; crossing over occurs Nuclear envelope breaks down Spindle fibers form from the

centrioles

Image Source: legacy.owensboro.kctcs.edu

HomologousChromosomes

Crossing Over

Genetic information exchanges = increased variation

From your mom

From

your dad

NuclearEnvelope

**Recall: In humans, 23 pairs of homologous chromosomes in a

human (2n = 46). Here, we are using 2 pairs (2n

= 4).

Centrioles: organize cell

during division

Your Body Cell (2n)Sister Chromatids

Act this out with our chromosomes

Meiosis Meiosis I (cont.)

Metaphase I Spindle fibers attach to

centromeres of chromosomes

Homologous pairs line up at equator of cell

Anaphase I Homologous

chromosomes separate and move along spindle fibers to opposite poles

Equator

Your Body Cell (2n)Sister Chromatids

Your Body Cell (2n)Sister Chromatids

(n) at each pole

(n) at each pole

Act this out with our chromosomes

Meiosis Meiosis I (cont.)

Telophase I

Spindles break

down

Chromosomes

uncoil, nuclei

reform

Cell divides into

two

Cytokinesis

(n) ChromosomesSister Chromatids

(n) ChromosomesSister Chromatids

Act this out with our chromosomes

Meiosis Meiosis II: 2 cells 4 cells

Prophase II Chromatin condenses into

chromosomes (again!) Nuclear envelopes break

down (again!) Spindle fibers form from

centrioles (again!) and attach to chromosomes

Metaphase II Centromeres of chromosomes

line up at equator of each cell (not in pairs!)

(n) ChromosomesSister Chromatids

(n) ChromosomesSister Chromatids

(n) ChromosomesSister Chromatids

(n) ChromosomesSister Chromatids

Equators

Act this out with our chromosomes

Meiosis Meiosis II (cont.)

Anaphase II Centromeres split Sister chromatids

separate & move to opposite poles

Telophase II 4 nuclei reform Spindles break down Chromosomes uncoil Cells divide

(n) ChromosomesSingle Chromatids

(n) at each pole

(n) at each pole

(n) at each pole

(n) ChromosomesSingle Chromatids

(n) at each pole

Cytokinesis

Act this out with our chromosomes

Meiosis Final Products

Spermatogenesis Oogenesis

Meiosis

Act this out with our chromosomes

Meiosis Spermatogensis

In males, only a special diploid (2n) cell called spermatocyte in a testis can undergo meiosis to create a sperm. 4 sperm cells are formed.

Image Source: www.mun.ca

Meiosis Oogensis

In females, only a special diploid (2n) cell called an oocyte in an ovary can undergo meiosis to create an ovum. 1 ovum is formed, 3 polar bodies that die are also formed.

Image Source: www.mun.ca

Practice Show me:

Interphase, G1 Interphase, G2 (Assume

Interphase S occurred) Prophase I Metaphase I Anaphase I Telophase I Prophase II Metaphase II Anaphase II Telophase II

Show me: Metaphase II Prophase I Interphase G1 Anaphase II Prophase II Telophase I Interphase G2 (Assume

Interphase S occurred) Anaphase I Telophase II Metaphase I

Reading/Work Time Cornell Notes on Section 10.2 (Meiosis) 10.2 Section Assessment:

#1-5 Chapter 10 Assessment:

#1, 4-6, 9, 10, 13, 15, 18, 25, 26-28, 30