Meiosis

​Meiosis

Multiple Choice

What is the name of the part where the chromosome is connected?

• telomere

• centromere

Meiosis

Meiosis

Creates 4 non-identical
haploid cells used for
sexual reproduction

What is Meiosis? … in simple terms

Sexual Reproduction and Genetics

▪A special type of cell division that results in
cells having half the number of
chromosomes - HAPLOID
▪Results in cells used only in sexually
reproducing organisms - GAMETES

Multiple Choice

Cells used only in sexual reproduction are called

• grains

• diploid

• snurffles

• gametes

Multiple Choice

A cell with half the number of chromosomes that is necessary for sexual reproduction.

• nanoid

• diploid

• haploid

• gigaloid

▪Human body cells have 46 chromosomes

General Overview

Sexual Reproduction and Genetics

▪Each parent contributes 23 chromosomes

▪Meiosis takes place in sex cells (gametes):

○ Female = egg cells in Ovaries

○ Male = sperm cells in Testes

▪One cell creates 4 NON-IDENTICAL

daughter cells

Multiple Choice

Healthy human cells contain how many chromosomes?

• 45

• 46

• 78

• 1

Multiple Choice

Human sex cells contain how many chromosomes?

• 10

• 72

• 46

• 23

Regents Biology

Recap: Mitosis

▪ 46 chromosomes to 46 chromosomes

◆ cells make exact copies

Body Cells
46

Mitosis

each diploid

diploid

46

46

Regents Biology

Meiosis: Sex Cells

▪ 46 chromosomes to 23 chromosomes

◆ half the number of chromosomes

23

46

egg cells

sperm cells

46

meiosis

haploid

diploid

23

23
23

23 23 23 23

Multiple Choice

What are normal body cells called?

• diploid

• haploid

• mushy

• spongy

Regents Biology

gametes

Fertilization = Diploid Again

▪ Why do sex cells have to be haploid? What

would happen if they weren’t?

23

46

egg

sperm

46

meiosis
46

fertilization

23

23

Zygote

23

Let’s look at
Chromosomes

23 pairs = 46 Chromosomes

Meiosis – Homologous Chromosomes

Sexual Reproduction and Genetics

▪Same length

▪Same centromere position

▪Carry genes that control the

same inherited traits

▪One is from mother, one is
from father = a matching set

Multiple Choice

Which of the following is true about homologous chromosomes?

• They are nothing alike

• The centromeres are in the same position

• They are different sizes

• The genes control different traits

Multiple Choice

Which of the following is true about homologous chromosomes?

• They are nothing alike

• The centromeres are in different positions

• They are the same size

• The genes control different traits

Multiple Choice

Which of the following is true about homologous chromosomes?

• They are nothing alike

• The centromeres are in different positions

• They are different sizes

• The genes control the same traits

Gene for

Brown
eyes (B)
from Mom

Gene for
Blue eyes
(b) from

Dad

Male or
Female?

Alleles

Mitosis vs Meiosis Overview

Haploid and Diploid Cells

▪ Human gametes contain 23 chromosomes.

Sexual Reproduction and Genetics

▪ A cell with n chromosomes is called a haploid

cell.

▪ A cell that contains 2n chromosomes is called a

diploid cell.

Meiosis

▪ An organism produces gametes to maintain the

same number of chromosomes from generation
to generation.

Meiosis

▪ The sexual life cycle

of animals involves
meiosis.

▪ Meiosis produces

gametes.

▪ When gametes combine

in fertilization, the total
number of chromosomes
is restored.

Multiple Choice

Which process produces gametes that have half of the number of original chromosomes?

• maturation

• meiosis

• mitosis

• photosynthesis

Phases of Meiosis

Sexual Reproduction and Genetics

Meiosis Part I

Interphase:

● Chromosomes

Replicate

▪How is this similar to Mitosis? How is it different?
This is the same as Mitosis

▪Prophase I

▪Pairing of homologous
chromosomes occurs.

▪Chromosomes
condense and consist of
two sister chromatids.

▪The nuclear membrane
breaks down.

▪Spindles form.

Meiosis Part I

▪How is this similar to Mitosis? How is it different?

In Mitosis - homologous chromosomes do NOT pair up -

all move independently of each other

Multiple Choice

Which of the following occur during prophase I?

• Pairing of homologous chromosomes

• The spindles break down.

• Nuclear membrane and nuclei reform

Sexual Reproduction and Genetics

▪ Prophase I

▪ Crossing over produces exchange of genetic

information.

▪ Crossing over—chromosomal segments are

exchanged between a pair of homologous
chromosomes.

Meiosis Part I

▪How is this similar to Mitosis? How is it different?
Crossing over does NOT happen in Mitosis

Multiple Choice

Which of the following occur during prophase I?

• Crossing over produces exchange of genetic information

• The spindles break down.

• Nuclear membrane and nuclei reform

Sexual Reproduction and Genetics

▪Metaphase I

▪Chromosome
centromeres attach
to spindle fibers.

▪Homologous
chromosomes line
up at the equator.

Metaphase I

Meiosis Part I

▪How is this similar to Mitosis? How is it different?Mitosis - Chromosomes line up independently in a single file, spindle

fibers still attach to centromeres

Multiple Choice

Which of the following occur during metaphase I?

• Crossing over produces exchange of genetic information

• The spindles break down.

• Homologous chromosomes line up at the equator

Multiple Choice

Which of the following occur during metaphase I?

• Crossing over produces exchange of genetic information

• The spindles break down.

• Chromosome centromeres attach to spindle fibers

Sexual Reproduction and Genetics

▪Anaphase I

▪Homologous
chromosomes
separate and move
to opposite poles of
the cell.

▪How is this similar to Mitosis? How is it different?

Meiosis Part I

In Mitosis - sister chromatids separate, but here the homologous pairs separate - with

copies (chromatids) still attached

Multiple Choice

Which of the following occur during anaphase I?

• Crossing over produces exchange of genetic information

• The spindles break down.

• Homologous chromosomes separate and move to opposite poles of the cell

Sexual Reproduction and Genetics

▪Telophase I

▪The spindles
break down.

▪Chromosomes
uncoil and form two
temporary nuclei.

▪The cell divides.

▪How is this similar to Mitosis? How is it different?

Meiosis Part I

Similar, but 23 chromosomes (w/their copies)

instead of 46 and no copies

Multiple Choice

Which of the following occur during telophase I?

• Crossing over produces exchange of genetic information

• The spindles break down.

• Homologous chromosomes separate and move to opposite poles of the cell

Multiple Choice

Which of the following occur during telophase I?

• Crossing over produces exchange of genetic information

• The cell divides

• Homologous chromosomes separate and move to opposite poles of the cell

▪Prophase II

Sexual Reproduction and Genetics

▪A second set of
phases begins
as the spindle
apparatus forms
and the
chromosomes
condense.

▪How is this similar to Mitosis? How is it different?

Meiosis Part II

Only 1 Prophase in Mitosis, otherwise same with spindle fibers forming and

chromosomes condensing

▪Metaphase II

Sexual Reproduction and Genetics

▪A haploid number
of chromosomes
line up at the
equator.

▪How is this similar to Mitosis? How is it different?

Meiosis Part II

Sister Chromatids line up, but only 23 instead of 46

Sexual Reproduction and Genetics

▪Anaphase II

▪The sister
chromatids are
pulled apart at the
centromere by
spindle fibers and
move toward the
opposite poles of
the cell.

▪How is this similar to Mitosis? How is it different?

Meiosis Part II

Similar to Mitosis, but with 23 instead of 46

Draw

Circle the chromosomes

Sexual Reproduction and Genetics

▪Telophase II

▪The chromosomes
reach the poles
▪Nuclear membrane and
nuclei reform

▪How is this similar to Mitosis? How is it different?

Meiosis Part II

Similar but have 4 cells with 23 instead of 2 with 46

Sexual Reproduction and Genetics

▪Cytokinesis

▪Results in four haploid
cells, each with n
number of
chromosomes.

▪How is this similar to Mitosis? How is it different?

After Meiosis Part II

4 non identical cells with 23 chromosomes

Meiosis vs Mitosis

Meiosis vs Mitosis