MEIOSIS REVIEW

​MEIOSIS REVIEW

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

Review: Chromosome

●

A chromosome is a structure
in the nucleus of a cell that
consists of one long molecule
of DNA that is condensed and
tightly coiled around proteins
called histones.

●

Each chromosome consists of
hundreds of genes that code
for proteins or RNA molecules.

sister

chromatids

centromere

DNA

chromosome

Multiple Choice

What are strands of hereditary material found on DNA?

• Chromosomes

• Genes

• Cells

• Nucleus

Multiple Choice

Where are chromosomes found in a cell?

• in the mitochondria

• in the cell membrane

• in the cytoplasm

• in the nucleus

Multiple Choice

Which of these is the correct order showing the largest to smallest parts of genetic material?

• DNA, Cell Membrane, Cell Nucleus Chromosomes, and Genes

• Cell Nucleus, Cell Membrane, Chromosomes, Genes, and DNA

• DNA, Genes, Cell Membrane, Cell Nucleus, and Chromosomes

• Cell Membrane, Cell Nucleus, Chromosomes, DNA, and Genes

Chromosomes

●Each cell in an organism’s body contains a
complete set of chromosomes, but the number of
chromosomes varies with the type of organism.
○Ex: humans have 23 pairs of chromosomes;
dogs have 39 pairs; and potatoes have 24
pairs.

●The pairs of chromosomes are known as
homologous pairs because they are similar in size
and contain similar genes.

●One of the chromosomes comes from the male
parent and the other from the female parent.

Chromosomes

●Somatic cells, or body cells, contain one pair of each chromosome, one
chromosome from mom and one from dad.

○These are referred to as diploid, or 2N, because they contain 2 of each
chromosome.

○In humans, the diploid number is 46 chromosomes.

●Sex cells, or egg and sperm, contain only one of each chromosome

○These cells are also known as germ cells or gametes

○A special process is used to separate the homologous chromosome so that
each gamete only has one of each.

○These are referred to as haploid, or N, because they contain 1 of each
chromosome.

○In humans, the haploid number is 23 chromosomes.

Multiple Choice

Sex cells (sperm & egg cells)

• Somatic cells

• Gametes

• Germ cells

• Mitochondria

Chromosomes

●

One pair of chromosomes in an
organism determines the sex of the
organism, either male or female; these
are known as sex chromosomes
(Chromosome 23).
○

XX = female

○

XY = male

●

All other chromosomes are known as
autosomes (Chromosomes 1 - 22).

Multiple Select

Select all items that comprise chromosomes.

• DNA

• Nucleus

• centrioles

• protein molecules

Match

The diagram depicts a pair of homologous chromosomes. Match each term and description to the appropriate location on the diagram. Each labeled area should have both a term and a description associated with it.

• Gene Loci

  Specific locations of genes on a certain chromosome

• alleles

  Variations of a gene in a particular locus on a chromosome

• gene

  Section of a chromosome that contains the code for manufacturing a product

1

2

3

• 1

• 2

• 3

Multiple Choice

Which sentence is FALSE?

• All organisms have 23 pairs of DNA.

• Chromosomes are made of genes.

• DNA is made out of 4 chemicals: adenine, cytosine, thymine, guanine

• DNA is the recipe for life.

Multiple Choice

Which of the following does NOT describe this picture?

• humans' 46 chromosomes

• one gene

• the human genome

• humans' 23 pairs of chromosomes

Meiosis

●The process of meiosis is essential to sexual reproduction just as mitosis is
to asexual reproduction.

●Sexual reproduction requires the fusion of gametes or sex cells
(fertilization).

●In order for the offspring produced from sexual reproduction to have cells
that are diploid (containing two sets of chromosomes, one set from each
parent), the egg and sperm cells (gametes) must be haploid (contain only
one of each type of chromosome).

●The cellular division resulting in a reduction in chromosome number is
called meiosis.

Meiosis

●

Meiosis occurs in two steps:
○

Meiosis I, in which the homologous chromosome pairs
separate, results in two haploid daughter cells with duplicated
chromosomes different from the sets in the original diploid
cell.

○

Meiosis II, in which the duplicated chromosomes from Meiosis
I separate, resulting in four haploid daughter cells called
gametes, or sex cells (eggs and sperm), with single
(unduplicated) chromosomes.

Meiosis

●Interphase precedes Meiosis I.

●Prophase I:

○The nuclear membrane breaks down during prophase I.

○The duplicated chromosomes condense and homologous chromosomes pair up. A
homologous chromosome pair consists of two chromosomes containing the same type of
genes. One chromosome in the pair is contributed by the organism’s male parent, the
other chromosome in the pair is contributed by the organism’s female parent.

○As in mitosis, each duplicated chromosome consists of two identical sister chromatids
attached at a point called the centromere.

○Because the homologous chromosome pairs very close to one another, an exchange of
chromosome genetic material between pairs occurs in a process called crossing over.

○Crossing over causes the daughter cells to have different gene combinations from the
original parent cell.

Meiosis

●Metaphase I:
○The paired homologous chromosomes are aligned along the equator of the
cell with one chromosome of a pair on one side and one chromosome of a
pair on the other side.

○Each pair is randomly oriented in terms of whether the paternal or
maternal chromosome is on a given side of the equator.

○The result is that 23 chromosomes, some from the mother and some from
the father, are lined up on each side of the equator. This arrangement is
called independent assortment and also causes the daughter cells to have
DNA that is different from the original parent cell.

Meiosis

●

Anaphase I:
○

The homologous chromosome pairs separate and move to
opposite poles of the cell.

○

Each daughter cell will receive only one chromosome from
each homologous chromosome pair.

○

Sister chromatids remain attached to each other.

Meiosis

○Telophase I & Cytokinesis:
■Chromosomes gather at the poles and cytokinesis begins.

■Cytokinesis occurs at the end of telophase I; the chromosomes
uncoil and the nuclear membrane reforms

■Each of the two daughter cells at the end of meiosis I contain only
one chromosome (consisting of two sister chromatids) from each
parental pair, and are therefore haploid.

■
Each daughter cell from meiosis I undergoes meiosis II.

Meiosis

●

There is no duplication of DNA between meiosis I and meiosis II.

●

Prophase II:
○

The nuclear membrane breaks down.

●

Metaphase II:
○

Chromosomes, made up of two sister chromatids, line up
across the center of the cell.

Meiosis

●Anaphase II:
○The chromosomes separate so that one chromatid from each
chromosome goes to each pole.

●Telophase II & Cytokinesis:
○The nuclear membrane reforms around each set of chromosomes.

○The cell undergoes cytokinesis.

○The four resulting daughter cells are still haploid (as they were at the
end of meiosis I) because meiosis II is almost identical to mitosis.

Meiosis

●The DNA of the daughter cells produced by meiosis is different from that of the
parent cells due to three sources of genetic diversity provided by sexual
reproduction and meiosis
○Fertilization combines the genetic material of two genetically unique
individuals (the two parents.

○Crossing-over produces new combinations of genes.

○Independent assortment allows for the possibility of about 8 million
different combinations of chromosomes.

B. continued...

6. Karyotypes show the chromosomes of an individual

a.

It's a picture of all an organism's chromosomes that shows if

there are any mutations in the number OR structure (shape) of a

chromosome.

b.

Used by geneticists to determine conditions like Down

Syndrome and others (Males with extra Y or X, females with only

1 X, etc.).

c.

Incorrect chromosomal numbers are caused by nondisjunction
(chromosomes get stuck together instead of separating as they

should)

https://ed.ted.com/on/nPeMSMrf

C. Body cells are diploid; gametes are haploid

1.

Diploid (2n): have 2 copies of
each chromosome, one from

each parent

2.

Haploid (n): have one copy of
each chromosome; or ½ the #

body cells have

C. continued...

3. Fertilization between egg & sperm (gametes)

occur in sexual reproduction to form body cells (n)

+ (n) = (2n)

4. Chromosome numbers must be

maintained to maintain homeostasis

a.

Mitosis makes more diploid cells
from other diploid cells (keeps

same # of chromosomes from the

start)

b.

Meiosis makes haploid cells from
diploid cells(cuts the chromosome

number in ½ )

Amoeba Sisters: Chromosomes & Karyotypes

Multiple Choice

Gametes are haploid cells. What does this mean?

• Nothing

• The have the same amount of chromosomes as a diploid cell

• The have double the amount of chromosomes from a diploid cell.

• They have half the amount of chromosomes from a diploid cell.

Multiple Choice

During which phase does the nucleus begin to disappear

• Telephase 1

• Prophase 1

• Anaphase 1

• Metaphase 1

Multiple Choice

During which phase do chromosomes begin to separate? 

• Metaphase 1

• Prophase 1

• Anaphase 1

• Metaphase 1 

Multiple Choice

At the end of Meiosis 1 how many cells are there?

• 4 diploid Cells

• 2 diploid Cells

• 4 haploid Cells

• 2 haploid Cells

Multiple Choice

True or False? DNA replicates during Meiosis 2

• True

• False

Multiple Choice

This image is showing what phase?

• Prophase 2

• Anaphase 2

• Metaphase 2

• Cytokinesis

Multiple Choice

At the end of Meiosis 2 how many cells are there? 

• 4 diploid cells

• 4 haploid cells

• 2 diploid cells 

• 2 haploid cells