Connect! Where did this cloud of butterflies come from? What are they doing? Look around your bio class. Why is each person different? Name 5 organisms.

Connect!

• Where did this cloud of butterflies come from?• What are they doing?• Look around your bio class. Why is each person different?• Name 5 organisms that use sexual reproduction.• How is sexual reproduction different from asexual reproduction?

Sexual Reproduction involves morethan just the act called sex!

Sexual Repro

fertilizationmeiosis development

gametes

sex cells

cell division

haploid sperm

haploid egg

complete offspring

differentiated cells

zygote

mitosis

requires

a special kind of of of

by

by

then into

into

called

which produces only such as

join to make a

SEXUAL REPRODUCTION

The Story: 3 Parts

1. Specialized sex cells are produced in the male and female. These are called gametes. They are made by meiosis.

2. Gametes join (fuse) their nuclei in the process of fertilization.

3. The fertilized egg called a zygote develops into an embryo.

Part 1: Making Eggs and Sperm

A. THE NUCLEUS:• In each body cell of an organism there are 2 copies of each

chromosome for that species. This is called diploid (2n). For example, fruit flies have 4 pairs of chromosomes in each of their nuclei of their body cells.

• What is the 2n # for humans?

• These pairs of chromosomes are called homologous because they are the same shape, same size, and contain genes for the same traits. Each of the homologous chromosomes in a pair is inherited from one’s parents. One from Ma and one from Pa.

Homologous Chromosome Analogy• Your 46 chromosomes are like volumes of two sets

of books. Each set is numbered from 1 to 23. For ex, you have two “volumes” of chromosome 22, that is, a pair of them.

• Think of your two sets of chromosomes as two sets of books on how to build a house.

• Your dad gave you one set. • Your mom had her own ideas about storage,

plumbing, and so on, and she gave you an alternate set of books. Her set covers the same topics but says slightly different things about many of them.

• These homologous chromosomes need to be replicated then divvied up into the gametes (sex cells).

B. MEIOSIS (also known as gametogenesis):

• Sperm and eggs are formed differently from all other cells!

• “Gameto” means gametes, and “genesis” means to create.

• So what does “gametogenesis” mean?

• Eggs and sperm are made by meiosis.

• Meiosis ONLY occurs in specialized organs called gonads. Most organisms have only female or male gonads, while others have both and are called hermaphrodites. An example is the earthworm.

• Meiosis reduces the chromosome number by one-half, producing gametes with only one copy of chromosomes which is called monoploid (aka haploid…or n)

Chunkin’ Time! What goes in the blank boxes?

Sexual Repro

fertilization development

cell division

complete offspring

differentiated cells

requires

a special kind of of of

by

by

then into

into

called

which produces only such as

join to make a

• What are gametes?• What is it called when gametes fuse their

nuclei?• Define zygote.• What type of cell division makes gametes?• What is the word for having 2 copies of each

chromosome in a cell? What is the symbol?• What cells are diploid? • What is the human diploid number?• What are chromosomes called that have the

same shape, size, and contain genes for the same traits?

I know, just a few more…

• Where do each of the homologous chromosomes in a pair come from?

• Explain the sets of books analogy.• Where does meiosis occur?• What is another name for meiosis?• Define hermaphrodite, and give an example.• What does meiosis do?• What term is used for gametes, since they have only

half the chromosome number of a body cell?• Give another term and the symbol.

The Steps of Meiosis

(remember this only occurs in the gonads)

• # of chromosomes in original cell?

• # of chromosomes in each daughter cell?

• Compare the daughter cell chromosomes to the parent cell and to each other.

• What term do we use for the differences in the cells formed by meiosis?

1. In a primary sex cell, each single-stranded chromosome replicates resulting in double-stranded chromosomes.

2. Chromosomes pair up forming tetrads. This is called synapsis.

• These homologous pairs align in the middle of the spindle apparatus. The spindle apparatus is very important because it moves chromosomes.

3. During synapsis, crossing over occurs. This is an exchange of the genetic information and increases variation within a species.

In other words, crossing over mixes up the genes of an organism as it is producing sperm or eggs.

Compare each chromatid to the others.

Do any carry the same message?

4. Homologous chromosomes separate and move along the spindle apparatus toward opposite ends of the cell.

5. The cytoplasm divides and 2 cells are formed.

Meiosis II

1. The double-stranded chromosomes line up in the middle of the spindle apparatus.

2. The centromeres replicate. This is crucial since centromeres hold the chromosomes together.

3. The now single-stranded chromosomes move along the spindle apparatus toward opposite ends of the cell. This is called disjunction.

4. The cytoplasm divides and 4 monoploid (haploid) cells are produced.

The Results of Meiosis

• Gametes such as eggs or sperm that can be used in fertilization

• These gametes contain only 1 copy of chromosomes (monoploid).

“You Decide” Book

Have you ever read one of those books where you decide what happens next? These books are neat because there are so many endings possible. You could think of mitosis as a short story that you read straight through and there’s just one ending possible.

With meiosis, though, there are many possible endings. Depending on how the homologous chromosomes separate after synapsis, and whether crossing over occurs, there are many different endings that are possible.

Chunk Time!• Go through the Meiosis fingerplay, making

sure you use the proper terms.• Describe crossing over, and what results

from it.• What is disjunction?• What type of cells are produced by meiosis?• How many gametes are produced?• Are gametes diploid or haploid?• How many chromosomes are in a human

egg?

What is happening here?

JFF!

Sources of Images• Gametes - img229.imageshack.us/.../91614070324607vv4.jpg• Fruit fly - members.tripod.com/c_rader0/fly.gif • Fruit fly chromosomes – modified from upload.wikimedia.org/.../400px-Chromosomes.JPG• Homologous chromosomes - www.dkimages.com/.../previews/916/90011467.JPG • Ma and Pa - www.pendemonium.com/images/inkwells/w809.jpg• Dexter’s dad and mom - http://upload.wikimedia.org/wikipedia/en/c/cf/Dexters_Dad.jpg,

http://upload.wikimedia.org/wikipedia/en/1/1e/Dexters_Mom.jpg• Fairly odd parents -

http://www.aaglobalind.com/images/retail-temporary-tattoos/novelty-temporary-tattoos/novelty-temporary-tattoos-images/F09004-Fairly-Oddparents-Tattoo-Sheet.jpg

• Earthworm - http://www.brynmawr.edu/biology/franklin/LPN/earthworm_on_sidewalk.jpeg• Steps of mitosis - http://publications.nigms.nih.gov/thenewgenetics/images/ch1_meiosis.jpg• Chromatid - http://www.anselm.edu/homepage/jpitocch/genbio/sphase.JPG• Tetrad, crossing over - http://images.google.com/imgres?imgurl=http://faculty.clintoncc.suny.edu/faculty/michael.gregory/files/Bio

%2520100/Bio%2520100%2520Lectures/meiosis/img020.gif&imgrefurl=http://faculty.clintoncc.suny.edu/faculty/michael.gregory/files/Bio%2520100/Bio%2520100%2520Lectures/Meiosis/meiosis.ht

• Cartoon - http://www.funnytimes.com/archives/files/art/19961211.jpg

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