Meiosis

Meiosis

A starfish is shown in the image. The starfish has lost one of its arms. What does this mean for the starfish?

Multiple Choice

Is there any chance that the arm will grow back?

• Yes

• No

Take a Look

https://www.youtube.com/watch?v=AaN6uRvfPLY

Section 3 Objectives

• Explain the difference between mitosis & meiosis

• Describe how chromosomes determine sex

• Explain why sex-linked disorders occur in one sex more often than the other

• Interpret a pedigree

Asexual Reproduction - Mitosis

• In asexual reproduction, only one parent cell is needed

• The structures inside the cell are copied, then the parent cell divides, making two exact copies

• This type of cell reproduction is called MITOSIS

• Most of the cells in your body and most single-celled organisms reproduce this way

Review - Cell Cycle

• The series of events a cell goes through as they grow and divide

• Mitosis is the ultimate cell division stage

• Our cells have to be constantly dividing & replacing to ensure they are healthy!

Review - Steps of Mitosis

• Mitosis is a type of cell division that results in 4 identical daughter cells

• Mitosis consists of four basic phases: Prophase, Metaphase, Anaphase, Telophase

• Mitosis and cytokinesis occur in the M phase of the cell cycle

Multiple Choice

What is the purpose of mitosis?

• Growth of an organism and Repair of damaged body cells

• To help the body get rid of extra cells

• To increase the amount of classwork you have to do

• To get rid of the nucleus

Multiple Choice

Mitosis is a type of

• sexual reproduction

• asexual reproduction

Sexual Reproduction

• 2 parent cells (sex cells or gametes) join together to form offspring that are different from both parents

• Chromosomes that carry the same sets of genes are called homologous chromosomes

• Each sex cell has only one of the chromosomes from the homologous pair

Fill in the Blank

What do you think is the advantage of reproducing sexually instead of asexually?

Meiosis

• Sex cells (gametes) are made during meiosis

• Meiosis is a copying process that produces cells with half the usual number of chromosomes

_{Genes and Chromosomes}

Genes & Chromosomes

• Walter Sutton studied meiosis in sperm cells in grasshoppers

• He found that body cells of grasshoppers have 24 chromosomes but the sex cells only had 12 chromosomes (exactly half)

• Walter proposed that genes are located on chromosomes

Steps of Meiosis

• During meiosis, chromosomes are copied once, and then the nucleus divides twice

• The resulting sex cells (sperm and eggs) have half the number of chromosomes of a normal body cell

• Meiosis results in 4 genetically different daughter cells each with half the number of chromosomes of the parent cell (also known as reduction division)

Meiosis: Crossing Over

• The exchange of genetic material of homologous chromosomes

• Creates genetic variation - this is the reason why we don't always look like our siblings

Multiple Choice

__________ is an American geneticist who studied the cells of grasshoppers.

• Gregor Mendel

• Walter Sutton

• Sir Isaac Newton

• Marie Curie

Multiple Choice

__________ is the process that reduces the number of chromosomes in half to form sex cells.

• Mitosis

• Reproduction

• Meiosis

• Fertilization

Multiple Choice

Meiosis is a type of

• Sexual Reproduction

• Asexual Reproduction

Mitosis vs. Meiosis

• Mitosis - 2 identical cells are produced - happens in somatic cells (body cells) - start 46 chromosomes, end 46 chromosomes

• Meiosis - 4 unique cells produced - produces gametes (sex cells) - start 46 chromosomes, end 23 chromosomes

Multiple Choice

What are somatic cells?

• body cells

• sex cells

Multiple Choice

What are gametes?

• human cells

• sex cells

• plant cells

• body cells

Multiple Choice

Mitosis forms

• 4 identical daughter cells

• 2 identical daughter cells

• 4 different daughter cells

• 2 different daughter cells

Multiple Choice

In meiosis, what is crossing over?

• the exchange of genetic material of homologous chromosomes

• homologous chromosome stay identical to each other

• homologous chromosome separate

• homologous chromosome walk across each other

Multiple Choice

The cells produced in MEIOSIS are identical (the same).

• True

• False

Multiple Choice

What are somatic cells?

• body cells

• sex cells

Multiple Choice

How many chromosomes do most humans have?

• 46

• 12

• 96

• identical to your age

Multiple Choice

Humans have a diploid number of 46 chromosomes in our body cells. How many chromosomes will our gametes have if they are considered HAPLOID?

• 46

• 92

• 23

• 10

Multiple Choice

Normal human cells have 46 chromosomes, how many will the germ cells have after meiosis?

• 46

• 23

• 12

• 92

^{Meiosis results in 4 genetically different daughter cells, each containing haploid number of chromosomes (23)}

How do chromosomes determine sex?

• XX = female

• XY = male

• The gender of a child is determined by the type of chromosome she/he is receiving from the father

Punnett squares are used to predict probabilities - 50% from mom, 50% from dad

Multiple Choice

Use the karyotype to identify the sex of the person.

• Female

• Male

Multiple Choice

What percent of children would you expect to be male?

• 25%

• 50%

• 75%

• 100%

Summary

• Mitosis is a type of asexual reproduction that leads to the production of 2 identical daughter cells

• Meiosis is a type of sexual reproduction that leads to the production of 4 genetically different daughter cells

• Crossing over in meiosis leads to genetic variation

• Sex determination is entirely dependent on the father

Exit Ticket

• Link has been posted in the chat

• Once you complete, you are good to leave the meets.

• Have a good day!