1. Meiosis
How sex cells are made!

2. Asexual vs. Sexual Reproduction
A. Asexual reproduction - quick and efficient.
1. Don’t need a partner.
2. But your offspring are all
clones— no variation!
Sex is not for everyone:
Because the environment is always changing, some offspring may not be as well adapted as the parents.
Sex can be dangerous - spreading disease, risk of predation
Sex requires energy to find a mate

3. Why sex? B. Sexual reproduction- takes more energy!
1.You and your mate must find each other
2. Must exchange genetic material.
3. It is energetically expensive to construct and use mate-attracting body parts.
Bottom Line: Why is sexual reproduction so AWESOME for you?
Because you and your mate BOTH pass characteristics to all your offspring, there will be natural VARIATION (differences) introduced by sex. These variations give your offspring selective advantages for survival in changing environments.

4. This will be important when we study EVOLUTION! Hint hint!
Variation thanks to sexual reproduction- all these puppies are slightly different genetically even though they had the same parents

5. Intro to Genetics What will we study in the next few days?
Meiosis- the process that makes sex cells which carry YOUR genetic info into your offspring
Karyotypes- what your chromosomes look like
Understanding how your genes get passed on
Linking genetics to evolution (next chapter)

6. Genetics- “to generate”
Genetics is the branch of biology that deals with the study that explains how organisms inherit characteristics- inheritance may come from sexual or asexual reproduction.
Asexual reproduction- mitotic division
Sexual reproduction- meiotic divisions

7. Two things are required in order for genetics to work:
You must inherit a single copy of every gene from both your parents. Since you have two biological parents, you will have TWO complete sets of genes.
2. When YOU make your own gametes (sex cells), your two sets of genes must be separated from each other. Each of your gametes will have only one set of genes.

8. Chromosome Number Diploid (2N) – 2 copies of each chromosome
Haploid (1N) – 1 copy of each chromosome
Homologous chromosomes – chromosomes that have same size, shape & gene sequence
Is this a karyotype of a diploid cell or haploid cell? How do you know?
How many chromosomes total?
This is a karyotype of a male. How do we know?
How many chromosomes did mom pass? Did dad pass? How do you know?
Is this person’s karyotype diploid or haploid? How do you know?
What does the term homologous chromosome refer to? How are homologous chromosomes part of this picture?

9. Chromosome Number- Somatic cell (human)
Diploid (2N) – 46
Haploid (1N) – 23
Homologous chromosomes – 23 pairs of homologues
Is this a karyotype of a somatic cell or gamete?
Is this a karyotype of a diploid cell or haploid cell? How do you know?
How many chromosomes total?
This is a karyotype of a male. How do we know?
How many chromosomes did mom pass? Did dad pass? How do you know?
Is this person’s karyotype diploid or haploid? How do you know?
What does the term homologous chromosome refer to? How are homologous chromosomes part of this picture?

10. Diploid vs. Haploid
Diploid- 2 sets of info; 1 set of chromosomes from mom, other set from dad; ONLY SOMATIC CELLS
Haploid- 1 set of genetic info; 1 set of chromosomes; ONLY GAMETES!
Which one is diploid? How many total SETS of xsomes does it have- 2 sets; how many total chromosomes does it have? 8; how many homologues does it have? 4
Which one is haploid?

11. Cystic fibrosis (CF) is caused by a defect in a gene called the cystic fibrosis transmembrane conductance regulator (CFTR) gene on CHROMOSOME 7 . This gene makes a protein that controls the movement of salt and water in and out of the cells in your body. In people with CF, the gene does not work effectively. This causes the thick, sticky mucus and very salty sweat that are the main features of CF.

12. How do organisms make gametes (1N) from germ cells (2N)?
Meiosis- a process that:
produces gametes
is a “reduction division”- reduces the chromosome number in half (2N  1N)
A diploid cell results in 4 UNIQUE and VARIED haploid cell
2 divisions
You have two sets of genes in your chromosomes, but your gametes must end up with just one set of chromosomes to contribute to your offspring.

13. Overview of Meiosis

14. Why don’t all of you look the same?
You and your siblings all have: 50% genetic info from mom 50% genetic info from dad
Why don’t all of you look the same?
CROSSING OVER-
*genetic “shuffling” of info
*nonsister chromatids cross parts of themselves during Prophase I of the first meiotic division (Meiosis I)
*genetic recombination occurs- you end up with gametes that are all a little different but still 50% mom and 50% dad info

15. Lab- “Meiosis Phases Activity”
Grab your lab books. Title activity as above.
Name, date, period.
You will work individually.
Cut out each phase of meiosis.
Paste/tape the phases in order (book pg )
Name each phase
Describe what is occurring at each phase.
Label “Meiosis I” and “Meiosis II”
Answer the following questions:
What is the importance of meiosis.
List 3 ways meiosis is DIFFERENT from mitosis.
List 2 ways meiosis is SIMILAR to mitosis.

16. Links to check out – useful info and animations
(this site has lots of great options for learning meiosis!)
(a very good reading that gets into the details)
(helpful notes on all the phases)

17. Interphase I
DNA Replication occurs (exact copy of DNA made)

18. Prophase I Chromosomes pair with their homologous chromosomes
Crossing-over: exchange of alleles between homologous chromosomes

19. Metaphase I Homologous chromosomes line up on equator
Spindle fibers attach to centromeres

20. Anaphase I
Homologous chromosomes separate

21. Telophase I & Cytokinesis
Nuclear membrane reforms
Cell separates into 2 cells
Daughter cells are haploid
Chromosome sets and alleles unique in each cell

22. Prophase II 2 haploid cells No chromosome replication
Each chromosome has 2 chromatids

23. Metaphase II Chromosomes line up on equator
Spindle fibers attach at the centromere

24. Anaphase II Sister chromatids separate
Chromatids pulled to opposite poles

25. Telophase II & Cytokinesis
New nuclear envelopes reform
4 daughter cells
All are haploid, 1N (one set of chromosomes)
Non-identical (different alleles)

26. Gamete formation In males, meiosis produces 4 sperm
In females, meiosis produces 1 egg and 3 polar bodies

27. Comparing Mitosis & Meiosis
Creates 2 diploid cells
Creates 4 haploid cells
2 daughter cells with identical sets of chromosomes and alleles
4 daughter cells with different alleles on each chromosome
Allows organism to grow and replace cells
Allows organisms to produce gametes for sexual reproduction
How organisms reproduce asexually
Animation