1. Meiosis and Sexual Reproduction

2. Asexual Reproduction Asexual Called vegetative reproduction in plants
“A” = Not
Sexual
Called vegetative reproduction in plants
A form of duplication using only mitosis.
Example, a new plant grows out of the root or a shoot from an existing plant.

3. Asexual Reproduction
Produces only genetically identical offspring since all divisions are by mitosis.
Offspring called meaning that each is an exact copy of the original organism
This method of reproduction is rapid and effective allowing the spread of an organism
Example: Bacterial growth
Since the offspring are identical, there is no mechanism for introducing .
clones
diversity

4. Asexual Reproduction
In prokaryotes and some one-celled eukaryotes, cells undergo _____ _____
Hydra reproduce by ________
Planaria reproduce by ____________
Several plants reproduce through vegetative reproduction.
Most of these organisms can reproduce sexually as well.
binary fission
Escherichia coli
Paramecium caudatum
budding
fragmentation

5. Why do organisms have sex?
Sexual reproduction increases variety by producing new genetic combinations.
It’s costly to the organism
It’s time-consuming
There are far fewer offspring

6. Sexual Reproduction Consists of Meiosis and Fertilization
Meiosis: Formation of two haploid sex cells (gametes).
Meiosis is a process to convert a ________ cell to a ________ gamete, and cause a change in the genetic information to increase diversity in the offspring.
In humans, meiosis only occurs in the ________
Spermatogenesis: In the ______(in males)
Oogenesis: In the _______ (in females)
Fertilization: Combination of genetic information from two separate cells that have one half the original genetic information
diploid
haploid
gonads
testes
ovaries

7. + = Sexual Reproduction
Gametes for fertilization usually come from separate parents
Female produces an _____
Male produces _______
Both gametes are haploid, with a single set of _____________.
The new individual is called a ______, with two sets of chromosomes (______).
Once the zygote begins to divide, it is called an _______.
egg
sperm
chromosomes
zygote
diploid
embryo

8. Chromosomes vary from species to species
Prokaryotes generally have only ___ major chromosome
Consisting of a single circle of DNA
Turkeys have 82!
Giant redwoods have 22!
A tropical fish has the same number of chromosomes as humans, which is ____
one 46

9. Chromosome Characteristics
Diploid set for humans; 2n = 46
Two types:
Autosomes (#1 – 22)
Sex Chromosomes (#23)

10. Chromosome Characteristics
Autosomes
Homologous chromosomes
Humans have 22 sets of 2
One from each parent
Sex chromosomes
Humans have 1 set of 2
Female-sex chromosomes are homologous (XX)
Male-sex chromosomes are non-homologous (XY)

11. What can Chromosomes tell us?
Scientists can organize chromosomes in a cell into a _________
karyotype
In a karyotype, chromosomes are arranged in order of size, banding pattern, and centromere position:
Let’s see if we can arrange a karyotype together:

12. What does this person pass on to the next generation?
What sex will this person be?
What does this person pass on to the next generation?

13. Meiosis: Reduction/Division
Two divisions:
Meiosis I &
Meiosis II

14. Prophase I Unlike Mitosis:
Homologous chromosomes group with other homologous chromosomes to form a “tetrad”
A “chiasma” occurs at the point where the chromosomes cross over
Like Mitosis:
Nuclear membrane disappears
Spindles form
Chromatin condenses into chromatids

15. Metaphase I Homologous chromosomes line up at the metaphase plate.
Microtubules (spindles) attach to the kinetochore

16. Anaphase I Homologous chromosomes separate.
Sister chromatids remain attached.

17. Telophase I
Two daughter cells are formed with each one containing only one chromosome of the homologous pair.
The daughter cells are now haploid.

18. Meiosis II: Gamete formation
Prophase II:
DNA does not replicate.
Prophase II is just like mitotic prophase.

19. Metaphase II:
All of the chromosomes line up at the metaphase plate.

20. Anaphase II: Centromeres divide
Sister chromatids migrate separately to each pole.

21. Telophase II: Cell division is complete.
Four haploid daughter cells are obtained

22. Summary of Meiosis