Genetic Variation
LHS Biology B
Sexual and Asexual Reproduction
• Organisms produce offspring in 2 different ways
• Sexual reproduction requires 2 parents
• Asexual reproduction only requires 1 parent
• Most organisms use one or the other, but some can
do both
Sexual Reproduction
• 2 parents’ genes combine to form a genetically
unique offspring
▫ Genetic variation comes from mutation, meiosis,
and random fertilization
• Usually takes more energy than asexual
reproduction
• Most organisms that you are most familiar with
use sexual reproduction
▫ Mammals, reptiles, birds, fish, amphibians, and
many plants
Asexual Reproduction
• 1 parent produces a genetic copy of itself
▫ Genetic Variation comes from mutation only
• Usually takes less energy and time than sexual
reproduction
• Some organisms that can use asexual reproduction
are: bacteria, some plants, sea stars, and hydra
Summary
Sexual Reproduction
Asexual Reproduction
•
•
•
•
• Disadvantage:
• Little genetic variation
Disadvantages:
Slower
Takes more energy
More complicated
▫ Rare organisms
• Major Advantage
• Genetic Variation
•
•
•
•
Advantages:
Faster
Saves Energy
Less Complicated
▫ Only 1 parent required
What type of reproduction?
http://www.youtube.com/watch?v=4JIytOL-Q18
http://www.youtube.com/watch?v=gEwzDydciWc
http://www.youtube.com/watch?v=5HMp-GXjHtg
Meiosis
• A type of cell division that produces reproductive
cells
▫ The cells produced are haploid, but come from a
diploid parent cell
• Diploid: A cell with 2 sets of chromosomes, one
from each parent
• Haploid: A cell with only one set of
chromosomes
http://vcell.ndsu.edu/animations/meiosis/movie-flash.htm
Meiosis
Results of Meiosis
• Produces 4 haploid cells called gametes
▫ Reproductive cells, sperm, egg
• 2 gametes (1 sperm and 1 egg) come together at
fertilization, resulting in a zygote
▫ This keeps the chromosome number from
changing each generation
Diploid: 4 chromosomes
Cell Division: Meiosis I
Cell Division: Meiosis II
Haploid: 2 chromosomes
Meiosis is different from Mitosis
• 2 Divisions: Meiosis I and Meiosis II
• Daughter cells are genetically unique
▫ Different from each other and the original cell
• Only occurs in certain organs of sexually
reproducing organisms
Challenge Question #1
• Is Meiosis happening in your body right now?
• Is Mitosis happening in your body right now?
• Explain :)
How to Keep them Straight
• MiTOsis happens in TOES
▫ Produces identical body cells
• MeIosis is why I am unique, why I am ME
▫ Produces unique gametes
Chromosomes Review
Meiosis I
• Pairs of chromosomes are divided
▫ One chromosome from each pair goes to each
daughter cell
• Produces cells with the haploid number of
chromosomes
• Each daughter cell gets one chromosome
from each pair
▫ The pairs split up randomly
Diploid: 4 chromosomes
Diploid: 4 chromosomes
Meiosis I
Haploid: 2 chromosomes
Haploid: 2 chromosomes
Meiosis II
• Basically like mitosis
▫ Chromotids seperate at the
centromere like mitosis
•Results in 4 haploid
daughter cells
▫4 functional sperm
▫1 functional egg and 3
nonfunctional haploid cells
(called polar bodies)
Challenge Question #2
• Explain the purpose of Meiosis in just a few
sentences.
Diploid: 4 chromosomes
Diploid: 4 chromosomes
Haploid: 2 chromosomes
Meiosis II
Haploid: 2 chromosomes
Fertilization
• Joining of egg and sperm to produce a zygote
▫ Zygote is a diploid cell
•Random Fertilization
▫Any sperm is equally likely to
fertilize any egg
▫Another source of genetic
variation
Challenge Question #3
• Draw and label a picture that models the process
of meiosis.
Discovery of DNA
• DNA is the genetic material that makes up
chromosomes
▫ When it is not condensed it is called chromatin
• It wasn’t that long ago that we didn’t know
about DNA
▫ See timeline on page 292
 World War II lasted from 1939 to 1949 for
reference
Image Credits
• Bruce the shark:
http://sloblogs.thetribunenews.com/sidetracked/files/2009/04/br
ucetheshark.jpg
• Sven the Reindeer:
http://static2.wikia.nocookie.net/__cb20131110022746/disney/im
ages/8/83/SVEN2.png
• Aphie and the Queen:
http://images1.wikia.nocookie.net/__cb20110429014022/disney/i
mages/e/eb/Queenbugslife.png
• Bacteria: http://www.bacteriamicroscopes.com/
• Strawberry plant:
http://strawberry.ifas.ufl.edu/daughter%20removal.htm
• Hydra: http://www.microscope-microscope.org/gallery/MarkSimmons/pages/hydra2.htm
• Sea Star: http://www.factzoo.com/invertebrates/starfish-sea-stararmed-sea-critter.html
Image Credits Continued
• Meiosis Diagram 1: http://drugline.org/img/term/meiosis-9348_3.jpg
• Mitosis & Meiosis side by side:
http://www2.le.ac.uk/departments/genetics/vgec/highereducation/topics/
cellcycle-mitosis-meiosis
• Chromosomes:
http://home.comcast.net/~clupold96/notes%20pages/chromosomes_tips.
htm
• Meiosis I:
http://faculty.clintoncc.suny.edu/faculty/michael.gregory/files/bio%20101
/bio%20101%20lectures/meiosis/meiosis.htm
• Meiosis II: http://3.bp.blogspot.com/czi5F0idF74/UFySnBEmB5I/AAAAAAAAAXM/MjWg4VsX34I/s640/Meio
sis+II.jpg
• Telophase II/Cytokinesis:
https://smartsite.ucdavis.edu/access/content/user/00002950/bis10v/wee
k4/4webimages/figure-09-14-11-photo.jpg
• Anaphase II:
https://smartsite.ucdavis.edu/access/content/user/00002950/bis10v/wee
k4/4webimages/figure-09-14-9-photo.jpg
• Fertilization:
http://www.studyblue.com/notes/note/n/genetics/deck/5461653