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

SummarySexual Reproduction Asexual Reproduction

• Disadvantages:• Slower• Takes more energy• More complicated

▫ Rare organisms

• Major Advantage• Genetic Variation

• Disadvantage:• Little genetic variation

• Advantages: • Faster• Saves Energy• Less Complicated

▫ Only 1 parent required

http://www.youtube.com/watch?v=4JIytOL-Q18

http://www.youtube.com/watch?v=gEwzDydciWc

http://www.youtube.com/watch?v=5HMp-GXjHtg

What type of reproduction?

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 chromosome

s

Haploid: 2 chromosom

es

Cell Division: Meiosis I

Cell Division: Meiosis II

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 chromosome

s

Diploid: 4 chromosome

s

Haploid: 2 chromosome

s

Haploid: 2 chromosom

es

Meiosis I

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 chromosome

s

Diploid: 4 chromosome

s

Haploid: 2 chromosome

s

Haploid: 2 chromosom

es

Meiosis II

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 Revised•A human body cell has 23 pairs of

chromosomes. How many chromosomes does a human gamete cell have?

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/brucetheshark.jpg

• Sven the Reindeer: http://static2.wikia.nocookie.net/__cb20131110022746/disney/images/8/83/SVEN2.png

• Aphie and the Queen: http://images1.wikia.nocookie.net/__cb20110429014022/disney/images/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/Mark-Simmons/pages/hydra2.htm

• Sea Star: http://www.factzoo.com/invertebrates/starfish-sea-star-armed-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/Meiosis+II.jpg

• Telophase II/Cytokinesis: https://smartsite.ucdavis.edu/access/content/user/00002950/bis10v/week4/4webimages/figure-09-14-11-photo.jpg

• Anaphase II: https://smartsite.ucdavis.edu/access/content/user/00002950/bis10v/week4/4webimages/figure-09-14-9-photo.jpg

• Fertilization: http://www.studyblue.com/notes/note/n/genetics/deck/5461653