Mitosis vs. MeiosisMitosis vs. Meiosis

Asexual vs. Sexual Asexual vs. Sexual ReproductionReproduction

MitosisMitosis

““The replication of the chromosomes and The replication of the chromosomes and the production of two nuclei in one cell; the production of two nuclei in one cell; usually followed by cytokinesis” (736).usually followed by cytokinesis” (736).

MitosisMitosis is the process of is the process of one cell dividing one cell dividing into two into two identical identical copies copies of the cell, of the cell, known as daughter cells.known as daughter cells.

Mitosis preserves the number of Mitosis preserves the number of chromosomes that each cell contains chromosomes that each cell contains ((diploid cells - 2Ndiploid cells - 2N))

Mitosis is used for Mitosis is used for growth, repair or growth, repair or asexual asexual reproduction.reproduction.

Asexual ReproductionAsexual Reproduction

New individuals originate from a New individuals originate from a single parentsingle parent

Either the Either the parent divides into two parent divides into two (or (or more) individuals more) individuals or new individuals or new individuals arise as budsarise as buds from the parent’s body from the parent’s body

The The only genetic changes only genetic changes arise as the arise as the result of result of mutationsmutations (chance events (chance events that change the DNA of the offspring)that change the DNA of the offspring)

Low genetic diversity.Low genetic diversity.

Asexual reproduction is a form of Asexual reproduction is a form of regeneration. Sponges, starfish and regeneration. Sponges, starfish and

salamanders are well known for salamanders are well known for regeneration.regeneration.

http://science.discovery.com/videos/kapow-superhero-science-limb-regeneration.html

Sexual ReproductionSexual ReproductionWhy does sex exist? Why does sex exist? 99.9% of 99.9% of

organisms bigger than bacteria do itorganisms bigger than bacteria do it.. It It increases diversity increases diversity of the offspring of the offspring

and species!and species!More diversity means more More diversity means more

resistance to disease, and the ability resistance to disease, and the ability to adapt to changing circumstances to adapt to changing circumstances in the environmentin the environment

GameteGamete In humans and many other animals, the In humans and many other animals, the

gametes (sex cells) are eggs (ova) and gametes (sex cells) are eggs (ova) and spermsperm. .

In flowering plants, these are ovules and In flowering plants, these are ovules and pollen pollen (sperm).(sperm).

Gametes continuedGametes continued

The The gametes contain only ½ the gametes contain only ½ the genetic informationgenetic information required to make required to make a new individual a new individual (Haploid: n)(Haploid: n)

What would happen if gametes were What would happen if gametes were created through mitosis, and had the created through mitosis, and had the normal number of chromosomes? normal number of chromosomes?

Consider a gamete like this from an Consider a gamete like this from an organism with 10 chromosomes….organism with 10 chromosomes….

How many chromosomes?How many chromosomes?

Gametes are Gametes are haploid cells, containing haploid cells, containing 1 complete set of “n” chromosomes1 complete set of “n” chromosomes. .

““n” for humans is 23n” for humans is 23 All other body cells are diploid, having All other body cells are diploid, having

“2n” or 2 complete sets of “2n” or 2 complete sets of chromosomes.chromosomes.

““Ploidy” refers to how many complete Ploidy” refers to how many complete sets of chromosomes there are.sets of chromosomes there are.

ThThere is often a large difference in the ere is often a large difference in the size of male vs. female gametes.size of male vs. female gametes.

The structure of a The structure of a chromosome after replicationchromosome after replication

The chromosomes come in The chromosomes come in pairs!pairs!

Homologous chromosomesHomologous chromosomes are are matching pairs of chromosomesmatching pairs of chromosomes, , similar in shape and content.similar in shape and content.

One chromosome of each pair came One chromosome of each pair came from the father (sperm), and one from the father (sperm), and one came from the mother (egg).came from the mother (egg).

Human chromosomes from skin cells. Human chromosomes from skin cells.

This is what stained This is what stained chromosomes really chromosomes really look likelook like

Chromosomes #1-22Chromosomes #1-22 are called are called autosomes autosomes and always make and always make matching pairsmatching pairs

Chromosome #23Chromosome #23 is is the the sex chromomsome sex chromomsome and can be either and can be either “X” “X” or “Y”or “Y”

Karyotype of the human Karyotype of the human chromosomes. chromosomes.

Geneticists literally Geneticists literally match up the match up the homologous homologous chromosomes from a chromosomes from a photograph to make a photograph to make a karyotype.karyotype.

They contain similar They contain similar genes but from the two genes but from the two different parents.different parents.

Humans have 2 sets of Humans have 2 sets of 23 chromosomes for a 23 chromosomes for a grand total of 46. “n” is grand total of 46. “n” is 23 for humans.23 for humans.

•Males have an X Males have an X and a Y and a Y chromosome #23, chromosome #23, so their sperm can so their sperm can either carry and either carry and “X” or a “Y”“X” or a “Y”•Females have two Females have two copies of the “X” copies of the “X” chromosome #23, chromosome #23, so their eggs so their eggs always carry an always carry an “X”“X”

The sex of the child is therefore The sex of the child is therefore determined by the male gamete determined by the male gamete

(sperm)(sperm)

MeiosisMeiosis

Haploid (n) cells or Haploid (n) cells or “gametes” are formed “gametes” are formed with with meiosismeiosis

Meiosis also jumbles Meiosis also jumbles up the genetic materialup the genetic material

This only happens in This only happens in your your gonadsgonads (ovaries (ovaries or testes)or testes)

Meiosis happens in two Meiosis happens in two phases or cell divisionsphases or cell divisions

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Crossing Over! One source of Crossing Over! One source of variation between gametesvariation between gametes

HUGE jump in HUGE jump in genetic diversity!genetic diversity!

Chromosomes Chromosomes “mom” or “dad” “mom” or “dad” already have, already have, randomly mix randomly mix themselves up!themselves up!

Then they assort Then they assort randomly into randomly into different gametes.different gametes.

Independent assortment of Independent assortment of chromosomes- another chromosomes- another

source of variation between source of variation between gametesgametes

Variation from Sexual Variation from Sexual ReproductionReproduction

Three main sources create MILLIONS of Three main sources create MILLIONS of optionsoptions Crossing over Crossing over causes mixing BEFORE meiosis causes mixing BEFORE meiosis

separates chromosomesseparates chromosomes Independent Assortment Independent Assortment during Anaphase (ex: In during Anaphase (ex: In

mom’s egg cells, each of the 23 sets will separate mom’s egg cells, each of the 23 sets will separate independently…some of her mom’s independently…some of her mom’s chromosomes may go to an egg, and some of her chromosomes may go to an egg, and some of her dad’s chromosomes)dad’s chromosomes)

Random FertilizationRandom Fertilization: it is random which egg and : it is random which egg and sperm meet during fertilizationsperm meet during fertilization