Mitosis vs. Meiosis

1
Mitosis vs. Meiosis

• Asexual vs. Sexual Reproduction

2
Mitosis

• The replication of the chromosomes and the
  production of two nuclei in one cell usually
  followed by cytokinesis (736).
• Mitosis is the process of one cell dividing into
  two identical copies of the cell, known as
  daughter cells.
• Mitosis preserves the number of chromosomes that
  each cell contains (diploid cells - 2N)
• Mitosis is used for growth, repair or asexual
  reproduction.

3
Asexual Reproduction

• New individuals originate from a single parent
• Either the parent divides into two (or more)
  individuals or new individuals arise as buds from
  the parents body
• The only genetic changes arise as the result of
  mutations (chance events that change the DNA of
  the offspring)
• Low genetic diversity.

4
Asexual reproduction is a form of regeneration.
Sponges, starfish and salamanders are well known
for regeneration.

• http//science.discovery.com/videos/kapow-superher
  o-science-limb-regeneration.html

5
Sexual Reproduction

• Why does sex exist? 99.9 of organisms bigger
  than bacteria do it.
• It increases diversity of the offspring and
  species!
• More diversity means more resistance to disease,
  and the ability to adapt to changing
  circumstances in the environment

6
Gamete

• In humans and many other animals, the gametes
  (sex cells) are eggs (ova) and sperm.
• In flowering plants, these are ovules and pollen
  (sperm).

7
Gametes continued

• The gametes contain only ½ the genetic
  information required to make a new individual
  (Haploid n)
• What would happen if gametes were created through
  mitosis, and had the normal number of
  chromosomes?
• Consider a gamete like this from an organism with
  10 chromosomes.

8
How many chromosomes?

• Gametes are haploid cells, containing 1 complete
  set of n chromosomes.
• n for humans is 23
• All other body cells are diploid, having 2n or
  2 complete sets of chromosomes.
• Ploidy refers to how many complete sets of
  chromosomes there are.

9
There is often a large difference in the size of
male vs. female gametes.
10
The structure of a chromosome after replication
11
The chromosomes come in pairs!

• Homologous chromosomes are matching pairs of
  chromosomes, similar in shape and content.
• One chromosome of each pair came from the father
  (sperm), and one came from the mother (egg).

12
Human chromosomes from skin cells.

• This is what stained chromosomes really look like
• Chromosomes 1-22 are called autosomes and always
  make matching pairs
• Chromosome 23 is the sex chromomsome and can be
  either X or Y

13
Karyotype of the human chromosomes.

• Geneticists literally match up the homologous
  chromosomes from a photograph to make a
  karyotype.
• They contain similar genes but from the two
  different parents.
• Humans have 2 sets of 23 chromosomes for a grand
  total of 46. n is 23 for humans.

14

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

15
The sex of the child is therefore determined by
the male gamete (sperm)
16
Meiosis

• Haploid (n) cells or gametes are formed with
  meiosis
• Meiosis also jumbles up the genetic material
• This only happens in your gonads (ovaries or
  testes)
• Meiosis happens in two phases or cell divisions

17


17
18
Crossing Over! One source of variation between
gametes

• HUGE jump in genetic diversity!
• Chromosomes mom or dad already have, randomly
  mix themselves up!
• Then they assort randomly into different gametes.

19
Independent assortment of chromosomes- another
source of variation between gametes
20
Variation from Sexual Reproduction

• Three main sources create MILLIONS of options
• Crossing over causes mixing BEFORE meiosis
  separates chromosomes
• Independent Assortment during Anaphase (ex In
  moms egg cells, each of the 23 sets will
  separate independentlysome of her moms
  chromosomes may go to an egg, and some of her
  dads chromosomes)
• Random Fertilization it is random which egg and
  sperm meet during fertilization

21
(No Transcript)