Reproduction

1
Reproduction
Biology The Science of Life Making New Life
The Basics of Reproduction
2
Why is Reproduction Necessary

• The survival of an individual does not require
  reproduction.
• An individual can live a long and fruitful life
  without ever reproducing.
• Individuals, however, will eventually die.
• Therefore, for the species to survive,
  reproduction is necessary.

3
Biological Success

• Biological success for a species lies in its
  members ability to reproduce and have offspring
  before death occurs.
• Extinction occurs if members of the species fail
  to reproduce or if they fail to leave enough
  offspring to allow for deaths as a result of
  accidents and disease.
• Successful reproduction is essential to the
  continued existence of a species.

4
Reproduction of a Cell vs. Reproduction of an
organism

• When a parent cell divides into two daughter
  cells through mitosis, the parent cell disappears
  and the two daughter cells replace it.
• When an entire organism reproduces, the parent
  often lives on in order to care for the offspring.

5
Reproduction

• Reproduction is the formation of new individuals
  that are like their parents.
• The ability to reproduce is a fundamental, unique
  characteristic of living organisms.
• New organisms grow, develop and eventually become
  large enough and mature enough to reproduce.
• The time in the life cycle when an organism
  becomes able to reproduce varies from species to
  species.

6
Life Cycle

• A life cycle is all the events that occur between
  the beginning of one generation and the beginning
  of the next.
• The term is usually used to refer to the time
  from birth to sexual maturity to the birth of the
  next generation.

7
Generation

• There are lots of ways to think of the word
  generation. For our purposes use the following
  example
• Great GrandparentsGeneration 1
• GrandparentsGeneration 2
• ParentsGeneration 3
• KidsGeneration 4
• GrandkidsGeneration 5
• We could carry this example all the way back to
  the first humans or even pre-human ancestors.

8
Reproductive Maturity

• Single celled organisms such as bacteria and
  yeast can only reproduce once before they die.
• Bacteria, can reproduce every 20 minutes.
• Multicellular organisms may reproduce several
  times in their lifetime.
• Multicellular organisms often require months or
  years to reach sexual maturity.

9
Reproductive Periods

• Some organisms, such as humans, outlive their
  reproductive periods.
• Other organisms continue to reproduce until they
  die.
• The giant tortoises of the Galapagos Islands may
  live up to 200 years.
• They cannot reproduce before about 40.
• Thereafter, they reproduce as long as they live.

10
Asexual Reproduction No Genetic Diversity

• In asexual reproduction, new individuals
  originate from a single parent.
• Parent divides into two or more individuals
• New individuals arise from as buds from the
  parents body
• Because new individuals come from only one
  parent, asexual reproduction does not increase
  genetic variation in a population.
• New individuals are genetically identical to the
  parent organism.
• http//www.teachersdomain.org/resource/tdc02.sci.l
  ife.repro.asexual/

11
Sexual Reproduction

• In complex organisms, reproduction generally
  requires two parents.
• Each parent contributes a unique sex cell called
  a gamete.
• The male gamete is called the sperm.
• The female gamete is called the egg.
• A new individual begins when the gametes unite by
  fusing together into a zygote.
• This process is called fertilization.

12
Gametes Carry Genetic Info

• The egg and sperm carry the genetic information
  which the parents will pass to the offspring.
• The new individuals develop in response to these
  genetic instructions.
• Because it combines genetic material from two
  different individuals, sexual reproduction
  increases the amount of genetic variation in a
  population.

13
Some Organisms Reproduce Both Asexually and
Sexually

• Most plants and some animals can reproduce both
  asexually and sexually.
• Potatoes can use sexual reproduction to produce
  seeds.
• They can also bud asexually through a process
  called vegetative reproduction. The little eyes
  on potatoes are actually buds.
• Buds are groups of cells that can undergo rapid
  mitosis and develop into new plants.

14
Some Organisms Reproduce Asexually and Sexually

• Sea stars are animals that can reproduce sexually
  or asexually.
• Sea star arms can regenerate an entire sea star
  as long as part of the central body is attached.

15
Different Gametes

• Most sexual organisms have two different types of
  gametes
• Large stationary gametes called eggs or ova
  produced by the female.
• Small mobile gametes called sperm produced by the
  male.

16
Sperm

• Sperm are usually quite small and simple.
• The nucleus is in the head.
• The tail is built for motility to move the sperm.
• In the middle are the mitochondria which produce
  energy for the tail to move.

A human sperm cell is about 5 micrometers in
diameter. A micrometer is 1 millionth of a meter.
17
Ovum or Egg

• Ovum are usually much larger than the sperm.
• In some cases 1000X larger.
• The ovum is usually much more complicated
• Nucleus
• Other organelles such as mitochondria and
  ribosomes.
• Reserve supply of food for the new organism.

The plural for ovum is ova
The ovaries are the organs that produce the ova
18
The Human Egg

• A woman has the maximum number of potential eggs
  (primary oocytes) while still a fetus.
• She has more than 7 million potential eggs. 
• An oocyte is the cell that develops into the egg.
  
• By birth the number has fallen to 1 or 2 million,
  and by puberty to about 300,000. 
• Only 300 to 400 reach maturity.
• A human oocyte is about 100 micrometers in
  diameter, which is large for a cell. 
• A micrometer is 1/1,000,000 of a meter.
• If it is not fertilized within a day of its
  ejection from the ovary, it dies.

19
An Egg is a Single Cell

• Every egg is only a single cell.
• This is true whether the egg is the size of a
  human oocyte or the size of an ostrich egg.
• An ostrich egg is about 18 cm long.
• It is 10,000 times bigger than a human oocyte.

20
Determining Sex

• In general the organism that produces sperm is
  male and the one that produces the ovum is
  female.
• However, some species change sex during their
  lifetime.
• This allows an individual to be whatever sex is
  most advantageous to a species at any given time.

21
Organisms That Change Sex

• The blue headed wrasse is a fish lives in
  tropical reefs and eats parasites off the scales
  of other fish.
• Usually one male lives with five or six females.
• The male is larger than the females.
• When the male dies, the largest female becomes
  male.
• Within an hour after the males death she starts
  acting like a male.
• Within two weeks she produces sperm.

22
Body Cells vs. Sex Cells

• In body cells, chromosomes occur in matching
  pairsone from the male parent and one from the
  female parent.
• Each member of the pair has genes that code for
  the same traits.
• The two chromosomes of a matching pair are called
  a homologous pair.
• Body cells are represented by the symbol 2n
  meaning diploid.
• What is the diploid in humans.

23
Gametes are Haploid

• Gametes not only look different than body cells.
• Gametes also contain only half the chromosomes of
  body cells23 chromosomes.
• The chromosomes that determine sex are the X and
  Y chromosomes.
• Females have two X chromosomes in their somatic
  cells.
• Males have an X and Y chromosome in their somatic
  cells.
• Do gametes only contain the sex chromosomes?

24
The Sex Chromosomes

• Every cell has the sex chromosomes.
• However, they are only activated in the gametes.
• The gametes have one of every chromosome, not
  just the X and Y chromosome.
• Each egg of a female will contain one X
  chromosome.
• Each sperm of a male will contain either an X or
  a Y chromosome.

25
(No Transcript)
26
Gametes Have Half the Chromosomes

• Gametes are haploid and are represented by the
  symbol n.
• The union of two haploid gametes to form a
  fertilized zygote restores the number of
  chromosomes to the diploid number.
• Gametes become haploid through a special type of
  cell division called meiosis.