1. Ch11_Reproduction
of Organisms
2. Lesson1_ Sexual
Reproduction and
Meiosis
3. What is Sexual Reproduction?
Sexual reproduction
egg
sperm
fertilization
zygote
5. Joining of 2 cells… Type of reproduction in which
genetic materials from two different cells combine
producing an offspring
5. Female; formed in the ovaries (haploid)
5. Male; produced in the testis (haploid)
5. Sperm + egg join to produce a new cell (offspring)
5. The new cell produced (diploid)
3. Diploid Cells
diploid
Body cells
Sex cells
5. Full set of chromosomes(2n; where n=the number of
chromosomes)
5. Somatic cells. All cells in the body that contain a full set
of chromosomes (diploid). * Are not directly involved in
reproduction (sperm/egg)
5. Gametes. Cells involved in the production of a new
organism (sperm and egg). These cells only contain half
of the full SET of chromosomes (haploid). So when they
join together they create a cell with a COMPLETE SET
of information.
4. Chromosomes
homologous
5. Chromosome # is unique to each organism. Humans
have a set of 23 (46 total), dropshila fly a set of 4
chromosomes (8 total), rice has a set of 12 chromosomes
(24 total).
5. Pairs of chromosomes that have genes for the traits that
are arranged in the same order.
5. A zygote will not develop properly if it has too many or
too little chromosomes.
3. Haploid cells
Haploid
Meiosis
5. Cells that have only one chromosome from each pair.
5. One diploid cell divides to form four haploid SEX cells.
3. The Phases of Meiosis
Meiosis I
Meiosis II
5. First half of cell division. Parent cell creates 2 UNIQUE
daughter cells that are diploid
5. Second division of the nucleus of the daughter cells from
Meiosis I. Four UNIQUE, HAPLOID daughter cells are
products of this phase.
4. Phases of Meiosis I
Interphase
5. During the life cycle of the cell, the cell grows, produces
organelles (cell parts) and duplicates DNA (genetic
material) before entering the M-phase (mitosis and
cytokinesis)
5. G1 Phase, S-Phase, G2 Phase
5. Chromosomes are made up of 2 chromatids (left and
right arms) attached by a centromere
Prophase I
5. Duplicated chromosomes condense and thicken
5. Homologous (same categories) chromosomes come
together and form pairs
5. Nuclear membrane disintegrates and nucleolus
disappears
5. Appearance of centrioles (animal cells) and spindle
fibers (microtubules)
5. Centrioles/Spindle fibers move to opposite poles
5. Crossing over takes place (chromosomes overlap and
swap information)
5. Chromosomes line up along the middle of the cell
5. Spindle fibers attach to the centromere of each
chromosome
Metaphase I
Anaphase I
Telophase I and
Cytokinesis
Product/Result
Prophase II
5. Chromosomes pairs separate and are pulled to opposite
ends of the cell
5. The nuclear membrane reforms around new sets of
chromosomes
5. Nucleolus reappears and the spindle fibers disappear
5. At the same time, the cell cytoplasm forms cleavage and
pinches off to form 2 separate cells (in plants, cleavage
does not occur, but rather the appearance of a cell plate
to later form a cell wall)
5. Two Unique Diploid daughter cells
5. Nuclear membrane breaks apart
Chromosomes do not
undergo replication (like it
did prior to prophase I)
Metaphase II
Anaphase II
Telophase II and
Cytokinesis
Products
5. Sister chromatids line up at the center (equator) of the
cell
5. Sister chromatids are pulled apart and move away to
opposite poles
5. During final phase, nuclear membrane forms around
each set of chromatids forming 4 new nuclei
5. Division of the cytoplasm occurs (cytokinesis) forming
four complete cells.
5. Four UNIQUE haploid cells (gametes)
3. Importance of Meiosis
4. Maintaining Diploid Cells
5. When haploid cells join together, during fertilization,
they create a diploid zygote (fertilized egg)
5. The fertilized egg, will then continue to undergo mitosis
throughout the entire life of the organism
4. Creating Haploid Cells
Crossing over
5. Helps maintain the correct number of chromosomes of
healthy organism in future generations
5. Increase genetic variation due to crossing over
5. Segments on the chromosome are exchanged between
homologous chromosomes.
5. Sex cells produces will be unique, since they are various
combinations of information
5. When cells combine to become a fertilized egg, the
increase of possible combinations contribute to genetic
variation within a species.
3. Difference in Mitosis and Meiosis
Mitosis
5. Occurs for growth and repair or replacement of damaged
tissue
5. Body Cells/Somatic Cells
5. Cell divides to form 2 identical daughter cells
5. The genetic information is the same as the
original/parental cell
5. Diploid (2 sets of chromosomes/Full set)
Meiosis
5. Occurs in the reproductive organs of multicellular
organisms and forms sex cells used for sexual
reproduction.
5. Gametes (sex cells): sperm and egg (ova)
5. Diploid cell divides twice to produce 4 different (unique)
daughter cells
5. Due to crossing over, multiple possible genetic
combinations are created
5. Haploid (1 set of chromosomes)
3. Advantages of Sexual Reproduction
4. Genetic Variation
Independent Assortment
5. Genes for different traits can segregate independently
during the formation of gametes. Due this genetic
variation increases within a species.
4. Selective Breeding (Artificial Selection)
5. When you choose a desired trait
5. Ex: broccoli… dog breeds
3. Disadvantages of Sexual Reproduction
Requires time and energy
5. Time required to grow and develop
5. Time required to find a mate
5. Exposure to disease, predators and harsh environmental
conditions (when looking for a mate)
5. Fertilization cannot take place during pregnancy (which
may last up to 2 years in some mammals)