Meiosis and Sexual Reproduction

Asexual Reproduction Asexual Called vegetative reproduction in plants “A” = Not Sexual Called vegetative reproduction in plants A form of duplication using only mitosis. Example, a new plant grows out of the root or a shoot from an existing plant.

Asexual Reproduction Produces only genetically identical offspring since all divisions are by mitosis. Offspring called meaning that each is an exact copy of the original organism This method of reproduction is rapid and effective allowing the spread of an organism Example: Bacterial growth Since the offspring are identical, there is no mechanism for introducing . clones diversity

Asexual Reproduction In prokaryotes and some one-celled eukaryotes, cells undergo _____ _____ Hydra reproduce by ________ Planaria reproduce by ____________ Several plants reproduce through vegetative reproduction. Most of these organisms can reproduce sexually as well. binary fission Escherichia coli Paramecium caudatum budding fragmentation

Why do organisms have sex? Sexual reproduction increases variety by producing new genetic combinations. It’s costly to the organism It’s time-consuming There are far fewer offspring

Sexual Reproduction Consists of Meiosis and Fertilization Meiosis: Formation of two haploid sex cells (gametes). Meiosis is a process to convert a ________ cell to a ________ gamete, and cause a change in the genetic information to increase diversity in the offspring. In humans, meiosis only occurs in the ________ Spermatogenesis: In the ______(in males) Oogenesis: In the _______ (in females) Fertilization: Combination of genetic information from two separate cells that have one half the original genetic information diploid haploid gonads testes ovaries

+ = Sexual Reproduction Gametes for fertilization usually come from separate parents Female produces an _____ Male produces _______ Both gametes are haploid, with a single set of _____________. The new individual is called a ______, with two sets of chromosomes (______). Once the zygote begins to divide, it is called an _______. egg sperm chromosomes zygote diploid embryo

Chromosomes vary from species to species Prokaryotes generally have only ___ major chromosome Consisting of a single circle of DNA Turkeys have 82! Giant redwoods have 22! A tropical fish has the same number of chromosomes as humans, which is ____ one 46

Chromosome Characteristics Diploid set for humans; 2n = 46 Two types: Autosomes (#1 – 22) Sex Chromosomes (#23)

Chromosome Characteristics Autosomes Homologous chromosomes Humans have 22 sets of 2 One from each parent Sex chromosomes Humans have 1 set of 2 Female-sex chromosomes are homologous (XX) Male-sex chromosomes are non-homologous (XY)

What can Chromosomes tell us? Scientists can organize chromosomes in a cell into a _________ karyotype In a karyotype, chromosomes are arranged in order of size, banding pattern, and centromere position: Let’s see if we can arrange a karyotype together: http://learn.genetics.utah.edu/content/begin/traits/karyotype/

What does this person pass on to the next generation? What sex will this person be? What does this person pass on to the next generation?

Meiosis: Reduction/Division Two divisions: Meiosis I & Meiosis II

Prophase I Unlike Mitosis: Homologous chromosomes group with other homologous chromosomes to form a “tetrad” A “chiasma” occurs at the point where the chromosomes cross over Like Mitosis: Nuclear membrane disappears Spindles form Chromatin condenses into chromatids

Metaphase I Homologous chromosomes line up at the metaphase plate. Microtubules (spindles) attach to the kinetochore

Anaphase I Homologous chromosomes separate. Sister chromatids remain attached.

Telophase I Two daughter cells are formed with each one containing only one chromosome of the homologous pair. The daughter cells are now haploid.

Meiosis II: Gamete formation Prophase II: DNA does not replicate. Prophase II is just like mitotic prophase.

Metaphase II: All of the chromosomes line up at the metaphase plate.

Anaphase II: Centromeres divide Sister chromatids migrate separately to each pole.

Telophase II: Cell division is complete. Four haploid daughter cells are obtained

Summary of Meiosis