CSCOPEUnit 08Lesson 02

PROCESS OF MEIOSIS

Asexual Reproduction Sexual Reproduction

• Uses only mitosis• Produces clones—genetically

identical offspring• Fast and effective

reproduction to spread organism

• No diversity

• Combination of two haploid sex cells

• Fertilization: combines genetic information from two separate cells with ½ of the original genetic information of parent organism

• Gametes are from separate parents. (female = egg, male = sperm)

• Zygote (new individual) has two sets of chromosomes, one from each parent

• Process changes diploid cells to haploid gametes—leading to an increase in diversity of offspring

ASEXUAL VS. SEXUAL REPRODUCTION

What is the advantage of an organism that reproduces sexually rather than asexually?An organism that reproduces sexually will have more genetic diversity than one that reproduces asexually.

ASEXUAL VS. SEXUAL REPRODUCTION

Four Phases: Prophase I Metaphase IAnaphase I (and)Telophase I

Genetic diversity results from meiosis I.

MEIOSIS I

Homologous (same) chromosomes pair (synapsis)

Homologous pairs called bivalents—two chromosome with four chromatids

Nuclear membrane dissolvesChromosomes attach to spindle fibers and

begin to move

PROPHASE I

Homologous chromosomes (bivalents) line up at the equator to form tetrads.

Random orientation results in diversity.50/50 chance of getting either parent’s

homologue for each chromosome

METAPHASE I

Tetrad

Homologous chromosomes separate.Chromosomes with TWO chromatids

move to opposite poles.Daughter cells will have 23 chromosomes

(haploid) but with two chromatids.

ANAPHASE I

Nuclear membrane begins to reform Cell may quickly move to meoisis II

TELOPHASE I

Similar to mitosis BUT no synthesis phase (no DNA replication)

Chromatids are NOT identical because of crossing over (recombination).

Separates chromatids and produces two daughter cells with 23 chromosomes that have one chromatid each

MEIOSIS II

Crossing Over: Exchange of genetic information between homologous chromosomes that results in recombinant chromosomes and genetic diversity

IMPORTANT CONCEPTS!!!

Independent Assortment: Chromosomes randomly line up during metaphase I, and there are various ways that the homologous chromosomes may line up—again resulting in genetic diversity

IMPORTANT CONCEPTS!!!

http://www.mhhe.com/biosci/ap/ap_prep/bioD6.html