4.2 Sexual Reproduction (Meiosis)

What is Sexual Reproduction?

• Produces genetic variability differences

• Genetic information is inherited from two parents

• Each parent contributes a copy of half of its genetic information but each offspring is genetically different from their parents

• It can be slightly different depending on the species of meiosis

What is Meiosis

• A process in which haploid gametes are formed

What is the purpose of meiosis?

• Ensures sex cells have the right type and number of chromosomes

• Ensure that when gametes come together the zygote receives the right type and number of chromosomes

Where does Meiosis occur ?

• In the reproductive organs of sexually reproducing organisms

• In humans its in the Sperm ( where dem balls produce sticky spidy strings )

• And Egg produced in the ovaries

Meiosis occurs in 2 divisions what are they? Each division is divided into ?

• the two divisons are Meiosis 1 and Meiosis 2

• Each division is divided into

• Prophase

• Metaphase

• Anaphase

• Telophase

Meiosis 1 (end of interphase)

• DNA copied

• Chromatin present

• Centrioles present

Meiosis 1 Prophase 1 is ?

• Chromosomes condense (shorten and thicken)

• each chromosomes have been copied during interphase and is now made up of 2 sister chromatids that are joined at the centromere

• Nuclear membrane begins to dissolve

• Centrioles separate and move to opposite ends of the cell

• This is where spindle fibers form

Crossing over occurs when ?

• Homologous chromosomes lie side by side length wise

• They often break and rejoin in several places

• Allows chromosomes to exchange genetic material

• Allows for greater genetic variation (difference) in a population of species

• It recombines genes in new ways

Meiosis 1 Metaphase 1

• Microtubules move homologous chromosomes to the middle of the cell

• Chromosomes have greater genetic variation as crossing over has already occurred

Meiosis 1 Anaphase 1

• Homologous pairs move to opposite ends of the cell as their centromeres separate

• Chromatids do not separate as they do in mitosis

Meiosis 1 Telophase 1

• Chromosomes may decondense slightly nuclear membranes may form

• 2 daughter cells with half the number o chromosomes of the parent cell

• Reduction division is complete

Meiosis II Prophase

• Nuclear membrane dissolves and spindle fibers begin to form

• DNA was not copied in between meiosis 1 and 2

Meiosis II Metaphase II

• Sister chromatids line up at the metaphase plate

Meiosis II Anaphase II

• Centromeres split and one chromatid of each chromosome is pulled to each of the opposite poles

Meiosis II telophase II

• Nuclear membrane begins to reform as meiosis

• 4 haploid cells result all of which are genetically different

A summary of meiosis

• Stage one is the separation of homologous pairs of chromosomes

• Stage 2 separation of sister chromatids

What is independent assortment ?

• Process in which chromosomes during meiosis line up and split in many different ways

• Half of your chromosomes come from your mother and the other come from your father

• This does not mean this is 50/50 split will be reflected in your gametes

• Some gametes may have more maternal chromosomes and the other may have more paternal chromosomes

What is the Purpose of intendent assortment?

• Genetic variability

• A wide variety of different chromosomes combinations in the gametes

Gametogenesis

• Formation of sex cells (gametes) in meiosis

• Some differences exist in the way male and female meiosis takes place to create sperm and egg cells

• Male meiosis - makes sperm

• female meiosis - makes eggs

Spermatogenesis - Male Meiosis

• Produces 4 functional cells caleed spermatids

• Spermatids undergo differentiation to become sperm