November 12th, 2013 Leave out your section 6.2 PN & vocab to

be stamped.

Seatwork instructions:Do you think it’s ethical to bring a species

back from extinction? Write 2-3 sentences explaining your position. You must support your claim using at least one piece of information from the video.

Agenda Nov. 12: Meiosis & crossing over Nov. 14: Mendelian genetics Nov. 19: Mendelian genetics cont. Nov. 21: Incomplete dominance &

codominance Nov. 26: Chapter 5-7 test: Cell division

& genetics

Mitosis

Mitosis

Learning Target LT:

Students will be able to describe the process of mitosis.

SC: I will be able to describe the similarities

and differences between the processes of mitosis and meiosis.

Meiosis Mitosis focuses on the replication of somatic

cells. Somatic cells make up most of your tissues and

organs. Ex. Eyeballs, kidney, spleen

Meiosis focuses on the replication of gametes. Gametes are sex cells which are used in sexual

reproduction. Ex. Ova (eggs) and spermatozoa (sperm)

Haploid & Diploid Somatic cells and

gametes have different numbers of chromosomes.

Somatic cells are diploids (2n), meaning that they have two sets of chromosomes.

Gamete cells are haploids (1n), meaning that they have one set of chromosomes.

Haploid & Diploid Analogy of a pair of

gloves: If you had 23 pairs

of gloves, you would have a total of 46 gloves.

Each pair has an identical partner.

Homologous Chromosomes Similarly, your somatic cells have 23

pairs of chromosomes, for a total of 46. “Paired” chromosomes are called

homologous chromosomes.

Homologous Chromosomes Chromosome pairs 1 through 22 are autosomes.

Autosomes contain genes that are not directly related to the sex of an organism.

The 23rd pair contains sex chromosomes that directly control the development of sexual characteristics. In humans, we say that an organism with two X

chromosomes is female (XX), and with one X and one Y is male (XY).

Meiosis Meiosis is a form of nuclear division that

divides a diploid cell (2n) into a haploid cell (1n).

It is essential for sexual reproduction – or the fusion of two gametes – to occur. During fertilization, you inherit one copy of

chromosomes from your mother’s egg (1n), and one copy of chromosomes from your father’s sperm (1n).

Sexual reproduction allows for genetic variability. Without it, we would all be clones of our parents.

Fertilization

1n Ovum 1n

Sperm

Haploid

2nZygote

Diploid

Asexual Reproduction Not all organisms utilize sexual

reproduction. Some organisms utilize asexual

reproduction, which results in offspring that are genetically identical to the parent. Prokaryotes and some eukaryotes

reproduce asexually. These organisms do not undergo meiosis.

Homologous chromosomes Homologous chromosomes are similar

– but not identical to each other. They are the same length & carry the

same genes. You inherited one homologous

chromosome from your father and one from your mother.

Sister chromosomes are duplicated, identical copies of a chromosome that are attached by the centromere.

Meiosis A cell undergoing meiosis divides twice: In Meiosis I, homologous chromosomes separate. In Meiosis II, sister chromatids separate. Result is four haploid cells.

Meiosis I Prophase I:

Cell prepares for division (nuclear membrane breaks down; centrioles & spindle fibers move and assemble).

Homologous chromosomes begin to condense and pair up.

Crossing over occurs.

Crossing Over Crossing over is the exchange of

chromosome segments between homologous chromosomes.

Crossing Over Crossing over results in a new

combination of genes. It is a form of recombination, which is

the mixing of any parental genes. It increases genetic diversity by creating

new, varied gene combinations on a chromosome.

It is responsible for siblings looking similar, but not identical to each other.

Meiosis I Metaphase I:

Spindle fibers align the homologous chromosomes along the cell equator.

Each side of the equator has chromosomes from both parents.

Meiosis I Anaphase I:

The paired homologous chromosomes separate from each other and move toward opposite sides of the cell.

Sister chromatids remain attached.

Meiosis I Telophase I:

The spindle fibers disassemble.

Nuclear membrane re-forms. Cell undergoes cytokinesis. Resulting cells have 23

duplicated chromosomes (sister chromatids).

Meiosis II Prophase II:

Centrosomes and centrioles move to opposite sides of the cell.

Spindle fibers begin to assemble.

Meiosis II Metaphase II:

Spindle fibers align the chromosomes (still attached as sister chromatids) along the cell equator.

Meiosis II Anaphase II:

Sister chromatids are pulled apart from each other and move to opposite sides of the cell.

Meiosis II Telophase II:

The nuclear membrane re-forms around the chromosomes.

Spindle fibers break down.

Cell undergoes cytokinesis.

Gametogenesis Meiosis results in haploid cells.

These cells are incapable of fertilization until gametogenesis occurs.

Male gametes undergo spermatogenesis and female gametes undergo oogenesis.

Spermatogenesis Spermatogenesis produces four, small

male gametes, known as spermatozoa.

Oogenesis Oogenesis produces one ovum (egg) and

two polar bodies. The ovum receives most of the organelles,

cytoplasm, and nutrients during cytokinesis. The polar bodies have little more than DNA

inside them and are eventually broken down.

Errors in Meiosis In very rare occasions, an error will

occur during meiosis in which one of the resulting gametes has one too many chromosomes, and another has one too few.

Some of these gametes can still be fertilized and produce viable offspring.

Trisomy The result of this fertilization is trisomy.

Individuals with trisomy have 47 chromosomes instead of 46.

Commonly known genetic disorders include: Trisomy 21 (Down syndrome) Trisomy 18 (Edwards syndrome) 47,XXX (Triple X syndrome) 47,XXY (Klinefelter syndrome) 47,XYY

Trisomy Resultant offspring have a specific set of symptoms

that is dependent on the type of genetic disorder. Trisomy 21:

Physical growth delays, a particular set of facial characteristics, & severe degree of intellectual disability.

47,XXY: Delayed development, less muscle mass, less facial and

body hair, larger breasts, & broader hips. 47,XXX:

The only genetic condition that usually results in no distinguishable difference between normal population.

Venn Diagram Create a venn diagram describing the

similarities and differences between mitosis and meiosis.

Homework Section 6.6:

Vocab PowerNotes Reinforcement

Snurfle meiosis Watch video: http://bit.ly/Snurfle Complete worksheet