Homework from last class:• Complete the Introduction to Meiosis and

Reproductive Systems worksheet

• Study for your Genetics and Reproductive Systems quiz

Quiz Time!

You have about 10 minutes to write the quiz.

Good luck!

2

Chapter 6 pp. 191-197

Ch. 6.1 Meiosis

MeiosisMeiosis: the form of cell division that produces

gametes (sex cells) with half the number of chromosomes as body cells

Diploid (2n) Haploid (n) parent cell sex cells

Meiosis only occurs in gonads (testes or ovaries)

Male: spermatogenesis: formation of sperm (spermatozoa)

Female: oogenesis: formation of eggs (ova)

Meiosis is similar to mitosis, but there are several differences:• Involves 2 cell divisions•Results in 4 cells with ½ the genetic information (n instead of 2n)

Meiosis occurs in 2 phases:

Meiosis I (1st cell division)

Meiosis II (2nd cell division)

Meiosis I

Meiosis II

Spermatogenesis & Oogenesis

Sperm formatio

n

Egg formatio

n

Meiosis I

Meiosis II

Spermatogenesis

Oogenesis

Meiosis I• Prior to meiosis I, DNA replicates once, in

interphase

Fig 6.4 p. 191

Meiosis I• In meiosis I, a pair of matching homologous

chromosomes, one from each parent, lines up at the equator

Homologous chromosomes: a pair of matching chromosomes

Fig 6.5 p. 191

Meiosis I• Homologous

chromosomes line up at the equator

• The homologous chromosome pair separates and moves to opposite poles of the cell

• 2 daughter cells result

Fig 6.5 p. 191

Crossing Over

Crossing over: event in meiosis I where non-sister chromatids exchange segments of DNA; results in variation in gametes

• As a result of crossing over, each chromosome picks up new genetic information from the other

Independent Assortment

Independent assortment: an event in meiosis I where homologous pairs of chromosomes separate and sort themselves into daughter cells

• Genes are shuffled leads to genetic diversity

Crossing Over and Independent Assortment

Fig 6.6A p. 192

Meiosis II

• DNA not replicated again before meiosis II begins

• Meiosis II is like mitosis (in both processes, the chromatids of each chromosome are pulled to opposite poles

• Each daughter cell inherits 1 chromatid from each chromosome

• 4 haploid (n) daughter cells result Fig 6.4

p. 191

Outcome of Meiosis II Fig 6.6B p. 193

Summary of Meiosis

Meiosis Animationhttp://highered.mcgraw-hill.com/sites/0072495855/student_view0/chapter28/

animation__how_meiosis_works.html

Chromosome Mutation in Meiosis

Chromosome mutations can occur spontaneously

• Chromosome mutations can cause genetic changes

• Parts of chromosomes can be inverted, deleted, duplicated or moved to another spot (see p. 194)

Mutagens can cause chromosome mutations

• Mutagens (ex. radiation, chemicals) can cause chromosome changes

• Can lead to genetic disease or death

Consequences of failed separation of chromosomes in meiosis

• Failed separation = a gamete may end up with no chromosome or too many copies of a chromosomes.

• Zygotes that result from these gametes rarely survive, and if they do, they will have serious genetic disorders.

Diagnosing Genetic DisordersThe chromosomes of an individual can be studied

Karyotype:

an image that shows the number of chromosomes a person has; used to diagnose genetic disorders

Down syndrome karyotype

Homework for next class:• Complete Activity 6-1D worksheet (if not

completed in class)• Complete Check Your Understanding questions 2,

3, 5, 6, 7, 9, 10, 11, 13, 15, 16 (p. 203)• Read over class notes and check class blog

http://www.msoonscience.blogspot.com

Works CitedImages taken from the following sources:http://biologydiva.pbworks.com/w/page/14796955/Chapter-22http://chsweb.lr.k12.nj.us/mstanley/outlines/meiosis/APMeiosis.htmhttp://www.bcscience.com/bc9/index.htmlhttp://geneticssuite.net/node/21http://www.sflorg.com/sciencenews/scn100608_01.html