Houston…We have a problem… Non-disjunction: Cell division in which the sister chromatids do NOT separate correctly, resulting in gametes with an abnormal number of chromosomes. This is how Down Syndrome happens…the chromosomes don’t separate correctly, and too many end up in the gamete. People with Down Syndrome have 47 chromosomes instead of ____. These are correct! No problem Notice there are NO chromosomes in these cells! Notice that non-disjunction occurred here too! 46

Click on Link for animation… Meiosis Overview

Compare & Contrast Mitosis & Meiosis Page 34 in Comp Book Compare & Contrast Mitosis & Meiosis Mitosis Meiosis * Occurs in body cells Both * Occurs in gametes cells * Divides once * Divides twice (meiosis 1 & II * Creation of new cells * Creates 2 cells * Creates 4 cells * DNA replicates once * Are genetically identical * Are NOT genetically identical * Increases genetic diversity

This results in gametes with abnormal numbers of chromosomes: Clicker Question #18 This results in gametes with abnormal numbers of chromosomes: meiosis mitosis non-disjunction crossing-over

This is an example of non-disjunction: Clicker Question #19 This is an example of non-disjunction: Color blindness Down Syndrome Cystic fibrosis Sickle cell anemia Karyotypes—Identify genetic diseases

Answer: NO...They are using Binary Fission Many Bacteria & protozoans do not need a partner to reproduce. Are they reproducing using mitosis? Answer: NO...They are using Binary Fission Binary Fission – Asexual form of reproduction used by some prokaryotes in which a cell divides into two genetically identical cells. (creates a new individual) SIMILAR/LIKE “cloning” themselves 1 bacterium could become 1,000,000,000 (billion) in 10 hours!

What are the advantages & disadvantages to being asexual & sexual? Asexual Reproduction Advantages Disadvantages Can reproduce without a partner… They don’t have to find a mate/partner. No genetic variation…They are clones. Its putting all your eggs in one basket. If a something kills the parent, it WILL kill ALL the offspring too. Easily becomes extinct with little change to environment. Able to reproduce quickly. The greater the number of offspring, the better the survival rate of the population. Quick reproduction is also a disadvantage because too many individuals will be competing with each other for food & space

What are the advantages & disadvantages to being asexual & sexual? Sexual Reproduction Advantages Disadvantages Genetic diversity! Has the ability to create endless recombination of genes (crossing-over) coming from 2 parents, all individuals are different in some way. Must find a partner. Very difficult if the population is low and spread out. Difficult to recover if the species is endangered. The species is more able to adapt to environmental changes Slow reproduction….takes time… Slow population growth

Prokaryotes reproduce using: Clicker Question #20 Prokaryotes reproduce using: meiosis mitosis binary fission binary fusion

Which of the following is an advantage of asexual reproduction Clicker Question #21 Which of the following is an advantage of asexual reproduction genetic diversity the ability to reproduce quickly the ability to adapt to new habitats slow reproduction

Which of the following is an advantage of sexual reproduction Clicker Question #22 Which of the following is an advantage of sexual reproduction genetic diversity the ability to reproduce quickly the ability to reproduce many offspring do not have to find a sexual partner

The End