MEIOSIS
Sexual Reproduction (two parents) Meiosis Sexual Reproduction (two parents)
https://www.youtube.com/watch?v=qCLmR9-YY7o
What is the advantage of sexual reproduction? Genetic Variation
3 things that contribute to genetic variation Independent assortment Crossing Over Random Fertilization These two processes occur during meiosis
Why Meiosis? Meiosis - cell division that halves the # of chromosomes when forming sex cells such as gametes or spores Meiosis is the production of sex cells (gametes). During meiosis, the number of chromosomes in the daughter cells are reduced from the number of chromosomes in the parent cell (this is extremely important).
How does Meiosis Occur? Animation of meiosis to use as a review Meiosis Animation from http://biology.clc.uc.edu/courses/bio104/meiosis.htm
Independent Assortment Random arrangement of pairs of chromosomes
What is crossing over? *Exchange of genetic material between homologous chromosomes *Occurs during prophase I of meiosis.
Crossing Over Crossing over often happens during meiosis. Have students notice that a segment of DNA has “crossed over” and exchanged with the other chromosome. This results in different combinations of genes for the offspring.
Crossing Over Animation taken from http://www.tokyo-med.ac.jp/genet/anm/mimov.gif
Is there anything that can wrong during meiosis? Yes! It is called nondisjunction. Chromosomes don’t separate properly and some gametes end up with too many or not enough chromosomes.
What happens if nondisjunction occurs? The gamete will die or result in conditions known as trisomy or monosomy. Trisomy - a person has more than 2 copies of the same chromosome. Monosomy – a person only has one copy of a chromosome.
How can you tell that? Take a picture of the chromosomes! This is known as a karyotype.
Normal Female Karyotype
Normal Male Karyotype
Abnormal Karyotype-Trisomy #21 Down’s Syndrome
Abnormal Karyotype – Monosomy of the X chromosome Turner’s Syndrome
Meiosis in males Called spermatogenesis Occurs in the testes Results in 4 viable gametes called sperm
Meiosis in females Called oogenesis Occurs in the ovaries Results in 1 viable gamete called the ovum (egg) and 3 polar bodies (these will die). Why does only one gamete survive? The one egg will need a rich storehouse of nutrients to nourish the young organism that develops when the ovum is fertilized.
Meiosis Review Is the beginning parent cell diploid or haploid (2n or n)? Diploid 2. Are the resulting daughter cells diploid or haploid (2n or n)? Haploid Questions are animated so you can ask each question and get an answer before going to the next question.
More Meiosis Review 3. How many daughter cells are produced? 4 Are the resulting daughter cells different from the parent cell? yes
More Meiosis Review 5. Are the resulting daughter cells different from each other? yes 6. How many chromosomes are in a human parent cell? 46 Questions are animated so you can ask each question and get an answer before going to the next question. 7. How many chromosomes are in a human daughter cell? 23
More Meiosis Review 8. What types of cells are produced by meiosis?
Let’s review Mitosis & Meiosis
Visual review of the differences between mitosis and meiosis
Mitosis vs. Meiosis √ √ √ √ √ √ Event Mitosis Meiosis Produces 4 cells Mitosis vs. Meiosis Event Mitosis Meiosis Produces 4 cells Produces 2 cells New cells identical New cells different New cells have the same number of chromosomes as parent New cells have fewer chromosomes than parent √ √ √ √ The answers are animated so you can have students answer the question before you reveal the answer. √ √
Mitosis vs. Meiosis √ √ √ √ √ Event Mitosis Meiosis Mitosis vs. Meiosis Event Mitosis Meiosis Beginning cells diploid (2n) Beginning cells haploid (n) Ending cells diploid (2n) Ending cells haploid (n) Produces egg and sperm Produces body cells (autosomes) √ √ The answers are animated so you can have students answer the question before you reveal the answer. √ √ √
https://www.youtube.com/results?search_query=meiosis+square+dance