Chromosomes, Mitosis and Meiosis Chromosomes, Mitosis and Meiosis Chapter 10.
Honors Biology Spring 2013. With a neighbor, discuss the following: What is meiosis? How does it...
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Transcript of Honors Biology Spring 2013. With a neighbor, discuss the following: What is meiosis? How does it...
Essential Questions
What is meiosis and why is it necessary?
What are the stages of meiosis?
How does meiosis compare to mitosis?
Haploid vs. Diploid
Diploid cells1. Body cells2. Contains homologous chromosomes3. 2N
B. Haploid cells1. Sex cells2. contains one member of each pair3. 1N
Meiosis
Meiosis– process which reduces by half the
number of chromosomes in a diploid cell
• meiosis occurs in sex organs of individual
Overview of Meiosis
A. Meiosis - formation of sex cells 1. Meiosis is cell division that results in a gamete containing half the number of chromosomes of its parent.2. Meiosis includes 2 steps that each closely resemble corresponding steps in mitosis.
Phases of Meiosismeiosis I•Prophase I•Metaphase I•Anaphase I•Telophase I &?•Cytokinesis PMAT I
Meiosis II•Prophase II•Metaphase II•Anaphase II•Telophase II &?• Cytokinesis PMAT II
Meiosis 1
Meiosis I - reduction division1. Interphase I2. Prophase I3. Metaphase I4. Anaphase I5. Telophase I
Meiosis 1: Prophase 1–chromatin condenses to form chromosomes–homologous chromosomes attach to form tetrads
Meiosis 1: Prophase 1
– when tetrads form, crossing over can occur
– crossing over is the
exchange of part of
homologous chromatids
Meiosis 1: Telophase and Cytokinesis
• telophase I– nuclear
membrane reforms
• cytokinesis– cytoplasm
splits
Meiosis 1: Results
• results– two haploid (n)
daughter cells = ½ the
number of chromosomes as
parent cell
Meiosis II
Meiosis II - separation of chromatids1. Interphase II2. Prophase II3. Metaphase II4. Anaphase II5. Telophase II
•telophase II–nuclear envelope reforms
•cytokinesis–cytoplasm splits
Meiosis II: Telophase and Cytokinesis
Ploidy
parent cell?•dipliod (2n)after meiosis I?•haploid (n) (monopliod)after meiosis II?•hapliod (n)
Purpose of Meiosis: Diversity
Meiosis and sexual reproduction significantly contribute to genetic variation among offspring.
Purpose of Meiosis: Gametes
• role of meiosis is to produce gametes
• meiosis in males– spermatogenesis– produces 4 sperm cells
• meiosis in females– oogenesis– produces 1 ovum (egg cell) and 3
polar bodies
Mitosis vs. Meiosis
where does is occur?• meiosis – sex organs; mitosis – somatic cells number of cell divisions?• meiosis – 2; mitosis – 1 number of cells produced?• meiosis – 4; mitosis – 2 ploidy of daughter cells?• meiosis – hapliod (n); mitosis – dipliod (2n) # of chromosomes compared to parent cell?• meiosis – ½ # chromosomes; mitosis – same