Chapter 5Part II: Meiosis

Learning Target

7. Recognize the type of daughter cells formed during meiosis and the chromosome number as compared to the parent cell.

9. Explain how meiosis and sexual reproduction increases genetic diversity

Meiosis

• Reduction division reduces 2n cells to 1n cells

• Two nuclear divisions 4 haploid daughter cells (no DNA replication after S phase)

• Produces gametes • Homologous Chromosomes (Matching

chromosomes 1 from Mom, 1 from Dad)

• Two parts Meiosis I and Meiosis II

Comparison of meiosis and mitosis

• Fig 5.14

Meiosis I

• Similar to Mitosis– Prophase I– Metaphase I– Anaphase I– Telophase I

Prophase I

• Exactly like Mitosis PLUS – Synapsis

• Homologous chromosomes pair up form tetrads

– Crossing-over• Tetrads wrap

around each other & exchange DNA

Metaphase I

• Tetrads pushed to center of cell

Anaphase I

• Tetrads pulled apart to opposite sides of cell (chromatids are still joined at centromere) separate independently (Independent Assortment)

Telophase I

• Reverse of Prophase I• Followed by Cytokinesis I

(Interkinesis)

Cytokinesis IInterkinesis

Meiosis II• EXACTLY LIKE

MITOSIS!!!

Results of Meiosis

• 1 cell (2n) 4 cells (1n)

• Genetic recombination

• Genetic variability

• Step-through animation • http://www.sumanasinc.com/webcontent/anisa

mples/majorsbiology/meiosis.html

Benefits of Meiosis

• Genetic variation increases chances of survival !

Learning Check

• 8. How would you describe the daughter cells that come from Meiosis?

• 9. What are ways genetic diversity is increased in Meiosis? (3 ways)

Learning Targets

8. Explain how chromosomes are transmitted to the next generation via mitosis or meiosis followed by fertilization.

10. Compare and contrast spermatogenesis and oogenesis.

• Requires both mitosis and meiosis

• In females meiosis is part of the process of oogenesis

• In males meiosis is part of spermatogenesis

• At fertilization, the resulting zygote divides by mitosis for the processes of growth and development

• Mitosis is used for repair throughout life

Human Life Cycle

Spermatogenesis

• 1 Primary spermatocyte (2n)

• 2 Secondary spermatocytes (1n)

• 4 spermatids (1n)

• 4 sperm cells

• Begins at puberty and continues throughout life

Oogenesis• Begins before birth with

Meiosis I– proceeds to Meiosis II– STOPS at Metaphase II– Primary oocyte (2n) – Secondary oocyte (1n) +

polar body (1n) (enters fallopian tube)

• If fertilization occurs, Meiosis II proceeds & 2o oocyte egg & polar body

• Benefit: 1 egg gets almost all the cytoplasm– Why?

Spermatogenesis and oogenesis

Comparison of meiosis and mitosis

• Fig 5.14

Learning Target

• 11. Describe the role of programmed cell death in development.

Cell Death…• Apoptosis…but why?

– Allows body to absorb nutrients from those cells

Learning Targets

12. Determine sex and chromosomal abnormalities from a karyotype.

Human Karyotypes

• How many chromosomes do humans have? – 23 PAIRS!

• A male genotype is:– XY

• A Female genotypes is:– XX

Learning Check!

• Gender?

• Abnormalities?

Learning Check!

• Gender?

• Abnormalities?