review of terms - brandeis · chapter 2 human heredity by michael cummings ©2006...
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Chapter 2 Human Heredity by Michael Cummings ©2006 Brooks/Cole-Thomson Learning
Review of Terms
• Haploid cells – (1n) with one copy of eachchromosome
• Diploid cells – (2n) with two copies ofeach chromosome
• Somatic – non-germline cells
• Gametes – sex cells (eggs and sperm)
Chapter 2 Human Heredity by Michael Cummings ©2006 Brooks/Cole-Thomson Learning
Meiosis I
• Reductional division
• A diploid cell divides and forms twohaploid cells
• In humans, the chromosome number isreduced from 46 to 23 chromosomes
Chapter 2 Human Heredity by Michael Cummings ©2006 Brooks/Cole-Thomson Learning
Prophase I• Chromosomes
coil• Nuclear
membranebreaks down
• Chromosomespair
• Recombinationmay occur
newly formingmicrotubules
Prophase I
Fig. 2.13a
Chapter 2 Human Heredity by Michael Cummings ©2006 Brooks/Cole-Thomson Learning
Metaphase I
• Chromosomepairs line up onthe midline
Metaphase I
spindleequator
one pair of homologouschromosomes
Fig. 2.13b
Chapter 2 Human Heredity by Michael Cummings ©2006 Brooks/Cole-Thomson Learning
Anaphase I
• Centromeres donot divide
• Chromosomepairs move toopposite poles
Anaphase I
Fig. 2.13c
Chapter 2 Human Heredity by Michael Cummings ©2006 Brooks/Cole-Thomson Learning
Telophase I
• Nuclearmembranereforms
• Chromosomesuncoil
After Cytokinesis• Two haploid cells
are produced
Telophase I
Fig. 2.13d
Chapter 2 Human Heredity by Michael Cummings ©2006 Brooks/Cole-Thomson Learning
Interkinesis
• No DNA synthesis occurs
Chapter 2 Human Heredity by Michael Cummings ©2006 Brooks/Cole-Thomson Learning
Meiosis IIBegins with Haploid Cells
Prophase II• Chromosomes coil• Spindle forms• Nuclear membrane breaks
down• Each chromosome is
composed of two sisterchromatids attached atthe centromere
Prophase II
Meiosis IIFig. 2.13e
Chapter 2 Human Heredity by Michael Cummings ©2006 Brooks/Cole-Thomson Learning
Metaphase II
• Chromosomes lineup on the midlineand attach tospindle fibers
Metaphase II
Fig. 2.13f
Chapter 2 Human Heredity by Michael Cummings ©2006 Brooks/Cole-Thomson Learning
Anaphase II
•Centromeresdivide
•Sister chromatidsmove to oppositepoles
Anaphase II
Fig. 2.13g
Chapter 2 Human Heredity by Michael Cummings ©2006 Brooks/Cole-Thomson Learning
Telophase II
• Nuclear membranereforms
• Chromosomes uncoil
After Cytokinesis• Four unique haploid
cells are produced
Telophase II
Fig. 2.13h
Chapter 2 Human Heredity by Michael Cummings ©2006 Brooks/Cole-Thomson Learning
Unique Haploid Gametes
• Random assortment of maternal andpaternal chromosomes
• Number of possible chromosomalcombinations = 223 or 8,388,608
• Recombination between chromosome pairsincreases the possible combinations
Chapter 2 Human Heredity by Michael Cummings ©2006 Brooks/Cole-Thomson Learning
Summaryof Mitosis
and Meiosis
Fig. 2.15
Chapter 2 Human Heredity by Michael Cummings ©2006 Brooks/Cole-Thomson Learning
Fig. 2-14, p.32
Members of chromosome pair
Each chromosome pairs withits homologue
Pairedhomologues separate
in meiosis I
Sister chromatidsseparate and become
individual chromosomesin meiosis II
Sister chromatidsSister chromatids
Chapter 2 Human Heredity by Michael Cummings ©2006 Brooks/Cole-Thomson Learning
Fig. 2-14a, p.32
Members of chromosome pair
Each chromosome pairs withits homologue
SisterchromatidsSister
chromatids
Chapter 2 Human Heredity by Michael Cummings ©2006 Brooks/Cole-Thomson Learning
Fig. 2-14b, p.32
Pairedhomologues separate
in meiosis I
Sister chromatidsseparate and become
individual chromosomesin meiosis II
Chapter 2 Human Heredity by Michael Cummings ©2006 Brooks/Cole-Thomson Learning
Fig. 2-16, p.34
Chapter 2 Human Heredity by Michael Cummings ©2006 Brooks/Cole-Thomson Learning
Fig. 2-16a, p.34
Chapter 2 Human Heredity by Michael Cummings ©2006 Brooks/Cole-Thomson Learning
Fig. 2-16b, p.34
Chapter 2 Human Heredity by Michael Cummings ©2006 Brooks/Cole-Thomson Learning
Fig. 2-16c, p.34
Chapter 2 Human Heredity by Michael Cummings ©2006 Brooks/Cole-Thomson Learning
Fig. 2-16d, p.34
Chapter 2 Human Heredity by Michael Cummings ©2006 Brooks/Cole-Thomson Learning
Meiosis
Chapter 2 Human Heredity by Michael Cummings ©2006 Brooks/Cole-Thomson Learning
Recombination
http://www.answersingenesis.org/home/area/magazines/tj/images/v17n1_demographics.jpg
Chapter 2 Human Heredity by Michael Cummings ©2006 Brooks/Cole-Thomson Learning
Mitosis
1. In somatic cells
2. Both haploid and diploid cells
3. 2n to 2n
4. One round of division
Meiosis
1. In germ cells
2. Only diploid cells
3. 2n to n
4. Two rounds of division
Chapter 2 Human Heredity by Michael Cummings ©2006 Brooks/Cole-Thomson Learning
Mitosis Meiosis
5. Homologous chromosomes do NOT pair
6. No (or very rare) recombination
7. Sister chromatids attach to spindle fibers from opposite poles
5. Homologous chromosomes pair
6. Recombination occurs
7. During metaphase I, homologous chromosomes attach to opposite spindle fibers
Chapter 2 Human Heredity by Michael Cummings ©2006 Brooks/Cole-Thomson Learning
Mitosis Meiosis
8. Centromeres divideIn anaphase
8. Centromeres do NOT divide during Meiosis I
Centromere dividesIn meiosis II
Chapter 2 Human Heredity by Michael Cummings ©2006 Brooks/Cole-Thomson Learning
Why is meiosis important?
1. Meiosis results in the production of haploid cells, which when fused restore and maintain chromosome number.
2. Meiosis allows for the generation of gametes with different combinations of paternal and maternal chromosomes, generating genetic diversity.
3. Recombination during meiosis allows for further generation of genetic diversity.