review of terms - brandeis · chapter 2 human heredity by michael cummings ©2006...

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)


Meiosis I

• Reductional division

• A diploid cell divides and forms twohaploid cells

• In humans, the chromosome number isreduced from 46 to 23 chromosomes


Prophase I• Chromosomes

coil• Nuclear

membranebreaks down

• Chromosomespair

• Recombinationmay occur

newly formingmicrotubules

Prophase I

Fig. 2.13a


Metaphase I

• Chromosomepairs line up onthe midline

Metaphase I

spindleequator

one pair of homologouschromosomes

Fig. 2.13b


Anaphase I

• Centromeres donot divide

• Chromosomepairs move toopposite poles

Anaphase I

Fig. 2.13c


Telophase I

• Nuclearmembranereforms

• Chromosomesuncoil

After Cytokinesis• Two haploid cells

are produced

Telophase I

Fig. 2.13d


Interkinesis

• No DNA synthesis occurs


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


Metaphase II

• Chromosomes lineup on the midlineand attach tospindle fibers

Metaphase II

Fig. 2.13f


Anaphase II

•Centromeresdivide

•Sister chromatidsmove to oppositepoles

Anaphase II

Fig. 2.13g


Telophase II

• Nuclear membranereforms

• Chromosomes uncoil

After Cytokinesis• Four unique haploid

cells are produced

Telophase II

Fig. 2.13h


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


Summaryof Mitosis

and Meiosis

Fig. 2.15


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


Fig. 2-14a, p.32

Members of chromosome pair

Each chromosome pairs withits homologue

SisterchromatidsSister

chromatids


Fig. 2-14b, p.32

Pairedhomologues separate

in meiosis I

Sister chromatidsseparate and become

individual chromosomesin meiosis II


Fig. 2-16, p.34


Fig. 2-16a, p.34


Fig. 2-16b, p.34


Fig. 2-16c, p.34


Fig. 2-16d, p.34


Meiosis


Recombination

http://www.answersingenesis.org/home/area/magazines/tj/images/v17n1_demographics.jpg


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


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


Mitosis Meiosis

8. Centromeres divideIn anaphase

8. Centromeres do NOT divide during Meiosis I

Centromere dividesIn meiosis II


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.

review of terms - brandeis · chapter 2 human heredity by michael cummings ©2006...

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