Meiosis-A prelude to reproduction

I. Terminology

• A. karyotype– 1. human 46

chromosomes

– 2. homologous pairs

– 3. diploid condition

– 4. note various sizes and shapes

B. Chromatin

• 1. 1.8 meters• 2. DNA• 3. exists in a non-dividing cell

C. Relationship between chromatin and chromosome

• 1. chromatin• 2. chromosomes• 3. histone proteins• 4. nucleosome

100µm

D. Terms of chromosome structure

• 1. Monad• 2. Dyad• 3. Centromere• 4. Sister chromatids

E. Homologous chromosome pairs

• 1. definition• 2. paternal vs.

maternal• 3. genes vs. alleles• 4. synapsis• 5. tetrad• 6. sister vs. nonsister

chromatids

How many chromosomes do you see?

83%

17%

0%0%

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1. 42. 83. 104. No clue

II. Review of mitosis

• A. Prophase• B. Metaphase• C. Anaphase• D. Telophase• E. Products

III. Meiosis overview

• A. Importance?• B. Two separate

divisions– Meiosis I reduction

division– Meiosis II “mitotic-like”

division

• C. Where does it occur?

D. What does meiosis produce?

IV. Meiosis I

• A. Prophase I• B. Metaphase I• C. Anaphase I• D. Telophase I• E. End products

V. Meiosis II

• A. Prophase II• B. Metaphase II• C. Anaphase II• D. Telophase II• E. Final products

VI. Comparison between mitosis and meiosis

Event Mitosis Meiosis I Meiosis II

Synapsis occurs

Sister chromatids separate

Homologous chromosomes separate

Crossing over occurs

Tetrads form

Haploid cells form

Identical daughter cells form

VII. Meiosis and simple inheritance

• A. Sex determination • 1. autosomes• 2. sex chromosomes• 3. products of meiosis• 4. nature of sperm

determines sex• 5. sex ratios

B. Inheritance of somatic traits

• 1. Theory of particulate inheritance• 2. Each body trait is affected by two alleles• 3. One inherited from father and other from mother• 4. Two factors separate upon gamete formation during

meiosis• 5. Terms of inheritance

a. dominant

b. recessive

c. genotype

d. phenotype

6. Inheritance of eye color

• a. Dominant allele produces pigment (E)• b. Recessive allele produces no pigment (e)• c. Possible genotypes• d. Resulting phenotypes

7. Sample problem

• In humans, freckles are dominant to no freckles. Mary, who has no freckles, is planning on having children with Paul. Paul, who has freckles, was born to a freckless woman. Mary wants to know the probability of her in utero son has of having freckles.

• How do we start?• List the symbols to be used to represent the alleles.• What is the mother’s phenotype? Genotype?• What is the father’s phenotype? What does his

genotype have to be?• What alleles are carried in the eggs and sperm of the

couple?• Create the punnett square.• What will be the name of the son which is not born yet?