Meiosis Notes Name: __________________________ NOTES#Date: _______________ Period: _____________

I) Background Informationa) Meiosis- the production of haploid cells with ____________________________

i) Meiosis means "to diminish". b) Key points of Meiosis

i) The process results in __________________________________

ii) Daughter cells are ____________________ iii) Daughter cells have unique combinations of chromosomes iv) Daughter cells do not have homologous pairs

v) Meiosis creates _________________________________ vi) Meiosis ensures variability in offspring

c) Gametes combine to create a zygote which is diploid (2N) - process of sexual reproduction II) Chromosome Structure

a) Chromosomes also have banding patterns unique to each one. These bands are caused by certain dyes.

b) Each chromosome has many _______________, or alternate forms of genes

c) Homologous Chromosomes – i) Each chromosome has a match, called

a ________________.

ii) This is why normal organisms always have an _______________________ of chromosomes.

iii) One homolog you received from your mother, the other you received from your father. iv) They are not exactly alike, but they are the same size, shape, and have the same banding

pattern.d) Sex Chromosomes

i) In humans, there are two chromosomes that determine sex. The X and the Y chromosome.

(1) If you have an _______ - you are female

(2) If you have an _______ - you are maleIII) Diploid vs. Haploid

a) Body cells have the full set of chromosomes – they are ____________ (In humans, 46)

b) Sex cells (sperm and eggs) have half a set – they are ______________ (In humans, 23)

IV) Meiosisa) Occurs in two stages - ____________________________________b) Crossing-Over

i) During prophase I, homologous pairs join together and exchange genetic information

ii) Exchange of DNA during prophase I increases ___________________________. Chromatids are no longer exact duplicates.

c) During metaphase, chromosomes line up in PAIRS, but they line up ________________________.

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d) This picture shows all the different possible arrangements for an organism with 6

chromosomes. – a phenomenon known as ____________________________________

e) Fertilization = combining the genes of two different parents. Offspring show variation.

V) Meiosis Ia) Purpose:

i) It is the reduction division, so it reduces the number of chromosomes in half, making the

daughter cells ____________________ (when the parent cell was diploid).

ii) It is during meiosis I that most of the __________________________ occurs. b) Prophase I

i) Just like in mitosis, during prophase, __________________________ occurs, the nuclear envelope and nucleoli disappear, and the spindle starts to form.

ii) As DNA condensation proceeds and the chromosomes first become visible,

they are visible as ____________________

iii) _______________________________________________.c) Metaphase I

i) ___________________________________________ii) It is during prophase I and metaphase I that _____________________

________________ is occurring.

iii) Keep in mind that it only happens when there are tetrads, so as soon as anaphase I starts going, genetic recombination is over.

d) Anaphase Ii) Tetrads pull apart and ________________________________ move toward

the poles. e) Telophase I

i) Chromosomes with two chromatids de-condense and a nuclear envelope reforms around them.

ii) _________________________________________.

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VI) Meiosis IIa) Purpose:

i) At the end of meiosis I, each chromosome still had two chromatids. That is double the amount of DNA that a cell should have. So, the entire reason to go through meiosis II is to reduce the amount of DNA back to normal-- basically, to split the chromosomes so that each daughter cell has only one chromatid per chromosome (the normal genetic content).

b) Prophase IIi) Chromosomes with two chromatids become visible as

they condense (and the nuclear envelope and nucleoli disappear, and the spindle is forming).

c) Metaphase IIi) Chromosomes with two chromatids line up at the

equator.

d) Anaphase IIi) Chromosomes split, so that a chromosome with only

one chromatid heads toward each pole.

e) Telophase IIi) Chromosomes with only one chromatid decondense

and get surrounded by new nuclear envelopes. ii) The four daughter cells are now all haploid and have

the right amount of DNA. iii) They are ready to develop into sperm or eggs now.

1. Compared to a normal body cell, a normal egg cell containsa. the same number of chromosomesb. half the number of chromosomesc. twice the number of chromosomesd. four times the number of chromosomes

2. A human skin cell contains 46 chromosomes. A frog sperm cell contains 12 chromosomes. Which pair of numbers shows the chromosome number of a normal gamete from each of these species? a. human 46; frog 12 b. human 46; frog 24 c. human 23; frog 24 d. human 23; frog 12

3. DNA replication occurs in preparation for a. mitosis, only b. meiosis, only c. both mitosis and meiosis d. neither mitosis nor meiosis

4. The following events occur during sexual reproduction:

A. mitosis C. fertilizationB. meiosis D. birth

Which sequence represents the correct order of these events during sexual reproduction? a. A → C → B → D c. B → C → A → Db. C → B → A → D d. B → A → C → D

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Compare and Contrast

MITOSIS MEIOSIS

Function

Type of cells that undergo this process

Location in Body

Number of Daughter

Cells Produced

Change in Chromosome

Number

Number of Divisions in the Nucleus

Difference in DNA Between Parent Cell &

Daughter Cells

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