Chapter 11: Meiosis and Sexual Reproduction

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42 Terms

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the main successes of an organism are

reproduction and survival

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reproduction

production of an offspring from an existing organism

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asexual (non-sexual) reproduction

doesn’t involve sex, and creates an offspring that’s genetically identical to the parent

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unicellular organisms such as yeasts, fungi, and protists use mitosis for

asexual (non-sexual) reproduction

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budding is a type of asexual (non-sexual) reproduction that involves

an organism making a tiny copy of itself that stays attached until both are equal in size, then it separates

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fission is a type of asexual (non-sexual) reproduction that involves

an organism splitting into 2 halves that develop, grow, and mature into 2 organisms

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sexual reproduction involves

gamete fusion to form a zygote

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gametes are

sex cells (sperm and egg)

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a zygote is

a fusion of sex cells (sperm + egg), 46 chromosomes in total

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hermaphroditism is a type of sexual reproduction that involves

an organism (hermaphrodites) producing both sperm and egg cells

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hermaphroditism is (1) but (2)

less advantageous for diversity, better than asexual reproduction

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gametes are formed via

meiosis

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gametes have (1) and are considered to be (2)

23 chromosomes (1 single set), haploid cells (1n)

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meiosis is important for

chromosome reduction from 46 to 23 each, so that when gametes fuse they have 46 in total instead of 92

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mitosis produces (1), which have (2) in total

diploid cells, 46 chromosomes

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an example of cells produced by mitosis is

somatic cells (e.g., body cells)

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meiosis produces (1), which have (2) in total

haploid cells, 23 chromosomes

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meiosis 1 involves the

reduction division of homologous chromosomes

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meiosis 1 produces

2 daughter cells with 1 chromosome that has 2 chromatids

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meiosis 2 involves the

separation of sister chromatids

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meiosis 2 produces

4 haploid cells that each have 1 chromosomes with 1 chromatid from 2 daughter cells from meiosis 1

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during prophase 1

chromosomes condense, nuclear envelope fragments, tetrad forms, crossing over occurs

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tetrad

homologous chromosomes brought together by synaptonemal complex

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synaptonemal complex

web of proteins that attach homologous chromosomes

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crossing over involves

the exchange of chromosomal segments between homologous non sister chromatids (one from each parent)

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crossing over occurs between all chromosomal pairs except (1) because (2)

sex chromosomes, they’re not identical

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recombinant chromosomes

chromosomes with crossed over segments

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non-recombinant chromosomes

chromosomes without crossed over segments

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during prometaphase 1

nuclear envelop breaks, spindle fibers attach to the kinetochore, homologous chromosomes are still attached.

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prometaphase 1 is different from mitosis prometaphase and metaphase 2 because

the chromosomes are in pairs (2 chromosomes, 4 chromatids total)

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during metaphase 1

homologous chromosomes orient in pairs (2 lines) at the cell center randomly, independent assortment occurs

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independent assortment

chromosomes can migrate to the poles in various order (e.g., mother chromosomes can go in the same direction, or opposite directions)

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during anaphase 1

microtubules pull tetrads apart

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during telophase 1

DNA will either condense and a nuclear envelope forms, or cytokinesis occurs without nuclear envelop reformation. Two new non-identical daughter cells are formed

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meiosis 2, which is nearly identical to meiosis 1, precedes a unique interphase that’s shorter because it doesn't have an S phase. this is called

interkinesis

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meiosis 2 occurs (1) because meiosis 1 produces (2)

twice, 2 daughter cells

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during prophase 2

Non-homologous chromosomes reform if they condensed after meiosis 1

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during prometaphase 2

microtubules attach to kinetochores present in each non homologous sister chromatid

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during metaphase 2

Non-homologous chromosomes align at the cell center in a single line (not in pairs)

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during anaphase 2

sister chromatids are pulled apart by microtubules

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during telophase 2

chromosomes arrive at opposite ends of the cell and start condensing, nuclear envelopes form. 4 non-identical daughter cells are formed

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two meiotic mechanisms that produce haploid genetic variation are

independent assortment and crossing over