Chapter 11: Meiosis and Sexual Reproduction

the main successes of an organism are

reproduction and survival

reproduction

production of an offspring from an existing organism

asexual (non-sexual) reproduction

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

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

asexual (non-sexual) reproduction

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

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

sexual reproduction involves

gamete fusion to form a zygote

gametes are

sex cells (sperm and egg)

a zygote is

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

hermaphroditism is a type of sexual reproduction that involves

an organism (hermaphrodites) producing both sperm and egg cells

hermaphroditism is (1) but (2)

less advantageous for diversity, better than asexual reproduction

gametes are formed via

meiosis

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

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

meiosis is important for

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

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

diploid cells, 46 chromosomes

an example of cells produced by mitosis is

somatic cells (e.g., body cells)

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

haploid cells, 23 chromosomes

meiosis 1 involves the

reduction division of homologous chromosomes

meiosis 1 produces

2 daughter cells with 1 chromosome that has 2 chromatids

meiosis 2 involves the

separation of sister chromatids

meiosis 2 produces

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

during prophase 1

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

tetrad

homologous chromosomes brought together by synaptonemal complex

synaptonemal complex

web of proteins that attach homologous chromosomes

crossing over involves

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

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

sex chromosomes, they’re not identical

recombinant chromosomes

chromosomes with crossed over segments

non-recombinant chromosomes

chromosomes without crossed over segments

during prometaphase 1

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

prometaphase 1 is different from mitosis prometaphase and metaphase 2 because

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

during metaphase 1

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

independent assortment

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

during anaphase 1

microtubules pull tetrads apart

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

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

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

twice, 2 daughter cells

during prophase 2

Non-homologous chromosomes reform if they condensed after meiosis 1

during prometaphase 2

microtubules attach to kinetochores present in each non homologous sister chromatid

during metaphase 2

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

during anaphase 2

sister chromatids are pulled apart by microtubules

during telophase 2

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

two meiotic mechanisms that produce haploid genetic variation are

independent assortment and crossing over