Ch 11: Meiosis and Sexual Reproduction

fertilization

combines cells (gametes) from 2 parents

does mixing chromosomes from 2 individuals increase or decrease genetic diversity?

increase

how is an organism’s sex determined?

it is an inherited phenotype characteristic determined in large by the presence or absence of certain chromosomes

phenotype

physical manifestations: what you can see, hormones in the body, etc.

what is SRY (sex determining region Y) required for?

testicular development

2 varieties of sex chromosomes

X and Y

true or false. sex cells are diploid.

false. sex cells are haploid.

by how much does meiosis reduce the number of chromosomes by?

half

the process of meiosis resembles mitosis but goes through how many rounds of division?

2: meiosis I and meiosis II

S Phase

chromosomes are duplicated during interphase. the resulting sister chromatids are held together at the centromere. the centrosomes are also duplicated

prophase I

chromosomes condense, and the nuclear envelope fragments. homologous chromosomes bind firmly together along their length, forming a tetrad. chiasmata form between non sister chromatids. crossing over occurs at the chiasmata. spindle fibers emerge from the centromeres

prometaphase I

homologous chromosomes are attached to spindle microtubules at the fused kinetochore shared by the sister chromatids. chromosomes continue to condense, and the nuclear envelope completely disappears

metaphase I

homologous chromosomes randomly assemble at the metaphase plate, where they have been maneuvered into place by the microtubules

anaphase I

spindle microtubules pull the homologous chromosomes apart. the sister chromatids are still attached at the centromere

telophase I and cytokinesis

sister chromatids arrive at the poles of the cell and begin to decondense. a nuclear envelope forms around each nucleus, and the cytoplasm is divided by a cleavage furrow. the result is two haploid cells. each cell contains one duplicated copy of each homologous chromosome pair

prophase I: homologous chromosomes pair and __________________ complex holds them close together in __________

synaptonemal, synapsis

prophase I: crossing over

segments of chromosomes can be exchanged

prophase i: visible structures at cross over points are called ____________

chiasmata

prophase I: the 4 chromatids held together by chiasmata are called a _______

tetrad

prometaphase I: spindle fiber microtubules attach to kinetochore proteins at _______________

centromeres

prometaphase I: homologous chromosomes are still held together at the ____________

chiasmata

prometaphase I: __________ membrane is completely broken down

nuclear

metaphase I: homologous chromosomes are arranged at cell equator with _____________ facing opposite poles

kinetochores

metaphase I: independent assortment

maternal and paternal chromatids orient randomly mixed when they migrate to poles

2 primary mechanisms for genetic variation in meiosis

crossing over and independent assortment

anaphase I: the microtubules pull the _______ apart

tetrads

anaphase I: ____________ are broken but sister chromatids remain attached at the ______________

chiasmata, centromere

telophase I and cytokinesis: separated chromosomes arrive at ___________ poles

opposite

telophase I and cytokinesis: if cytokinesis does occur, ______ do not reform

nuclei

cytokinesis in animal and fungal cells

occurs via a cleavage furrow that constricts

cytokinesis in plant cells

form a cell plate that ultimately produces cell walls that separate the daughter cells

3 injections of genetic variation

crossing over, independent assortment, fertilization

prophase II

sister chromatids condense. a new spindle begins to form. the nuclear envelope starts to fragment

prometaphase II

the nuclear envelope disappears, and the spindle fibers engage the individual kinetochores on the sister chromatids.

metaphase II

sister chromatids line up at the metaphase plate

anaphase II

sister chromatids are pulled apart by the shortening of the kinetochore microtubules. non kinetochore microtubules lengthen the cell

telophase II and cytokinesis

chromosomes arrive at the poles of the cell and decondense. nuclear envelope surrounds the four nuclei. cleavage furrows divide the two cells into four haploid cells

prophase II: if chromosomes decondensed in telophase I, they _____________ now

recondense

true or false. prophase II: if centrosomes were duplicated, they migrate to opposite poles and new spindles form

true

prometaphase II: nuclear envelopes completely ____________

disappear

prometaphase II: _______ is fully formed

spindle

prometaphase II: each sister chromatid forms a ______________ and attached to __________ from opposite poles

chromatid, microtubules

metaphase II and anaphase II: events process as in mitosis and sister _________ separate and move toward opposite ______

chromatids, poles

telophase II and cytokinesis: the chromosomes arrive at opposite poles and ____________

decondense

telophase II and cytokinesis: nuclear ____________ form around chromosomes

envelopes

telophase II and cytokinesis: cytokinesis separates the two cells into ______ unique ________ cells

four, haploid

which produces genetically unique cells: mitosis or meiosis?

meiosis

in what process do homologous chromosomes pair to form tetrads?

meiosis

which process produces genetically identical clones?

mitosis