meiosis

meiosis I

-is the first round of meiotic division and consists of prophase I, prometaphase I, and so on. -it reduces the number of chromosome sets from two to one

reduction division

-the first cell division in meiosis, the process by which germ cells are formed. -In reduction division, the chromosome number is reduced from diploid (46 chromosomes) to haploid (23 chromosomes)

meiosis II

-the second round of meiotic division takes place in a way that is similar to mitosis -includes prophase II, prometaphase II, and so on.

haploid cells

A cell containing only one set of chromosomes

diploid cells

A cell containing two sets of chromosomes

interphase

A cell preparing to undergo meiosis duplicates its chromosomes during

16

A diploid organism whose somatic (nonsex) cells each contain 32 chromosomes produces gametes containing _____ chromosomes.

prophase I

Crossing over occurs during _____.

Crossing over creates new combinations of genes present on a single chromosome.

During meiosis I, homologous chromosomes form a tetrad and crossing over occurs. What is the outcome of crossing over?

prophase I

During meiosis, segments of nonsister chromatids can trade places. This recombination of maternal and paternal genetic material is a key feature of meiosis. During what phase of meiosis does recombination occur?

homologous chromosomes stick together in pairs.

During prophase I of meiosis,

life cycles

Fertilization and meiosis alternate in sexual ____________.

cell growth

G1 phase is the first phase of interphase and is focused on ____ ______.

meiosis

Gametes are produced by _____.

versions

Homologous chromosomes possess the same genes arranged in the same order but may possess different __________ of some of these genes.

5

In a cell containing 10 chromosomes, meiosis results in the formation of daughter cells containing __________ chromosomes.

DNA of the chromosomes is replicated

In the S phase of interphase ________.

Two of the embryos will be trisomic for chromosome 18, and two will contain a single copy of chromosome 18.

In theory, when a nondisjunction for chromosome 18 occurs during meiosis I, four gametes can be produced. If these gametes are fertilized with unaffected gametes from the second parent, what observations would you make concerning the resulting embryos?

four haploid cells.

Meiosis starts with a single diploid cell and produces

23

Normal human gametes carry _____ chromosomes.

prophase I, metaphase I, anaphase I, telophase I, cytokinesis, meiosis II

The correct order of events during meiosis is

prophase II

The first phase of meiosis II. ________ is identical to mitotic prophase, except that the number of chromosomes was reduced by half during meiosis I.

its cells each have one set of chromosomes

When we say that an organism is haploid, we mean that _____.

chiasmata

X-shaped regions where crossing over occurred.

gametes

____ fuse with another haploid gamete to produce a a diploid cell

variation

_____ is introduced during meiosis, as well as when the gametes combine in fertilization

fertilization

__________ occurs when the fusion of two gametes, usually from different individuals, restoring the diploid state.

fertilization

a union of two cells from two individual organisms

crossing over (occurs in prophase I)

an exchange of chromosome segments between non-sister homologous chromatids occurs and is called _________ _____.

tetrads

at the end of prophase I, the pairs are held together by only at the chiasmata and are called ______ because the four sister chromatids of each pari of homologous chromosomes are now visible

meiosis

different mutations are continually reshuffled from one generation to the next and different parents combine their unique genomes and the genes are mixed into different combinations by the process of ________.

sister chromatids

during DNA duplication of the S phase, each chromosome becomes _______ _______, and are held together at the centromere until they are pulled apart during meiosis II.

metaphase I

during _____ the homologous chromosomes are arranged in the center of the cell with the kinetochores facing opposite poles

animals

in _______ haploid cells containing a single copy of each homologous chromosome are found only within gametes

telophase II

in _______ the chromosomes arrive at opposite poles and begin to decondense

anaphase II

in _______ the sister chromatids are pulled apart by the spindle fibers and move toward opposite poles

prometaphase II

in ________ the nuclear envelopes are completely broken down and the spindle is fully formed

metaphase II

in _________ the sister chromatids are maximally condensed and aligned at the center of the cell

animal cell

in an ______ _____, the centromeres that organize the microtubules of the meiotic spindle also replicate.

G1, S, and G2

in meiosis, interphase consists of ____, ____, and ___ phases

alternation of generations

in which the two stages, haploid and diploid, are apparent to one degree or another depending on the group, as with plants and some algae

Diploid organisms

inherit one copy of each homologous chromosome from EACH parent; all together, they are considered a full set of chromosomes

fertilization

joins the two haploid gametes and restores the diploid condition

homologous chromosomes

matched pairs containing genes for the same traits in identical locations among there length

diploid cells

most animal and plants are _____

Meiosis

produce offspring with new combinations of alleles

meiosis

reduces the number of chromosome sets so that there will not be a continually doubling in the number of chromosome sets in every generation

undergoes the final preparations for meiosis

the G2 phase of interphase ________.

recombinant

the ________ sister chromatid has a combination of maternal and paternal genes that did not exist before the crossover.

-chromosome duplication -nuclear divison

the achieve the reduction in chromosome number, meiosis consists of one round of ________ ________ and two rounds of ________ ___________.

meiosis II

the connected sister chromatids remaining in the haploid cells from meiosis I will be split to form four haploid cells

meiosis

the division of the contents of the nucleus that divides the the chromosomes among gametes.

germ cells

the gametes are formed from diploid _______ _______, a special cell line that only produces gametes.

diploid-dominant

the multicellular diploid stage is the most obvious life stage

haploid-dominant

the multicellular haploid stage is the most obvious life stage, such as with all fungi and some algae

somatic cell

the non-reproductive cells of a multicellular organism

synapsis

tight pairing of homologous chromosomes

prometaphase I

when the attachment of the spindle fiber microtubules to the kinetochore proteins at the centromeres occur