Ch 13 Meiosis
Terms in this set (35)
Produces haploid gametes; cells have half the number of chromosome sets as the original cell
each gamete receives one member of each pair of homologous chromosomes
meiosis consists of one round of DNA replication, followed by two rounds of nuclear division.
produces 4 daughter cells
two sets of chromosomes. (2n)
one set from each parent.
Pairs of homologous chromosomes
pair of chromosomes that have the same length, centromere position, and gen loci, but maybe have different alleles. One homologous chromosome is inherited from the organism's father, the other from mother.
any cell in a multicellular proganism except a sperm or egg or their precursors
How many chromosomes in human somatic cells and gametes?
46 in somatic cells and 23 in gametes
a chromosome that is not directly involved in determining sex; not a sex chromosome
A display of the chromosome pairs of a cell arranged by size and shape. Chromosome pairs 1-22 are autsomes with similar appearance between homologues.
one set of chromosomes (n)
gametes are haploid
created by meiosis
sperm and egg cells
fertilized egg; when haploid sperm fuses with haploid egg
alternation of generations
A life cycle in which there is both a multicellular diploid form, the sporophyte, and a multicellular haploid form, the gametophyte; characteristic of plants and some algae.
The multicellular diploid stage is called sporophyte. Meiosis in the sporophyte produces haploid cells called spores. Unlike a gamete, haploid spore doesn't fuse with another cell but divides mitotically, generating a multicellular haploid stage called the gametophyte.Cells of the gametophyte create gametes by mitosis. Fusion of two haploid gametes at fertilization results in a diploid zygote, which develops into the next sporophyte generation. Therefore, the sporophyte generation produces a gametophyte as its offspring, and the gametophyte generation produces the next sporophyte generation
haploid cells produced by sporophytes during meiosis
The pairing and physical connection of duplicated homologous chromosomes mediated by synaptonemal protein complex.
sites of crossing over
prophase 1 (early prophase)
Chromosomes begin to condense and homologs loosely pair up. Paired homologs become physically connected to each other through synapsis.Crossing over occurs between homologues and the nonsister chromatids swap alleles. Now chromosome contain a mix of parental genes.
prophase 1 (mid prophase)
Synapsis ends with the disassembly of the synaptonemal complex and thechromosomes in each pair move apart slightly. Each homologous pair has a chiasmata. Spindles form, centrosomes move, nuclear encelope breaks down.
porphase 1 (late prophase)
microtubules from one pole attach to the two kinetochores. The homologou pairs move toward the metaphase plate.
Homologous pairs (tetrads) line up at the metaphase plate held together by the chiasmata, with one chromosome in each pair facing each pole. Both chromatids of one homolog are attached to kintechore microtubules from one pole; those of the other homolog are attached to microtubules from the opposite pole.
Breakdown of proteins responsible for sister chromatid cohesion along chromatid arms allows homologs to separate
The homologs move toward opposite pole, guided by the spindle apparatus. Sister chromatid cohesion persists at the centromere, causing chromatids to move as a unit toward the same pole.
telophase 1 and cytokinesis
at the beginning of telophase 1, each half of the cell has a complete haploid set of duplicated chromosomes. Each chromosome is composed of two sister chromatids; one or both chromatids include regions of nonsister chromatid DNA. Cytokinesis usually occurs simultaneously with telophase 1, forming two haploid daughter cells.
same as mitosis except cells are haploid and sister chromatids are not identical
spindle apparatus form. Chromosomes, which are still composed of two chromatids associated at the centromere, move toward the metaphase 2 plate.
the chromosomes are positioned at the metaphase plate. Because of crossing over in meiosis 1, the two sister chromatids of each chromosome are not genetically identical. The kinetochores of sister chromatids are attached tomicrotubules extending from opposite poles.
breakdown of proteins holding the sister chromatids together at the centromere allows the chromatids to separate. The chromatids move toward opposite poles as individual chromosomes.
telophase 2 and cytokinesis
nuclei form, the chromosomes begin decondensing, and cytokinesis occurs. The meiotic division of one parent cell produces foru daughter cells each iwth a hapoid set of unduplicated chromosomes. The four daughter cells are genetically distinct from one another and from the parent cell.
mitosis vs meiosis
DNA replication occurs during interphase in both divisions.
Mitosis divides once, meiosis divides twice.
synapsis does not occur in mitosis, but occurs udring porphase 1 along with crossing over in meiosis.
Mitosis gets two daughter cells, each diploid (2n) and genetically identical to the parent cell. Meiosis gives four daughter cells, each haploid (n), containing half as many chromosomes as the parent cell and genetically different from the parent cell and from each other.
types of genetic variations
independent assortment of chromosomes
Independent assortment of chromosomes
random orientation of homologous pairs in metaphase 1; each pair lines up independent of neighboring pairs. Possible combination is 2^n (n=the pairs of chromosomes)
produces recombinant chromosomes
Each chromosome contains alleles from each parent
Fusion of gametes from two individuals further increase possible 2n combination because each gamete is one of 2^23 possible arrangements
How many chromosomes in the beginning and end of mitosis, meiosis 1, meiosis 2
beginning of mitosis: 46; end of mitosis: 46
beginning of meiosis 1: 46; end of meiosis 1: 23
beginning of meiosis 2: 23; end of meiosis 2: 23
How many homologues in the beginning and end of mitosis, meiosis 1, meiosis 2
beginning of mitosis:0; end of mitosis: 0
beginning of meiosis 1: 23; end of meiosis 1:0
beginning of meiosis 1: 0; end of meisis 2: 0
How many sister chromatids in the beginning and ned of mitosis, meiosis 1, meiosis 2?
beginning of mitosis: 92; end of mitosis: 46
beginning of meiosis 1: 92; end of meiosis 1: 46
beginning of meiosis 2: 46; en of meiosis 2: 23