bf 3: meiosis sexual reproduction

diploid (2n)

cell or organism that has 2 complete sets of chromosomes- each set inherited from a parent

haploid (n)

cell that contains one complete set of a chromosome. gametes sperm and egg

gametes

reproductive cells that are haploid and fuse during fertilization to form a diploid zygote

zygote

diploid cell formed when 2 haploid gametes fuse during fertilization; 1st cell of a new organism

chiasmata (singular chiasma)

physical point of contact between nonsister chromatids of homologous chromosomes where crossing over has occurred during meiosis i

crossing over

process during prophase i of meiosis in which nonsister chromatids of homologous chromosomes exchange dna segments, increase genetic variation

synapsis

pairing and physical connection of homologous chromosomes during prophase i of meiosis, forming a structure called tetrad

prophase 1

chromosomes condense, homologous chromosomes pair up through synapsis, forming tetrads, crossing over, chiasmata are visible at crossover points, nuclear envelope breaks down; spindles form

metaphase 1

tetrads align at the metaphase plate, orientation is random; independent assortment, contributes to genetic variation

anaphase 1

homologous chromosomes separate and move to opposites poles, sister chromatids stay together due to cohesion at their centromeres

telophase 1 & cytokinesis

chromosomes arrive at poles, cells divide into two haploid [n] cells, each with duplicated chromosomes [sister chromatids still joined]

prophase 2

chromosomes condense again; if decondensed, new spindles form in each haploid cell

metaphase 2

chromosomes; each with 2 sister chromatids, line up individually at the metaphase plate

anaphase 2

sister chromatids separate as the centromeres divide, individual chromatids move to opp poles

telophase 2 & cytokinesis

chromatids arrive at the poles and decondense, nuclear membrane reform, each cell divides, resulting in 4 genetically identical haploid cells

independent assortment

during metaphase 1, homologous chromosome pairs line up randomly at the metaphase plate

random fertilization

not part of meiosis, works with meiosis to increase variation, combination of two random sperm and egg

divisions of mitosis

1

divisions of meiosis

2