In meiosis Homologous chromosome

1 in meiosis

1.1 prophase i
1.2 metaphase i
1.3 anaphase i
1.4 meiosis ii

in meiosis

during process of meiosis, homologous chromosomes can recombine , produce new combinations of genes in daughter cells.



sorting of homologous chromosomes during meiosis.

meiosis round of 2 cell divisions results in 4 haploid daughter cells each contain half number of chromosomes parent cell. reduces chromosome number in germ cell half first separating homologous chromosomes in meiosis , sister chromatids in meiosis ii. process of meiosis longer meiosis ii because takes more time chromatin replicate , homologous chromosomes oriented , segregated processes of pairing , synapsis in meiosis i. during meiosis, genetic recombination (by random segregation) , crossing on produces daughter cells each contain different combinations of maternally , paternally coded genes. recombination of genes allows introduction of new allele pairings , genetic variation. genetic variation among organisms helps make population more stable providing wider range of genetic traits natural selection act on.

prophase i

in prophase of meiosis i, each chromosome aligned homologous partner , pairs completely. in prophase i, dna has undergone replication each chromosome consists of 2 identical chromatids connected common centromere. during zygotene stage of prophase i, homologous chromosomes pair each other. pairing occurs synapsis process synaptonemal complex - protein scaffold - assembled , joins homologous chromosomes along lengths. cohesin crosslinking occurs between homologous chromosomes , helps them resist being pulled apart until anaphase. genetic crossing-over, type of recombintion, occurs during pachytene stage of prophase i. in addition, type of recombination referred synthesis-dependent strand annealing (sdsa) occurs. sdsa recombination involves information exchange between paired homologous chromatids, not physical exchange. sdsa recombination not cause crossing-over.

in process of crossing-over, genes exchanged breaking , union of homologous portions of chromosomes’ lengths. structures called chiasmata site of exchange. chiasmata physically link homologous chromosomes once crossing on occurs , throughout process of chromosomal segregation during meiosis. both non-crossover , crossover types of recombination function processes repairing dna damage, particularly double-strand breaks. @ diplotene stage of prophase synaptonemal complex disassembles before allow homologous chromosomes separate, while sister chromatids stay associated centromeres.

metaphase i

in metaphase of meiosis i, pairs of homologous chromosomes, known bivalents or tetrads, line in random order along metaphase plate. random orientation way cells introduce genetic variation. meiotic spindles emanating opposite spindle poles attach each of homologs (each pair of sister chromatids) @ kinetochore.

anaphase i

in anaphase of meiosis homologous chromosomes pulled apart each other. homologs cleaved enzyme separase release cohesin held homologous chromosome arms together. allows chiasmata release , homologs move opposite poles of cell. homologous chromosomes randomly segregated 2 daughter cells undergo meiosis ii produce 4 haploid daughter germ cells.

meiosis ii

after tetrads of homologous chromosomes separated in meiosis i, sister chromatids each pair separated. 2 haploid(because chromosome no. has reduced half. earlier 2 sets of chromosomes present, each set exists in 2 different daughter cells have arisen single diploid parent cell meiosis i) daughter cells resulting meiosis undergo cell division in meiosis ii without round of chromosomal replication. sister chromatids in 2 daughter cells pulled apart during anaphase ii nuclear spindle fibers, resulting in 4 haploid daughter cells.