during prophase 1 homologous chromosomes exchange segments of dna in a specific process called crossing over.
during prophase 1 homologous chromosomes exchange segments of dna in a specific process called crossing over.
during prophase 1 homologous chromosomes exchange segments of dna in a specific process called?
crossing over
chromosome segregation occurs at two separate stages during meiosis called prophase i and prophase ii (see meiosis diagram). in a diploid cell there are two sets of homologous chromosomes of different parental origin (e.g. a paternal and a maternal set). during the phase of meiosis labeled “interphase s” in the meiosis diagram there is a round of dna replication, so that each of the chromosomes initially present is now composed of two copies called chromatids. these chromosomes (paired chromatids) then pair with the homologous chromosome (also paired chromatids) present in the same nucleus (see prophase i in the meiosis diagram). the process of alignment of paired homologous chromosomes is called synapsis (see synapsis). during synapsis, genetic recombination usually occurs. some of the recombination events occur by crossing over (involving physical exchange between two chromatids), but most recombination events involve information exchange but not physical exchange between two chromatids (see synthesis-dependent strand annealing (sdsa)). following recombination, chromosome segregation occurs as indicated by the stages metaphase i and anaphase i in the meiosis diagram.
chromosome segregation
prophase i is typically the longest phase of meiosis. during prophase i, homologous chromosomes pair and exchange dna (homologous recombination). this often results in chromosomal crossover. this process is critical for pairing between homologous chromosomes and hence for accurate segregation of the chromosomes at the first meiosis division. the new combinations of dna created during crossover are a significant source of genetic variation, and result in new combinations of alleles, which may be beneficial. the paired and replicated chromosomes are called bivalents or tetrads, which have two chromosomes and four chromatids, with one chromosome coming from each parent. the process of pairing the homologous chromosomes is called synapsis. at this stage, non-sister chromatids may cross-over at points called chiasmata (plural; singular chiasma). prophase i has historically been divided into a series of substages which are named according to the appearance of chromosomes.
meiosis