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A tetrad is the association of a pair of homologous chromosomes (4 sister chromatids) physically held together by at least one DNA crossover. This physical attachment allows for alignment and segregation of the homologous chromosomes in the first meiotic division. In most organisms, each replicated chromosome (composed of two identical sisters ...
Alternatively, in much the same way as reproductive structures (e.g., the penis and the clitoris) are considered homologous because they share a common origin in embryonic tissues, [2] behaviors—or the neural substrates associated with those behaviors [3] —can also be considered homologous if they share common origins in development.
A pair of homologous chromosomes, or homologs, is a set of one maternal and one paternal chromosome that pair up with each other inside a cell during fertilization. Homologs have the same genes in the same loci , where they provide points along each chromosome that enable a pair of chromosomes to align correctly with each other before ...
This image shows haploid (single), diploid (double), triploid (triple), and tetraploid (quadruple) sets of chromosomes. Triploid and tetraploid chromosomes are examples of polyploidy. Polyploidy is a condition in which the cells of an organism have more than two paired sets of ( homologous ) chromosomes .
Meiosis I segregates homologous chromosomes, which are joined as tetrads (2n, 4c), producing two haploid cells (n chromosomes, 23 in humans) which each contain chromatid pairs (1n, 2c). Because the ploidy is reduced from diploid to haploid, meiosis I is referred to as a reductional division .
Compare sister chromatids to homologous chromosomes, which are the two different copies of a chromosome that diploid organisms (like humans) inherit, one from each parent. Sister chromatids are by and large identical (since they carry the same alleles, also called variants or versions, of genes) because they derive from one original chromosome.
The kinship coefficient is a simple measure of relatedness, defined as the probability that a pair of randomly sampled homologous alleles are identical by descent. [12] More simply, it is the probability that an allele selected randomly from an individual, i, and an allele selected at the same autosomal locus from another individual, j, are ...
[citation needed] While in this formation, homologous sites on two chromatids can closely pair with one another, and may exchange genetic information. [ 6 ] Because there is a small probability of recombination at any location along a chromosome, the frequency of recombination between two locations depends on the distance separating them.