Question

Contrast the genetic content and the origin of sister versus nonsister chromatids during their earliest appearance in prophase I of meiosis. How might the genetic content of these change by the time tetrads have aligned at the equatorial plate during metaphase I?

Answer 1

Answer:

Sister chromatids are identical  forms of chromatids  of a chromosomes. They are mostly  formed by semi-conservative replication of DNA molecule of a single  chromosome.Thus they  are  like  'photocopies' of  original parent  chromosomes; joined together at the Centromere.

They are exactly similar in all ramification; with the same gene and allele compositions..

However; slight differences  arise between the two identical sisters due to  mutation from errors at replication;and also in  the  length of telomere repeats.

Non-sister chromatids are dissimilar forms of  chromatids of a chromosomes formed  when each half of  a chromosome  at fertilisation from separate   haploid sex-cells, of each parent. fused.They contain different genetic composition;because  they are not on the same homologous chromosomes.Therefore crossing -over ensure variation.

However, they are genetically  similar in composition; if they  are contained in homologous chromosomes. This is because Synapsis of bivalent of these chromosomes allow genetic material to be shared by  chromosomal crossing-over between the non-sister chromatids  on the chromosomes ; therefore identical genetic characteristics are shared .

Explanation: