In prophase 1:
Chromosomes become visible, crossing-over occurs, the nucleolus disappears, the meiotic spindle forms, and the nuclear envelope disappears.
In metaphase 1:
The pairs of chromosomes (bivalents) become arranged on the metaphase plate and are attached to the now fully formed meiotic spindle. The centrioles are at opposite poles of the cell.
<span>The migration routes of Homo sapiens reveal
that they went through many environmental and physical challenges but adapted
everything much quickly in comparison to the other animals. The evolution
allowed other species also to adopt these changes but it took them a long time
to fit in the new environment, a sub species of a species adopted the new and
the previous one could not, but Homo sapiens invented ways and tools to combat
and evolve much quickly. It included their living, dietary needs, clothing and
much more.</span>
Evolution is the change in an animal over time. Evolution causes this one animal to branch out into many different species of animals.
How evolution starts- There is a mutation in the genes of one animal. If the mutation helps the animal, than the animal breeds and passes on this mutation. This is natural selection. Natural selection is the starting point of evolution because all of the helpful mutations get passed down to change the species over time for the animals' benefit.
I really hope this helps you
Answer:
Prophase 1
Explanation:
Prophase I :It can be divided into five stages:
1)Leplotene: In this stage, chromosome becomes visible and shorten as a single structure.
2)Zygotene: Homologous / sister chromosome pair up. This process is known as synapse. Synapse is the process of attachment of homologous /sister chromosome. One pair comes from the male parent while the other comes from the female parent.
3)Pachytene: Bivalents shorten.
4)Diplotene:Point of attachment of non-sister chromatids. The two chromosomes are seen to be joined at several points along their length. These points are known as Chiasmata.(Chiasmata, a cross). The paternal gene A, B, C may swap for the maternal gene a, b, c for instance, leading to a new gene combination in the resulting chromatids. This is referred to as *CROSSING OVER*.
5)Diakenesis: Homologous centromere move apart.
So, crossing over occurs in *Prophase 1.
