Prophase 1 is essentially the crossing over and recombination of genetic material between non sister chromatids – this results in the genetically unidentical, haploid daughter chromatid cells.

During prophase II, chromosomes condense and the nuclear envelope breaks down, if needed. The centrosomes move apart, the spindle forms between them, and the spindle microtubules begin to capture chromosomes.

Prophase II prepares the cell for secondary meiotic division where two haploid cells eventually form four haploid cells, each containing half of the genetic information previously contained in the original, replicated diploid cell.

Prophase I is the beginning phase of Meiosis I while Prophase II is the beginning phase of Meiosis II. There is a long interphase before Prophase I, whereas Prophase II occurs without an interphase. The pairing of homologous chromosomes occurs in Prophase I, whereas such process cannot be seen in Prophase II.

Prophase I is divided into five phases: leptotene, zygotene, pachytene, diplotene, and diakinesis.

During prophase I, the homologous chromosomes condense and become visible as the x shape we know, pair up to form a tetrad, and exchange genetic material by crossing over. During prometaphase I, microtubules attach at the chromosomes’ kinetochores and the nuclear envelope breaks down.

During prophase, chromatin condenses into chromosomes, and the nuclear envelope, or membrane, breaks down. In animal cells, the centrioles near the nucleus begin to separate and move to opposite poles (sides) of the cell.

At the start of prophase I, the chromosomes have already duplicated. During prophase I, they coil and become shorter and thicker and visible under the light microscope. The duplicated homologous chromosomes pair, and crossing-over (the physical exchange of chromosome parts) occurs.

Autosomes

Each chromosome contains a few thousand genes, which range in size from a few thousand bases up to 2 million bases. During most of the cell cycle, interphase, the chromosomes are somewhat less condensed and are not visible as individual objects under the light microscope.

The cell has two sets of each chromosome; one of the pair is derived from the mother and the other from the father. The maternal and paternal chromosomes in a homologous pair have the same genes at the same locus, but possibly different alleles.

A pair of chromosomes made up of two homologs. Homologous chromosomes have corresponding DNA sequences and come from separate parents; one homolog comes from the mother and the other comes from the father. Homologous chromosomes line up and synapse during meiosis.

having the same relative position

It occurs during meiosis. Crossing over is the exchange of chromosome segments between non-sister chromatids during the production of gametes. The effect is to assort (shuffle) the alleles on parental chromosomes, so that the gametes carry combinations of genes different from either parent.

Crossover occurs between non-sister chromatids of homologous chromosomes. The result is an exchange of genetic material between homologous chromosomes. Now, when that sister chromatid is moved into a gamete cell it will carry some DNA from one parent of the individual and some DNA from the other parent.

The answer is that all chromatids can undergo crossover, though recombination between sisters is suppressed. The structure formed by two synapsed chromosomes is called a “bivalent” (pronounced BIV-uh-lent, not bi-VALE-unt). There are four chromatids in a bivalent.

What would happen if crossing over occurred between sister chromatids? Nothing would happen because sister chromatids are genetically identical or nearly identical. Daughter cells would not be genetically identical, and they could contain two copies of the same allele.

Crossing over is estimated to occur approximately fifty-five times in meiosis in males, and about seventy-five times in meiosis in females.

Crossing over is essential for the normal segregation of chromosomes during meiosis. Crossing over also accounts for genetic variation, because due to the swapping of genetic material during crossing over, the chromatids held together by the centromere are no longer identical.

Crossing over is a random event based on chance. Usually, crossing over between nonsister chromatids will occur between genes when they are relatively far apart on the homologous chromosomes when pairing occurs. This results in the production of an equal number of nonrecombinant and recombinant chromosomes.

Result of Crossing-Over Here, parts of homologous chromosomes can be exchanged. After crossing-over occurs, the homologous chromosomes separate to form two daughter cells. These cells go through meiosis II, during which sister chromatids separate. In the end, there are four possible gametes.

Crossing-over is the exchange of genetic material between homologous chromosomes. It results in new combinations of genes on each chromosome. When cells divide during meiosis, homologous chromosomes are randomly distributed to daughter cells, and different chromosomes segregate independently of each other.

In crossing over, genetic information is exchanged between homologous chromosomes. This exchange creates new combinations of genes, leading to increased genetic variation in the offspring. Both alleles are for the dominant trait.