Question:

Does crossing over occur during the stage of meiosis called prophase 1?

Answer:

Crossing-over is another name for recombination or physical exchange of equal pieces of adjacent non-sister chromatids. When crossing-over occurs chromatids break and may be reattached to a different homologous chromosome. This does occur during Prophase 1. AnswerParty!

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meiosis Biology
Molecular genetics

Molecular genetics is the field of biology and genetics that studies the structure and function of genes at a molecular level. Molecular genetics employs the methods of genetics and molecular biology to elucidate molecular function and interactions among genes. It is so called to differentiate it from other sub fields of genetics such as ecological genetics and population genetics.

Along with determining the pattern of descendants, molecular genetics helps in understanding developmental biology, genetic mutations that can cause certain types of diseases. Through utilizing the methods of genetics and molecular biology, molecular genetics discovers the reasons why traits are carried on and how and why some may mutate.


Cellular processes

A biological process is a process of a living organism. Biological processes are made up of any number of chemical reactions or other events that results in a transformation.

Regulation of biological processes occurs where any process is modulated in its frequency, rate or extent. Biological processes are regulated by many means; examples include the control of gene expression, protein modification or interaction with a protein or substrate molecule.

Genetics Mitosis
Cell biology

Cell biology (formerly cytology, from the Greek kytos, "contain") is a scientific discipline that studies cells – their physiological properties, their structure, the organelles they contain, interactions with their environment, their life cycle, division and death. This is done both on a microscopic and molecular level. Cell biology research encompasses both the great diversity of single-celled organisms like bacteria and protozoa, as well as the many specialized cells in multicellular organisms such as humans, plants, and sponges.

Knowing the components of cells and how cells work is fundamental to all biological sciences. Appreciating the similarities and differences between cell types is particularly important to the fields of cell and molecular biology as well as to biomedical fields such as cancer research and developmental biology. These fundamental similarities and differences provide a unifying theme, sometimes allowing the principles learned from studying one cell type to be extrapolated and generalized to other cell types. Therefore, research in cell biology is closely related to genetics, biochemistry, molecular biology, immunology, and developmental biology.


Chromosomal crossover

Chromosomal crossover (or crossing over) is the exchange of genetic material between homologous chromosomes that results in recombinant chromosomes. It is one of the final phases of genetic recombination, which occurs during prophase I of meiosis (pachytene) during a process called synapsis. Synapsis begins before the synaptonemal complex develops, and is not completed until near the end of prophase I. Crossover usually occurs when matching regions on matching chromosomes break and then reconnect to the other chromosome.

Crossing over was described, in theory, by Thomas Hunt Morgan. He relied on the discovery of the Belgian Professor Frans Alfons Janssens of the University of Leuven who described the phenomenon in 1909 and had called it 'chiasmatypie'. The term chiasma is linked if not identical to chromosomal crossover. Morgan immediately saw the great importance of Janssens' cytological interpretation of chiasmata to the experimental results of his research on the heredity of Drosophila. The physical basis of crossing over was first demonstrated by Harriet Creighton and Barbara McClintock in 1931.


Genetic recombination

Genetic recombination is the process by which two DNA molecules exchange genetic information, resulting in the production of a new combination of alleles. In eukaryotes, genetic recombination during meiosis can lead to a novel set of genetic information that can be passed on to progeny. Most recombination is naturally occurring. During meiosis in eukaryotes, genetic recombination involves the pairing of homologous chromosomes. This may be followed by information exchange between the chromosomes. The information exchange may occur without physical exchange (a section of genetic material is copied from one chromosome to another, without the donating chromosome being changed)(see SDSA pathway in Figure); or by the breaking and rejoining of DNA strands, which forms new molecules of DNA (see DHJ pathway in Figure). Recombination may also occur during mitosis in eukaryotes where it ordinarily involves the two sister chromosomes formed after chromosomal replication. In this case, new combinations of alleles are not produced since the sister chromosomes are usually identical. In meiosis and mitosis, recombination occurs between similar molecules (homologs) of DNA. In meiosis, non-sister homologous chromosomes pair with each other so that recombination characteristically occurs between non-sister homologues. In both meiotic and mitotic cells, recombination between homologous chromosomes is a common mechanism used in DNA repair.

Genetic recombination and recombinational DNA repair also occurs in bacteria and archaea.

Chromatid Chiasma
Homologous chromosome

Homologous chromosome is a set of one maternal chromosome and one paternal chromosome that pair up with each other inside a cell during meiosis. These copies have the same genes in the same locations, or loci, as one another. These loci provide points along each chromosome which enable a pair of chromosomes to align correctly with one another before separating during meiosis or mitosis. Genetic recombination occurs during meiosis in cells containing these parental chromosomes, producing genotypes in the offspring that are new and different combinations of the parental alleles. This recombination is due to either pairs of homologous chromosomes randomly segregating into two different daughter cells, or by crossing over , a process where homologous chromosomes exchange lengths of their genetic material. This is the basis for Gregor Mendel’s laws of genetics that characterize inheritance patterns of genetic material from an organism to its offspring.

recombination

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