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Showing posts with label centromere. Show all posts
Showing posts with label centromere. Show all posts

Saturday, April 6, 2013

Dicentric Chromosomes, Centromere Positioning, Autosomes & Allosomes

Still catching up! Days 26 - 28. See Hope for Trisomy for more educational posts!

Day 26: Dicentric Chromosome

On our 26th day of MARCHING into TRISOMY AWARENESS MONTH, we are going to share about a STRUCTURAL ABNORMALITY that we have not mentioned before. A DICENTRIC CHROMOSOME is the result of a rearrangement that places two centromeres on the same chromosome. The interaction of radiation with these chromosomes causes the break and then it becomes unstable, which often involves a loss of some genetic material. The formation of a dicentric chromosome is highly specific to ionizing radiation and its frequency serves as a measure of radiation exposure received by a person. In the event of higher exposure to radiation, such breaks may occur in more than one chromosome. Share because you Care. ♥

Day 27: Metacentric, Submetacentric, Acrocentric, and Telocentric Centromere Positions

On our 27th day of MARCHING into TRISOMY AWARENESS MONTH, we are going to share about four types of chromosomes based on the position of the centromere. The four types are Metacentric, Submetacentric, Acrocentric, and Telocentric. Metacentric is a type of chromosome having two equal arms because the centromere is in the median position. Submetacentric is a type of chromosome where the centromere is slightly away from the centre and therefore chromatids of one side are a little longer than the other side. Acrocentric is a type of chromosome where the centromere is located closer to one end and therefore the chromatids on the opposite side are very long. The small round structure is referred to as a satellite, and the thin strands at the satellite region are termed the Nucleolar Organiser Region. Telocentric is a type of chromosome where the centromere is placed at one end of the chromatid, hence only one arm. The telocentric chromosomes are not seen in human cells. Share because you Care. ♥

Day 28: Autosomes and Allosomes

On our 28th day of MARCHING into TRISOMY AWARENESS MONTH, we are going to share about the chromosome types that are divided into two categories, those being the AUTOSOMES and ALLOSOMES. AUTOSOMES are the structures that contain the hereditary information. They do not contain the information related to reproduction and sex determination. Autosomes are identical in both male and females. The human body contains 22 pairs of autosomes. An ALLOSOME is a sex chromosome that differs from an ordinary autosome in form, size, or behavior. The X chromosomes are present in the ovum and either the X or Y chromosome can be present in the sperm. If the offspring receives one X chromosome from the mother as well as father, it results in a female child (XX). If the offspring receives one X chromosome from the mother and one Y chromosome from the father, it results in a male child (XY). It is the donation of the X or Y chromosome by the father that determines the sex of the offspring. Since only males have a Y chromosome, then there must be a gene that makes the individual a male. Scientists have identified and isolated this gene and have termed it the SRY gene. Interestingly enough, this gene does not activate until 6 weeks after conception. Once activated, female structures are destroyed and the individual develops as a male. Share because you Care. ♥


Monday, March 11, 2013

Chromosome Craziness - Centromeres, Structural & Numerical Abnormalities

Be sure to follow Hope for Trisomy on Facebook to get a fun fact all through the month! We are always posting stories, news link, uplifting thoughts... So you'll want to come "like" us!

DAY 8:

On our 8th day of MARCHING into TRISOMY AWARENESS MONTH, we are going to share why the CENTROMERE is so important in the structure of a chromosome. The centromere divides the chromosome into the short and long arms. The centromere is usually not located exactly in the center of the chromosome, and in some cases, is located almost at the chromosome's end. The centromere is important particularly during mitosis (which is the process where a single cell divides resulting in generally two identical cells, each containing the same number of chromosomes and genetic content as that of the original cell). When the centromere is not functioning properly, the chromatids do not align and separate properly, thus, resulting in the wrong number of chromosomes in the daughter cells. This is when we see conditions such as Down syndrome (Trisomy 21), Edwards syndrome (Trisomy 18), and Patau syndrome (Trisomy 13). Share because you Care. ♥


DAY 9:

On our 9th day of MARCHING into TRISOMY AWARENESS MONTH, we are going to share some history about chromosomes. Did you know that before the chromosomes could be precisely identified they were placed in seven groups? A (chromosomes 1–3), B (chromosomes 4–5), C (chromosomes 6–12 and X), D (chromosomes 13–15), E (chromosomes 16–18), F (chromosomes 19–20), and G (chromosomes 21–22 and Y) ♥ Share because you Care


DAY 10:

On our 10th day of MARCHING into TRISOMY AWARENESS MONTH, we are going to share about chromosome abnormalities. Although there are many types of chromosome abnormalities, they can be organized into two basic groups; NUMERICAL and STRUCTURAL ABNORMALITIES. A NUMERICAL ABNORMALITY is when an individual is missing either a chromosome from a pair (monosomy) or has more than two chromosomes of a pair (trisomy). An example of a condition caused by numerical abnormalities is Down Syndrome, also known as Trisomy 21 (an individual with Down Syndrome has three copies of chromosome 21, rather than two). Turner Syndrome is an example of monosomy, where the individual - in this case a female - is born with only one sex chromosome, an X. A STRUCTURAL ABNORMALITY is when the chromosome's structure is altered, such as in deletions, duplications, translocations, inversions, and rings. Most chromosome abnormalities occur as an accident in the egg or sperm. Therefore, the abnormality is present in every cell of the body. Some abnormalities, however, can happen after conception, resulting in mosaicism, where some cells have the abnormality and some do not. Share because you Care. ♥

DAY 11:

On our 11th day of MARCHING into TRISOMY AWARENESS MONTH, we are going to share a little bit more about NUMERICAL ABNORMALITIES. A numerical abnormality is also referred to as an ANEUPLOIDY (an abnormal number of chromosomes). The 4 common categories of aneuploidy are; Nullisomy, Monosomy, Trisomy, and Tetrasomy. NULLISOMY is when a chromosome is missing altogether. Generally, embryos that are nullisomic don't survive to be born. MONOSOMY is when an individual is missing a chromosome from a pair. TRISOMY is when one extra copy of a chromosome is present. TETRASOMY is when four total copies of a chromosome are present. Tetrasomy is extremely rare. Chromosomal abnormalities, in the form of aneuploidy, are very common among humans. Roughly 8 percent of all conceptions are aneuploid, and it's estimated that up to half of all miscarriages are due to some form of chromosome disorder. Share because you Care. ♥