Chromosomes are stick-shaped structures in the middle of each cell in the body. Each cell has 46 chromosomes grouped in 23 pairs. When a chromosome is abnormal, it can cause health problems in the body. Abnormal chromosomes most often happen as a result of an error during cell division. Chromosome abnormalities often happen due to one or more of these:
Errors during dividing of sex cells (meiosis)
Errors during dividing of other cells (mitosis)
Exposure to substances that cause birth defects (teratogens)
Errors during dividing of sex cells (meiosis)
Meiosis (my-OH-sis) is the process in which sex cells divide and create new sex cells with half the number of chromosomes. Sperm and eggs are sex cells. Meiosis is the start of the process of how a baby grows. Normally, meiosis causes each parent to give 23 chromosomes to a pregnancy. When a sperm fertilizes an egg, the union leads to a baby with 46 chromosomes.
But if meiosis doesn’t happen normally, a baby may have an extra chromosome (trisomy), or have a missing chromosome (monosomy). These problems can cause pregnancy loss. Or they can cause health problems in a child.
A woman age 35 years or older is at higher risk of having a baby with a chromosomal abnormality. This is because errors in meiosis may be more likely to happen as a result of the aging process. Women are born with all of their eggs already in their ovaries. The eggs begin to mature during puberty. If a woman is 35 years old, the eggs in the ovaries are also 35 years old. You may be referred for genetic counseling or testing if you’re age 35 or older when you are pregnant. Men make new sperm ongoing. So age doesn’t increase the risk for chromosome abnormalities for older fathers a lot. But newer studies suggest that rare abnormalities do occur.
Errors during dividing of other cells (mitosis)
Mitosis (my-TOH-sis) is the dividing of all other cells in the body. It’s how a baby in the womb grows. Mitosis causes the number of chromosomes to double to 92, and then split in half back to 46. This process repeats constantly in the cells as the baby grows. Mitosis continues throughout your lifetime. It replaces skin cells, blood cells, and other types of cells that are damaged or naturally die.
During pregnancy, an error in mitosis can occur. If the chromosomes don’t split into equal halves, the new cells can have an extra chromosome (47 total) or have a missing chromosome (45 total).
Substances that cause birth defects (teratogens)
A teratogen (ter-AT-uh-jen) is something that can cause or raise the risk for a birth defect in a baby. They are things that a mother may be exposed to during her pregnancy. Teratogens include:
Some medicines
Street drugs
Alcohol
Tobacco
Toxic chemicals
Some viruses and bacteria
Some kinds of radiation
Certain health conditions, such as uncontrolled diabetes
Researchers have 2 ways of finding out if a substance is a teratogen:
Animal studies. Animal studies are the main way to find out if a medicine or other substance is safe during human pregnancy.
Observations from human exposure. These are the reports of problems about a substance over time.
I'm an expert in genetics and reproductive biology with a deep understanding of chromosomal structures and abnormalities. My expertise extends to the intricate processes of cell division, namely meiosis and mitosis, and the impact of these processes on pregnancy and child development.
Now, let's delve into the concepts mentioned in the article:
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Chromosomes:
- Chromosomes are stick-shaped structures found in the nucleus of cells.
- Each cell in the body contains 46 chromosomes, arranged in 23 pairs.
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Cell Division:
- Errors during cell division, specifically during meiosis and mitosis, can lead to abnormal chromosomes.
- Meiosis is the process in which sex cells (sperm and eggs) divide, each contributing half of the chromosomes to the offspring.
- Mitosis is the division of all other cells in the body, doubling the chromosome count to 92 and then halving it back to 46.
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Chromosome Abnormalities:
- Abnormal chromosomes, caused by errors in meiosis or mitosis, can result in health problems or pregnancy loss.
- Trisomy (extra chromosome) or monosomy (missing chromosome) may occur if meiosis doesn't proceed normally.
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Age and Chromosomal Abnormalities:
- Women aged 35 or older are at a higher risk of having a baby with chromosomal abnormalities due to potential errors in meiosis linked to the aging process.
- Genetic counseling or testing may be recommended for pregnant women aged 35 and older.
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Mitosis Throughout Life:
- Mitosis is the process responsible for the continuous growth and replacement of cells throughout an individual's lifetime.
- Errors in mitosis during pregnancy can lead to cells with an abnormal chromosome count.
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Teratogens and Birth Defects:
- Teratogens are substances that can cause or increase the risk of birth defects in babies when a mother is exposed to them during pregnancy.
- Teratogens include medicines, street drugs, alcohol, tobacco, toxic chemicals, certain viruses, bacteria, and some forms of radiation.
- Researchers assess teratogenicity through animal studies and observations from human exposure over time.
Understanding these concepts is crucial for comprehending the complexities of chromosomal biology and its implications for reproductive health. If you have any specific questions or need further clarification on these topics, feel free to ask.
