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why do we have 23 pairs of chromosomes

chromosomes Rod shaped bodies found in the nucleus of cells that contain genetic information (DNA). Parents pass on their
genes The basic units of genetic material inherited from our parents. A gene is a section of DNA which controls part of a cell's chemistry - particularly protein production. to their offspring in their sex cells. female sex cells are called egg cells, or ova male sex cells are called sperm. A pair of chromosomes carry the same genes in the same place, on each chromosome within the pair. However, there are different versions of a gene called alleles. These alleles may be the same (homozygous) on each pair of chromosomes, or different (heterozygous), for example, to give blue eyes or brown eyes. Sex cells only contain one chromosome from each pair. When an egg cell and sperm cell join together, the fertilised egg cell contains 23 pairs of chromosomes. One chromosome in each pair comes from the mother, the other from the father. Which chromosome we get from each pair is completely random. This means different children in the same family will each get a different combination. This is why children in the same family look a little like each other and a little like each parent, but are not identical to them. A set of chromosomes can be separated from its cell, spread out on a microscope slide and magnified many thousands of times. When stained and photographed, they look like this: The highlighted pair of chromosomes are called the sex chromosomes; they are a pair.

The longer sex chromosome is called the X chromosome, the shorter one the Y chromosome. females are XX males are XY. You have probably seen people who have Down syndrome. They have certain physical features, such as a flatter face and upward slanting eyes. They may have medical problems, too, such as heart defects. Kids with Down syndrome usually have trouble learning and are slower to learn how to talk and take care of themselves. But despite their challenges, kids with Down syndrome can go to regular schools, make friends, enjoy life, and get jobs when they're older. Getting special help early often when they are just babies and toddlers can be the key to healthier, happier, more independent lives. To understand why Down syndrome happens, you need to understand a little about chromosomes. What are chromosomes? They're thread-like structures within each cell and are made up of genes. Genes provide the information that determines everything about people, from hair color to whether they are girls or boys. Most people have 23 pairs of chromosomes, for a total of 46. But a baby with Down syndrome has an extra chromosome (47 instead of 46) or one chromosome has an extra part. This extra genetic material causes problems with the way their bodies develop. About half of babies with Down syndrome are born with heart defects, which means their hearts developed differently and don't work as they should.

Usually, these problems can be corrected by surgery. Some babies may have intestinal problems that also require surgery to fix. Kids with Down syndrome are more likely to get infections that affect their lungs and breathing. When they do get infections, they often last longer. They may have eye or ear problems or digestion problems like. Some may develop leukemia, a type of cancer. Each person with Down syndrome is different and may have one, several, or all of these problems. Kids with Down syndrome tend to grow and develop more slowly than other children do. They may start walking or talking later than other babies. Special help, such as and, can give kids a boost with their walking and talking skills. Do a Lot of People Have Down Syndrome? Down syndrome is not, so you can't catch it from someone else. You are born with it. No one gets Down syndrome later in life. It's one of the most common genetic birth defects (a birth defect is a problem that happens while a baby is still growing inside his or her mother). Now you know that Down syndrome is caused by a problem with a chromosome. You might already know that we get our chromosomes from our mother and father. Remember the 23 pairs of chromosomes half are from your mom and half are from your dad. But doctors aren't sure why this chromosome problem happens to some babies. It's nothing the mom or dad did before the child was born.

Anyone can have a baby with Down syndrome. But the older the mother, the greater the risk. At one time, most kids with Down syndrome did not live past childhood. Many would often become sick from infections. Others would die from their heart problems or other problems they had at birth. Today, most of these health problems can be treated and most kids who have it will grow into adulthood. can help with infections and can correct heart, intestinal, and other problems. If the person gets leukemia, medical treatments can be very successful. Down syndrome is something a person will have all of his or her life. But scientists continue to do research in the hope of finding ways to prevent Down syndrome or at least improve the health and lives of people who have it. What's Life Like for Kids With Down Syndrome? Many kids with Down syndrome go to regular schools and may attend regular classes. Some need special classes to help them in areas where they have more trouble learning. Their parents work with teachers and others to come up with a plan for the best way for each child to learn. Kids with Down syndrome like their playtime, too. They play sports and participate in activities, such as music lessons or dance classes. Kids with Down syndrome may look different, but they want to be treated the same way all kids want to be treated with respect, fairness, and friendship.

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