Understanding Genetics Study of traits passed from parent(s) to child

Heredity and Genetics Heredity: the biological process by which certain traits are transmitted from parents to their children. Genetics: the study of how traits are passed from parents to child through heredity.

How Does it Work It all starts with chromosomes, long, threadlike structures in the nucleus, or central portion, of each human cell. On each chromosome there are hundreds of genes. A gene is a hereditary unit that determines a particular trait, such as eye color. Almost all cells in the human body contain 23 pairs of chromosomes, or 46 in all. Ova and the sperm cells are the exception, they only contain 23 chromosomes each.

How Does it Work When an ovum and sperm unite at conception, they create a single cell with 46 chromosomes-23 from the sperm and 23 from the ovum. The number of possible combinations is over 64 trillion different genetic combinations. Every cell in our body has a copy of those 46 chromosomes-a genetic blueprint for each unique individual.

Dominant and Recessive Traits A child receives two genes from each parent for each trait, two for eyes, two for hair, two for mouth, and so on. Sometimes both parents have the same gene, like they both have brown eyes, and in that case the child will have brown eyes. Sometimes they are different, like the mother will have blue and the father will have brown. The dominant gene will be expressed. A weaker trait such as the blue eyes is recessive, both parents would have to have the same recessive gene to be expressed in the child. Could parents with both brown eyes have a blue eye child? Yes, if each parent carries the recessive gene for blue eyes.

Gender Determination Will the baby be a boy or girl? The answer is settled as soon as the sperm fertilizes an ovum.

Genetic Disorders Genetic Disorders- are medical conditions caused by errors in genes or chromosomes. Nearly 4,000 genetic disorders afflict humans.

Common Genetic Disorders Down Syndrome Cystic Fibrosis Muscular Dystrophy Sickle-Cell Tay-Sachs PKU

Down Syndrome Human cells normally contain 23 pairs of chromosomes. One chromosome in each pair comes from your father, the other from your mother. The cause of Down syndrome is one of three types of abnormal cell division involving the 21st chromosome. All three abnormalities result in extra genetic material from chromosome 21, which is responsible for the characteristic features and developmental problems of Down syndrome. The three genetic variations that can cause Down syndrome include: Trisomy 21. More than 90 percent of cases of Down syndrome are caused by trisomy 21. A child with trisomy 21 has three copies of chromosome 21 — instead of the usual two copies — in all of his or her cells. This form of Down syndrome is caused by abnormal cell division during the development of the sperm cell or the egg cell. Mosaic Down syndrome. In this rare form of Down syndrome, children have some cells with an extra copy of chromosome 21, but not all. This mosaic of normal and abnormal cells is caused by abnormal cell division after fertilization. Translocation Down syndrome. Down syndrome can also occur when part of chromosome 21 becomes attached (translocated) onto another chromosome, before or at conception. Children with translocation Down syndrome have the usual two copies of chromosome 21, but they also have additional material from chromosome 21 stuck to the translocated chromosome. This form of Down syndrome is uncommon.

Down Syndrome Is it inherited? Most cases of Down syndrome aren't inherited. They're caused by a mistake in cell division during the development of the egg, sperm or embryo. Translocation Down syndrome is the only form of the disorder that can be passed from parent to child. However, only about 4 percent of children with Down syndrome have translocation. And only about half of these cases are inherited from one of the parents. In these cases, the mother or father is a balanced carrier of the translocation, which means he or she has some rearranged genetic material, but no extra genetic material. A balanced carrier has no signs or symptoms of Down syndrome, but he or she can pass the translocation on to children. The chance of passing on the translocation depends on the sex of the parent who carries the rearranged chromosome 21: If the father is the carrier, the risk is about 3 percent. If the mother is the carrier, the risk is about 12 percent.

Down Syndrome

Cystic Fibrosis In cystic fibrosis, a defective gene alters a protein that regulates the normal movement of salt (sodium chloride) in and out of cells. This results in thick, sticky secretions in the respiratory and digestive tracts, as well as in the reproductive system. It also causes increased salt in sweat. The affected gene, which is inherited from a child's parents, is a recessive gene. With recessive genes, children need to inherit two copies of the gene, one from each parent, in order to have the disease. If children inherit only one copy, they won't develop cystic fibrosis, but will be carriers and possibly pass the gene to their own children. If two people who carry the defective gene conceive a child, there's a 25 percent chance the child will have cystic fibrosis, a 50 percent chance the child will be a carrier of the cystic fibrosis gene, and a 25 percent chance the child will neither have the disease nor be a carrier. People who carry the cystic fibrosis gene are healthy and have no symptoms — they may be carriers and not know it. Although parents often blame themselves when a child is born with cystic fibrosis, it's important to remember that the causes of cystic fibrosis are not the result of anything a parent consciously does. Average lifespan 30 years old

Muscular Dystrophy Signs and symptoms vary according to the type of muscular dystrophy. In general, muscular dystrophy symptoms may include: Muscle weakness Apparent lack of coordination Progressive crippling, resulting in fixations (contractures) of the muscles around your joints and loss of mobility Many specific signs and symptoms vary from among the different forms of MD. Each type is different in the age of onset, which parts of the body the symptoms primarily affect and how rapidly the disease progresses.

Sickle-Cell Disease Sickle cell anemia is caused by a mistake in the gene that tells your body to make hemoglobin — the red, iron-rich compound that gives blood its red color. Hemoglobin is a component of every red blood cell in your body

Sickle Cell Disease Symptoms Anemia. Sickle cells are fragile. They break apart easily and die, leaving you chronically short on red blood cells to carry oxygen to your tissues — a condition known as anemia. Without enough red blood cells in circulation, your body can't get the oxygen it needs to feel energized. That's why anemia causes fatigue. Episodes of pain. Periodic episodes of pain, called crises, are a major symptom of sickle cell anemia. Pain develops when sickle-shaped red blood cells block blood flow through tiny blood vessels to your chest, abdomen and joints. Pain can also occur in your bones. The pain may vary in intensity and can last for a few hours to a few weeks. Some people experience only a few episodes of pain. Others experience a dozen or more crises a year. If a crisis is severe enough, you may need hospitalization so that painkillers can be injected into your veins (intravenously). Hand-foot syndrome. Swollen hands and feet are often the first signs of sickle cell anemia in babies. The swelling is caused by sickle-shaped red blood cells blocking blood flow out of the hands and feet. Jaundice. Jaundice is a yellowing of the skin and eyes that occurs because of liver damage or dysfunction. Occasionally, people who have sickle cell anemia have some degree of jaundice because the liver, which filters harmful substances from the blood, is overwhelmed by the rapid breakdown of red blood cells. In people with dark skin, jaundice is visible mostly as yellowing of the whites of their eyes. Frequent infections. Sickle cells can damage your spleen, an organ that fights infection. This may make you more vulnerable to infections. Doctors commonly give infants and children with sickle cell anemia antibiotics to prevent potentially life-threatening infections, such as pneumonia. Stunted growth. Red blood cells provide your body with the oxygen and nutrients you need for growth. A shortage of healthy red blood cells can slow growth in infants and children and delay puberty in teenagers. Vision problems. Some people with sickle cell anemia experience vision problems. Tiny blood vessels that supply your eyes may become plugged with sickle cells. This can damage the retina — the portion of each eye that processes visual images.

Sickle Cell

Tay-Sachs Disease Infants with Tay-Sachs disease appear to develop normally for the first few months of life. Then, as nerve cells become distended with fatty material, a relentless deterioration of mental and physical abilities occurs. The child becomes blind, deaf, and unable to swallow. Muscles begin to atrophy and paralysis sets in. Other neurological symptoms include dementia, seizures, and an increased startle reflex to noise. Just like most genetic disorders both parents must be carriers, and it is more common among Jewish or European decent. Can be screened for. http://video.google.com/videosearch?hl=en&safe=active&um=1&q=tay%20sachs&ndsp=18&ie=UTF-8&sa=N&tab=iv&start=0#hl=en&safe=active&um=1&q=tay+sachs&ndsp=18&ie=UTF-8&sa=N&tab=iv&start=10

PKU Left untreated, this condition can cause problems with brain development, leading to progressive mental retardation and seizures. However, PKU is one of the few genetic diseases that can be controlled by diet. A diet low in phenylalanine and high in tyrosine can be a very effective treatment. There is no cure. Damage done is irreversible so early detection is crucial. Fortunately this is a routine test given to newborns to detect early.

Genetic Counseling Genetic counseling is the process by which patients or relatives, at risk of an inherited disorder, are advised of the consequences and nature of the disorder, the probability of developing or transmitting it, and the options open to them in management and family planning in order to prevent, avoid or improve it. This complex process can be seen from diagnostic (the actual estimation of risk).

Genetic Counseling Genetic counselors provide information and support to families who have members with birth defects or genetic disorders, and to families who may be at risk for a variety of inherited conditions. They identify families at risk, investigate the problems present in the family, interpret information about the disorder, analyze inheritance patterns and risks of recurrence and review available testing options with the family. A person may also undergo genetic counseling after the birth of a child with a genetic condition. In these instances, the genetic counselor explains the condition to the patient along with recurrence risks in future children. In all cases of a positive family history for a condition, the genetic counselor can evaluate risks, recurrence and explain the condition itself.