Patterns of Inheritance

Transcription

1 Patterns of Inheritance Some diseases are caused by changes in genes (mutations). Remember, there are always two copies of each gene in a person, but changes in the genes can cause some genetic diseases. If you have a genetic disease, you have it from the time you are born. You don t catch it later in life, even if symptoms don't show up until adulthood. You also can t cure a genetic disease, because you can t change your genes. However, scientists are trying to find cures for many genetic diseases. Different genetic diseases are inherited different ways, depending on the type of gene, and how it is passed on from parents to their children during meiosis, when egg and sperm cells are made. Dominant Conditions In a dominant condition, only one changed gene will cause the condition. So, if a parent has the disease, they have a 50% chance of passing it on to their children. a a chondroplasia is a dominant genetic bone growth disorder that causes the most common type of dwarfism. People with achondroplasia usually are shorter than 5 feet tall. Other physical differences include: bowed legs, decreased muscle tone, larger head, shorter arms and legs (especially the upper arm and thigh), and spine curvatures. There usually are not delays or mental retardation. 1

2 Dominant Conditions If one parent has achondroplasia, there is a 50% chance that they will have a child with the condition. However if both parents have it, and the baby gets both changed genes, they often do not live beyond a few months. a a Recessive Conditions In a recessive condition, both genes must be changed to cause the condition. If only one gene is changed, that person is a carrier. For a carrier, the other, unchanged gene does the work of the changed gene. They don t have the disease, but their children could be at risk. But, to have a child with a recessive condition, both parents must be a carrier. Everyone carries 4 8 recessive lethal disease genes. (Most carriers don t know they have a recessive gene.) 2

3 C c C C C C c c Cystic Fibrosis Cystic Fibrosis (CF) is a disease where the body makes too much mucus.the mucus builds up in the lungs, which makes it hard to breathe. Extra mucus in the digestive tract makes it hard for that person to get enough nutrients for their body to grow properly. Sickle Cell Disease Sickle Cell is also a recessive disease, so both parents must be carriers to have a child with Sickle Cell. carrier is said to have Sickle Cell Trait, because even though they are usually healthy, they do have some symptoms. Sickle Cell Disease person who has sickle cell disease does not have round red blood cells. Their red blood cells are crescent shaped, like a sickle. These sickled cells have trouble carrying oxygen, and have trouble passing through small blood vessels. If the sickled cells block a blood vessel, the blood can t flow, which causes extreme pain in the joint, and can damage the organs and tissues that doesn t get enough oxygen. 3

4 S S S S S Sex linked Some genes are on chromosomes 1 22, but other genes are on the X or Y chromosome. We say these genes are sexlinked, because they are on the sex chromosomes. Mostly, we deal with X chromosome diseases. There are some genes on the Y chromosome that cause diseases, but not as many. Whether someone is a carrier or has a sex linked condition is a bit more complicated than dominant or recessive conditions. 4

5 With a sex linked condition, males either have the disease or they don t. Females can be carriers. Females can have the disease, but it is rare they have to have a changed gene on both X chromosomes. X H X female carrier XX female, not a carrier X H Y male with Hemophilia XY male, doesn t have Hemophilia X H X H female with Hemophilia X H X X Y Hemophilia People with Hemophilia are missing a clotting factor, so their blood doesn t clot properly. They bruise more easily and bleed more if they get cut or hurt. X H Y X H Y X X H X X 5

6 Queen Victoria of England is well known for having had Hemophilia in her family. Prince William Prince Harry Incomplete Dominance For conditions that have incomplete dominance no phenotype is dominant or recessive. Blood Types are partially incompletely dominant. There are 3 genes for Blood type:, B, and O. The O gene is recessive to and B, but neither the or B gene is dominant over each other. This makes 4 blood types. Type has either or O genotype. Type B has either BB or BO genotype. Type O is OO genotype. Type B is B genotype. 6

7 Rh (Rhesus) factor you either have or don t have the Rh factor on the surface of your red blood cells. You are positive if you have it, and negative if you don t. When you get a blood transfusion, you have to match the Rh factor as well as the blood type. If you have 100 blood donors: 84 donors are RH + : 38 are O+ 34 are + 9 are B+ 3 are B+ 16 donors are RH : 7 are O 6 are 2 are B 1 is B 7

8 B O O O O O O If Mrs. Thomas' kids have O blood type, we know Mrs. Thomas must have O genotype. But, if they have blood type, Mrs. Thomas could have genotype or O genotype. Blood types used to be used for paternity tests, but they couldn t prove someone was the father, only if they weren't the father. Why? 8

9 patterns of inheritance.notebook Nondisjunction Nondisjunction is when the chromosome pairs don t separate properly during meiosis. This causes an imbalance in the chromosomes in the daughter cells. daughter cell could be missing a chromosome from one of its pairs. This is called monosomy. If there is an extra chromosome in addition to the pair, it is called trisomy. Having extra or missing chromosomes usually causes health problems, birth defects, and mental retardation or developmental delays (being slower to learn). n example of genetic condition caused by nondisjunction is Down Syndrome. 9

10 Multi factorial Conditions Some diseases are caused by a combination of genes and environment. Environment includes diet, exercise, and lifestyle. Because of your family history, you may have a greater chance than the average person to have the disease, but environment may decide if you actually develop the disease or not. Many diseases are Multi factorial, including: diabetes, high blood pressure, and some cancers. The Geee! in genome website: 10