Patterns of Inheritance By: Itzel Acevedo Biology

Genetic traits in Humans Mendel’s law apply to inheritance of many human traits. Eyes and hair color involves several genes. Recessive phenotypes always result from the homozygous genotype aa. Dominant doesn’t apply that a phenotype is either normal or more common than a recessive phenotype. Wild-type traits are not specified by dominant alleles, dominance means that a heterozygote carries only a single copy of dominant phenotype in genetics. To determine the inheritance, geneticist collect information about family history. The hey assemble the information into a family tree-Pedigree. To analyze this pedigree the geneticist applies logic and the Mendelian laws.

Inherited Disorders Most human disorders are recessive, range in severity from relatively mild, such as albinism(lack of pigment) to life-threatening. People who have recessive disorders are born to normal parents to heterozygote, who carries of the recessive allele for the disorder. Most common fatal genetic disease is cystic fibrosis- is carried by 1 in 25 people of European ancestry.it is not distributed to all ethnic groups. Mating of close relatives-inbreeding is more likely to produce offspring homozygous for recessive traits. Geneticists debate the extent to human inbreeding increases the risk of inherited disease. Human disorders are caused by dominant disorders, some are nonlethal conditions-extra fingers, toes or webbed fingers or toes. Achondroplasia is a form of dwarfism-the head and torso are body developed, but legs and arms are short. Homozygous dominant genotype causes death of the embryo, only heterozygote have this disorder. Huntington’s disease-degenerative disorder of the nervous system that doesn’t appear until years of age.

Genetic Legacy Genetic testing-most children with recessive disorders are born to healthy parents, genetic risks are determine by prospective parents who carry recessive allele. Fetal testing-harmful genetic conditions in a fetus, genetic testing before birth requires the collection of fetal cells-performed in wks. Of pregnancy. Fetal Imaging-techniques enable a physician to examine a fetus directly for anatomical deformities. Mostly used procedure is ultrasound imaging- uses sound waves to produce pictures of fetus. Newborn screening-genetic disorders can be detected at birth by tests. One program is phenylketonuria-recessive inherited disorder.

Phenotypes Genes that are passed along from generation to generation to simple rules of probability. Complete Dominance- dominant allele has the same phenotype effect whether present in one or more copies. Incomplete dominance-appearance of F1 hybrids falls between the phenotypes of the two parental varieties. They are also in humans. One case involves recessive allele that can cause hypercholesterolemia-high levels of cholesterol in the blood.

Genes have more than 2 alleles in population ABO blood group phenotype in humans involves 3 alleles on a single gene. This 3 alleles produce 4 phenotypes. Persons blood group may be O,A,B, OR AB-they refer to carbohydrates, may be found on the surface of red blood cells. The clumping reaction is the basis of a blood-typing test performed in a laboratory. Each person inherits one alleles from each parent. Recessive homozygote have type O blood because their blood cells have neither A nor the B carbohydrates. Codominant-are 1A and 1B, both are expressed in heterozygous individuals who have type AB blood.

Sickle Cells Each gene specifies one heredity character, most influence multiple characters called pleiotropy- example is a sickle-cell disease in humans. Sickled cells are destroyed by the body and the destruction of the cells may lower the individuals red cell count, causing anemia and general weakening in the body. Sickle cells accumulate in the spleen damaging it. Sickle-cell disease is the most common inherited disorder among African descent. The most common types of sickle cell disease are SS, SC and S beta thalassemia.

Single Character Polygenic inheritance-the additive effects of 2 or more genes on a single phenotype character.