Text of COMPLEX INHERITANCE AND HUMAN HEREDITY. * CH. 11.1 BASIC PATTERNS OF HUMAN INHERITANCE * MAIN IDEA...
COMPLEX INHERITANCE AND HUMAN HEREDITY
* CH. 11.1 BASIC PATTERNS OF HUMAN INHERITANCE * MAIN IDEA THE INHERITANCE OF A TRAIT OVER SEVERAL GENERATIONS CAN BE SHOWN IN A PEDIGREE. * QUESTION: If someone looks more like one parent than the other, did that person inherit more genes from that parent?
* RECESSIVE GENETIC DISORDERS * Mendels work was ignored for 30 years until scientists began looking at heredity. * Recessive traits are expressed when the individual is homozygous recessive for that trait. * Individuals with at least one dominant trait will NOT express the recessive trait. * An individual who is heterozygous for a recessive disorder is called a carrier. * Examples of recessive genetic disorders are: * Cystic fibrosis * Albinism * Galactosemia * Tay-Sachs disease
* RECESSIVE GENETIC DISORDERS CONTINUED * CYSTIC FIBROSIS * One of the most common recessive genetic disorders among Caucasians is cystic fibrosis, which affects the mucus producing glands, digestive enzymes and sweat glands. * People develop a thick mucus that clogs the ducts in the pancreas, interrupts digestion, and blocks the tiny respiratory pathways in the lungs. * People with cystic fibrosis are at a higher risk of infection because of the mucus in their lungs * Treatments are physical therapy, medication, special diets, and the use of replacement digestive enzymes. * Genetic tests are available to determine if a person is a carrier.
* RECESSIVE GENETIC DISORDERS * ALBINISM * Albinism is caused by altered genes, resulting in the absence of the skin pigment melanin in hair and eyes. * Albinism is also found in animals. * People with albinism have white hair, very pale skin, and pink pupils. * Lack of pigment in eyes causes vision problems. * TAY-SACHS DISEASE * Gene for Tay-Sachs disease (TSD) is located on chromosome 15. * Disease is predominantly among Jews of eastern European descent. * TSD is caused by the absence of the enzymes responsible for breaking down fatty acids, which build up in the brain, inflating brain nerve cells and causing mental deterioration.
* DOMINANT GENETIC DISORDERS * Some genetic disorders are caused by the dominant allele. So if you do not have the disorder you are homozygous recessive for the trait. * Some types of dominant genetic disorders include: * Huntingtons disease affects the nervous system with systems first appearing between the ages of 30 and 50 years old. * Systems include: loss of brain function, uncontrollable movements and emotional disturbances. * Genetic tests are available to detect this dominant allele, but there are no preventive treatment or cure for this disease.
* DOMINANT GENETIC DISORDERS CONTINUED * Achondroplasia (most common form of dwarfism) have a small body size and limbs that are short. * Individuals with achondroplasia have a normal life expectancy and will reach a height of about 4 feet. * 75% of individuals with achondroplasia are born to parents of average size. * Believed to be caused by new mutation or a genetic change.
* PEDIGREES * Pedigree is a diagram that traces the inheritance of a particular trait through several generations of a family. * Symbols are used to illustrate the inheritance of a trait. * Males are represented by squares = * Females are represented by circles = * Person who expresses the trait being studied is represented by a filled in square or circle = * Person who does not express the trait is represented by an unfilled square or circle. = * Half-filled square or circle means the person is a carrier. =
* PEDIGREES Continued * Horizontal line between 2 symbols shows that the individuals are married * Brackets show the offspring of the parents. Offspring are listed in descending birth order from left to right and are connected to each other and their parents. * Pedigree uses a numbering system where Roman numerals represent generations and individuals are numbered by birth order using Arabic numbers.
* INFERRING GENOTYPES * Pedigrees are used to help figure out the genotypes * Pedigrees are also used to help figure out dominant and recessive traits. * Dominant traits are easier to recognize because they are expressed * Recessive traits are only seen if the person is homozygous recessive for the trait * Need to follow the recessive trait for several generations to figure out which parents & grandparents were the carriers of the recessive allele.
* SECTION 11.2 COMPLEX PATTERNS OF INHERITANCE * MAIN IDEA Complex inheritance of traits does not follow inheritance patterns described by Mendel * QUESTIONS: What possible eye colors are there? * Do you think that eye color is inherited by a simple dominant/recessive manner?
* INCOMPLETE DOMINANCE * REVIEW dominant/recessive traits the dominant trait is expressed, even if the organism is heterozygous. * Incomplete dominance is when a heterozygous organism shows a blending of the dominant and recessive trait. * Ex: cross a red flower with white flower and the heterozygous flower will be pink. R * Written: C=color for the trait, C R for red flowers & C W for the white flower. A heterozygous flower color is written C R C W
* INCOMPLETE DOMINANCE PUNNETT SQUARE
* CODOMINANCE * In codominance both alleles are expressed in the heterozygous condition. * EX: Homozygous black chicken & homozygous white chicken will produce heterozygous black and white chickens. * SICKLE CELL DISEASE * Sickle cell disease is a codominant inheritance * Common in people of African descent and affects the red blood cells ability to carry oxygen * Ex: if you are heterozygous for sickle cell disease your body produces both normal blood cells and sickle cells * People living in malaria areas being heterozygous for sickle cell disease also have a higher resistance to malaria * Allows the sickle trait to continue to be passed down.
* MULTIPLE ALLELES * Some forms of inheritance are determined by more than 2 alleles. This is referred to as multiple alleles. * EX: blood * BLOOD GROUPS IN HUMANS * The different types of blood that humans can have are: A, B, AB, and O * A & B are dominant to O; but A & B together are codominant * Blood type is written: * A = I A * B = I B * AB = I A I B * O = ii * Rh factors are either + or - & written Rh+ or Rh- and + is dominant over -
* SEX DETERMINATION * Each cell in your body, except gametes, contains 46 chromosomes or 23 pairs of chromosomes. * One pair of chromosomes, the sex chromosomes, determines an individuals gender. * There are 2 types of sex chromosomes, X & Y. * XX chromosomes = girls * XY chromosomes = boys * Males determine sex of the baby * The other 22 pairs of chromosomes are called autosomes
* DOSAGE COMPENSATION * Human females have 22 pairs of autosomes and 1 pair of X chromosomes. * Human males have 22 pairs of autosomes and 1 X and 1 Y * There are a lot of genes on the X chromosomes, but Y chromosomes only contain genes that pertain to male characteristics * In female body cells one X chromosome is randomly chosen to be turned off or X-inactivation * Turned off X chromosome is referred to as a Barr body
* SEX-LINKED TRAITS * If a trait is located on the X chromosome it is called a sex-linked trait or X-linked. * Males only have 1 X chromosome, so if that trait is dominant or recessive it is expressed. * Females have 2 X chromosomes, so their traits follow the dominant recessive pattern. * COLORBLINDNESS (Red/Green) * Colorblindness is a recessive X-linked trait. * Punnett squares for X-linked traits are written: * EX: X B = normal vision; X b = colorblind; Y chromosome
* X-Linked colorblind Punnett square X B Y X B X b X B X B X B Y X B X b X b Y
* HEMOPHILIA * Hemophilia is a recessive sex-linked disorder. People with hemophilia have a delayed clotting of their blood. * Hemophilia was passed through a lot of the royal families * Men died more frequently and at an early age because of the absence of clotting factors * 20 th century learned about the clotting factors & now it is given to people with hemophilia.
* POLYGENIC TRAITS * Polygenic traits are traits that are controlled by multiple pairs of genes. * EX: skin color, height, eye color, and fingerprint patterns * When looking at the frequency of polygenic traits the results you see will be a bell shaped curve.
* ENVIRONMENTAL INFLUENCES * Environment also has an effect on phenotypes. * EX: you may inherit a gene that gives you the tendency to have heart disease. * Environment factors such as diet and exercise can contribute to the occurrence and seriousness of the disease. * Other environmental factors that can affect phenotype are: * Sunlight * Water * Temperature
* Ch. 10.3 CHROMOSOMES AND HUMAN HEREDITY * KARYOTYPE STUDIES * Karyotypes is a study used by scientists to study the whole chromosomes using images of chromosomes stained during metaphase (mitosis). * Sister chromatids are arranged by looking at their length, centromere location, and the banding. * A