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*CHAPTER 11 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 *Mendel’s 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: *Huntington’s 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. * PEDIGREE *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. *Written: C=color for the trait, CR for red flowers & CW for the white flower. A heterozygous flower color is written CRCW * 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 = IAIB *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 individual’s 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 1Y *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: XB = normal vision; Xb = colorblind; Y chromosome *X-Linked colorblind Punnett square XB Y XB XBXB XBY Xb XBXb XbY *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 *20th 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. *Arranged by decreasing size of the sister chromatids. *22 autosome chromosomes are arranged first *Sex chromosomes X’s & Y’s are placed last *Information that karyotypes can give us are: *Sex of the individual *Different genetic disorders * KARYOTYPE *TELOMERES *At the ends of each chromosomes are protective caps called telomeres. *Scientists believe that the telomeres might be involved in both aging and cancer *NONDISJUNCTION *Nondisjunction is when the sister chromatids fail to separate. *If nondisjunction occurs either during Anaphase I or Anaphase II the gametes will not have the correct number of chromosomes. *Results: gametes either have an extra chromosome or is missing a chromosome *Trisomy is when you have a set of 3 chromosomes of one kind. *In humans, altering the # of chromosomes is associated with serious human disorders or death. * DOWN SYNDROME * Down Syndrome occurs when there is an extra #21 chromosome (trisomy 21) * Characteristics for Down Syndrome include: * Distinctive facial features * Short stature * Heart defects * Mental disability * Frequency of Down Syndrome increases with the age of the mother. * SEX CHROMOSOME * Nondisjunction with the sex chromosomes can result in the following conditions: * Turner’s syndrome = XO * Klinefelter’s syndrome = XXY * Death = OY * Other abnormalities with the sex chromosomes include: XXX, XYY