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Advanced Genetics Pedigrees Graphic representation of genetic inheritance Pedigree Symbols Unaffected Male Carrier Male Unaffected Female Carrier Female Heterozygous Genotype Affected Male Deceased Male Affected Female Deceased Female Pedigree Symbols Mated Adults Parents with children Reading Pedigrees Generation 1 Person 1 Carrier Male Generation 2 Affected Male Person 5 Generation 3 Affected Female Person 3 Simple Recessive Heredity • Must inherit 2 recessive alleles to display trait (Homozygous) – Example: rr, tt, ss, pp • MOST genetic disorders are caused by recessive alleles 2 Recessive Disorders (1) Cystic fibrosis: • A defective gene that causes the body to produce unusually thick, sticky mucus that: – Clogs the lungs & leads to life-threatening infections – Obstructs the pancreas and stops the body from breaking down food and absorbing nutrients. • Treatment: medication, diet, & physical therapy Genotypes CC Cc cc Phenotypes NormalNo CF Normal- no CF but is a carrier of the disease Affectedhas CF 2 Recessive Disorders (2) Phenylketonuria (PKU): • Phenylalanine (amino acid) cannot be broken down and builds up in the central nervous system causing mental disability. • Symptoms: delayed mental and social skills, seizures, skin rashes, tremors, and unusual position of hands to some. • Prevention: All babies blood tested at birth. • Treatment: special diet Genotypes PP Pp pp Phenotypes Normal- No PKU Normal- but is a carrier of the disease Affected- has PKU Simple Dominant Heredity • Must inherit 1 dominant allele to display trait – Example: RR, Rr • Examples: tongue rolling, free earlobes, hitchhiker’s thumb, widow’s peak, dimples, almond shaped eyes, cleft chin, freckles. Dominant Disorder (1) Huntington’s disease: • Results from genetically programmed loss of brain cells, called neurons in certain areas of the brain. • Onset is normally between ages 30-40 • Treatment: prescribe a number of medications to help control emotional and movement problems, but no treatment for actual loss of brain cells. Genotypes HH Hh hh Phenotypes Has Huntington’s Has Huntington’s Normal- No Huntington’s Dominant Disorder (1) Huntington’s disease: • Behavior changes may occur before movement problems. – Examples: Hallucinations, irritability, moodiness, or restlessness • Abnormal and unusual movements – Examples: Facial movements, quick, sudden or wild jerking movements, slow, uncontrolled movements. • Dementia that slowly gets worse – Example: Disorientation or confusion, loss of judgment and memory, personality changes and speech changes Practice • If a man with cystic fibrosis marries a female carrier, what is the percentage chance that they will have children with cystic fibrosis? Man with cystic fibrosis: What is his genotype? ____________ Female carrier: What is her genotype? ________________ Inheritance patterns are often more complex than predicted by simple Mendelian genetics. • Each character that Mendel studied is controlled by a simple gene. • Each gene has only two alleles, one of which is completely dominant to the other. • The heterozygous offspring always looked like one of the parents because one allele was dominant to the other. When do we go beyond simple Mendelian Genetics? • When alleles are not completely dominant or recessive • When a gene has more than two alleles • When a gene produces multiple phenotypes Degrees of Dominance • Alleles show different degrees of dominance and recessiveness in relation to each other. • In Mendel’s crosses we’ve seen Complete Dominance – BB (Brown) Bb (Brown) bb (Blue) Incomplete Dominance • Incomplete dominance: Inheritance pattern where phenotypes of heterozygous individual is intermediate (a blend) between the 2 homozygous individuals producing a new trait. • • • • Neither allele is dominant over the other All capital letters because all dominant. The letters can be the same or different The third (inbetween) phenotype appears in the heterozygous (hybrid) condition. • Hint: Phenotype of offspring will look like a “blend” of parent’s phenotypes. Example In carnations the color red (R) is incompletely dominant over white (r). The hybrid color is pink. Give the genotypic and phenotypic ratio from a cross between 2 pink flowers. Rr X Rr R r R RR Rr r Rr rr Genotypic = 1 RR : 2 Rr : 1 rr Phenotypic = 1 red : 2 pink : 1 white Practice • In 4 o’clock flowers, when red flowers [R] and blue flowers [r] are crossed, purple flowers are created. Show the cross between two purple flowers. R r R r RR Rr Rr rr What percentage of the offspring are homozygous? 50% What percentage of the offspring are purple? 50% Codominance • Codominance: Inheritance pattern where phenotypes of both homozygous parents are produced in heterozygous offspring so that both alleles are expressed equally. • All capital letters because all dominant. • The letters can be the same or different. • Two dominant alleles are expressed at the same time so both phenotypes are expressed. • Hint: Phenotype of offspring will look like ”____ & _____”. Example In certain chickens black feathers are codominant with white feathers. A Black chicken (BB) is crossed with a White chicken (WW) which results in Checkered chicken (BW) offspring. BB X WW W W B BW BW B BW BW Example Checkered color represents a codominant allele in chickens. What phenotypes would be created when 2 checkered chickens are crossed? BW X BW B B W BB BW W BW WW Practice • A farmer’s herd consist of black [B], white [W], and roan color. Upon examination, it can be seen that the coat of a roan horse consist of both black and white hairs. The farmer has decided to cross two roan horses. B W B BB W BW WW BW What percentage of the offspring is black? 25% What percentage of the offspring is roan? 50% What percentage of the offspring is white? 25% Codominant Diseases (1) Sickle Cell Anemia • Hemoglobin protein, the protein that carries oxygen in the blood, is mutated and causes the red blood cells (normally round shaped) to be shaped like bananas. – Caused by a point mutation on DNA • Mostly affects people of African ancestry, but also occurs in other ethnic groups. – 1 in 12 African Americans have sickle cell trait, which means they carry a single gene for the disease, but do not have the disease. Genotypes NN NS SS Phenotypes Normal- RBC ½ sickle RBC & ½ normal RBC All sickled RBC Normal Red Blood Cells and Sickle Cells • When sickle-shaped cells block small blood vessels, less blood can reach that part of the body. • Tissue that does not receive a normal blood flow eventually becomes damaged. Malaria: A mosquito-borne disease of the blood. • Potentially fatal blood disease caused by a parasite that is transmitted to humans and animal hosts by the mosquito. • Human parasite digests the red blood cell’s hemoglobin and changes the properties of the cell it inhabits. – This change causes the cell to stick to the walls of blood vessels. • Especially dangerous when the infected blood cells stick to the capillaries in the brain, obstructing blood flow, a condition called cerebral malaria. Sickle Cell Anemia and Malaria • Each year, malaria attacks about 400 million people, two to three million of whom succumb to the illness. • Most malaria victims are children. Practice • A sickle cell anemic male marries a female with half normal RBC and half sickled. What percentage of their offspring would have sickle cell? Multiple Alleles • Multiple alleles: The presences of more than 2 alleles for a trait. • Remember: Each individual will only have two alleles for a trait but there are several alleles to choose from. • Examples: – Coat color in pigeons – 3 alleles – BA = ash, B= Blue, & b= brown Multiple Alleles • 2 or more alleles of the same gene that code for a single trait • In humans, blood type is determined by 3 alleles – A, B, and O BUT each human can only inherit 2 alleles •Blood types are controlled by Multiple alleles. 1. Dominant – A and B (codominance) Recessive – O 2. Blood type – A = AA or AO B = BB or BO AB = AB O = OO Blood Typing Chart Phenotypes Genotypes Blood Type A IAIA or IAi Blood Type B IBIB or IBi Blood Type AB IAIB Blood Type O ii Why is blood type important? • Blood Transfusion • Paternity/Maternity Testing • Crime Scene Investigation Practice • A father has a Blood Type AB. The mother has homozygous Blood Type A. Can the child have Blood Type O? Practice • A man is accused of fathering 2 children. Child 1 is blood type O and Child 2 is blood type B. The mother is heterozygous for blood type B. The man is blood type AB. Could he father both children? Sex determination • Human somatic cells = 46 chromosomes (Diploid) • Human gametes = 23 chromosomes (Haploid) Sex determination • Chromosomes # 1-22 pairs: – Autosomes: Control things other than gender • Chromosomes #23 pair: – Sex chromosomes: control gender Baby XX Mother XY Father Sex-linked Inheritance • Sex Linked Traits controlled by genes on the sex chromosomes. • Most sex-linked traits are on the X-chromosomes. How are Sex-Linked Traits inherited? Fathers (XY) can only pass X-linked disorders to daughters (XX) Mothers (XX) can pass Xlinked disorders to both sons (XY) and daughters (XX) Types of Sex-Linked Traits • X-linked traits are traits whose allele is carried on the X chromosome. – Most disorders are carried on the X chromosome, so males are more likely to inherit them. • Y-linked traits are traits whose allele is carried on the Y chromosome. – Most Y-linked mutations lead to sterility, and can not be inherited. Sex-linked Trait Examples • Hemophilia: Your body cannot clot blood • Red-Green color blindness: Cannot tell the difference between red and green. • Both examples are on the X chromosomes and are recessive. Hemophilia in the Royal Family Colorblindness • For sex-linked traits, you must write genotypes like: C • XCXC : Normal color vision female • XCXc : Normal color vision female (carrier) • XcXc : Color-blind female • XCY : Normal color vision male • XcY : Color-blind male c Hemophilia • For sex-linked traits, you must write genotypes like: H • XHXH : Normal clotting female • XHXh : Normal clotting female (carrier) • XhXh :Hemophilic female • XHY : Normal clotting male • XhY : Hemophilic male h Practice • A woman who is a carrier for hemophilia marries a normal man. Show the possible results of this cross and answer the following questions: – A. What is the probability that this couple could have a son with hemophilia? – B. What is the probability that they could have a daughter with hemophilia? Sex-Linked Trait Facts • Sex-linked traits occur more so in males than females because: • Males only need one “bad” gene on the X chromosome. • Females need two “bad” genes on both X chromosomes. Polygenic Inheritance • Polygenic inheritance: Inheritance pattern of a trait controlled by two or more genes; genes may be on the same or different chromosomes. • Polygenic inheritance usually shows up as a range of variation. – ex: Hair color, eye color, height, and skin color. Chromosomal Number • Normal Somatic Cell = 46 chromosomes • Scientists look at chromosome number information by using a karyotype. • A karyotype is a picture of an individual’s chromosomes. Detecting Genetic Disorders Amniocentesis is used to detect genetic disorders by analyzing the amniotic fluid that surrounds an embryo. Female with Down’s syndrome Chromosomal Number Mutations • Sometimes cells have too many or too few chromosomes: • (1) Trisomy = 1 extra chromosome = 47 • (2) Monosomy = 1 less chromosome = 45 • Caused by nondisjunction during Meiosis Down syndrome – (Trisomy 21) 47 chromosomes, extra chromosome at pair #21 Down Syndrome • Autosomal chromosome disorder where there are three of chromosome-21. • common physical traits: low muscle tone, small stature, an upward slant to the eyes, and a single deep crease across the center of the palm. • Life expectancy increased from 25 in 1983 to 60 today. • Attend school, work, participate in decisions that affect them, and contribute to society in many wonderful ways. • Experience mental processing delays, but the effect is usually mild to moderate and is not indicative of the many strengths and talents that each individual possesses. Abnormal Chromosome # Disorders Individuals can have the wrong number of sex chromosomes Females (no X chromosome) - XO: Turner Syndrome Physical Traits: Short Stature, premature ovarian failure, webbed neck, and normal overall intelligence. Turner’s syndrome – only 45 chromosomes, missing a sex chromosome (X) Girls affected – short, slow growth, heart problems Abnormal Chromosome # Disorders Males (extra X chromosome) -XXY: Klinefelter Syndrome • puberty- make as much testosterone which can lead to a taller, less muscular body, less facial and body hair, and broader hips than other boys. • teens- may have larger breasts, weaker bones, and a lower energy level than other boys. • adulthood- look similar to males without the condition, although they are often taller. They are also more likely than other men to have certain health problems, such as autoimmune disorders, breast cancer, vein diseases, osteoporosis, and tooth decay. Klinefelter’s syndrome – 47 chromosomes, extra X chromosomes (XXY) Boys affected – low testosterone levels, underdeveloped muscles, sparse facial hair • Having an extra set of chromosomes is fatal in animals, but in plants it makes them larger and hardier. Hardier