Which of the following disorders is fake? “Werewolf Syndrome” Congenital generalized hypertrichosis – a rare disorder characterized by excessive hair growth on the face and the upper body “Vampire Syndrome” Familial photodermatitis - When exposed to the sun, the skin blisters and gives pain, drinking blood relieves symptoms “Blue-Skin Syndrome” Methomoglobinemia – the enzyme diaphorase is absent from the red blood cells, and doesn’t allow for the conversion from methomoglobin back to hemoglobin Vampire syndrome is the FALSE syndrome Congenital generalized hypertrichosis… The Fugate family of Troublesome Creek,Kentucky… GENETICS Analyzing Heredity Introduction Heredity: the transmission of traits from parents to offspring Ideas of heredity have been around for all of recorded history It’s always been noticeable that children resemble their parents Sometimes characteristics are so noticeable that they can be traced for many generations There are several famous examples… The Hapsburgs, the ruling family of Austria (1200s – WWI) One relative, the Archduke Francis Ferdinand, was shot by a Serbian rebel. This assassination began WWI. The “Hapsburg Lip” was a protruding lip that’s evident in portraits of the family that span over 400 years… Royal families of Europe, beginning with Queen Victoria of England Passed on hemophilia Excessive bleeding due to an ineffective clotting factors It was passed on to the families of other nations as Victoria’s ancestors were married to others of their social status 1800’s: Most scientists believed in a blending of inheritance White rabbit + Black rabbit = Gray rabbit This didn’t hold true Basic Vocabulary before we begin: Chromosomes Genes Alleles Heterozygous homozygous Genetic Symbols Female symbol: Represents the hand mirror & comb of Venus Male symbol: Represents the shield & spear of Mars Gregor Mendel 1822: Born into a low- income family in what would become Czechoslovakia Entered the monastery to receive an education Eventually became an abbot for the church, meanwhile carried on experiments Mendel, cont’d… Was creative in his approach to science Took quantitative (numerical) data and analyzed it mathematically His work was ignored until after his death Mendel worked with Pisum sativum, garden peas, to study inheritance they come in a many varieties The male and female parts are in the same flower – an individual can self-pollinate itself or cross-pollinate with another individual Mendel’s Monohybrid Traits Mendel’s Experiments: 1. He allowed each variety (ex: purple-flowered vs. white- flowered) to self-pollinate for several generations Each was true-bred for a particular trait (seed shape, flower color, etc) He called these true-bred plants his parental, or P, generation 1. (P generation) 2. He crossbred two P: x varieties from the P generation… called the offspring the first filial, or F1, generation 3. Allowed the F1 F1: generation to self- pollinate… called the offspring the second filial, or F2, generation F2: Monohybrid Cross – a cross that tracks a single trait (ex: flower color) P generation: x All purple -called purple F1 generation: “dominant” -called white “recessive” -705 purple F2 generation: -224 white ~ 3:1 ratio F2: When Mendel self-pollinated the white flowered F2 individuals, ALL offspring were white When he self-pollinated the purple F2 individuals, he found only 1/3 to be true- breeding The other 2/3 gave another 3:1 ratio of p:w From this he devised a theory… Mendel’s Theory: 1. Parents pass on genes, not necessarily traits 2. Alternative forms of a gene that govern a specific trait ( hair color) are called alleles and are represented by by lower case or In this plant, capitalized letters. these might be (H,h) the individual’s two genes for flower color Remember, chromosomes come in homologous pairs, which have the same types of genes, but not the exact same genes, since one chromosome in each pair is from the mother of the organism, one is from the father. Chromosome 1 2 Chromosome 3 4 Weight Eye color Insulin Homologous Pair = 2 chomosomes with Height Lips same genes Hair Color Chromosomes 1 and 3 were from Mom, 2 and 4 were from Dad. …more theory 3. For every trait, an individual has two genes -If the alleles are the same, it is “homozygous.” -If they are different, it is “heterozygous.” 4. Your set of alleles is your genetic make-up or “genotype.” Your appearance is your “phenotype.” 5. You get one allele for each trait from each parent, and then pass on one of these two to each child. 6. In heterozygous individuals, only the dominant allele is expressed. The recessive allele is there but is not expressed. *It should be noted that in humans, over 600 traits have been shown to be single-factor inheritance traits, like those seen in peas. *Many others, however, are “polygenic” and have several more factors involved… Mendel’s Two Laws: Law of Segregation: The members of each pair of alleles separate when gametes form You only give one of each homologous pair of chromosomes to each gamete Law of Independent Assortment: Pairs of alleles separate independently (ex: flower color is independent of seed color) Exception to the rule: We now know this does not hold true if both genes are located on the same chromosome! Whatever these two genes code for, they will be passed on together because they are part of the same chromosome Analyzing Heredity Capital letters represent dominant alleles Lower-case letters represent recessive alleles What is dominance? A dominant gene is the gene that is expressed in an individual who has both alleles of that gene. For example, a heterozygous individual with a gene for purple color and a gene for white color expresses the purple gene and therefore appears purple. (dominance demo) Is “dominant” the same as “common” or “stronger”? No. Many genes are rare but dominant. Dwarfism and polydactyly (having more than 5 fingers) are both dominant traits, but only 1/400 babies is born with a 6th finger. Probability = the likelihood that an event will occur, or # of occurrences of a targeted event total # of occurrences Use the rule of multiplication when you need to find the probability of two or more independent events. Chance of a coin landing heads… ½ Chance of a coin landing heads, then tails… ½x½=¼ Chance of a coin, in two tosses, landing heads once and tails once… (½ x ½) + (½ x ½) = ¼ + ¼ = ½ H then T or T then H Monohybrid Cross One way to analyze is the Punnett square (named after the inventor, Reginald Punnett) T = tall pea plant t = short pea plant genotype: TT x tt phenotype: tall x short PUNNETT SQUARE T T t Tt Tt 4 out of 4 offspring (ALL) will be Tt, tall t Tt Tt Tt x Tt T t T TT Tt t Tt tt 1 out of 4 will be TT, tall 2 out of 4 will be Tt, tall 1 out of 4 will be tt, short 1 : 2 : 1 genotypic ratio… 3 : 1 phenotypic ratio TT : Tt : tt tall : short Single Factor Inherited Traits in Humans Tongue rolling Hitchhiker’s thumb Handedness Widow’s Peak Ear lobes (attached or free) Dihybrid Cross – a cross involving two pairs of traits P: purple p: white T: tall t: short TtPp x TtPp TP Tp tP tp TP TTPP TTPp TtPP TtPp Tp TTPp TTpp TtPP Ttpp tP TtPP TtPp ttPP ttPp tp TtPp Ttpp ttPp ttpp 9:3:3:1 ratio purple/tall : purple/short : white/tall : white/short Complex Patterns of Heredity – exceptions to what we have learned Incomplete Dominance: when neither allele is dominant or recessive Ex: snapdragons r = red w = white *rw individuals are pink Codominance: multiple dominant alleles exist that can be expressed at the same time ex: red & white hairs are both dominant in horses Hr = red Hw = white *HrHw individuals are “roan” colored (have both fully red and fully white hairs) Continuous Variation: when several genes influence a trait ex: in humans, height shows continuous variation… you don’t have just short vs. tall people – you have a continuous range ex: skin color: 3 hypothetical genes for skin coloration. The “dark skin” allele for each gene (A,B,C) contributes one unit of darkness to the phenotype. So, a person that is AABBCC would be very dark, while a person with aabbcc, would be very light. Those people with AaBbCc would be in the middle. Pleiotropy: When one gene has multiple effects ex: Sickle-cell – blood can’t carry oxygen well; resistance to malaria Epistasis: one gene has the ability to turn off another ex: in mice, black is dominant over brown (B = black, b = brown) There’s another gene that simply codes for the ability to produce pigment in the first place (C = pigment, c = no pigment / albino) Bbcc no color (albino) BbCc black Environmental Influences: phenotype can depend on the surroundings (while the genotype does not) ex: the color of the arctic fox changes from brown during the summer time to white during the winter for camouflage ex: During development, the colder parts of a Siamese cat turn a darker color, while the warmer parts retain more of a white color Sex-Linked Traits Sex-linked traits are carried on the X chromosome, and are recessive An example is hemophilia A man with hemophilia is NOT just “hh” He only has ONE X chromosome. He is represented as XhY. Men are much more likely to have sex-linked traits, because they only have one chance (one X) to get the healthy allele! Color blindness is another sex-linked trait Q: A woman who is a carrier for color-blindness has a child with a healthy man. What are the chances they will have a child who is color-blind? A: The woman is XBXb. The man is XBY. The punnett square looks like this: XB Xb XB XBXB XBXb Y XBY X bY ¼ chance. Tests for Colorblindness Con’t… A person with normal vision will see a 5. A person with red/green colorblindness will see a 2. Human Genetics Family pedigrees can be analyzed: = female = female carrier = male = male carrier = female with disorder = male with disorder Sample pedigree chart… A horizontal line signifies marriage, or having children A vertical line signifies children, or offspring Bracket, overhead connections signify siblings Pedigree Analysis… •Is this trait dominant or recessive? Pedigree analysis… It must be RECESSIVE, because if it was dominant the parents would have had the trait as well More pedigree analysis… What type of inheritance pattern does this pedigree most likely show? This is most likely a SEX-LINKED trait Remember: genes code for proteins that have a specific function For many genes, there may be only one allele Example: If all humans make the protein keratin the same way, with no variation, then this allele may only exist as a “K” New alleles come about via mutations Mutations, caused by “mutagens,” usually have harmful effects (although beneficial effects are possible) Harmful effects of mutations are what cause genetic disorders These disorders can be either dominant or recessive, and can strike at various points in life If a trait or a disorder is not sex-linked it is “autosomal” Recessively inherited disorders: Heterozygous individuals are “normal” in phenotype The disorder shows up only in homozygous recessive individuals (ex: aa, but not Aa) Disorders are often distributed only among certain ethnicities. Why? During less technological and global periods of time, societies were more isolated If an altered gene (mutation) popped up somewhere, it would stay within that society until individuals migrated in or out and mixed with other populations 1 in 25 caucasians is a carrier of cystic fibrosis. What are the chances that someone with an African-American mother and a white father is a carrier? (1/25) x (1/2) = 1/50 A 2% chance. Using the given numbers, what are the chances that two, undiagnosed white individuals have a child with cystic fibrosis? (1/25) x (1/25) = 1/625 chance they are both carriers (Cc & Cc) (1/625) x (1/4) = 1/2500 chance their child will have cystic fibrosis... A 0.04% chance. A man named John and a woman named Carol each had a sibling who died of a lethal, recessive disorder. Neither of them has the disorder, but they have not been tested to see if they are carriers. What are the chances that they will have a child with the disorder? Their parents must have each been Tt & Tt, which gave a 1TT:2Tt:1tt ratio of children This means there is a 2/3 chance that each is a carrier (2/3) x (2/3) = 4/9 chance that both are carriers (Tt x Tt) (4/9) x (1/4) = 1/9 chance their child will have the disorder For the most part, it is always very unlikely that two carriers for the same rare disorder will meet and have children These chances are greatly increased when individuals are related Called “sanguineous” (same-blood) matings, and are indicated in pedigrees with a double line Rules and laws, present in numerous societies for thousands of years, came about through the observation that stillbirths and birth defects are much more common when parents are related Such effects are observable in many domesticated animals and endangered populations Ex: Many pure-bred dogs suffer disorders (deafness in Dalmatians) Ex: Florida panthers have a crooked tail Dominant Disorders Why are dominant disorders more rare than recessive disorders? Unless it strikes late in life (like Huntington’s), an individual who carries even one of the alleles will have the disorder If it strikes before the individual has any children, then that person will not be able to pass on the allele and the mutation will stop with them Multifactorial Disorders Diseases with a multifactorial basis involve a genetic component but also a significant environmental influence Includes heart disease, diabetes, cancer, alcoholism, and many mental illnesses Lifestyle has a very large effect Ex: exercise, a healthy diet, abstinence from smoking, and dealing well with stress all greatly reduce the risk of heart disease Well-Known Genetic Disorders: Cystic fibrosis – mucus clogs lungs, liver, pancreas (European) Sickle cell anemia – poor blood, oxygen circulation (African) Tay-Sachs disease – deterioration of CNS (Jews) Phenylketonuria – Failure of brain to develop Hemophilia – Failure of blood to clot Huntington’s Disease – Deterioration of brain tissue Muscular Dystrophy – Wasting away of muscle Marfan Syndrome – disproportional growth, early death Achondroplasia – one form of dwarfism Dominant or Recessive? DOMINANT. Explanation: Tt Tt tt TT or Tt Dominant or Recessive? CAN’T TELL. Explanation: Could be either dominant or recessive. Dominant or Recessive? RECESSIVE. Explanation: Tt Tt TT or Tt tt Sex-Linked? NO (at least not sex-linked recessive). Explanation: If the mother were XhXh, then each of her sons would have to be XhY and show the trait. They do not, and so it cannot be sex- linked.
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