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Genome references • Ch “X and Y”: Conflict (sexual antagonism) • Ch 9: Disease (Blood Type/ Disease) • Ch 15: Sex (Genetic Imprinting) • Ch 4: Fate (Huntingtons) Where do we get genetic variability in a population? 1. Random Mating --Sexual Reproduction --Meiosis --crossing over 2. Mutation NonMendelian Inheritance Patterns There are other patterns of inheritance that do not follow Mendel’s Principles. Be sure you recognize what is different or what Law is violated by these different patterns. 1. Co-dominance=when two alleles are both expressed (neither masks the other) • Ex = human blood type • 3 different alleles = IA, IB, and i that code for A, B, and “o” blood types. • IAIB Type AB blood (Co-dominant) (genotype) (phenotype) Why the different blood types? • Because there is a connection between blood type and susceptibility to disease. • Genome Chapter 9 (“Disease”) --AB nearly completely resistant to Vibrio cholera (a diarrheal) disease --O slightly more resistant to malaria 2. Incomplete Dominance • Also known as “blending” b/c neither allele in a pair is fully expressed • Example seen in Shorthorn Cattle C = color gene with alleles possible = CR (red), CW (white) • Cross a red bull with a white cow (Punnett Square) Shorthorn Cattle CR CW (Roan) 3. Linked genes = found on the same chromosome • Ex: the genes for petal shape & color are linked (C=curved or c=straight / W=white or w=blue); C & w are linked, c & W are linked • Cross two heterozygotes (Punnett Square) • What Mendelian law do these results violate? Crossing over switches linked genes Recombination Frequency • Linkage map can be determined by using recombination frequency calculations • See p. 293-5 Nondisjunction 4. Epistasis (“stopping”) • A gene at one locus alters (usu. inhibits) the phenotypic expression of a gene at another location. • Ex: Fig 14.12 on p. 273 ( labradors) 5. Sex-linked Traits • Also known as “X-linked” • Example = Color blindness in humans / normal color seeing is dominant to color blindness but the gene that codes for this trait is linked (found on) the X chromosome • X-C codes for normal color vision • X-c codes for color blindness • y doesn’t code for color-seeing What # do you see? • Light-sensitive opsin proteins made in the eye & necessary for color vision, are encoded by a cluster of genes on the X chromosome. • Mutations in these genes can lead to an insensitivity to certain colors (like red and green) when seen together. Eye Color in Fruit Flies 6. X Inactivation • The phenomenon in a female by which one X chromosome (either Mom’s or Dad’s) is randomly inactivated in an early embryonic cell, with fixed inactivation of that same X in all cells descended from that cell. Ex: Tortoise Shell Cat • X inactivation is not restricted to females. It also occurs in males with Klinefelter syndrome who have more than one X chromosome. The phenomenon is also called lyonization after geneticist Mary Lyon who first described it. 7. Sex-influenced Traits • Aka, Gender-influenced • Usually influenced by sex hormones like estrogen, testosterone • Examples include baldness in humans, plumage in birds, horns on cattle 8. Multiple Alleles (vs. just two) • Sometimes a trait is coded for by more than just two alleles • Example = human blood type has 3 alleles A, B, or O @ 9q34 9. Polygenic Traits • More than one set of genes coding for a trait (NOT the same as multiple alleles) • Eye color is influenced by many genes coding for different kinds of pigment as well as where in the iris those pigments are found (some have been located on chromosomes 15 & 19) 10. Environmentally-influenced • Color of the Hydrangea flower determined by the pH of the soil • Acidic soilblue flower • Basic soilpink flower • How about “intelligence” in humans? 11. Transposons (Jumping Genes) & Their Effect On The Kernel Color Of Indian Corn • The explanation? Involves "jumping genes" or transposons, and earned Dr. Barbara McClintock the Nobel Prize in Medicine (1983). Grains of Indian corn come in different colors like purple or yellow. But what happens when they appear mottled (have streaks)? • This mottling effect defies Mendel's basic principles of genetics b/c individual grains may be multicolored rather than just one single color or another (purple vs. yellow). How do Jumping Genes Work? • Transposons are genes that move from one location to another within or between chromosomes. In the pigmented layer of corn grains, the position of transposons may inhibit or block pigment production in some cells. • Examples (from “DNA’s New Twists”): -- “Air gene” in Volvox when cold -- P element betw. Drosphilia species via mite gut infection Transposons move directly from one position to another within the genome using a transposase enzyme to "cut and paste" them within the genome. 12. Genomic Imprinting • A fundamental belief of Mendelian principles of inheritance is that a gene's parent of origin does not influence its dominance or recessiveness in determining phenotype. (Ex: if you inherit a dominant allele from either parent, the offspring will express it, right?) • However, in sexually reproductive organisms, the parental origin of genetic alleles often determines their fates. For these imprinted genes, the diploid offspring distinguishes between maternally-inherited and paternallyinherited alleles, and selectively expresses only one of them while inactivating the other. • In recent years it has become apparent that the parental origin of genetic material DOES have an impact on gene expression and this effect has become known as genomic (genetic) imprinting. Who’s your Daddy? See http://epigenome.eu/en/2,5,126 on how ligers created by male lions mating with female tigers are much larger than tigons created by a male tiger with a female lion. Genetic Cause of PWS • In Prader-Willi syndrome, these critical genes are missing (deleted) from the father’s chromosome 15, functioning improperly because of an imprinting defect. Who gave me the defects now? • When a deletion of chromosome 15q11-q13 region is found on the mother’s chromosome 15, the result is an entirely different = Angelman syndrome. • Because the genetic errors happen in the same section of chromosome 15, PWS and AS are sometimes called “sister” syndromes even though the disorders have few features in common. • The two syndromes are not at the same genetic locus, but are controlled by genes that are within a small region of chromosome 15 leading to very different phenotypes: • Prader-Willi Severe obesity, hyperactivity & severe mental retardation. • Angelman Absence of speech, mild to moderate mental retardation, small hands/feet, laugh a lot, dancing gait so called “Happy Puppet syndrome.” Treatment for Angelmann’s? • Science News 1/28/2012 (p. 8) • Class of chemotherapy drugs turns on the inactive gene of Dad’s chromosome in the brain cells of mice. Evolutionary Significance? • A widely accepted hypothesis for genomic imprinting is the "parental conflict hypothesis" (Moore and Haig 1991) = the inequality between parental genomes due to imprinting is a result of the differing interests of each parent in terms of the evolutionary fitness of their genes. (Read Genome “X/Y Conflict.” ) • The father is more 'interested' in the growth of his offspring, at the expense of the mother. The mother's interest is to conserve resources for her own survival while providing sufficient nourishment to current and subsequent litters. Accordingly, paternally expressed genes tend to be growth promoting whereas maternally expressed genes tend to be growth limiting. (mouse study) The Legacy of Solid Gold • Scientists have pinpointed the genetic mutation on chromosome 18 that causes lambs to develop large and muscular rumps--a trait known as callipyge, from the Greek for 'beautiful buttocks.’ • Only lambs that inherit the callipyge mutation from their father but not their mother develop the trait. Crespi & Babcock: Our minds, too, are shaped by conflict between our parents’ genes. Mothers: want offspring w/ moderate demands. Fathers: want behaviors that get more resources from mom; nurse, demand more attention. Angelman & Prader-Willi syndromes arise from mutations to imprinted genes • In Angelman, the • In Prader-Willi, same segment of mom’s genes are silenced, allowing genes is deleted so these offspring Dad’s genes to act w/out constraint. make few They nurse a lot, demands of they smile, laugh mother—do not gaining attention. nurse More on Parental Tug-of-War • Children w/ autism show signs of father-imprinting (aggressive growth of placentas). • Children w/ schizophrenia appear to be influenced by mother-dominated genes (low birth weight & slow growth benefit mom). • Autistic: difficult time figuring out what people are feeling paternal genes may reduce such distractions so they get more resources from Mom. • Schizophrenic: too concerned about others (too much empathy, even believe inanimate objects are talking to them) maternal genes boost our abilities to be in-tune w/others. Crespi & Badcock Pedigree Analysis Autosomal Recessive Sex-linked Recessive Autosomal Dominat