Review: Dna and Red Eye Essay

Tuesday, December 4th * DdHhxDdHh * Female=horizontal axis * Male=vertical axis * Segregation of Dd allele * DdxDd= monohybrid cross 4:8:4=1:2:1 ratio * Same thing happens with Hh * When evaluating both genes together remember the product rule probability * 9/16 have both dominant traits * 3/16 have Dd but little hh * 3/16 have dd but HH * 1/16 have dd and hh * But there are many ways that genes can interact with each other to influence development of a trait * Incomplete dominance * RR= red * Rr= pink * Rr= white * RrxRr= RR (1/2), Rr(2/4), rr (1/4) * Genotype x environment interaction = environmental factors influence gene expression * Fruit fly- wings don’t develop (recessive mutation in which the appearance of the trait is altered by the environment) * If raised at a higher temperature, increase rate of production of enzyme, therefore thing wings will grow * Environment influences phenotype and genotype * Siamese cat/Himalayan rabbits * Pigment enzyme is more active in cooler temperature * When body is warmer, there is less pigment (chest) * Refrigerated cats= all chocolate color * Hairless dogs= another gene interaction * No hair= cant tell what color * Epistasis= one trait standing over (masks) the expression of the second trait * Most simple= Dihybrid * For example: complete baldness (bb) masks the hair color gene expression (C- or cc) since there is no hair there to be colored * Dark hair- 9/16 B-C- * Blonde hair- 3/16 B-cc * Bald- 3/16 bbc- * Bald – 1/16 bbcc * =9:3:4 * Agouti (A) * Yellow (A^y) * Yellowxyellow= 2/3 yellow and 1/3 yellow * This is a 2:1 ration * How can get a ratio like that? * How can you get a trait expressed that was masked in the parents * Two heterozygous mate * When two yellow mice are mated, one genotypic class dies. This is a recessive lethal. (you must be homozygous to die) * THE MOST common kind of mutation * Each of us are probably heterozygous at ½ dozen or more different lethal genes * CANNNOT be homozygous or you will die * Basic questions: * What kind of gametes can the parents produce? * BbxBb * Type and proportion of the genotype * What are their phenotypes * Exception! * Females-XX-2 copies * Males-XY- 1 copy * sex linkage = a gene located on the X chromosome * consider the example of a normal female who marries a man with a the recessive sex linked (= X linked) trait “hemophilia” * X^A X^Z x X^a Y * If sperm carries X chromosome= female * About ½ probability of male or female (slightly more male, because Y chromosome is a little smaller) * Depends on dominance in female * Male gets only X chromosome from his mother * Hemophilia cannot pass from father to son, bc dad gives only x chromosomes to daughters * A gene linkage on the x chromosome can differ in the expression in males and females * Higher frequency in color blindness in sons * Sex- linked= located on the X chromosome * Sex-limited= on any chromosome, but the phenotype is present on only one sex * Sex-influenced gene= the trait is more severe or common in one of the sexes * Stomach has no hole * Found in newborns when they have explosive vomiting * More common in 1st born males

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