Lesson 5 Handout_Genetic Interactions (1) PDF

BIO 170_FUNDAMENTALS OF GENETICS LESSON 5_ GENE INTERACTIONS MODIFICATIONS TO GENE MENDEL’S CLASSIC RATIOS INTERACTIONS GENE INTERACTION When...

BIO 170_FUNDAMENTALS OF GENETICS LESSON 5_ GENE INTERACTIONS MODIFICATIONS TO GENE MENDEL’S CLASSIC RATIOS INTERACTIONS GENE INTERACTION When more than one gene is studied simultaneously Discontinuous variation When discrete phenotypic categories are produced that vary from one another in a qualitative way Continuous variation Phenotypic categories vary in a quantitative way 2 JTIMPERIAL 1 BIO 170_FUNDAMENTALS OF GENETICS LESSON 5_ GENE INTERACTIONS genes exhibit independent assortment but do not act independently in their phenotypic expression instead, the effects of genes at one locus depend on the presence of genes at other loci Interaction between the effects of genes at different loci (genes that are not allelic) the products of genes at different loci combine to produce new phenotypes that are not predictable from the single-locus effects alone 3 genes at two loci interact to produce a single characteristic Fruit color in the pepper Capsicum annuum 4 JTIMPERIAL 2 BIO 170_FUNDAMENTALS OF GENETICS LESSON 5_ GENE INTERACTIONS a dominant allele R at the first locus produces a red pigment; the recessive allele r at this locus produces no red pigment A dominant allele C at the second locus causes decomposition of the green pigment chlorophyll; the recessive allele c allows chlorophyll to persist 5 A CHICKEN’S COMB IS DETERMINED BY GENE INTERACTION BETWEEN TWO LOCI WALNUT (R_P_) dominant allele at each of the two loci ROSE (R_pp) dominant allele only at the first locus PEA (rrP_) dominant allele only at the second locus SINGLE (rrpp) only recessive alleles at both loci 6 JTIMPERIAL 3 BIO 170_FUNDAMENTALS OF GENETICS LESSON 5_ GENE INTERACTIONS 7 Epistasis is a form of gene interaction in which one gene masks the phenotypic expression of another gene at a different locus. similar to dominance, except that dominance entails the masking of genes at the same locus (allelic genes) There are no new phenotypes produced by this type of gene interaction. 8 JTIMPERIAL 4 BIO 170_FUNDAMENTALS OF GENETICS LESSON 5_ GENE INTERACTIONS EPISTATIC VERSUS HYPOSTATIC epistatic alleles that are alleles masking the effect hypostatic alleles whose effect is alleles being masked 9 HOW DO WE SOLVE EPISTATIC PROBLEMS? We are dealing with polygenic traits as in the previous section, however we now have one pair of alleles masking the other. This means we will still be using dihybrid crosses! 10 JTIMPERIAL 5 BIO 170_FUNDAMENTALS OF GENETICS LESSON 5_ GENE INTERACTIONS RECESSIVE OR DOMINANT? Epistasis can be described as either recessive epistasis or dominant epistasis. Let’s look at an example of recessive epistasis…. 11 LABRADOR RETRIEVERS Fur color in Labrador Retrievers is controlled by two separate genes.  Fur color is a polygenic trait! Gene 1: Represented by B : Controls color Gene 2: Represented by E : Controls expression of B 12 JTIMPERIAL 6 BIO 170_FUNDAMENTALS OF GENETICS LESSON 5_ GENE INTERACTIONS LABRADOR RETRIEVERS If a Labrador retriever has a dominant B allele, they will have black fur. If they have two recessive alleles (bb) they will have brown fur. 13 LABRADOR RETRIEVERS If a retriever receives at least one dominant “E” allele, they will remain the color that the “B” allele coded for. Either black of brown However, if a dog receives a pair of homozygous recessive “e” alleles, they will be golden regardless of their “B” alleles! 14 JTIMPERIAL 7 BIO 170_FUNDAMENTALS OF GENETICS LESSON 5_ GENE INTERACTIONS LABRADOR RETRIEVERS BBEE/BbEe Black retrievers bbEE/bbEe Brown retrievers Bbee/Bbee/bbee Golden retrievers 15 16 JTIMPERIAL 8 BIO 170_FUNDAMENTALS OF GENETICS LESSON 5_ GENE INTERACTIONS TRY THIS CROSS… You have decided to cross your golden retriever (bbee) with the neighbor’s chocolate retriever (bbEe). What color pups will they have? 17 bbee X bbEe FOIL: be FOIL: bE or be Genotypes of F1 generation: bbEe and bbee Pups phenotypes: Brown and golden 18 JTIMPERIAL 9 BIO 170_FUNDAMENTALS OF GENETICS LESSON 5_ GENE INTERACTIONS Cross these parents below and give me the phenotypic ratios of their F1s. Problem 1. EeBb x eebb Problem 2. eeBb x Eebb Answers Prob 1. pr is 1/4 black:1/4 choclate:2/4 yellow Prob 2. pr is 1/4 black:1/4 choclate:2/4 yellow 19 EXAMPLE 2 20 JTIMPERIAL 10 BIO 170_FUNDAMENTALS OF GENETICS LESSON 5_ GENE INTERACTIONS 21 Squash fruit color is controlled by two genes. Gene 1 is represented by a W Gene 2 is represented by a G Allele W is epistatic to G and g—it suppresses the expression of these pigment-producing genes. W is a dominant epistatic allele because, in contrast with e in Labrador retriever coat color, a single copy of the allele is sufficient to inhibit pigment production 22 JTIMPERIAL 11 BIO 170_FUNDAMENTALS OF GENETICS LESSON 5_ GENE INTERACTIONS SQUASH FRUIT COLOR Genotypes and Phenotypes: W_/G_ white W_/gg white ww/G_ green ww/gg yellow 23 SQUASH FRUIT COLOR Which allele is epistatic in squash color? The dominant W allele is epistatic How do you know? Because every time a dominant W allele shows up in a squash genotype, the squash fruit color is white. 24 JTIMPERIAL 12 BIO 170_FUNDAMENTALS OF GENETICS LESSON 5_ GENE INTERACTIONS TRY THIS CROSS…. Cross a green squash (wwGg) with a white squash (Wwgg). What color are the offspring? 25 wwGg X Wwgg FOIL: Wg or wg FOIL: wG or wg F1 generation genotypes: Phenotypes: 26 JTIMPERIAL 13 BIO 170_FUNDAMENTALS OF GENETICS LESSON 5_ GENE INTERACTIONS 27 WITH ALBINISM REGARDLESS OF WHAT KIND OF SKIN COLOR YOU SHOULD HAVE, IF YOU HAVE THE EPISTATIC ALLELES FOR ALBINISM THEN YOU WILL BE AN ALBINO. 28 JTIMPERIAL 14 BIO 170_FUNDAMENTALS OF GENETICS LESSON 5_ GENE INTERACTIONS PIGMNENT is produced in a two-step pathway in snails. 29 SUMMER SQUASH EXHIBITING VARIOUS FRUIT-SHAPE PHENOTYPES 30 JTIMPERIAL 15 BIO 170_FUNDAMENTALS OF GENETICS LESSON 5_ GENE INTERACTIONS MODIFIED DIHYBRID MENDELIAN RATIOS 1. Duplicate Recessive (9:7) Recesssive at one either locus masks the expression of the dominant phenotype at the other locus. 2. Single Recessive (9:3:4) Recessive Trait at one locus masks the effect of the second locus. 31 MODIFIED DIHYBRID MENDELIAN RATIOS 3. Duplicate Dominant (15:1) The dominant trait at either locus will expression one phenotype, the other phenotype is homozygous at both loci. 4. Single Dominant (12:3:1) Dominant trait at one locus masks the expression of the second locus. 5. Dominant ´ Recessive (9:6:1) Duplicate effects from the two loci. The phenotypes are: Two dominant One dominant None dominant. 32 JTIMPERIAL 16 BIO 170_FUNDAMENTALS OF GENETICS LESSON 5_ GENE INTERACTIONS SUMMARY 33 34 JTIMPERIAL 17 BIO 170_FUNDAMENTALS OF GENETICS LESSON 5_ GENE INTERACTIONS MODIFIED DIHYBRID MENDELIAN RATIOS 35 ADDITIONAL PATTERNS OF INHERITANCE THAT DEVIATE FROM A MENDELIAN PATTERN INCLUDE: Maternal effect and epigenetic inheritance Involve genes in the nucleus Extranuclear inheritance Involves genes in organelles other than the nucleus Mitochondria Chloroplasts 36 JTIMPERIAL 18 BIO 170_FUNDAMENTALS OF GENETICS LESSON 5_ GENE INTERACTIONS MATERNAL EFFECT Maternal effect refers to an inheritance pattern for certain nuclear genes in which the genotype of the mother directly determines the phenotype of her offspring Surprisingly, the genotypes of the father and offspring themselves do not affect the phenotype of the offspring This phenomenon is due to the accumulation of gene products that the mother provides to her developing eggs The phenotype of the progeny is determined by the mother’s genotype NOT phenotype The genotypes of the father and offspring do not affect the phenotype of the offspring 37 MATERNAL INHERITANCE IN THE FOUR-O’CLOCK PLANT Carl Correns discovered that pigmentation in Mirabilis jalapa (the four o’clock plant) shows a non-Mendelian pattern of inheritance Leaves could be green, white or variegated (with both green and white sectors) Correns determined that the pigmentation of the offspring depended solely on the maternal parent and not at all on the paternal parent This is termed maternal inheritance 38 JTIMPERIAL 19 BIO 170_FUNDAMENTALS OF GENETICS LESSON 5_ GENE INTERACTIONS 39 Crosses for leaf type in four o’clock illustrate cytoplasmic inheritance 40 JTIMPERIAL 20 BIO 170_FUNDAMENTALS OF GENETICS LESSON 5_ GENE INTERACTIONS GENETIC MATERNAL EFFECT the phenotype of the offspring is determined by the genotype of the mother the genes are inherited from both parents, but the offspring’s phenotype is determined not by its own genotype but by the genotype of its mother 41 In genetic maternal effect, the genotype of the maternal parent determines the phenotype of the offspring. Shell coiling in snails is a trait that exhibits genetic maternal effect. 42 JTIMPERIAL 21 BIO 170_FUNDAMENTALS OF GENETICS LESSON 5_ GENE INTERACTIONS SEX INFLUENCES ON HEREDITY 43 GENETIC BACKGROUND AND THE ENVIRONMENT MAY ALTER PHENOTYPIC EXPRESSION 44 JTIMPERIAL 22 BIO 170_FUNDAMENTALS OF GENETICS LESSON 5_ GENE INTERACTIONS PENETRANCE AND EXPRESSIVITY penetrance percentage of individuals that show at least some degree of expression of a mutant genotype Ex. If 15 percent of flies with a given mutant genotype show the wild-type appearance, the mutant gene is said to have a penetrance of 85 percent. expressivity reflects the range of expression of the mutant genotype. Ex. Flies homozygous for the recessive mutant gene eyeless exhibit phenotypes that range from the presence of normal eyes to a partial reduction in size to the complete absence of one or both eyes 45 Variable expressivity as shown in flies homozygous for the eyeless mutation in Drosophila. Gradations in phenotype range from wild type to partial reduction to eyeless. 46 JTIMPERIAL 23 BIO 170_FUNDAMENTALS OF GENETICS LESSON 5_ GENE INTERACTIONS 47 48 JTIMPERIAL 24 BIO 170_FUNDAMENTALS OF GENETICS LESSON 5_ GENE INTERACTIONS GENETIC BACKGROUND: POSITION EFFECTS POSITION EFFECT the physical location of a gene in relation to other genetic material may influence its expression Ex. if a region of a chromosome is relocated or rearranged (called a translocation or inversion event), normal expression of genes in that chromosomal region may be modified 49 Position effect, as illustrated in the eye phenotype in two female Drosophila heterozygous for the gene white. (a) Normal dominant phenotype showing brick-red eye color. (b) Variegated color of an eye caused by translocation of the white gene to another location in the genome. 50 JTIMPERIAL 25 BIO 170_FUNDAMENTALS OF GENETICS LESSON 5_ GENE INTERACTIONS ENVIRONMENTAL INFLUENCES ON GENE EXPRESSION External environmental factors play an important role in modifying the phenotype coded by genes, both in embryonic development and in later life. GENOTYPE Provides an organisms with its genetic potential- a possible phenotype. ENVIRONMENTAL FACTORS Act on organism as it grows to produce an individual with a unique phenotype. NOTE: Even identical twins have minor differences in their appearance due to factors such as diet. 51 ENVIRONMENTAL FACTORS INCLUDE SUCH VARIABLES AS: WIND EXPOSURE WATER AVAILABILITY ACIDITY TEMPERATURE SOIL TYPE LIGHT PREDATION 52 JTIMPERIAL 26 BIO 170_FUNDAMENTALS OF GENETICS LESSON 5_ GENE INTERACTIONS 53 TEMPERATURE EFFECTS ON PHENOTYPE Chemical activity depends on the kinetic energy of the reacting substances, which in turn depends on the surrounding temperature. Example: Evening primrose produces red flowers when grown at 23°C and white flowers when grown at 18°C 54 JTIMPERIAL 27 BIO 170_FUNDAMENTALS OF GENETICS LESSON 5_ GENE INTERACTIONS COLOR POINTING Some breeds of cat and rabbit have distinctive darker fur on the extremities (called pointing) Pigment production is controlled by a temperature sensitive enzyme and only the extremities are cool enough to allow the enzyme to function EXAMPLE: Siamese cats, Himalayan rabbits 55 56 JTIMPERIAL 28 BIO 170_FUNDAMENTALS OF GENETICS LESSON 5_ GENE INTERACTIONS SEX DETERMINATION The sex of some animals is determined by the temperature at which they were incubated during embryonic development EXAMPLE: crocodiles, American alligators, and turtles In some species: - high incubation temperature produce males - low incubation temperatures produce females - in some species the opposite is true 57 ALTITUDE EFFECTS ON PHENOTYPE Plants of the same species produce a smaller or stunted phenotype with higher altitude. Such patterns are observable in vegetation growing on mountainsides. This may be due to the combined effects of: 1. Wind exposure 2. Cooler temperatures 3. Water availability 4. Rarified atmosphere (low oxygen) 58 JTIMPERIAL 29 BIO 170_FUNDAMENTALS OF GENETICS LESSON 5_ GENE INTERACTIONS EFFECTS OF OTHER ORGANISMS ON PHENOTYPES PREDATION The activity orpresence of predators may cause a permanent change in the phenotype of prey. EXAMPLE: Body shapes in Daphnia 59 EFFECTS OF OTHER ORGANISMS ON PHENOTYPES SEX DETERMINATION The presence of other members of the same species may control the determination of sex in other individuals of the group. EXAMPLE: Sandaggers wrasse (parrotfish) 1. These fish live in groups comprising females and juveniles with a single male. 2. In the presence of the male, all juvenile fish of this species grow into females. 3. When the male dies, the dominant female will change her sex to become a male for the group. 60 JTIMPERIAL 30 BIO 170_FUNDAMENTALS OF GENETICS LESSON 5_ GENE INTERACTIONS NUTRITIONAL EFFECTS Auxotroph In microorganisms, mutations that prevent synthesis of nutrient molecules are quite common, such as when an enzyme essential to a biosynthetic pathway becomes inactive EXAMPLE: bread mold Neurospora If can no longer synthesize the amino acid leucine, proteins cannot be synthesized If leucine is present in the growth medium, the detrimental effect is overcome. 61 NUTRITIONAL EFFECTS Cannot metabolize the amino acid phenylketonuria phenylalanine galactosemia Cannot metabolize galactose lactose intolerance Cannot metabolize lactose If the dietary intake of the involved molecule is drastically reduced or eliminated, the associated phenotype may be ameliorated 62 JTIMPERIAL 31 BIO 170_FUNDAMENTALS OF GENETICS LESSON 5_ GENE INTERACTIONS LIGHT EFFECTS 1. Plants of the same 2. Most plants will 3. Human skin will tan species will adopt grow abnormally long (become browner) different growing stems and lack when exposed to behaviors when the pigmentation if grown direct sunlight over a light varies. in low light levels. period of time. 63 ACIDITY EFFECTS The color of some flowers is determined by the pH of the soil they grow in. EXAMPLE: Flower color in hydrangeas Acid soil – pink flowers Alkaline soil – blue flowers 64 JTIMPERIAL 32 BIO 170_FUNDAMENTALS OF GENETICS LESSON 5_ GENE INTERACTIONS CHEMICAL EFFECTS The tragic instances of babies born with deformities caused by women taking drugs during pregnancy. EXAMPLE: thalidomide The sedative drug caused improper development of the fetus leading to abnormally stunted limbs. 65 66 JTIMPERIAL 33