FIG. 18.13 Relationship between number of genes and their effect on complex traits. Many Most of the genes affecting the trait have relatively small effects. For a typical complex trait, only a few genes have a relatively large effect. Few Small Large Magnitude of gene effect Number of genes affecting the trait

FIG. 18.13 Relationship between number of genes and their effect on complex traits. Many Most of the genes affecting the trait have relatively small effects. For a typical complex trait, only a few genes have a relatively large effect. Few Small Large Magnitude of gene effect Number of genes affecting the trait

Human Heredity: Principles and Issues (MindTap Course List)

11th Edition

ISBN:9781305251052

Author:Michael Cummings

Publisher:Michael Cummings

Chapter5: The Inheritance Of Complex Traits

Section: Chapter Questions

Problem 22QP: Height in humans is controlled by the additive action of genes and the action of environmental...

See similar textbooks

Similar questions

The Online Mendelian Inheritancein Man (OMIM) databaseis a catalog of human genesand human disorders that are inheritedin a Mendelian manner. Genetic disordersthat arise from major chromosomalaberrations, such as monosomyor trisomy(the loss of a chromosome orthe presence of a superfluous chromosome,respectively), are not included.The OMIM database, updated daily, is aversion of the book Mendelian Inheritancein Man, conceived and edited by Dr. VictorMcKusick of Johns Hopkins University,until he passed in 2008.The OMIM entries provide links to awealth of information, including DNAand protein sequences, chromosomalmaps, disease descriptions, and relevantscientific publications. In this exercise,you will explore OMIM to answer questionsabout the recessive human diseasesickle-cell anemia and other Mendelianinherited disorders.Exercise I – Sickle-Cell AnemiaIn this chapter, you were introduced torecessive and dominant human traits.You will now discover more about sicklecellanemia as an…
Two alleles at one locus produce three distinctphenotypes. Two alleles of two genes lead tofive distinct phenotypes. Two alleles of six geneslead to 13 distinct phenotypes. (These statementsassume that the alleles at any one locus arecodominant or incompletely dominant andthat each gene makes an equal contributionto the phenotype.)a. Derive a formula to express this relationship. (Letn equal the number of genes.)b. Each of the most extreme phenotypes for a traitdetermined by two alleles at one locus are foundin a proportion of 1/4 in the F2 generation. If twoalleles of two genes determine the trait, each extreme phenotype will be present in the F2 as 1/16of the population.In common wheat (Triticum aestivum),kernel color varies from red to white andthe genes controlling the color act additively,that is, alleles for each gene are incompletelydominant and each gene contributes equallyto the color. A true-breeding red variety iscrossed to a true-breeding white variety, and1/256 of the F2…
A DNA variant has been found linked to a rare autosomal dominant disease in humans and can thus beused as a marker to follow inheritance of the diseaseallele. In an informative family (in which one parentis heterozygous for both the disease allele and the DNA marker in a known chromosomal arrangementof alleles, and his or her mate does not have the samealleles of the DNA variant), the reliability of such amarker as a predictor of the disease in a fetus is related to the map distance between the DNA markerand the gene causing the disease.Imagine that a man affected with the disease(genotype Dd) is heterozygous for the V1and V2forms of the DNA variant, with form V1on the samechromosome as the D allele and form V2on the samechromosome as d. His wife is V3V3dd, where V3isanother allele of the DNA marker. Typing of the fetusby amniocentesis reveals that the fetus has the V2andV3variants of the DNA marker. How likely is it thatthe fetus has inherited the disease allele D if thedistance…
In individuals affected by cystic fibrosis, salt crystals may appear afterperspiration dries up. In addition, the disease causes respiratory disorderswhich can be both debilitating and lethal. It occurs in individuals homozygousfor the recessive gene. Two normal parents had a daughter with thesymptoms of this disease, and a normal son who marries a normal womanwith an afflicted A test (salt concentration in perspiration of heterozygotes ishigher than normal) disclosed that both are indeed carriers of the gene. If thefirst child born to the mating in (b) was defective, what is the probability thatthe 2nd child would also be defective?Express answer in fraction form
. The production of pigment in the outer layer of seedsof corn requires each of the three independently assorting genes A, C, and R to be represented by at leastone dominant allele, as specified in Problem 64. Thedominant allele Pr of a fourth independently assortinggene is required to convert the biochemical precursorinto a purple pigment, and its recessive allele pr makesthe pigment red. Plants that do not produce pigmenthave yellow seeds. Consider a cross of a strain of genotype A/A ; C/C ; R/R ; pr/pr with a strain of genotypea/a ; c/c ; r/r ; Pr/Pr.a. What are the phenotypes of the parents?b. What will be the phenotype of the F1?c. What phenotypes, and in what proportions, willappear in the progeny of a selfed F1?d. What progeny proportions do you predict from thetestcross of an F1?
This problem examines possible biochemical explanations for variations of Mendel’s 9:3:3:1 ratio. Exceptwhere indicated, compounds 1, 2, 3, and 4 have different colors, as do mixtures of these compounds. Aand B are enzymes that catalyze the indicated steps ofthe pathway. Alleles A and B specify functional enzymes A and B, respectively; these are completelydominant to alleles a and b, which do not specify anyof the corresponding enzyme. If functional enzyme ispresent, assume that the compound to the left of thearrow is converted completely to the compound to theright of the arrow. For each pathway, what phenotypicratios would you expect among the progeny of a dihybrid cross of the form Aa Bb × Aa Bb?a. Independent pathwaysCompound 4Compound 2Compound 3Compound 1Enz AEnz Bb. Redundant pathwaysCompound 1 Compound 2Enz BEnz Ac. Sequential pathwayCompound 1 Compound 2 Compound 3Enz A Enz Bd. Enzymes A and B both needed to catalyze the reaction indicated.Compound 1 Compound 2
Many genetic disorders exhibit locus heterogeneity. Define andgive two examples of locus heterogeneity. How does locus heterogeneityconfound a pedigree analysis?
Bloom syndrome is an autosomal recessive disease that exhibitshaploinsufficiency. A recent survey showed that people heterozygousfor mutations at the BLM locus are at increased risk of colon cancer.Suppose you are a genetic counselor. A young woman is referred to youwhose mother has Bloom syndrome; the young woman’s father has nofamily history of Bloom syndrome. The young woman asks whether sheis likely to experience any other health problems associated with herfamily history of Bloom syndrome. What advice would you give her?
Unusual Gain-of-Function Alleles AreAlmost Always Dominant WHY?
Null mutations are valuable genetic resources becausethey allow a researcher to determine what happens to anorganism in the complete absence of a particular protein. However, it is often not a trivial matter to determinewhether a mutation represents the null state of the gene.a. Geneticists sometimes use the following test forthe nullness of an allele in a diploid organism: If theabnormal phenotype seen in a homozygote for theallele is identical to that seen in a heterozygote(where one chromosome carries the allele in question and the homologous chromosome is known tobe completely deleted for the gene) then the alleleis null. What is the underlying rationale for thistest? What limitations might there be in interpreting such a result?b. Can you think of other methods to determinewhether an allele represents the null state of a particular gene?
For Mendelian inheritance, the nuclear genotype (i.e., the allelesfound on chromosomes in the cell nucleus) directly influences anoffspring’s traits. In contrast, for non-Mendelian inheritance patterns, the offspring’s phenotype cannot be reliably predicted solelyfrom its genotype. For the following traits, what do you need toknow to predict the phenotypic outcome?A. Dwarfism due to a mutant Igf2 alleleB. Snail coiling directionC. Leber hereditary optic neuropathy
Six months pregnant, an expectant mother had a routineultrasound that showed that the limbs of the fetus wereunusually short. Her physician suspected that the babymight have a genetic form of dwarfism called achondroplasia,an autosomal dominant trait occurring with a frequency of about1 in 27,000 births. The parents were directed to a genetic counselorto discuss this diagnosis. In the conference, they learnedthat achondroplasia is caused by a mutant allele. Sometimes itis passed from one generation to another, but in 80 percent ofall cases it is the result of a spontaneous mutation that arisesin a gamete of one of the parents. They also learned that mostchildren with achondroplasia have normal intelligence and a normallife span. It has been suggested that prenatal genetic testing for achondroplasiabe made available and offered to all women. Wouldyou agree with this initiative? What ethical considerationswould you consider when evaluating the medical and societalconsequences of offering…