Genetics Chapter 4
Which of the following symbols indicate a wild-type allele?
+
In cats, orange coat color is determined by the b allele, and black coat color is determined by the B allele. The heterozygous condition results in a coat pattern known as tortoiseshell. This gene is X-linked. What kinds of offspring would be expected from a cross of an orange male and a tortoiseshell female?
-orange female -tortoiseshell female -orange male -black male
Pattern baldness is a sex-influenced trait, with heterozygous males exhibiting the trait. What would be the probability of the daughters exhibiting the trait from a woman with pattern baldness and a male without pattern baldness?
0%
Why do multiple and lethal alleles often result in modifications of the classic Mendelian monohybrid and dihybrid ratios? Select the two correct statements.
1. Multiple alleles mean that there are more than two alternatives of a gene at a given locus. A diploid organism has two homologous gene loci that may be occupied by different alleles of the same gene. This can result in many different phenotypes for traits, which may not follow typical Mendelian ratios. 2. When an essential gene is mutated, it can result in a lethal phenotype. In this case, classic Mendelian monohybrid and dihybrid ratios will not be observed.
In Dexter and Kerry cattle, animals may be polled (hornless) or horned. The Dexter animals have short legs, whereas the Kerry animals have long legs. When many offspring were obtained from matings between polled Kerrys and horned Dexters, half were found to be polled Dexters and half polled Kerrys. When these two types of F1 cattle were mated to one another, the following F2 data were obtained: 3/8 polled Dexters 3/8 polled Kerrys 1/8 horned Dexters 1/8 horned Kerrys A geneticist was puzzled by these data and interviewed farmers who had bred these cattle for decades. She learned that Kerrys were true breeding. Dexters, on the other hand, were not true breeding and never produced as many offspring as Kerrys. Provide a genetic explanation for these observations. Select the four correct statements.
1. The Dexter breed is heterozygous. 2. The Kerry breed is homozygous recessive. 3. Polled is caused by an independently assorting dominant allele, whereas horned is caused by the recessive allele to polled. 4. The homozygous dominant type is lethal.
A deficiency of the enzyme glucose-6-phosphate dehydrogenase (G6PD) is inherited as an X-linked recessive trait in humans. A phenotypically normal woman (whose father had G6PD) is married to a man with normal G6PD function. What fraction of their sons would be expected to have G6PD deficiency?
1/2
In the mouse, gene B can produce black pigment from a colorless precursor molecule. A mouse having at least one B allele can produce black pigment, whereas the homozygous recessive mouse (bb) cannot and is albino. The agouti locus (A) can convert the black pigment to brown in the presence of at least one dominant A allele, whereas the homozygous recessive (aa) cannot convert the black pigment to brown. What would be the probability of an albino mouse offspring if the parents were genotypes AaBb and AAbb?
1/2
The white-eye gene in Drosophila is recessive and sex-linked. Assume that a white-eyed female is mated to a wild-type male. What would be the phenotypes of the offspring?
1/2 wild-type females, 1/2 white-eyed males
A couple each with blood type AB and normal pigmentation have a child with AB blood type and albinism. What is the probability that their next child will have the same phenotype as the first child?
1/8
Pattern baldness is a sex-influenced trait, with heterozygous males exhibiting the trait. What would be the probability of the sons exhibiting the trait from a woman with pattern baldness and a male without pattern baldness?
100%
Many of the color varieties of summer squash are determined by several interacting loci: AA or Aa gives white, aaBB or aaBb gives yellow, and aabb produces green. Assume that two fully heterozygous plants are crossed. Give the phenotype ratio of the offspring
12 (white):3 (yellow):1 (green)
Assume that a dihybrid cross for two different traits (AaBb × AaBb) is made in which the gene loci are autosomal, independently assorting, and both incompletely dominant. What phenotypic ratio would you expect from such a cross?
1:2:1:2:4:2:1:2:1
Mice have a set of multiple alleles of a gene for coat color. Four of those alleles are as follows: C = full color (wild) cch = chinchilla cd = dilution c = albino Given that the gene locus is not sex-linked and that each allele is dominant to those lower in the list, what would be the phenotypic ratio of a cross between a mouse of full color (heterozygous for dilution) and a mouse with the chinchilla coat color (heterozygous for albino)?
2 full color: 1 chinchilla: 1 dilution
What is the ratio expected for offspring of a cross between two yellow mice?
2 yellow: 1 agouti
The following F2 results occur from a typical dihybrid cross: purple: A_B_ 9/16 white: aaB_ 3/16 white: A_bb 3/16 white: aabb 1/1 If a double heterozygote (AaBb) is crossed with a fully recessive organism (aabb), what phenotypic ratio is expected in the offspring?
3 (white): 1 (purple)
A couple in which one parent is blood type A and the other is blood type B, and both have normal pigmentation, have a child that is blood type O and has albinism. What is the probability that their next child will have normal pigmentation and blood type A?
3/16
Which of the following statements is always true when mutations occur in genes whose products are essential to an organism's survival?
A homozygote for a recessive lethal allele will not survive.
Croaking in frogs is inherited by one gene with a pair of alleles −− dominant uttering (RR) and recessive muttering (rr). Eye color is inherited by epistatic interaction of two genes with the following possible phenotypes: A_B_ −− blue eyes; A_bb−− purple eyes and aaB_or aabb−− green eyes. The frog geneticist mated purple utterer and green utterer with the following results: 3/8 purple, utterers 1/8 purple, mutterers 3/8 green, utterers 1/8 green, mutterers What were the genotypes of the parents?
AabbRr×aabbRr
An individual test his blood type by placing drops of blood in anti-A sera and anti-B sera with the results as follows: What is the blood type of this individual?
B
What is the difference between incomplete dominance and codominance?
In codominance, both phenotypes are expressed in heterozygotes. In incomplete dominance, the heterozygote shows a phenotype that is intermediate between the two homozygotes
________ occurs when the offspring's phenotype is under the control of the mother's nuclear gene products that are present in the egg
Maternal effect
Part A. Use this pedigree to determine which pairs of family members listed below share mitochondrial DNA. Part B. In the pedigree below, individual I-1 has Leber hereditary optic neuropathy (LHON), an inherited form of vision loss caused by a mutation in mitochondrial DNA. Which members of her family will also inherit LHON? Part C. Sometimes, a mother who is affected with a mitochondrial disease will have an unaffected child. Which of the following could explain this observation?
Part A. -II-1 and IV-1 -II-2 and III-6 Part B. II-2, II-3, II-4, III-1 Part C. -The mitochondrial disease may have a variable age of onset, and asymptomatic children may develop the condition later in life. -The phenotype could be affected by nuclear genes, which could differ among children -The affected mother could be heteroplasmic.
Consider the following three pedigrees, all involving the same human trait: Part A. Which sets of conditions can be excluded? Part B. For any set of conditions that you excluded, indicate the individuals in generation II (1-9) that were instrumental in your decision to exclude that condition. Part C. Given your conclusions in parts A and B, indicate the genotype of individuals II-1, II-6, and II-9.
Part A. -recessive and X-linked -dominant and X-linked -dominant and autosomal Part B. 3, 4, and 8 Part C. A_ A_ Aa
As this illustration shows, four o'clock plants can have green leaves, white leaves, or variegated leaves (leaves with areas of white and areas of green). The white regions of the leaves lack functioning chloroplasts. The transmission of leaf color in four o'clock plants demonstrates organelle inheritance. In this problem, you will explore this inheritance pattern. Part A. Which of the following crosses between four o'clock plants could produce progeny plants with green leaves? Part B. For the four crosses between four o'clock plants listed in the table below, only one of the possible offspring is listed for each cross. Can you use this information to determine which parent in each cross is the female? Part C. When a variegated female four o'clock plant is crossed with any male plant, progeny plants can have either green, white, or variegated leaves. Which of the following statements correctly explain this result?
Part A. -variegated (female) x variegated (male) -variegated (female) x white (male) -green (female) x white (male) Part B. 1. Plant 2 2. Plant 1 3. Could be either plant 4. Plant Part C. -The female plant produces some gametes that are heteroplasmic. -Leaf phenotype is determined by the number of normal or mutant chloroplasts inherited from the female parent. -The female plant produces some gametes that are homoplasmic.
The following genotypes of two independently assorting autosomal genes determine coat color in rats: A_B_ (gray) A_bb (yellow) aaB_ (black) aabb (cream) A third gene pair on a separate autosome determines whether any color will be produced. The CCCC and CcCc genotypes allow color according to the expression of the AA and BB alleles. However, the cccc genotype results in albino rats regardless of the AA and BB alleles present. Part A. What are the genotype(s) and phenotype(s) of the parents who produced the following F1 offspring? F1: 9/16 gray: 3/16 yellow: 3/16 black: 1/16 cream Part B. What are the genotype(s) and phenotype(s) of the parents who produced the following F1 offspring? F1: 9/16 gray: 3/16 yellow: 4/16 albino Part C. What are the genotype(s) and phenotype(s) of the parents who produced the following F1 offspring? F1: 27/64 gray: 16/64 albino: 9/64 yellow: 9/64 black: 3/64 cream
Part A. -AaBbCC (gray) -AaBbCc(gray) Part B. -AaBbCc(gray) -AABbCc (gray) Part. C. AaBbCc (gray)
In pigs, coat color may be sandy, red, or white. A geneticist spent several years mating true-breeding pigs of all different color combinations, even obtaining true-breeding lines from different parts of the country. For crosses 1 and 4 in the following table, she encountered a major problem: her computer crashed and she lost the F2F2 data. She nevertheless persevered and, using the limited data shown here, was able to predict the mode of inheritance and the number of genes involved, as well as to assign genotypes to each coat color. Attempt to duplicate her analysis, based on the available data generated from the crosses shown. Part A. What is the mode of inheritance and how many genes are involved? Part B. What are the genotypes of the coat colors? Part C. What is the outcome of the F2 in cross 1? Answers are listed in the following order: red:sandy:white. Part D. What is the outcome of the F2 in cross 4? Answers are listed in the following order: red:sandy:white.
Part A. 2 genes, epistasis Part B. Red: AABB, AABb, AaBB, AaBb Sandy: AAbb, Aabb, aaBb, aaBB White: aabb Part C. 9 : 6 : 1 Part D. 9 : 6 : 1
Epistasis is the interaction between genes such that one gene influences or interferes with the expression of another gene, leading to a specific phenotype. Epistatic genes can be dominant or recessive. Use your knowledge of epistasis to determine the genotypes of offspring in the following crosses. Part A. In freshwater snails, pigment color is influenced by two genes. If two heterozygous pigmented freshwater snails were crossed and offspring were produced in a ratio of 9 pigmented snails to 7 albino snails, what are the genotypes of the offspring? Part B. Is this an example of dominant or recessive epistasis? Part C. In sheep, coat color is influenced by two genes. Gene A influences pigment production, while gene B produces black or brown pigment. If two heterozygous white sheep were crossed and offspring were produced in a ratio of 12 white sheep to 3 black sheep to 1 brown sheep, what are the genotypes of the offspring? Part D. Is this an example of dominant or recessive epistasis? Part E. In laborador retrievers, pigment color is influenced by two genes. Gene A determines the type of pigment produced and gene B affects whether the pigment gets deposited in the hair shaft. If two heterozygous black laborator retrievers were crossed and offspring were produced in a ratio of 9 black dogs to 3 brown dogs to 4 yellow dogs, what are the genotypes of the offspring? Part F. Is this an example of dominant or recessive epistasis?
Part A. Genotype(s) of Pigmented Snails: A_B_ Genotype(s) of Albino Snails: A_bb, aaB_, aabb Part B. recessive epistasis Part C. Genotype(s) of White Sheep: A_B_ and A_bb Genotype(s) of Black Sheep: aaB_ Genotype(s) of Brown Sheep: aabb Part D. dominant epistasis Part E. Genotype(s) of Black Dogs: A_B_ Genotype(s) of Brown Dogs: aaB_ Genotype(s) of Yellow Dogs: A_bb and aabb Part F. recessive epistasis
The specification of the anterior−−posterior axis in Drosophila embryos is initially controlled by various gene products that are synthesized and stored in the mature egg following oogenesis. Mutations in these genes result in abnormalities of the axis during embryogenesis, illustrating maternal effect. Part A. How do such mutations vary from those involved in organelle heredity that illustrate extranuclear inheritance? Part B. Devise the first cross of the set of parallel crosses and expected outcomes involving mutant genes that contrast maternal effect and organelle heredity.
Part A. Maternal effect genes are often carried from grandparent through carrier (unaffected) mother to offspring unlike organelle genes that affect every generation. Part B. P1 Aa x aa F1 Aa x aa Genotype A Phenotype
Horses can be cremello (a light cream color), chestnut (a reddish brown color), or palomino (a golden color with white in the horse's tail and mane). Of these phenotypes, only palominos never breed true. The following results have been observed: Part A. From these results, determine the mode of inheritance. Part. B. Using the symbols Cch and Cc, indicate which genotypes yield which phenotypes. Part C. Predict the F1 result of many initial matings between cremello and chestnut horses. Part. D. Predict the F2 result of many initial matings between cremello and chestnut horses.
Part A. incomplete dominance Part B. Cch Cch CHESTNUT Cc Cc CREMELLO Cch Cc PALOMINO Part C. all palomino Part D. 1/4 chestnut; 1/2 palomino; 1/4 cremello
In foxes, two alleles of a single gene, P and p, may result in lethality (PP), platinum coat (Pp), or silver coat (pp). Part A. What ratio is obtained when platinum foxes are interbred? Part B. Is the P allele behaving dominantly or recessively in causing lethality? Part C. Is the P allele behaving dominantly or recessively in causing platinum coat color?
Part A. 2/3 platinum, 1/3 silver Part B. Recessivity Part C. Dominantly
A geneticist from an alien planet that prohibits genetic research brought with him two true-breeding lines of frogs. One frog line croaks by uttering "rib-it rib-it" and has purple eyes. The other line croaks more softly by muttering "knee-deep knee-deep" and has green eyes. He mated the two frog lines, producing F1 frogs that were all utterers with blue eyes. A large F2 generation then yielded these ratios: 27/64 blue, utterer 12/64 green, utterer 9/64 blue, mutterer 9/64 purple, utterer 4/64 green, mutterer 3/64 purple, mutterer Part A. How many total gene pairs are involved in the inheritance of both eye color and croaking? Part B. How many total gene pairs are involved in the inheritance of both eye color and croaking? Part C. Assign gene symbols for all phenotypes Part D. Indicate the genotypes of the P1, F1 and F2 frogs. Part E. After many years, the geneticist isolated pure-breeding strains of all six F2 phenotypes. Indicate the F1 and F2 phenotypic ratios of a cross between a blue, mutterer and a purple, utterer.
Part A. 3 Part B. According to the obtained relationships one would conclude that croaking is due to ONE GENE PAIR, whereas eye color is due to TWO GENE PAIRS. Because there is a 9 TO 4 TO 3 ratio regarding eye color, some gene interaction (a RECESSIVE EPISTASIS) is indicated. Part C. Croaking: R_ = "rib-it"; rr = "knee-deep" Eyes: A_B_ = blue; A_bb = purple; aaB_ (or aabb) = green Part D. P1 AAbbRR = purple-eyed, "rib-it" utterer aaBBrr = green-eyed, "knee-deep" mutterer F1: AaBbRr = blue-eyed, "rib-it" utterer F2: 27/64 A_B_R = blue-eyed, "rib-it" utterer 12/64 aaB_R_or aabbR_ = green-eyed, "rib-it" utterer 9/64 A_B_rr = blue-eyed, "knee-deep" mutterer 9/64 A_bbR_ = purple-eyed, "rib-it" utterer 4/64 aaB_rr or aabbrr = green-eyed, "knee-deep" mutterer 3/64 A_bbrr = purple- eyed, "knee-deep" mutterer Part E. F2 ratio would be 9 (blue-eyed, utterer) to 3 (blue-eyed, mutterer) to 3 (purple-eyed, utterer) to 1 (purple-eyed, mutterer). F1 would be blue-eyed and utterer.
Pigment in mouse is produced only when the CC allele is present. Individuals of the cc genotype have no color. If color is present, it may be determined by the AA and aa alleles. AA or Aa results in agouti color, whereas aa results in black coats. Part A. What F1 and F2 genotypic and phenotypic ratios are obtained from a cross between AACC and aacc mice? Part B. In the cross between agouti female whose genotype was unknown and male of the aacc genotype, what is the genotype of female parent for the following phenotypic ratio? 8 agouti and 8 colorless Part C. In the cross between agouti female whose genotype was unknown and male of the aacc genotype, what is the genotype of female parent for the following phenotypic ratio? 9 agouti and 10 black Part D. In the cross between agouti female whose genotype was unknown and male of the aacc genotype, what is the genotype of female parent for the following phenotypic ratio? 4 agouti, 5 black, and 10 colorless
Part A. F1: A_C_ - agouti F2: A_C_ = 9/16 - agouti A_cc = 3/16 - white aaC_ = 3/16 - black aacc = 1/16 - white Part B. AACc Part C. AaCC Part D. AaCc
Part A. Which term describes the individual in a pedigree whose phenotype was first brought to the attention of a medical researcher? Part B. Which of the following statements about autosomal recessive traits is true? Part C. What is the most likely mode of transmission for a trait that is not expressed in parents but is expressed by one half of the sons?
Part A. Proband Part B. If neither parent expresses the trait, but the offspring does, both parents must be heterozygous for the trait. Part C. Rare X-linked recessive
Three gene pairs located on separate autosomes determine flower color and shape as well as plant height. The first pair exhibits incomplete dominance, where color can be red, pink (the heterozygote), or white. The second pair leads to the dominant personate or recessive peloric flower shape, while the third gene pair produces either the dominant tall trait or the recessive dwarf trait. Homozygous plants that are red, personate, and tall are crossed with those that are white, peloric, and dwarf. Part A. Determine the F1 genotype(s). Part B. Determine the F1 phenotype(s). Part C. If the F1 plants are interbred, what proportion of the offspring will exhibit the same phenotype as the F1 plants?
Part A. RrPpDd Part B. pink, personate, tall Part C. 18/64
In Shorthorn cattle, coat color may be red, white, or roan. Roan is an intermediate phenotype expressed as a mixture of red and white hairs. For this problem, use "A" to indicate the allele that produces red hair and "a" to indicate the allele that produces white hair. The following phenotypic data are obtained from various crosses: Cross 1: red × red → all red Cross 2: white × white → all white Cross 3: red × white → all roan Cross 4: roan × roan → 1/4 red: 1/2 roan: 1/4 white Part A. How is coat color inherited? Part B. What is the genotype of parents in cross 1? Part C. What is the genotype of offspring in cross 1? Part D. What is the genotype of parents in cross 2? Part E. What is the genotype of offspring in cross 2? Part F. What are the genotypes of parents in cross 3? Part G. What is the genotype of offspring in cross 3? Part H. What is the genotype of parents in cross 4? Part I. What are the genotypes of offspring in cross 4?
Part A. by incomplete dominance, because roan coat is a result of the reduction of pigment levels Part B. AA Part C. AA Part D. aa Part E. aa Part F. AA and aa Part G. Aa Part H. Aa Part I. AA, Aa and aa
Labrador retrievers may be black, brown, or golden in color. Although each color may breed true, many different outcomes occur if numerous litters are examined from a variety of matings, where the parents are not necessarily true-breeding. The following results show some of the possibilities. Part A. What is the mode of inheritance that is consistent with these data?
Part A. epistasis
Three autosomal recessive mutations in Drosophila, all with tan eye color (r1, r2, and r3), are independently isolated and subjected to complementation analysis. Part A. Of the results shown below, which, if any, are alleles of one another? Cross 1: r1 × r2 → F1 r1 × r2 → F1: all wild-type eyes Cross 2: r1 × r3 → F1 r1 × r3 → F1: all tan eyes Part B. Predict the results of the cross that is not shown-that is, r2 × r3.
Part A. r1 and r3 Part B. all wild-type eyes
Merle is a marking pattern in canine coats that appears as a marbling of color in a solid coat. The merle gene displays incomplete dominance. CSCS individuals display a solid coat CMCS individuals are merle and show patches of fur with a lighter, mottled effect CMCM individuals are "double merle" and show patches of fur with much more pronounced lightening Another gene, FGF5, also influences coat phenotype and determines whether dogs display long or short coats, with short coats being dominant to long coats. Part A. Determine the proportion of offspring phenotypes that would result when two merle dogs mate, if one dog is true-breeding for the long-coat trait and the other dog is true-breeding for the short-coat trait. Part B. Determine the proportion of offspring phenotypes that would result when two merle dogs mate, if both dogs are heterozygous (Ll) for the gene that regulates coat length. Part C. Interestingly, double merles are subject to a variety of health problems, including hearing loss and vision deficiencies. Therefore, it is not recommended that breeders breed for the double merle phenotype. If you were in the business of breeding dogs, which of the following crosses would you avoid in an effort to not produce double merle puppies?
Part A: double merle with short coat: 1/4 double merle with long coat: 0 merle with short coat: 1/2 merle with long coat: 0 solid with short coat: 1/4 solid with long coat: 0 Part B. double merle with short coat: 3/16 double merle with long coat: 1/16 merle with short coat: 3/8 merle with long coat: 1/8 solid with short coat: 3/16 solid with long coat: 1/16 Part C. merle x merle
Comb shape in chickens represents one of the classic examples of gene interaction. Two gene pairs interact to influence the shape of the comb. The genes for rose comb (R) and pea comb (P) together produce walnut comb. The fully homozygous recessive condition (rrpp) produces the single comb. Assume that a rose-comb chicken is crossed with a walnut-comb chicken and the following offspring are produced: 17 walnut, 16 rose, 7 pea, 6 single. What are the probable genotypes of the parents?
Rrpp × RrPp
Based on the following pedigree, with blood types provided (and ignoring the Bombay phenotype), what conclusions about paternity can be drawn?
This can be the father of the daughter but not the son.
Mutations in which the level of expression is based on environmental conditions is an example of ________.
a conditional mutation
Below is a pedigree of a fairly common human hereditary trait in which the boxes represent males and the circles represent females. Shading symbolizes the abnormal phenotype. Given that one gene pair is involved, what is/are the possible mode(s) of inheritance?
autosomal recessive
In the mouse, gene B can produce black pigment from a colorless precursor molecule. A mouse having at least one B allele can produce black pigment, whereas the homozygous recessive mouse (bb) cannot and is albino. The agouti locus (A) can convert the black pigment to brown in the presence of at least one dominant A allele, whereas the homozygous recessive (aa) cannot convert the black pigment to brown. What color fur would a mouse have with the genotype aaBB?
black
Individuals from two separate true-breeding strains of white deer mice are crossed yielding all grey offspring. White is recessive to gray color based on crossing mice from each strain with a grey mouse. Which of the following would best explain this result?
complementation
A condition in which one gene pair masks the expression of a nonallelic gene pair is called ________.
epistasis
Fruit flies homozygous for the eyeless mutation demonstrate various gradations in phenotype. This represents an example of ________.
expressivity
Because of the mechanism of sex determination, males of many species can be neither homozygous nor heterozygous. Such males are said to be ________.
hemizygous
A human disorder resulting from a mitochondrial DNA mutation such as MERFF might show various levels of expression among children of a mother with MERFF. This is most likely the result of ________.
heteroplasmy
Some genes and mutations vary in their phenotypic expression. What term describes a disorder that is NOT expressed by everyone who carries a mutation?
incomplete penetrance
A mutation in a gene that results in a loss of a functional product of that gene best defines what type of mutation?
null
The following coat colors are determined by alleles at one locus in horses: palomino = golden coat with lighter mane and tail cremello = almost white chestnut = brown Based on this data set, which of the following is the correct statement?
palomino is the incomplete dominant form of chestnut and cremello alleles
90% of children that inherit a mutated retinoblastoma gene develop the disease. This represents an example of ________.
penetrance
The phenomenon of a gene which has multiple phenotypic effects on an individual is referred to as ________.
pleiotropy
The MN blood group is a codominant trait as a result of which of the following?
presence of both M and N cell surface glycoproteins on the same blood cell
A gain-of-function mutation __________.
results in an increased quantity of the normal gene product
A gene in which the heterozygous condition is displayed differently in males and females is referred to as __________.
sex-influenced
A trait exhibited in one sex but not the other is referred to as ________.
sex-limited
A cross was made between homozygous wild-type female Drosophila and yellow-bodied male Drosophila. All of the resulting offspring were phenotypically wild type. Offspring of the F2 generation had the following phenotypes: Which is correct for the mode of inheritance of this gene?
sex-linked recessive
Complementation analysis is used to determine __________
whether two mutations that produce the same phenotype reside in the same or different genes
