Chapter 14
One character in peas that Mendel studied was yellow versus green seeds. A cross between a homozygous yellow line (YY) and a homozygous green line (yy) will result in F1 plants that are heterozygous (Yy) for this trait and produce yellow seeds. When an F1 plant undergoes meiosis, what gamete types will it produce, and in what proportions?
1. (1/2)Y (1/2)y
Two organisms with genotype AaBbCcDdEE mate. These loci are all independent. What fraction of the offspring will have the same genotype as the parents?
1/16
What number and types of chromosomes are found in a somatic cell in an animal with a diploid number of 48?
48 chromosomes (24 from each parent, including one sex chromosome from each)
Every gene is a sequence of ____ at a specific position along a chromosome called a _____. Diploid cells have two sets of chromosomes, one set inherited from each parent, that form _____. The homologs of a chromosome pair contain the same genetic loci. Therefore, each genetic locus is represented _____ in a diploid cell. Variations in inherited characteristics is due to the presence of ____, which are alternative versions of genes. You know that alleles are alternative versions of a gene. What makes alleles different from each other?
DNA nucleotides; locus homologous pairs twice alleles; genes They have different sequences of DNA nucleotides
In his breeding experiments, Mendel first crossed true-breeding plants to produce a second generation, which were then allowed to self-pollinate to generate the offspring. How do we name these three generations?
P, F1, and F2
What is the probability that each of the following pairs of parents will produce the indicated offspring? (Assume independent assortment of all gene pairs.) AABBCC × aabbcc → AaBbCc AABbCc × AaBbCc → AAbbCC AaBbCc × AaBbCc → AaBbCc aaBbCC × AABbcc → AaBbCc
1 1/32 1/8 1/2
Which of the following relationships among alleles of a single gene best explains the observation that a single change in the gene encoding α-keratin results in chickens with frizzled feathers, increased food consumption, higher heart rate and delayed sexual maturity?
pleiotropy
The information contained in DNA is used to make which of the following product(s)?
proteins, mRNA and tRNA
Which of the following do you expect if an individual is heterozygous for the sickle-cell trait?
they will not develop sickle-cell disease
Which of the following statements correctly explains the fact that all seven of the pea plant traits studied by Mendel obeyed the principle of independent assortment?
All of the genes controlling the traits were on different chromosomes
A diploid animal is dihybrid at the Head shape (H) and Tail length (T) loci. Which of the following gamete genotypes can it produce?
Ht
Which of the following statements correctly explains the observation that parents with two different phenotypes produced offspring with a phenotype that is a blend of the two parental varieties?
Neither of the parental alleles is dominant over the other
Each chromosome in this homologous pair possesses a different allele for flower color. Which statement about this homologous pair of chromosomes is correct?
These homologous chromosomes represent a maternal and a paternal chromosome.
An obstetrician knows that her patient's fetus is at risk for a serious disorder that is detectable biochemically in fetal cells. The obstetrician would most reasonably offer which of the following procedures to her patient?
amniocentesis or CVS
What is an allele?
an alternative version of a gene
Radish flowers may be red, purple, or white. A cross between a red-flowered plant and a white-flowered plant yields all-purple offspring. The flower color trait in radishes is an example of which of the following inheritance patterns?
incomplete dominance
Which of the following is true about a plant with the genotype AABbcc?
it is homozygous at two loci
In pea plants, the tall phenotype is dominant to the dwarf phenotype. If a heterozygous pea plant is crossed with a homozygous tall pea plant, what is the probability that the offspring will be dwarf in size?
0
In a cross of individuals who both possess this genotype, AaBbCc, what proportion of the offspring is predicted to have the genotype, AABBCC?
1/64
What fraction of the offspring from a cross between two animals with the genotype AaBbCc are expected to be homozygous recessive for the three traits?
1/64
Assuming independent assortment at all loci, what is the probability that a cross between the following parents, AABbCc × AaBbCc, will produce an AaBbCc offspring?
1/8
How many unique gametes could be produced through independent assortment by an individual with the genotype AaBbCCDdEE?
8
Gene S controls the sharpness of spines in a type of cactus. Cacti with the dominant allele, S, have sharp spines, whereas homozygous recessive ss cacti have dull spines. A second gene, N, determines whether or not cacti have spines. Homozygous recessive nn cacti have no spines at all. If cacti heterozygous for both traits, SsNn, were allowed to self-pollinate, the offspring would segregate into which of the following phenotype ratios?
9 sharp-spined: 3 dull-spined: 4 spineless
In a particular plant, green seed color is dominant to blue. If two plants with green seeds were crossed and resulted in 302 green and 98 blue seed plants, what was the most probable genotype of each parent?
Gg x Gg
Assume that a GG allele stands for the green pod color, a gg allele−−yellow pod color, an II allele−−inflated pod shape, and an ii allele−−constricted pod shape. Two pea plants heterozygous for the characters of pod color and pod shape are crossed. Which gamete types will the obtained heterozygous plant form?
Gi, gI, GI, gi
Human civilizations developed practice regarding inheritance before the scientific grounding of the practices had been determined. Which of the following genetic principles scientific support for the societal taboo against closely related people having children?
Heterozygous loci can mask harmful traits in an individual
Select the correct explanation for the fact that a carrier of a recessive genetic disorder does not have the disorder.
In a recessive disorder, only a single functioning allele is necessary to determine a normal phenotype.
Which of the following scenarios describes an example of epistasis?
In many mammals one genotype (ee) prevents any fur color from delevoping
One of two major forms of neurofibromatosis results from inheriting a dominant allele of a gene with affected individuals having phenotypes that range from mild to very severe. Which of the following is the best explanation for why a young child is the first in her family to be diagnosed with a severe form of the condition?
One of the parents has a mild expression of the gene
Quantitative characters vary in a population along a continuum. How do such characters differ from the characters investigated by Mendel in his experiments on peas?
Quantitative characters are due to polygenic inheritance, the additive effects of two or more genes on a single phenotypic character. A single gene affected all but one of the pea characters studied by Mendel.
Just for fun, imagine that "shirt-striping" is a phenotypic character caused by a single gene. Construct a genetic explanation for the appearance of the family in the above photograph, consistent with their "shirt phenotypes." What are the presumed allele combinations for "shirt-striping" in each family member? What is the inheritance pattern shown by the child?
The parents ShSh and SvSv, and the child is ShSv multiple alleles; codominance
Feather color in budgies is determined by two different genes: Y for pigment on the outside of the feather, and B for pigment on the inside of the feather. YYBB, YyBB, or YYBb is green; yyBB or yyBb is blue; YYbb or Yybb is yellow; and yybb is white. A blue budgie is crossed with a white budgie. Which of the following results in the offspring is most possible?
blue and white offspring
Which of the following inheritance patterns describes the ability of a single allele to have multiple phenotypic effects?
pleiotropy
A radish is a root vegetable that produces flowers that may be red, purple, or white. A cross between a red-flowered plant and a white-flowered plant yields all-purple offspring. The part of the radish we eat may be oval or long, with long being the dominant trait. If true-breeding red-flowered, long radishes long radishes are crossed with true-breeding white oval radishes, the F1 will be expected to exhibit which of the following phenotypes?
purple and long
Black fur in mice (B) is dominant to brown fur (b). Short tails (S) are dominant to long tails (s). What fraction of the progeny of crosses BbSs × BBss will be expected to have black fur and long tails?
1/2
Which of the following calculations requires the use of the addition rule of probability?
Calculating the probability of a child having either sickle-cell anemia or cystic fibrosis if parents are each heterozygous for both.
Gene S controls the sharpness of spines in a type of cactus. Cacti with the dominant allele, S, have sharp spines, whereas homozygous recessive ss cacti have dull spines. Also, a second gene, N, determines whether or not cactuses have spines. Homozygous recessive nn cactuses have no spines at all. What phenotypes would be expected from a cross between a true-breeding sharp-spined cactus and a spineless cactus?
all sharp-spined progency
The figure shows the pedigree of a family. Dark-shaded symbols represent individuals with one of the two major types of colon cancer. Numbers under the symbols are the individual's age at the time of diagnosis. Males are represented by squares, females by circles. Based on this pedigree, this trait is most likely inherited
as a dominant trait
The law of ____ states that genes have alternative forms, or alleles. In a ____ organism, the two alleles of a genes separate during ____ and gamete formation; each sperm of egg carries only one allele or each pair. This law explains the ____ ratio of the F2 phenotypes observed when ____ self-pollinate. Each organism inherits one allele for each gene from each parent. In _____ individuals, the two alleles are different, and expression of the ____ allele masks the phenotypic effect of the _____ allele. In _____ individuals, the two alleles are identical . The _____ states that the pair of alleles for a given gene segregates into gametes independently of the pair of alleles for any other gene. This law explains the _____ ratio of the F2 phenotypes in a cross between ____.
segregation diploid meiosis 3:1 monohybrids heterozygous dominant recessive homozygous independent assortment 9:3:3:1 dihybrids
Which of the following best describes how an individual with genotype AaBbCCDdEE can make gametes with eight different genotypes.
the inheritance of a particular copy of one chromosome does not affect the inheritance of a different chromosome
Which of the following best describes how an individual with genotype AaBbCCDdEE can make haploid gametes with different genotypes?
the inheritance of a particular copy of one chromosomes does not affect the inheritance of a different chromosome.
Skin color in a certain species of fish is inherited via a single gene with four different alleles. Each allele confers a unit of color darkness such that having allele S1 confers one unit of color, S2 has two units, S3 has three units, and S4 confers four units. A fish of this type has the genotype S1S3, and its mate has the genotype S2S4. What proportion of their offspring would be expected to have five units of color?
1/2
The genotype of F1F1 individuals in a tetrahybrid cross is AaBbCcDdAaBbCcDd. Assuming independent assortment of these four genes, what are the probabilities that F2F2 offspring will have the following genotypes? aabbccdd AaBbCcDd AABBCCDD AaBBccDd AaBBCCdd
1/256 1/16 1/256 1/64 1/128
Use the figure and the following description to answer the question. In a particular plant, leaf color is controlled by gene locus D. Plants with at least one allele D have dark green leaves, and plants with the homozygous recessive dd genotype have light green leaves. A true-breeding, dark-leaved plant is crossed with a light-leaved one, and the F1 offspring is allowed to self-pollinate. The predicted outcome of the F1 cross is diagrammed in the Punnett square shown in the figure, where 1, 2, 3, and 4 represent the genotypes corresponding to each box within the square. Which of the boxes marked 1-4 correspond to plants with dark leaves? Which of the boxes marked 1-4 correspond to plants with a heterozygous genotype? Which of the boxes marked 1-4 correspond to plants that will be true-breeding?
1, 2, and 3 2 and 3 only 1 and 4 only
1. If two phenotypically normal tigers that are heterozygous at this locus are mated, what percentage of their offspring will be cross-eyed? 2. What percentage of cross-eyed tigers will also be white?
1. 25% 2. 100%
Which of the following statements correctly describes the terms monohybrid cross and dihybrid cross?
A dihybrid cross involves organisms that are heterozygous for two characters that are being studied, and a monohybrid cross involves organisms that are heterozygous for only one character being studied.
Look at the Punnett square, which shows the predicted offspring of the F2 generation from a cross between a plant with yellow-round seeds (YYRR) and a plant with green-wrinkled seeds (yyrr). Select the correct statement about wrinkled yellow seeds in the F2 generation.
The change that an individual taken at random from the F2 generation produces wrinkled seeds is 25% and the change that the same individual produces yellow seeds is 75%.
Hutchinson-Gilford progeria is an exceedingly rare human genetic disorder in which individuals look very old even as young children, experience very early senility and severe coronary artery disease, and have a life expectancy of 13 years. Which of the following statements represents the most likely assumption regarding this disorder?
The disorder may be due to mutation in a single protein-coding gene
Mendel crossed true breeding yellow-seeded and green-seeded pea plants and then allowed the offspring to self-pollinate to produce an F2 generation. The results were as follows: 6,022 yellow and 2,001 green (8,023 total). Which of the following statements correctly describes the relationship of the allele for green seeds to the allele for yellow seeds?
The green allele is recessive to the yellow allele
Which of the following sentences state a significant conclusion that Gregor Mendel drew from his experiments with pea plants?
Traits are inherited in discrete units and are not the result of "blending"
Height in humans generally shows a normal (bell-shaped) distribution. What type of inheritance most likely determines height?
a combination of polygenic inheritance and environmental factors
Pea plants produce either purple or white flowers with purple showing complete dominance. A gardener was given plants with purple flowers. Which of the following types of crosses would best allow her to determine the genotype of her plant in one generation?
a testcross
You cross a true-breeding, red-flowered snapdragon with a true-breeding, white-flowered one. All of the F1 are pink. What does this say about the parental traits?
red shows incomplete dominance over white
Albinism is a recessive trait where an individual does not produce the pigment melanin. A man and woman both produce melanin, but both have one parent with albinism. What is the probability that their first child will have albinism?
1/4
In human blood types, Rh positive is a trait that shows simple dominance over Rh negative. The Rh phenotype is recorded by stating "positive" or "negative" after the individuals ABO blood type. A woman who has blood type A positive has a daughter who is type O positive and a son who is type B negative. Which of the following phenotypes is possible for the father?
B positive
Phenylketonuria (PKU) is a recessive human disorder in which an individual cannot appropriately break down the amino acid phenylalanine. This amino acid is not naturally produced by humans. Which of the following treatments would be most effective for people with PKU?
Regulate the individual's diet to severely limit the uptake of phenylalanine.
The following question refers to the figure of a family's pedigree chart, some of whose members exhibit the dominant trait, W. Affected individuals are indicated by a dark square or circle. What is the genotype of individual II-5? What is the likelihood that a future child of IV-3 and IV-4 will have the trait? What is the probability that individual III-1 is Ww?
ww 50% 1
A man with type A blood marries a woman with type B blood. Their child has type O blood. 1. What is the genotype of the man? 2. What is the genotype of the woman? 3. What is the genotype of the child? 4. What genotypes would you expect in future offspring from this marriage? 5. What frequencies would you expect the offspring genotypes?
1. I A i 2. I B i 3. ii 4. ii, I A i, I B i, I A I B 5. I A I B: 1/4 I A i: 1/4 I B i: 1/4 ii: 1/4
1. The result of the following cross indicates the orange eyes are _____ black eyes. 2. If B represents the allele for black eyes (dominant) and b represents the allele for orange eyes (recessive), what would be the genotypic ratio of a cross between a heterozygous black-eyed MendAlien and an orange-eyed MendAlien? 3. If B represents the allele for black eyes (dominant) and b represents the allele for orange eyes (recessive), what would be the phenotypic ratio of a cross between a heterozygous black-eyed MendAlien and an orange-eyed MendAlien?
1. recessive to 2. 0 homozygous black (BB): 1 heterozygote (black) (Bb): 1 homozygous orange (bb) 3. 1 black: 1 orange
If the parent or offspring genotypes or phenotypes are known, the pattern of inheritance can be predicted. Two organisms, with genotypes BbDD and BBDd, are mated. Assuming independent assortment of the two loci, which of the following genotypic ratios in offspring would occur?
1BBDD:1BbDD:1BBDd:1BbDd
In a certain species of diploid fish a single gene controls skin color. Researchers have found four different alleles of this gene within the fish population. How many different gamete genotypes are possible in an individual of this species?
2
When a dominant allele coexists with a recessive allele in a heterozygote individual, how do they interact with each other?
They do not interact at all.
A gene for the MN blood group has codominant alleles M and N. If both children in a family are of blood type M, which of the following situations is possible?
each parent is either M or MN
Ten plants of the same genotype are planted in a large flower garden. Later that year, some of the ten plants have blue flowers and others have pink flowers. This can be best explained by which of the following statements?
environmental factors such as soil pH affect the phenotype
Does alkaptonuria appear to be caused by a dominant allele or by a recessive allele?
recessive
Albinism is a recessive trait where an individual does not produce the pigment melanin. A man and woman who both produce melanin have one child out of three who has albinism. What are the genotypes of the man and woman?
Both parents must be heterozygous
Folk singer Woody Guthrie died of Huntington's disease, an autosomal dominant disorder. Which statement below must be true?
It is very likely that at least one of Woody Guthrie's parents also had the allele for Huntington's disease
Keisha and Jerome each have a sibling with sickle-cell disease. Neither Keisha nor Jerome nor any of their parents have the disease, and none of them have ever been tested to see if they carry the sickle-cell allele. Based on this incomplete information, calculate the probability that if this couple has a child, the child will have sickle-cell disease.
1/9
In maize (corn plants) a dominant allele I inhibits kernel color, while the recessive allele i permits color when homozygous. At a different locus, the dominant allele P causes purple kernel color, while the homozygous recessive genotype pp causes red kernels. If plants heterozygous at both loci are crossed, what will be the phenotypic ratio of the offspring? _____ colorless: _____ purple: _____ red
12:3:1
In rabbits, the homozygous genotype LCLC has straight legs, LCLc results in deformed legs, and LcLc results in very short legs. The genotype FBFB produces black fur, FBFb brown fur, and FbFb white fur. If a cross is made between brown rabbits with deformed legs and white rabbits with deformed legs, what percent of the offspring would be expected to have deformed legs and white fur?
25%
Two true-breeding stocks of pea plants are crossed. One parent has red, axial flowers, and the other has white, terminal flowers; all F1 individuals have red, axial flowers. Among the F2 offspring, what is the probability of producing plants with white axial flowers?
3/16
What would be the expected frequency of agouti brown offspring in the litter? Suppose you mate two mice with the genotypes AYaBb x AYaBb . Considering only the live-born offspring, what would be the expected frequency of mice with yellow fur? In a cross between two mice that are heterozygous for agouti, black, color, and piebaldism, what is the probability that offspring will have solid black fur along with large patches of white fur? (Hint: Consider each gene separately; then use the multiplication rule.
3/16 2/3 9/256
A newly discovered diploid mammal has three characteristics that show simple Mendelian inheritance. Each characteristic is controlled by a single gene (A, B, or C). If a male with genotype AABBCc is crossed with a female with genotype AabbCc, what proportion of the offspring are expected to have the same phenotype as the male parent?
3/4
Phenylketonuria is an inherited disease caused by a recessive allele. If a woman and her husband are both carriers, what is the probability that their first child will be a girl without phenylketonuria?
3/8
When Mendel set up a Parental (P) cross between true breeding purple and white flowered plants to generate the F1 and then allowed the F1 to self-pollinate to generate the F2 he saw a dominant to recessive ratio of 3:1. What phenotypic ratio would be expected if he crossed the F1 with the original purple parent?
4:0
In some parts of Africa, the frequency of individuals who are heterozygous for the sickle-cell anemia allele is higher than the frequency in North America, presumably because this reduces the frequency of malaria. Such a relationship is related to which of the following?
Darwin's theory of natural selection
Which of the following describes why Mendel continued some of his experiments into the F2 or F3 generation?
Following multiple generations allowed him to determine whether a recessive trait would reappear
Which of the following statements about the law of segregation is correct?
It describes the inheritance of different chromosomes relative to one another
Which of the following statements about the law of independent assortment is correct?
It describes the inheritance of different genes relative to one another
Marfan syndrome in humans is caused by an abnormality of the connective tissue protein fibrillin. Patients are usually very tall and thin, with long spindly fingers, curvature of the spine, sometimes weakened arterial walls, and sometimes eye problems, such as lens dislocation. Which of the following would you conclude about Marfan syndrome from this information?
It is pleiotropic
Why did all of the F1 offspring of Mendel's purple and white flowered pea cross always look like one of the two parental varieties?
One allele was dominant
Over the past half century, there has been a trend in the United States and other developed countries for people to marry and start families later in life than did their parents and grandparents. What effects might this trend have on the incidence (frequency) of late-acting dominant lethal alleles in the population?
The frequency of late-acting dominant lethal alleles will decrease faster than before
Normal hemoglobin is a tetramer, consisting of two molecules of ββ-globin and two molecules of αα-globin; normal hemoglobin molecules do not associate with each other. In sickle-cell disease, the change in a single amino acid results in mutant hemoglobin tetramers, which associate with each other and assemble into large fibers. Based on this information alone, what can we conclude about the changes in the structure of sickle cell hemoglobin as compared to normal hemoglobin?
altered primary and quaternary structure
Gene S controls the sharpness of spines in a type of cactus. Cacti with the dominant allele, S, have sharp spines, whereas homozygous recessive ss cacti have dull spines. Also, a second gene, N, determines whether or not cacti have spines. Homozygous recessive nn cacti have no spines at all. The relationship between genes S and N is an example of which of the following inheritance patterns?
epistasis
Consider pea plants with the genotypes GgTt and ggtt. How many types of gametes can be produced by each of these two plants?
four, one
Label each mutant line with the best statement from the list below. Labels may be used once, more than once, or not at all.
twist- the mutant allele is dominant to its corresponding wild-type allele forked- the mutant allele is dominant to its corresponding wild-type allele pale- the mutant allele is neither dominant nor completely recessive to its corresponding wild-type allele
A brown dog crossed with a yellow dog produced 12 brown offspring. A second brown individual was obtained. When the yellow dog was crossed with this animal, six brown and six yellow offspring were born. Which of the following best explains the results of the second cross?
yellow is a recessive trait, brown is a dominant trait
Feather color in budgies is determined by two different genes, Y for pigment on the outside of the feather, and B for pigment on the inside of the feather. YYBB, YyBB, or YYBb is green; yyBB or yyBb is blue; YYbb or Yybb is yellow; and yybb is white. Two blue budgies were crossed. Over the years, they produced 22 offspring, five of which were white. What are the most likely genotypes for the two blue budgies?
yyBb and yyBb
1. What is the difference between heterozygous and homozygous individuals? 2. When constructing a Punnett square, the symbols on the outside of the boxes represent _______, while those inside the boxes represent _______. 3. True or false? The same phenotype can be produced by more than one genotype. 4. True or false? In diploid organisms, a dominant phenotype will only be expressed if the individual is homozygous dominant for that trait. 5. If an organism with the genotype AaBb produces gametes, what proportion of the gametes would be Bb? 6. Two mice are heterozygous for albinism (Aa) . The dominant allele (A) codes for normal pigmentation, and the recessive allele (a) codes for no pigmentation. What percentage of their offspring would have an albino phenotype? 7. A tall, purple-flowered pea plant (TtPp) is allowed to self-pollinate. (The recessive alleles code for short plants and white flowers.) The phenotypic ratio of the resulting offspring is 9:3:3:1. What is the genotype of the plant whose phenotype appeared once out of every 16 offspring (the "1" in the 9:3:3:1 ratio)?
1. All of the gametes from a homozygote carry the same version of the gene while those of a heterozygote will differ. 2. gametes, progency 3. True 4. False 5. None 6. 25 7. ttpp
A man has six fingers on each hand and six toes on each foot. His wife and their daughter have the typical number of digits. Remember that extra digits is a dominant trait. What fraction of this couple's children would be expected to have extra digits?
1/2
Having polydactyly (extra digits on hands and feet) is a dominant trait. A man has polydactyly. His wife and oldest daughter do not have polydactyly. The couple's second child has polydactyly. What is the probability that their next (third) child will have extra digits?
1/2
Imagine that you are a genetic counselor, and a couple planning to start a family comes to you for information. Charles was married once before, and he and his first wife had a child with cystic fibrosis. The brother of his current wife, Elaine, died of cystic fibrosis. Neither Charles, Elaine, nor their parents have cystic fibrosis. What is the probability that Charles and Elaine will have a baby with cystic fibrosis? Express your answer as a fraction using the slash symbol and no spaces (for example, 1/16).
1/6
When Mendel crossed yellow-seeded and green-seeded pea plants, all the offspring were yellow-seeded. Which of the following genotypic ratios was expected when Mendel crossed the F1 yellow-seeded plants with green-seeded plants?
1:1
Hemochromatosis is an inherited disease caused by a recessive allele. If a woman and her husband, who are both carriers, have three children, what is the probability of each of the following? All three children are of normal phenotype. One or more of the three children have the disease. All three children have the disease. At least one child is phenotypically normal.
27/64 37/64 1/64 63/64
Which of the following statements best describes the addition rule of probability?
It is the probability that either one of two independent events will occur
How would you determine whether the curl allele is dominant or recessive? How would you obtain true-breeding curl cats? How could you be sure they are true-breeding?
Matings of the original mutant cat with true-breeding noncurl cats will produce both curl and noncurl F1 offspring if the curl allele is dominant, but only noncurl offspring if the curl allele is recessive. You would obtain some true-breeding offspring homozygous for the curl allele from matings between the F1 cats resulting from the original curl × noncurl crosses no matter whether the curl trait is dominant or recessive. You know that cats are true-breeding when curl c curl matings produce only curl offspring
Gene S controls the sharpness of spines in a type of cactus. Cacti with the dominant allele, S, have sharp spines, whereas homozygous recessive ss cacti have dull spines. A second gene, N, determines whether or not cactuses have spines. Homozygous recessive nn cactuses have no spines at all. Which of the following explain why a crossing a true breeding spineless cactus with a dull-spined cactus could result in both sharp- and dull-spined offspring?
The spineless cactus was heterozygous at the S locus
Which of the following statements correctly describes how Mendel explained why traits disappeared in the F1 generation and then reappeared in the F2 generation?
Traits can be dominant or recessive, and the recessive traits were "hidden" by the dominant ones in the F1.
In cattle, roan coat color (mixed red and white hairs) occurs in the heterozygous (CRCW) offspring of red (CRCR) and white (CWCW) homozygotes. Which of the following crosses would produce offspring in the ratio of 1 red:2 roan:1 white?
roan x roan
Which of the following phenotypes is an example of polygenic inheritance?
skin pigmentation in humans
Various procedures can be used to detect genetic disorders before birth. Among the tests discussed in this chapter, which is the least invasive (list first), and which two allow the chromosomes of the fetus to be examined?
ultrasound imaging; chorionic villus sampling and amniocentesis
