Ch.14 - Mendelian GeneticsSee all chapters
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Ch.14 - Mendelian Genetics
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Independent Assortment

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Mendel's Experiment
Independent Assortment
Extensions to Mendel
Genetic Counseling

Concept #1: Dihybrid Cross and Independent Assortment

Concept #2: Probability Rules

Practice: What is the probability that the offspring of a dihybrid cross (YyRr x YyRr) will be yellow?

Practice: What is the probability that the offspring of a dihybrid cross (YyRr x YyRr) will be green and wrinkled?

Practice: What is the probability that the offspring of a dihybrid cross (YyRr x YyRr) will be yellow or round?

Additional Problems
You continue your genetic analysis by crossing the forked and pale mutant lines with each other. The leaves of the F1 are light green (intermediate between pale and wild-type leaves) and forked. The F2 has six phenotypic classes: You designate the forked mutant allele as F (wild type = f+ ) and the pale mutant allele as p (wild type = P). Using these allele symbols, identify the genotypes of the six F2 classes
Which of the following phenomena is a consequence of Independent Assortment?a. For any gene displaying complete dominance, heterozygous individuals exhibit the dominant phenotype.b. Pure breeding plants, when mated with each other, produce completely homozygous offspring.c. The phenotypic ratio among phenotypes produced from an F1 X F1 dihybrid cross is 9:3:3:1.d. Smooth seed trait is dominant to wrinkled seed trait in peas.
Gene S controls the sharpness of spines in a type of cactus. Cactuses with the dominant allele, S, have sharp spines, whereas homozygous recessivess cactuses have dull spines. At the same time, a second gene, N, determines whether or not cactuses have spines. Homozygous recessive nn cactuses have no spines at all. A cross between a true-breeding sharp-spined cactus and a dull spineless cactus would produce ___________.a. all spineless progenyb. all sharp-spined progenyc. 50% sharp-spined, 50% dull-spined progenyd. 25% sharp-spined, 50% dull-spined, 25% spineless progenye. It is impossible to determine the phenotypes of the progeny
A testcross is a mating of an individual with an unknown genotype and an individual that: a. Is heterozygousb. Is homozygous dominantc. Is homozygous recessived. Has any known genotypee. Wild type
A dihybrid cross is a mating between two individuals that are each ______________ for ___________ gene (genes).  a. Homozygous, one b. Homozygous, two c. Homologous, two d. Heterozygous, one e. Heterozygous, two
Independent assortment explains _______.a. why meiosis in a cell of genotype AaBb cannot yield Ab gametesb. why a collection of meiotic products that includes gametes of genotype Ab will also include gametes of genotype AB in roughly the same proportionc. why meiosis in a cell of genotype Aa yields A gametes and a gametes, but no Aa gametesd. why meiosis in a cell of genotype Aa yields A gametes and a gametes in roughly equal numbers
In a cross AaBbCc x AaBbCc, what is the probability of producing the genotype AABBCC?a. 1/4b. 1/8c. 1/16d. 1/32e. 1/64
If a pea plant is heterozygous for yellow seeds (Yy), which gametes could it produce?  a. Y b. Y or y c. y d. Yy e. YYyy
If you cross RrYy and RRyy pea plants, what fraction of the offspring will have round yellow peas? R=round, r=wrinkled, Y=yellow, y=green.  a. 100% b. 75% c. 25% d. 0% e. 50%
Which gametes can a RrYy plant produce?  a. Rr or Yy b. RY or ry c. RrYy d. RY, Ry, rY, or ry e. R or r
Which gametes can a RRyy plant produce?  a. RR or yy b. Ry c. RY or ry d. RRyy e. R or y
Mendel studied pea plants dihybrid for seed shape (round versus wrinkled) and seed color (yellow versus green). Recall thatthe round allele (R) is dominant to the wrinkled allele (r) andthe yellow allele (Y) is dominant to the green allele (y).The table below shows the F1 progeny that result from selfing four different parent pea plants.Use the phenotypes of the F1 progeny to deduce the genotype and phenotype of each parent plant.Complete the table by dragging the correct label to the appropriate location. Labels can be used once, more than once, or not at all. 
A plant grown from a [round, yellow] seed is crossed with a plant grown from a [wrinkled, yellow] seed. This cross produces four progeny types in the F1 [round, yellow], [wrinkled, yellow], [round, green], and [wrinkled, green]. Use this information to deduce the genotypes of the parent plants. Indicate the genotypes by dragging the correct label to the appropriate location. 
Hairy noses in gremlins (H) is dominant to hairless noses (h), and beady little eyes (B) are dominant to large, soulful eyes (b). In a cross of HhBb x HHbb, what fraction of the progeny will have hairy noses and soulful eyes?a. 1/2b. 3/16c. 9/16d. 1/16e. 3/8
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. The genes for flower color and location assort independently. If 1,000 F2 offspring resulted from the cross, approximately how many of them would you expect to have red, terminal flowers?a. 250b. 750c. 190d. 65e. 565
Any dihybrid cross should theoretically yield a 3:1 phenotypic ratio. a. True    b. False
Feather color in budgies is determined by two different genes Y and B, one for pigment on the outside and one for 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, 5 of which were white. What are the most likely genotypes for the two blue budgies?a. yyBB and yyBBb. yyBB and yybbc. yyBB and yyBbd. yyBb and yybbe. yyBb and yyBb
Given the cross PpQqRrSS x PPQqRRSs, what proportion of offspring are expected to be PPQQRRSS?a. 1/32b. zeroc. 3/64d. 1/16
Purebreeding boa constrictors that are tan colored with a normal color pattern are mated to purebreeding boa contrictors that are orange colored with a swirl color pattern. All of the offspring have tan with a normal color pattern. If an F1 individual is crossed to a pure breeding orange swirl pattern individual what proportion of their offspring should be orange with a normal color pattern, assuming that the two loci are controlled by automsomal loci that assort independently?A) ½B) < ¼  C) ¼D) 0E) all of them
You decide to designate the twist allele as FT to distinguish it from the forked allele F. Using the following allele symbols, identify the genotypes of the three F2 classes by dragging one label to each class. Labels may be used once, more than once, or not at all.
An individual with genotype AaBbccDd is crossed to an individual with genotype aaBbCcDd.  What is the probability that their first offspring will have genotype aabbCcDD?a) 1/64  b) 1/32 c) 1/16 d) 1/8e) 1/4
After the cell below is finished dividing, what will be a possible genotype for one of the daughter cells?a. rTdMb. RrTtDdMmc. RTDMd. RTdme. RrTTDdMm
In rabbits, the homozygous CC is normal, Cc results in deformed legs, and cc results in very short legs. The genotype BB produces black fur, Bb brown fur, and bb white fur. If a cross is made between brown rabbits with deformed legs and white rabbits with deformed legs, what percentage of the offspring would be expected to have deformed legs and white fur?A) 100%B) 25%C) about 66%D) 50%E) 33% 
When crossing one parent having an RRBbDd genotype with another parent having an RrBbDd genotype, what is the probability that they will have an RrBBDd offspring?a. 1/8b. 1/16c. 1/32d. 3/16e. 1/64
In a species of butterfly, the blue-wing allele (B) is dominant to the yellow wing allele (b) and the allele for long antennae (L) is dominant to the allele for short antennae (l). If a butterfly is homozygous recessive for antennal length, its wings always end up being blue. If one butterfly is Bbll and a second butterfly is BbLl, what is the chance that they will produce offspring that have short antennae and blue wings?a. zerob. 3/8c. 1/2d. 3/4e. 1/1
Crossing the forked and twist mutants You continue your analysis by crossing the forked and twist lines. Your results are as follows: Which of the following statements best explains the outcome of this cross? a. The forked mutation has recombined with the twist mutation. b. The forked mutation and the twist mutation are codominant alleles of the same locus. c. The forked mutation is incompletely dominant to the twist mutation. d. The twist mutation is incompletely dominant to the forked mutation. e. The forked mutation is epistatic to the twist mutation. f. The twist mutation is epistatic to the forked mutation.
Contrast genes that are Independently Sorted verses those that are Linked.
Starting with a cross between AA and aa, the proportion of heterozygotes in the F2 progeny will be:A. 1/16B. 1/8C. 1/4D. 1/3E. 1/2
Among 160 offspring of the F2 from a dihybrid cross of independently assorting loci A and B, how many will have the phenotype AB?A. 15B. 80C. 90D. 160
In Loch Ness Monsters, three humps is dominant to two humps, and fire-breathing ability is dominant to non-fire-breathing. I crossed a three-humped, fire-breathing monster with a two-humped, non-fire-breathing monster. All of my baby monsters were three-humped and fire-breathing.A. What were the genotypes of the mom and dad monsters.B. What are the genotypes of the babies?C. If I crossed a baby brother with a baby sister, what would the expected genotypic and phenotypic frequencies be?
In rabbits, black fur (B) is dominant to brown (b), and spotted coat (S) is dominant to solid coat (s).A. Give the genotypes of the parents if a black, spotted male is crossed with a brown, solid female and all of the offspring are black and spotted.B. Give the genotypes of the parents if some of the offspring were brown and spotted. Show the Punnet square for this cross.C. What is the probability of obtaining three brown, spotted offspring from the cross in part B?
in sesame plants, the one-pod condition (P) is dominant to the three-pod condition (p), and normal leaf (L) is dominant to wrinkled leaf (l). Pod type and leaf type are inherited independently. Determine the genotypes as best as you can for the two parents for all possible matings producing the following offspring.a) 318 one-pod normal, 98 one-pod wrinkledb) 74 one-pod normal, 72 one-pod wrinkled, 76 three-pod normal, 72 three-pod wrinkled
Cystic fibrosis in humans is caused by recessive mutations in a single gene located in an autosome and follows mendelian laws. A normal couple has two children. The first child has cystic fibrosis, and the second child is unaffected. What is the probability that the second child is a carrier (heterozygous) for the mutation that causes the disease?
Suppose two parents, a father with genotype AaBbCcDdee and a mother with the genotype aabbCcDDEe, wanted to have children. Assume each locus follows Mendelian inheritance patterns for dominance. What proportion of the offspring will have each of the following characteristics? Round your answers to two decimal places.A. same genotype as the fatherB. phenotypically resemble the fatherC. same genotype as the motherD. phenotypically resemble the motherE. phenotypically resemble neither parent
In a population, are dominant characteristics always more frequent than recessive ones?
Consider three independent genes with two alleles, denoting the dominant forms of the alleles as A, B, and C, and the recessive forms as a, b, and c.Construct a diagram for the second generation of a cross of the two pure line strains AbC and aBC, assuming reproduction by selfing after the first filial generation. Include the expected proportions of each second generation combination of traits.
A brown mink is crossed with a silver mink. They produce all brown F1 offspring. These brown F1 offspring were crossed among themselves. What is the ratio of offspring would these F1s produce?A. 60 brown and 0 silverB. 45 brown and 15 silverC. 30 brown and 30 silverD. 60 silver and 0 brown.
Two plants are crossed, resulting in offspring with a 1:1 phenotype ratio for a particular trait. This suggests _____.A. that one parent is heterozygous and the other is a homozygous recessiveB. incomplete dominanceC. that the parents were true-breeding for contrasting traitsD. that the parents were both heterozygousE. that one parent is heterozygous and the other is homozygous dominant
A violet-flowered, long-stemmed hybrid pea plant was crossed with a true-breeding white-flowered, short-stemmed pea plant with the following offspring: 47 violet, long-stemmed plants; 40 white, long-stemmed plants; 38 violet, short-stemmed plants; and 41 white, short-stemmed plants. If two of the white, long-stemmed plants above were crossed, you would expect to get which of the results listed below?A. all white, long-stemmedB. 1/2 white, short-stemmed; 1/2 white, long-stemmedC. 3/4 white, long-stemmed; 1/4 white, short-stemmedD. 9/16 violet, long-stemmed plants; 3/16, white, long-stemmed plants; 3/16 violet, short-stemmed plants; 1/16 white, short-stemmed plantsE. They do not all have the same genotype so the expected progeny can not be determined
In tomatoes, red fruit color is dominant to yellow. A red fruit plant is crossed with anoter red fruit plant and the crosses produces 30 red fruit plants and 10 yellow fruit plants. Use the symbols R/r for fruit color.a. Prepare a Punnet square to illustrate the cross.b. What is the chance that red fruit plants are homozygous dominant? Show your work.
In poultry, rose comb is controlled by a dominant allele and its recessive allele controls single comb.A.Give the genotype and phenotype produced from crossing a pure-breeding rose comb chicken with a pure-breeding single comb chicken.B. Give the results of the backcross if the F1 hybrid with both pure-breeding parents.
How many different kinds of gametes can be produced by an individual with the genotype AaBbCCddEEFF?A. 2B. 4C. 8D. 16E. 64
Given the parents AABBCc x AabbCc, assume simple dominance for each trait and independent assortment. What proportion of the progeny will be expected to phenotypically resemble the first parent with genotype AABBCc?A. 1/4B. 3/8C. 3/4D. 1
In tomatoes, the flesh can be either red or yellow. The following crosses involving plants of these two phenotypes are made.a. What phenotype is dominant?b. What are the genotypes of the parents and offspring in each case?
In roses, B=big thorns, and b=little thorns. Cross a heterozygous big thorned rose (Bb) with a homozygous recessive little thorned rose (bb). Show the Punnet square, and provide thephenotypic and genotypic ratios.
In probiscus monkeys, N=long nose, and n=short nose. Cross a homozygous dominant long-nosed monkey (NN) with a homozygous recessive short-nosed monkey (nn). Show the Punnet square, and provide the phenotypic and genotypic ratios.
Assuming independent assortment, an individual of genotype SsYyAa would produce gametes of genotypes (in their proper proportions) ___________.A. 1/6 SYA, 1/6 SYa, 1/6 Sya, 1/6 sYa, 1/6 syA, and 1/6 syaB. 1/8 SYA, 1/8 SYa, 1/8 SyA, 1/8 Sya, 1/8 sYA, 1/8 sYa, 1/8 syA, and 1/8 syaC. 1/2 SYA, and 1/2 syaD. 1/4 SYA, 1/4 SyA, 1/4 sYa, and 1/4 sya
In rabbits, the allele of the gene for short hair (S) is dominant over the allele for long hair (s) and the black hair (B) is dominant over brown hair (b). The hair color and hair length genes are on separate pairs of chromosomes. For a cross between a SsBb and a ssBb rabbit, what are the expected genotypes and phenotypes in the offspring?
In guineapigs, a cross between black furred and brown furred parenrs gives offspring with 100% black fur. A cross between a long furred and short furred parents gives offspring with 100% short fur. What would be the genotypic and phenotypic ratios predicted for a cross between a heterozygous black furred, long furred male and a brown furred, homozygous short furred female?
Independent assortment occurs when pairs of homologous chromosomes line up at the equator during metaphase of:A. meiosis IIB. mitosis IIC. mitosis ID. meiosis IE. It is not during metaphase
Mating oif two organisms produces a 1:1 ratio of phenotypes in the progeny. The parental genotypes are:A. Aa x AaB. Aa x aaC. AA x aaD. AA x AA
In chickens, the dominant allele Cr produces the creeper phenotype (having extremely short legs). However, the creeper allele is lethal in the homozygous condition. If two creepers are mated, what proportion of their living progeny will be creepers?A. 2/3B. 1/2C. 1/4D. 1/3E. 3/4
In guinea pigs, rough coat (R) is dominant over smooth coat (r). A rough coat-coated guinea pig is bred to a smooth one, giving 8 rough and 7 smooth progeny in the F1 generation. What are the genotypes of the parents?a. Rr x Rrb. RR x rrc. rr x rrd. Rr x rre. RR x Rr
In foxes, two alleles of a single gene, P and p, may result in lethality (PP), platinum (Pp), or silver coat (pp). If you breed two platinum foxes and produce 12 offspring, how many of each of the following phenotypes do you expect?Is the P allele acting as a dominant lethal or a recessive lethal in foxes?
Individuals whose genotype is represented by the alleles Aa are described genotypically as _____.A. heterozygousB. dihybridC. homozygousD. homologousE. dominant
In cats, the hair can be either short or long (angora). A cat fancier made the following crosses with results shown below:a. Which phenotype is dominant?b. What are the genotypes of the parents and offspring of the crosses?c. If the short-haired offspring from cross 3 were bred to their short parent, what kinds of kittens would be expected and in what proportions?d. If the short-haired offspring from cross 3 were bred to the short-haired parent ofcross 2, what kinds of kittens would be expected and in what proportions?
Imagine that two unlinked autosomal genes with simple dominance code in goats for size where L is large and l is small, where B is brown and b is white. If a small white male goat mates with a large, brown female goat of an unknown genotype, what is the probability that they would produce small, white offspring.
Consider the following cross: (P1) A/a ; B/b ; C/c ; D/D ; E/e x (P2) a/a ; b;b ; C/C ; D/d ; E/e(a) What proportion of the progeny will phenotypically resemble Parent 1? Show your calculations.(b) How many different progeny genotypes would result from this cross?
In the garden pea, Mendel studies independent assorting genes and found that purple flowers (P) are dominant over white (p) and axial flowers (A) are dominant over terminal flowers (a). If a pure-breeding white, axial plant is crossed to a pure-breeding purple, terminal plant:A. What are the genotypes of the P1?B. What are the phenotypes and ratios predicted in the F1 and F2 from selfed F1? Show your work.