GENETICPROBLEMS

Question 1

• How many different kinds of gametesgametes could the following individuals produce?

1.1. aaBbaaBb2.2. CCDdeeCCDdee3.3. AABbCcDDAABbCcDD4.4. MmNnOoPpQqMmNnOoPpQq5.5. UUVVWWXXYYZzUUVVWWXXYYZz

Answer

• Remember the formulaRemember the formula 22nn

• WhereWhere n = # of heterozygousn = # of heterozygous

1.1. aaaaBbBb = 2= 22.2. CCCCDdDdeeee = 2= 23.3. AAAABbCcBbCcDDDD = 4= 44.4. MmNnOoPpQqMmNnOoPpQq = 32= 325.5. UUVVWWXXYYUUVVWWXXYYZzZz = 2= 2

Question 2

• In dogs, In dogs, wire-hairedwire-haired is due to a is due to a dominant gene dominant gene (W),(W), smooth-hairedsmooth-haired is due to its recessive allele is due to its recessive allele (w)(w)

• WW, Ww WW, Ww = wire haired= wire haired

• wwww = smooth haired= smooth haired

Answer

If a If a homozygous wire-hairedhomozygous wire-haired dog is mated dog is mated with a with a smooth-haired dogsmooth-haired dog, what type of , what type of

offspring could be producedoffspring could be produced

WWww

WWww WWww

WWwwFF11 generation generation

all heterozygousall heterozygous

W WW W

ww

ww

Question 3

• What type(s) of offspring could be produced in What type(s) of offspring could be produced in the the FF22 generation generation??

• Must breed the Must breed the FF11 generation generation to get the to get the FF22..

• Ww x WwWw x Ww

Answer

W wW w

W WW WwW WW Ww FF22 generation generation

w Ww www Ww ww

genotype: 1:2:1 ratiogenotype: 1:2:1 ratiophenotype: 3:1 ratiophenotype: 3:1 ratio

Question 4

• Two Two wire-haired dogswire-haired dogs are mated. Among the are mated. Among the offspring of their first litter is a offspring of their first litter is a smooth-haired smooth-haired puppup..

• If these, two If these, two wire-haired dogswire-haired dogs mate again, what mate again, what are the chances that they will produce another are the chances that they will produce another smooth-haired pupsmooth-haired pup??

• What are the chances that the pup will What are the chances that the pup will wire-wire-hairedhaired??

Answer

W wW w

W WW WwW WW Ww FF22 generation generation

w Ww www Ww ww

-- 1/4 or 25% chance for smooth-haired1/4 or 25% chance for smooth-haired- 3/4 or 75% chance for wire-haired- 3/4 or 75% chance for wire-haired

Question 5

• A A wire-hairedwire-haired male is mated with a male is mated with a smooth-hairedsmooth-haired female. The mother of the female. The mother of the wire-hairedwire-haired male was male was smooth-hairedsmooth-haired..

• What are the What are the phenotypesphenotypes and and genotypesgenotypes of the pups they could produce?of the pups they could produce?

• Breed: Ww x wwBreed: Ww x ww

Answer

W wW w

w Ww www Ww ww

w Ww www Ww ww

phenotypes: 2:2 ratiophenotypes: 2:2 ratiogenotypes:genotypes: 2:2 ratio2:2 ratio

Question 6

• In snapdragons, In snapdragons, red flower (R)red flower (R) color is color is incompletely dominant over incompletely dominant over white flower (r)white flower (r) color.color.

• The The heterozygous (Rr)heterozygous (Rr) plants have plants have pinkpink flowers.flowers.

RR RR - red flowers- red flowers

Rr Rr - pink flowers- pink flowers

rr rr - white flowers- white flowers

Question 6

• If a If a red-flowered plantred-flowered plant is crossed with a is crossed with a white-white-flowered plantflowered plant, what are the , what are the genotypesgenotypes and and phenotypesphenotypes of the plants of the plants FF11 generation generation??

• RRRR x x rr rr

Answer

R RR R

rr Rr RrRr Rr FF11 generationgeneration

r r Rr RrRr Rr

phenotypes:phenotypes: 100% 100% pinkpinkgenotypes:genotypes: 100% 100% heterozygousheterozygous

Question 7

• What What genotypesgenotypes and and phenotypesphenotypes will be will be produced in the produced in the FF22 generation generation??

• Rr Rr x x RrRr

Answer

R rR r

RR RRRR Rr Rr FF22 generationgeneration

rr RrRr rrrr

phenotypes: 1:2:1 ratiophenotypes: 1:2:1 ratiogenotypes: 1:2:1 ratiogenotypes: 1:2:1 ratio

Question 8

• What kinds of offspring can be produced if a What kinds of offspring can be produced if a red-flowered plantred-flowered plant is crossed with a is crossed with a pink-pink-flowered plantflowered plant??

• RRRR x x RrRr

Answer

R R

R RR RR

r Rr Rr

50%: red flowered50%: pink flowered

Question 9

• What kind of offspring is/are produced if a What kind of offspring is/are produced if a pink-flowered plantpink-flowered plant is crossed with a is crossed with a white-white-flowered plantflowered plant??

• Rr Rr x x rr rr

Answer

R r

r Rr rr

r Rr rr

50%: white flowered50%: pink flowered

Question 10

• In humans, In humans, colorblindness (cc)colorblindness (cc) is a recessive is a recessive sex-linked traitsex-linked trait..

• Remember:Remember: XX - femaleXX - female

XY - maleXY - male

Question 10

• Two Two normal peoplenormal people have a have a colorblind colorblind sonson..

• What are the What are the genotypesgenotypes of the parents? of the parents?

• XXCCXX_?_? x x X XCCYY

• What are the What are the genotypesgenotypes and and phenotypesphenotypes possible among their other children?possible among their other children?

Answer

XXCC Y Y parents parents

XXCC X XCCXXCC X XCCYY

XXcc X XCCXXcc XXccYY

50%: female (one normal, one a carrier)50%: female (one normal, one a carrier)50%: male (one normal, one colorblind)50%: male (one normal, one colorblind)

Question 11

• A couple has a A couple has a colorblindcolorblind daughter. daughter.

• What are the possible What are the possible genotypesgenotypes and and phenotypesphenotypes of the parents and the daughter? of the parents and the daughter?

Answer

XXcc Y Y

XXCC X XCCXXcc X XCCYY

XXcc XXccXXcc XXccYY

parents: parents: XXccYY and and XXCCXXcc or or XXccXXcc

father father colorblindcolorblind

mother mother carriercarrier or or colorblindcolorblind

daughter: daughter: XXccXXcc - colorblind - colorblind

Question 12

• In humans, the presence of In humans, the presence of frecklesfreckles is due to a is due to a dominant gene dominant gene (F)(F) and the and the non-frecklednon-freckled condition is due to its recessive allele condition is due to its recessive allele (f).(f).

• Dimpled cheeks (D)Dimpled cheeks (D) are dominant to are dominant to non-non-dimpled cheeks (d).dimpled cheeks (d).

Question 12

• Two persons with Two persons with frecklesfreckles and and dimpleddimpled cheekscheeks have two children: one has have two children: one has frecklesfreckles but but no no dimplesdimples and one has and one has dimplesdimples but but no frecklesno freckles..

• What are the What are the genotypesgenotypes of the parents? of the parents?

Parents:Parents: FF__DD__ x F x F__DD__

Children: F_Children: F_dd dd x x ffffD_D_

ff ffd d dd

Question 12b

• What are the possible What are the possible phenotypesphenotypes and and genotypesgenotypes of the children that they could of the children that they could produce?produce?

• Breed:Breed: FfDd x FfDd FfDd x FfDd

• This is a This is a dihybrid crossdihybrid cross

Answer

• Possible gametes for both: FD Fd fD fdPossible gametes for both: FD Fd fD fd

FD FD Fd fD fd Fd fD fd

FD FD FFDD FFDd FfDD FfDdFFDD FFDd FfDD FfDd

Fd Fd FFDd FFDd FFddFFdd FfDd FfDd FfddFfdd

fD fD FfDD FfDd FfDD FfDd ffDD ffDdffDD ffDd

fd fd FfDd FfDd FfddFfdd ffDdffDd ffddffdd

Answer 12b

PhenotypePhenotype Freckles/Dimples:Freckles/Dimples: 99

Freckles/no dimples:Freckles/no dimples: 33

no freckles/Dimples:no freckles/Dimples: 33

no freckles/no dimples:no freckles/no dimples: 1 1

Phenotypic ratio will always be 9:3:3:1 Phenotypic ratio will always be 9:3:3:1 for dihybrid crosses.for dihybrid crosses.

Answer 12b

Genotypic ratio:Genotypic ratio: FFDDFFDD - 1- 1FFDdFFDd - 2- 2FFddFFdd - 1- 1FfDDFfDD - 2- 2FfDdFfDd - 4- 4FfddFfdd - 2- 2ffDDffDD - 1- 1ffDdffDd - 2- 2ffddffdd - 1- 1

Question 13

• What are the chances that they would have a What are the chances that they would have a child whom lacks both child whom lacks both frecklesfreckles and and dimplesdimples??

• This child will have a genotype of This child will have a genotype of ffddffdd

• Answer:Answer: 1/161/16

Question 14

• A person with A person with frecklesfreckles and and dimplesdimples whose whose mother lacked both mother lacked both frecklesfreckles and and dimplesdimples marries a person with marries a person with frecklesfreckles but not but not dimplesdimples whose father did not have whose father did not have frecklesfreckles or or dimplesdimples..

• Breed:Breed: FfDdFfDd x x FfddFfdd

• Possible gametesPossible gametes: : FD Fd fD fdFD Fd fD fd x x Fd fdFd fd

Question 15

• In dogs, the inheritance of hair color involves In dogs, the inheritance of hair color involves a a gene Bgene B for for black hairblack hair and and gene bgene b for for brown brown hair bhair b..

• A A dominant Cdominant C is also involved. It must be is also involved. It must be present for the present for the colorcolor to be synthesized. to be synthesized.

• If this gene is not present, a If this gene is not present, a blondblond condition condition results.results.

BB, Bb - black hairBB, Bb - black hair CC, Cc - colorCC, Cc - color

bbbb - brown hair - brown hair cccc - blond - blond

Question 16

• A A brownbrown haired male, whose father was a haired male, whose father was a blondblond, is mated with a , is mated with a blackblack haired female, haired female, whose mother was whose mother was brownbrown haired and her haired and her father was father was blondblond..

Male: Male: bbCc (gametes: bC bc)bbCc (gametes: bC bc)

Female: Female: BbCc (gametes: BC Bc bC BbCc (gametes: BC Bc bC bc)bc)

• What is the expected ratios of their puppies?What is the expected ratios of their puppies?

Answer 16

BCBC Bc Bc bC bC bcbc

bCbC BbCC BbCc bbCC bbCc BbCC BbCc bbCC bbCc

bcbc BbCc Bbcc bbCc bbcc BbCc Bbcc bbCc bbcc

Offspring ratios:Offspring ratios:Black:Black: 3/83/8Brown:Brown: 3/83/8Blond:Blond: 2/8 or 1/42/8 or 1/4

Question 17

• Charlie Chaplin, a film star, was involved in a Charlie Chaplin, a film star, was involved in a paternitypaternity case. The woman bringing suit had case. The woman bringing suit had two children, on whose two children, on whose blood type blood type waswas A A and the and the other whose other whose blood type blood type waswas B B..

• Her Her blood typeblood type was was OO, the same as Charlie ’s!, the same as Charlie ’s!

• The judge in the case awarded damages to the The judge in the case awarded damages to the woman, saying that Charlie had to be the father woman, saying that Charlie had to be the father of at least one of the children.of at least one of the children.

Answer 17

• Obviously, the judge should be sentenced to Obviously, the judge should be sentenced to BiologyBiology. For Charlie to have been the father of . For Charlie to have been the father of both children, his both children, his blood typeblood type would have had to be would have had to be what?what?

IIAA I IBB Answer Answer

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