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Genetics Practice Problems
Name_________________________
Date ______ Period____Group____
Introductory Problems
1. If black coat color is dominant and white is recessive, what symbol should you assign
to the black allele? ______ & the white allele? _____
2. Using the above alleles, what is the genotype for an individual who is:
Homozygous dominant_________
Heterozygous__________
Homozygous recessive__________
o Which of the above genotypes are pure-breeding (if you cross two parents that look a
certain way, the offspring will all come out like the parents) :__________________
o Which of the above genotypes are not pure-breeding:_______________________
3. What is another word for phenotype? ___________________________________
4. What would the phenotype be for an individual whose genotype is:
a. BB:________________ bb:________________ Bb:___________________
5. Define the following terms:
a. P1 generation:_______________________________________________
b. F1 generation:_______________________________________________
c. F2 generation:_______________________________________________
6. List all of the possible alleles which can be passed on in a gamete by a parent with the
following genotypes:
a ) BB: _________
b ) bb: __________
c ) Bb: __________
7. Where do you write the possible gametes that a parent can create on the Punnett
Square?
Black coat color is dominant in guinea pigs and white is recessive. An individual who is
homozygous dominant for black coat is crossed with an individual who is homozygous
recessive for white coat. What will the genotypes and phenotypes of the F1 generation
be? (HINT: figure out parents’ alleles first, then use a Punnett Square)
8. Allele(s) of homozygous dominant black parent: ________________________
9. Allele(s) of homozygous recessive white parent: ________________________
Punnett Square:
10. Using the Punnett square that you just made, list the genotypes(s) of the F1
generation: _________________________________
11. Phenotypes(s) of the F1 generation: _________________________________
12. If 2 individuals from that F1 generation mate, what will the genotypes for the F1 cross
be? ________________ X ________________
13. What would their phenotypes be? __________________ X _________________
14. What allele(s) could each parent pass on? ________________________________
15. Draw the Punnett Square for the F1 cross just described:
16. What genotype(s) will the F2 generation have? __________________________
17. What % of the F2 generation will be homozygous dominant? _______%
18. What % of the F2 generation will be heterozygous? _______%
19. What % of the F2 generation will be homozygous recessive? _______%
20. What is the ratio of genotypes? _________ : _________ : _________
21. What phenotypes will the F2 generation have? ____________________________
22. What % of the F2 generation will show the dominant phenotype? ________%
23. What % of the F2 generation will show the recessive phenotype? ________%
24. What is the ratio of phenotypes in the F2 generation? _______ : _______
Co-Dominance and Multiple Alleles
25. How many phenotypes will result from a cross involving codominance? _______
26. What will the heterozygous offspring look like in codominance? __________________
_____________________________________________________________________
27. In shorthorn cattle, when a red bull (RR) is crossed with a white cow (WW), the
offspring are roan (intermingled red and white hairs). Show the Punnett Square to
illustrate this cross.
28. Why couldn’t the rancher simply breed 2 roan cattle if they wanted to establish a herd
of only roans? (refer to Punnett Square above) _____________________________
29. What does “multiple alleles” mean? ________________________________________
_______________________________________________________________________
30. How many phenotypes result from multiple alleles? ________________________
31. List all possible genotypes which would give the blood type phenotypes listed:
a) Type A: ___________________
c) Type AB: __________________
b) Type B: ___________________
d) Type O: ___________________
32. What are the possible blood types of children in these families?
a) Type A mother, Type A father: ______________________________________
b) Type A mother, Type O Father: _____________________________________
c) Type B mother, Type AB father: _____________________________________
d) Type AB mother, Type AB father: ___________________________________
e) Type A mother, Type B father: ______________________________________
Sex-Linked and Polygenic Traits
33. What does “polygenic inheritance” mean? ___________________________________
_____________________________________________________________________
34. Give two examples of human traits governed by polygenic inheritance:
a) _________________ b) ________________
35. On which chromosome is an X-linked trait located? ________________________
36. Which parent is the carrier of an X-linked trait? ___________________________
37. How many “disease” alleles of a disease caused by a recessive X-linked gene does:
d. a man need to be affected: ______
e. a woman need to be affected: ______
f. a woman need to be a carrier: ______
38. How do you write the allele for a normal X-linked gene? ____________________
39. How do you write the allele for a disease-causing X-linked gene? _____________
40. List all possible alleles which individuals with the following genotypes could pass on to
their offspring:
g. XNY: ____________________
d. XNXN: _____________________
n
h. X Y: ____________________
e. XNXn: _____________________
n
n
i. X X : ___________________
41. Red-green color blindness is inherited as an X-linked recessive trait. If a color-blind
woman marries a man who has normal vision, what would be the expected genotypes
and phenotypes of their children? (answer in percentages).
42. Illustrate with a Punnett Square.
Pedigree Problems
43. What is a pedigree? ____________________________________________________
44. In cattle, the polled (hornless) trait is dominant and horned is recessive. A certain
polled bull is mated to three cows.
Cow A, which is horned, gives birth to a polled calf.
Cow B, also horned, produces a horned calf.
Cow C, which is polled, produces a horned calf.
What are the genotypes of the four parents & the calves? DRAW A PEDIGREE (flow
chart) BELOW to illustrate the problem & fill in the genotypes:
45. Both Mrs. Smith and Mrs. Jones had babies the same day in the same hospital. Mrs.
Smith took home a baby girl, Shirley. Mrs. Jones took home a baby girl, Jane. Mrs.
Jones began to suspect, however, that her child had been accidentally switched with
the Smith baby in the nursery. Blood tests were made. Mr. Smith was Type A. Mrs.
Smith was type B. Mr. Jones was type A. Mrs. Jones was Type A. Shirley was type O,
and Jane was Type B.
Had a mix-up occurred? ______ Illustrate with two pedigree charts that include genotypes:
Dihybrid Cross Problems
46. What is a dihybrid cross? ________________________________________________
_______________________________________________________________________
47. How do you know by looking at the genotype that it is dihybrid?
48. List the possible alleles in the gametes from a parent with the following genotypes:
a) BBDD: ____________________
f) Bbdd: ______________________
b) BbDD: ____________________
g) bbDD: _____________________
c) BBDd: _____________________
h) bbDd: ______________________
d) BbDd: _____________________
i) bbdd: _______________________
e) BBdd: _____________________
49. What is the typical phenotype ratio of offspring in a dihybrid cross?