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Name_________________________________Date_______________Period_______
Genetics Exam Review – KEY
Note: Most of the problems are answered, however due to the nature of the Punnett
squares it is difficult to produce the answers in a Word document.
Gregor Mendel
Nucleotides
Egg
Absent
Parent
Heredity
Recessive
N
Offspring
Haploid
Gametes
Traits
Pea Plants
Meiosis
2N
Sperm
Dominant
Zygote
Diploid
Half
1. Genetics is the study of heredity
2. Heredity is defined as the passing of traits from parent to their offspring
3. Skin, nerve, and muscle cells are classified as autosomal cells or body cells and possess a full set of
chromosomes. Diploid or(2N).
4. Fertilization is the union of a sperm and an egg to form a zygote, or
a fertilized egg. Reproductive cells are called gametes.
5. Gametes must have half the number of chromosomes, or one chromosome from each pair.
Cells with half the number of chromosomes are called haploid (N).
6. In order for cells to become haploid, cells undergo a division process called meiosis.
7. Gregor Mendel is the “Father” of modern genetics, who grew
Pea Plants to understand important concepts of genetics and heredity.
8. dominant- stronger of two genes expressed, will be visible if present; represented
by a capital letter.
9. recessive- describing a trait that is hidden by a dominant trait; can only be
expressed when the dominant gene (allele) is absent.
10. In a litter of kittens, some are black and some are brown. The kittens have different traits because their
DNA contains different arrangements of nucleotides.
Name Mendel’s three laws of inheritance and define them.
1. Principle of Dominance – dominant trait hides or masks the recessive trait
2. Law of Segregation – when gametes form, the two alleles responsible for the
individual’s traits separate from each other; the alleles then recombine in fertilization
3. Law of Independent Assortment - Alleles for different traits are distributed to sex cells
independently of one another.
10. Definea. Allele:
How are alleles represented?___________________________________
b. Gene:
c. Genotype:
d. Phenotype:
e. trait –
List any 3 traits of the pea plant we crossed-_________________________________________
____________________________________________________________________________
List traits of the humans we crossed- ______________________________________________
List traits of the cats we crossed - ________________________________________________
____________________________________________________________________________
11. If the gene pairs are identical, a person is called___homozygous
12. If the gene pairs are different, a person is called___heterozygous.
Place the following genotypes in the correct category: (some will be used more than once)
Cc, HH, gg, Ii, PP,dd, Aa, Ww, Ff, uu, pure, mixed, hybrid, true-breeding
a. Homozygous dominant – HH, PP, pure, true-breeding
b. Homozygous recessive – gg, dd, uu, pure, true-breeding
c. Heterozygous –Cc, Ii, Aa, Ww, Ff, mixed, hybrid
Genetics Problems:
13. Name the 6 steps to follow when working monohybrid genetic problem:
1.
2.
3.
4.
5.
6.
trait
alleles
cross
punnett square
genotype
phenotype
Name the additional step used when working Dihybrid problems find the gametes 2n, FOIL
(Mendelian) COMPLETE DOMINANCE: One trait is completely dominant over the other.
14. In pea plants, round seed shape (R) is dominant to wrinkled seed shape (r).
a. A homozygous (true-breeding) round plant would have what genes for this trait? RR
b. What is the phenotype for a plant with the genotype Rr? round
15. Define Parental Generation (P1) first cross in a breeding experiment, typically true-breeding of
homozygous dominant trait with a homozygous recessive trait
a. Write an example of a P1 cross using the alleles in question 14. RR x rr
Work the P1 showing all steps.
Trait: seed shape
Alleles: R-round, r-wrinkled
Cross: RR x rr
Punnett:
X
R
R
r
Rr
Rr
r
Rr
Rr
Genotypes:
RR – 0
Rr – 4
Rr – 0
100% Rr
Phenotypes
Round - 4
Wrinkled - 0
100% Round
d. The first generation offspring in a breeding experiment is called the F1 or first filial generation.
What is the genotype of the offspring in the F1 generation – 100% heterozygous or 100% Rr
What is the phenotype of the offspring in the F1 generation – 100% Round
Cross two members of the F1 showing all steps.
Trait: seed shape
Alleles: R-round, r-wrinkled
Cross: Rr x Rr
Punnett:
X
R
r
R
RR
Rr
r
Rr
rr
Genotypes:
RR – 1
Rr – 2
Rr – 1
25% RR
50% Rr
25% rr
Phenotypes
Round - 3
Wrinkled - 1
75% Round
25% wrinkled
What is the probability of this cross producing round seeds?75%
wrinkled seeds?25%
f. What is the name of the man that developed the grid system used in solving genetic crosses?
RC Punnett
A red-flowered plant was crossed with a white-flowered variation of the plant. All of the flowers on the next
generation of plants were red. Decide which flower color is recessive for this plant and which is dominant
Red is dominant over white, the white color was hidden by the red in the first generation, White must be
recessive
Answer the Question:
15. Cross two heterozygous parents, where Blue (B) is dominant to white (b), what are the phenotypic and
genotypic ratios of the F1 generation?
Cross: Bb X Bb
Punnett Square:
X
B
B
B
BB
Bb
b
Bb
bb
Phenotypic Ratio: 3:1 (F1 generation)
Genotypic Ratio: 1:2:1 (F1 generation)
16. TT x tt represent what generation?P1
17. What is the genotype of TT? homozygous dominant
18. What is the phenotype of TT? tall
19. What generation is represented by the cross Tt x Tt?First filial or F1
What is the genotypic ratio? (This type of cross has the same ratio every time!)
1:2:1
What is the phenotypic ratio? (same every time!) Are you starting to recognize it?
3:1
20. Explain monohybrid. A crossing of a single trait, helps to predict the potential offspring and the
probability of the offspring
21. Using gene symbols, give an example of monohybrid using the letter B. BB X bb
A particular variety of pea plant can produce axial flowers or terminal flowers. Axial is dominant. Terminal is
recessive. If a particular plant produces ONLY terminal flowers, its genotype
must be
aa - it must be homozygous recessive
22. Explain Dihybrid. A crossing of TWO traits
22. Using gene symbols, give any example of Dihybrid using the letters B and T. BbTt X BBTT
23. In the formula 2n = G, the “n” means number of heterozygous pairs in the parent
The “G” means number of gametes
24. To determine the possible allele pairs, use the FOIL method.
25. Tell the number of different gamete possibilities. Show the formula for each.
RRTt 21 = 2
RrTt 22 = 4
rrtt 20 = 1
26. Use the FOIL method to determine the gametes.
RRTt
Rt, Rt
RrTt
RT, Rt, rT, rt
rrtt
rt
27. What generation is the Dihybrid cross? RRtt x rrTT.
Parent since all traits are homozygous and the parents’ traits are opposite traits
28. In rabbits, the coat color black (B) is dominant over brown (b). Short hair is dominant (S) over long (s).
Show the seven steps for a cross between a homozygous black, heterozygous short-haired male and a brown
homozygous long-haired female.
Traits: coat color, hair length
Alleles: B-black, b= brown
S – short hair, s = long hair
Cross: BBSs x bbss
Gametes: BBSs – 21 = 2 BS, Bs
bbss - 20
bs
This will be a 2 x 1 cross. 2 gamete possibilities from male and one from the female.
X
BS
Bs
bs
BbSs
Bbss
30. A red-flowered plant was crossed with a white-flowered variation of the plant. All of the flowers on the
next generation of plants were red. Decide which flower color is recessive for this plant and which is
dominant. Show your work.
Repeat question
Use each of the terms below only once to complete the passage.
dihybrid
gene
genotypes
monohybrid
phenotypic ratio
A cross between plants that involves one characteristic is called a (31. ) monohybrid
cross. Mendel also performed (32. ) dihybrid crosses, which involve two
( 33 ) gene pairs, with pea plants. When he crossed two pea plants that were heterozygous for both
seed shape (Rr) and for seed color (Yy), he observed a 9:3:3:1 (34.) phenotypic ratio among the
seeds of the offspring.
A Punnett square shows the possible phenotypes and (35.) genotypes of the offspring
36.
RRYy
Round, yellow
37. What are the genotypes of the parents in this cross? RrYy X RrYy
38. What fraction of this cross will be recessive for both traits? Only 1/16 rryy
1/2
1/4
1/8
1/16
39. What is the phenotypic ratio for this cross. 9:3:3:1
(Hint:Notice both parents are heterozygous)
40. In cats, the allele for tabby (T) is dominant over the allele for stripeless (t). Two tabby cats are bred and
produce four offspring. Three are tabby and one is stripeless. What is the genotype and ratio of the offspring.
Show your work.
3 tabby, one stripeless means that the tabby cat bred were heterozygous for the trait.
Tt X Tt – produces 3 tabby and one stripeless
41. What is meant by incomplete dominance.neither trait is dominant over the other, a mixing or blend will
occur
42. Give an example. Show all steps.
43. Define Codominance-both traits are dominant, when mated both traits will be seen, the outcome is
typically spots or stripes
44. In chicken, black feather color(B) is codominant to white feather color (W). The heterozygous individual is
a combination of black and white feathers that results in a checkered pattern (BW) call erminette. Cross a
checkered chicken with a checkered chicken. Show all steps.
BB – black
WW – white
BW - erminette
BW X BW
Genotypes: BB – 1, WW – 1, BW - 2
Phenotypes black -1, white – 1, erminette - 2
45.What percentage of the offspring will be Black 25% White 25%
46. In man, polydactylism (an extra finger on each hand) is due to a dominant factor. When one parent is
polydactylous and the other normal, what proportion of their children would you expect to be polydactylous if
the polydactylous parent had a normal mother? P- polydactylous p-normal
P – polydactyl p – normal
Cross: Pp X pp
What percentage of the offspring will be normal? 50% What is the probability of having a normal child? 50%
What percentage of the offspring will be polydactylous? 50%
47. Can two brown-eyed people have a blue-eyed child? Show your work YES!
Bb XBb
What percentage of the offspring will have Brown eyes? 75%
What is the probability of having a child with Brown eyes? 3:1 or 3/4
What percentage of the offspring will have Blue eyes? 25%
What is the probability of having a child with Blue eyes? 1:3 or 1/4
48. A woman has a rare abnormality of the eyelids called ptosis, which makes it impossible to open her eyes
completely. The condition has been found to depend on a single dominant gene. (P)
The woman’s father has ptosis, but her mother had normal eyelids. Her father’s mother had normal eyelids.
P – ptosis
p - normal
PP, Pp will have ptosis
pp - normal
Father’s genotype – PP (he has to be) Mother’s genotype- pp Woman’s genotype – Pp (she had to get a p
from mom)
What proportion of the children she bears will have ptosis, if she marries a normal man?
Pp X pp
50% normal pp, 50% ptosis Pp