Download GENETICS PROBLEMS WORKSHEET

GENETICS PROBLEMS WORKSHEET (I)
► First and second laws
1. In guinea pigs, curly hair (H) is dominant over straight hair (h). Work out the F1 and F2 generations of a cross between a
homozygous curly haired guinea pig and a homozygous straight haired guinea pig. Include all possible genotypes and
phenotypes.
2. In the pea plant, tall stem (T) is dominant over dwarf stem (t). A homozygous tall stem plant is crossed with a homozygous
dwarf stem plant. Discuss genotypes and phenotypes of F1 and F2 generations.
3. The light color of the eyes in humans is a recessive trait while the dark color of the eye is dominant. Both parents of a child
with light color eyes have dark color eyes; how are their genotypes?
4. In the cross of two black flies 216 black descendants and 72 white descendants are obtained. Black color is dominant in this
species. Explain the genotype of the flies that have been crossed and explain the obtained offspring.
5. In fruit flies, long wings (L) is dominant over vestigial wings (l). If a vestigial winged fly is crossed with a homozygous long
winged fly, what genotype and phenotype possibilities are expected in the F1 and F2 generations?
6. The color of the body of a species of bumblebee is determined by two alleles: A  grey; a black; A>a. Explain the
genotypes of the parents and the offspring in the following crosses:
a) grey X black  45 grey
b) grey X black  30 grey and 21 black
c) grey X grey  50 grey and 16 black
d) black X black  62 what color?
7. In cattle, the hornless condition (H) is dominant and the horned condition is recessive. A bull without horns is crossed with
three different cows:
a) a horned cow that delivers a hornless calf
b) a horned cow that delivers a horned calf
c) a hornless cow that delivers a horned calf
What are the genotypes of the four parents?
8. Black hair (G) is dominant over white hair (g) in guinea pigs. A heterozygous black haired male is mated with a white female.
Write the genotype for each of the guinea pigs, set up a Punnett square and show all possible genotypes that could result from
the union of these two guinea pigs.
► Intermediate inheritance
9. In some cases the dominance of an allele is not complete over the other, we talk then of co-dominant alleles and intermediate
inheritance. In the Andalucian chicken we can find individuals with white feathers, individuals with black feathers and “blue”
individuals (in fact they have black and white feathers). If we cross two “blue” individuals…, how will be their descendants?
What proportions will we find of each type?
10. In certain plant of the desert two varieties can be found one with white flowers and another one with violet flowers. The F2
generation of a cross of the two varieties resulted in 1 plant with violet flowers, 2 plants with light violet flowers and 1 plant with
white flowers. Make a diagram with the cross and explain the type of inheritance.
11. In the plant Mirabilis jalapa we can find individuals with red flowers, individuals with white flowers and individuals with pink
flowers. In the cross of two plants with pink flowers we obtain 49 plants with red flowers, 98 plants with pink flowers and 49
plants with white flowers. Explain why and make a diagram with the cross.
► Testcross
12. Black hair (G) is dominant over white hair (g) in guinea pigs. What would be the best way to find out if a black female guinea
pig is homozygous or heterozygous for the trait of the color of the hair?
13. A black male guinea pig and a black female guinea pig had a male black descendant and we need to find out if it is
homozygous or heterozygous. With which type of female should we cross it? Explain the reason.
► Human inheritance of the sex
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14. A human couple has 6 male children. What is the probability that the 7 child is also a male?
15. What is the chance of a woman and her husband having 6 daughters in a row?
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16. A human couple has 6 children, 2 sons and four daughters. If the woman gives birth to a 7 child, what is the probability that
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the 7 child will be a son?
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► Basic concepts and 1 and 2
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laws revisited
17. Two plants are mated and 250 offspring are phenotypically classified. 61 plants display the recessive phenotype and 189
plants display the dominant phenotype. Assuming classical Mendelian patterns of inheritance, what are the most likely
genotypes of the parent plants?
a) heterozygous and heterozygous
b) recessive and heterozygous
c) recessive and homozygous dominant
d) heterozygous and homozygous dominant
e) homozygous dominant and homozygous dominant
f) recessive and recessive
18. Mate the following statements with the concepts they define:
1. The genetic makeup of an organism
2. Part of a chromosome that codes for a certain hereditary trait
3. The outward, visible expression of the hereditary makeup of an organism
4. The shifting of gene positions in chromosomes
5. A sequence of three adjacent nucleotides that codes for a single amino acid
6. The condition where two inherited alleles are different
7. One of several varieties of a gene
8. The condition where two inherited alleles are the same
9. The place in a chromosome where certain gene can be found
● A) Heterozygous
● B) Crossover
● C) Locus
● D) Genotype
● E) Phenotype
● F) Gene
● G) Allele
● H) Codon
● I) Homozygous
19. One hundred and twenty offspring are counted in a genetic cross. Ninety appear to show the dominant phenotype and thirty
appear recessive. What are the most likely genotypes of the parents?
a) AA and aa
b)Aa and aa
c) Aa and Aa
d) aa and aa
e) Aa and AA
20. B and b represent, respectively, the dominant and the recessive alleles of a gene pair. Half of the F1 generation expresses
the recessive condition, and the other half expresses the dominant condition. What are the most likely genotypes of the P
generation?
a) Bb and bb
b) BB and bb
c) BB and Bb
d) Bb and Bb
e) bb and bb
► Sex-linked inheritance
21. In humans hemophilia is a disease produced by a defective recessive gene whose locus is in the X chromosome. A normal
woman whose father was a hemophiliac marries a normal man. a) Determine the genotype of the woman and the man. b)
Determine the possible genotypes for their children. c) What percent of male and female children would be hemophiliacs? d)
What percent normal? e) Would any be carriers?
22. In humans color blindness is a disease produced by a defective recessive gene whose locus is in the X chromosome. What
proportion of genotypes do we expect in the descendants of a color blind man and a carrier woman? If they have eight children,
how many of them will be color blind?
If you cannot see a number in the drawing on the left you could be color blind
23. What percent of color blind children do we expect from the following couples?
a) A color blind woman and a normal man
b) A normal non-carrier woman and a color blind man
c) A color blind woman and a color blind man
24. The Lesch-Nyhan syndrome is produced by a recessive gene sex-linked to chromosome X. It is characterized by
neurological and behavioral abnormalities and the overproduction of uric acid. Self-injury (including biting and head banging) is
the most common and distinctive behavioral problem in individuals with Lesch-Nyhan syndrome. Determine the possible
genotypes and phenotypes of the children of a carrier woman and a normal man.
► Lethal genes
25. We call lethal genes to those that produce the death of the individual who have them. In most of the cases they are the
cause of a natural abortion and the individual dies before it is born. a) Why these alleles are usually recessive and the normal
alleles dominant? Some geneticists have calculated that every single human being is carrier of maybe 30 lethal genes in
heterozygosis. b) What relationship can it have with the increased probability of abortion in consanguineous marriages?
26. If a woman is carrier of a recessive lethal gene in one of her X chromosomes, discuss how her children will be if she marries
with a normal man.
27. When the genes do not produce death directly but reduce significantly the life expectancy are called deleterious genes.
Huntington's disease (HD) is a neurodegenerative genetic disorder that affects muscle coordination and leads to cognitive
decline and behavioral symptoms. It typically becomes noticeable in mid-adult life. HD is the most common genetic cause of
abnormal involuntary writhing movements called chorea, which is why the disease used to be called Huntington's chorea. HD
is produced by an autosomal dominant allele in chromosome 4. Discuss the probability of developing the disease in an
individual whose mother had HD.
► Family tree (=pedigree chart)
28. In the human eyes brown color is dominant over blue color. Determine the genotypes of all the members of these family.
29. A woman with brown eyes, which has two brothers, marries a man with brown eyes, which has a brother and two sisters,
and produces a boy with brown eyes. When their son marries a woman with blue eyes, they have a girl with blue eyes. All of the
boy’s aunts and uncles have brown eyes, as do his grandparents. However, his mother, the little girl’s grandmother, has an
uncle with blue eyes. Trace the family history of eye color and determine how the little girl could have blue eyes.
30. A human couple, without any known problem in the eyes, has four children:
a) a normal daughter, that has a normal son and a son and a daughter that are both color blind.
b) a normal daughter, that has three sons and one daughter, all normal sighted.
c) a color blind son, that has two normal sighted daughters.
d) a normal son, that has two daughters and one son, all normal sighted.
Draw the family tree and write on it the probable and certain genotypes.
► Multiple allelism: the inheritance of blood groups
31. In humans there are four phenotypes for the blood group: A, B, AB and 0. They are produced by the diploid combinations of
A
B
three different alleles: the allele I determines blood type A, the allele I determines blood type B and the allele i determines
A
B
blood of type 0. I and I are co-dominant while the allele i is recessive. Make a table with the correspondence between the
possible genotypes and phenotypes in the AB0 system.
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32. In humans the blood type Rh is determined by a dominant allele (D) while the blood type Rh is determined by a recessive
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allele (d). Explain the genotypes and phenotypes of the children of this cross AB Rh and 0 Rh .
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33. A man with blood type A Rh and a woman with blood type B Rh have five children:
a) Lorenzo with blood type A Rh
b) Catalina with blood type AB Rh
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c) Julia with blood type 0 Rh
d) Fidel with blood type B Rh
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e) Alfonso with blood type 0 Rh
Explain the genotypes of the parents and decide if any of the children is adopted.
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34. Rodolfo with blood type AB Rh and Ada with blood type 0 Rh have the following children: Richard that is AB+; Cecilia that
is 0-; Adriano that is A+; Marcial that is B+ and Azucena that is 0+. What are the adopted children?
35. According the data of the previous problem it is true that:
a) Adriano cannot donate blood to his brother Marcial
b) Azucena can donate blood to her sister Cecilia
c) Cecilia and Ada could have different genotype
d) Rodolfo cannot receive blood from any of his children
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► The 3 law
36. In an animal commonly used in the lab the trait “spotted skin” (A) is dominant over the trait “solid color” (a) and the trait
“black color” (B) is dominant over “brown color” (b). Work out the genotypes and phenotypes of the F1 and F2 of the cross
AABB X aabb.
37. According the data of the previous problem find out the phenotypes and genotypes of the following cross: AaBb X aabb.
38. In Pisum sativum the trait “tall stem” (A) is dominant over the trait “dwarf stem” (a) and the trait “smooth seed” (B) is
dominant over the trait “wrinkled seed” (b) .
a) What proportions can be expected in the phenotypes of the F2 of the cross AAbb X aaBB?
b) What proportions can be expected in the phenotypes of the F1 of the cross AaBb X aabb?
39. In an insect of laboratory the allele “long wings” (L) is dominant over the allele “short wings” (l) and the allele “hairy antenna”
(H) is dominant over the allele “smooth antenna” (h). What will be the probability of obtaining the following results?
a) a gamete Lh from an individual LLHh.
b) a gamete LH from an individual LlHh.
c) an individual LLHH in the F1 of the cross llhh X LLHH.
d) an individual LLHH in the F1 of the cross LlHh X LlHh.
e) an insect with long wings and hairy antennas in the F1 of the cross llhh X LLHH.
f) an insect with long wings and hairy antennas in the F1 of the cross of both di-hybrid parents.
g) an insect with long wings and smooth antennas of the cross LlHh X LlHh.
40. In humans, cataract and osteogenesis imperfecta (= brittle bone disease) are both produced by dominant alleles whose loci
are in different chromosomes. A man with cataract and normal bones, whose father had normal eyes, marries a woman with
normal eyes but with osteogenesis imperfecta, although her father had normal bones. What is the probability that the first child
of this couple has:
a) none of these diseases.
b) cataract and normal bones.
c) osteogenesis imperfecta but normal eyes.
d) both of these diseases.
41. A woman with genotype AaBb marries a man with genotype AABb. Assuming independent assortment and random
recombination, what is the chance that the child will phenotypically express the recessive allele for both genes?
► Miscellanea
42. When a homozygous recessive organism is crossed with a heterozygous organism, what percent of the progeny will be
heterozygous?
43. A testcross:
a) determines whether a dominant-appearing individual is homozygous dominant or heterozygous for the trait.
b) suggests that the unknown dominant-appearing individual is homozygous if any of the offspring of the testcross are
recessive.
c) suggests that the unknown dominant-appearing individual is heterozygous if none of the offspring of the testcross are
recessive.
d) is used to determine whether an individual is homozygous dominant or homozygous recessive for a given trait.
e) is used to determine whether or not a trait is sex-linked.
44. In humans, tongue rolling is a dominant trait and those with the recessive condition cannot roll their tongues. Arturo can roll
his tongue, but his mother could not. He mates with Graciela who cannot roll her tongue. What is the probability that their first
born child will not be able to roll his tongue?
45. As a genetic advisor to a hospital you are confronted with the following problem: two women had babies in the hospital at
about the same time on the same day. Mrs. Cartman took home a boy (Eric), and Mrs. Simpson took home a girl (Lisa).
However, in her postpartum daze, Mrs. Simpson thought she recalled the delivery room nurses commenting on her child as
being a boy. The blood types of all concerned parents were determined as follows:
Mr. Cartman = B; Mrs. Cartman = AB; Eric = A;
Mr. Simpson = B; Mrs. Simpson = O; Lisa = O;
Has there been an interchange of babies? Support your conclusion or be fired.
46. An organism with genotype QqRr only produces two different gametes genotypes QR and qr. This violates which principle of
the mendelian genetics?
a) codominance
b) dominance
c) independent assortment
d) linkage
e) segregation
47. In Pisum sativum purple flowers is dominant over white flowers (P > p) and round seeds are dominant to wrinkled seeds
(R > r). Consider the following crosses and answer the questions.
a) Pprr X ppRr; how many offspring are purple with wrinkled seeds?
b) ppRR X Pprr; how many offspring are purple with round seeds?
c) pprr X PpRr; how many offspring are white with wrinkled seeds?
48. In a common garden plant the trait “long leaf” (L) is dominant over the trait “short leaf” (l) but the color of the flowers follows
an intermediate inheritance finding plants with red, white and pink flowers. In the cross of a long leafed homozygous plant with
red flowers and a short leafed plant with white flowers, what will be the proportions of the different genotypes and phenotypes in
F1 and F2?
49. Pfeiffer syndrome is a dominant genetic disease that occurs when certain bones in the skull fuse too early in the
development of a child, leading to distorted head and face shape. If a man heterozygous for the allele that causes Pfeiffer
syndrome marries a woman who is homozygous for the non-mutant allele, what is the chance that their first child will have this
syndrome?
50. In certain plants called snapdragons, the heterozygous phenotype is a blend of the two homozygous phenotypes.
Homozygous dominant plants are red, heterozygous plants are pink, and homozygous recessive plants are white. What type of
inheritance pattern is this? (a) complete dominant (b) codominance (c) incomplete dominante (d) none of the above