LABORATORY #5: Genetics Lab

Laboratory Exercise #5.3 Mendelian Genetics Problems

Complete all genetics problems. Do your work on a separate sheet of paper if more space is needed.

  1. A card is drawn from a deck of 52 cards. What is the probability the card:
  2. will be the ace of hearts?
  3. will be a king?
  4. will be a king or a seven?
  1. You roll a single dice (a die). What is the probability that you will roll:
  2. a number divisible by 3?

b. an even number?

  1. In a single throw of two dice, what is the probability that:
  2. a seven will appear?
  1. a doublet (two of the same number) will appear?
  1. an even and an odd number will appear?
  1. two numbers over 4 will appear? (This means totaling over 4)
  1. A bag contains 6 blue marbles, 4 red marbles and 2 green marbles (i.e. 12 marbles). If you select a single marble at random from the bag, what is the probability that it will be:
  2. red =
  3. blue =
  4. green =
  5. white =
  6. pink =
  7. red or white =
  8. green or white =
  1. If you toss a coin six times, what is the probability you will:
  2. get six heads =
  3. get five heads and one tails –
  4. get three tails and three heads –
  5. get four heads and two tails -

Monohybrid Problems

Do each of the following with a Punnett square or a Pedigree Chart. If needed, do your work on a separate sheet of paper

  1. In humans, six fingers (F) is the dominant trait and five fingers (f) is the recessive trait. Both parents are heterozygous for six fingers.

What is the phenotype of the father and mother?

What is the genotype for each parent?

What is the probability of them having six-fingered children?

Five fingered children?

  1. A mutant cucumber plant has flowers that fail to open when mature. Crosses can be done with the plant by manually opening and pollinating the flowers with pollen from another plant. When closed X open crosses were done, all F1 progeny were open. The F2 progeny after crossing F1 progeny were 145 open and 59 closed. A cross of closed X F1 plants gave 81 open and 77 closed. How is the closed trait inherited?

  1. In humans, a dimple in the chin is a dominant characteristic.

a. A man who does not have a dimple has children with adimpledwoman whose mother lacked the dimple. What proportion of their children would be expected to have a dimple?

b. A man with a dimple and a woman who lacks a dimple produce a child who lacks a dimple. What is the man’s genotype?

  1. You have just purchased a black stallion of unknown genotype. You mate him to a red mare and she delivers twin foals, one red and one black. Can you tell from these results how color is inherited, assuming that alternative alleles of a single gene are involved? What crosses would you perform to work this out?
  1. In humans, true brown eyes, B, are dominant over true blue eyes, b. A brown-eyed man has 8 children with a blue eyed woman. They are all brown eyed. What are the possible genotypes of all members of this family?
  1. The parents of a blue-eyed man were brown eyed. He has children with a woman who had brown eyes. Her father was brown eyed and her mother was blue eyed. Their one child has blue eyes. What are the most probable genotypes of all the individuals mentioned?

7. George and his father have brown eyes (i.e. at least one B allele), while his mother and sister have blue eyes (i.e. bb). George’s paternal grandparents both had brown eyes (i.e. at least one B allele), while his maternal grandparents had blue eyes (i.e. bb). George has children with Helen. Helen has brown eyes (i.e. at least one B allele). Her father had blue eyes (i.e. bb), while her mother had brown eyes (i.e. at least one B allele). Helen’s paternal grandparents had brown eyes, while one of her maternal grandparents had blue eyes. Draw a pedigree chart for this family. Determine all genotypes of all individuals.

8. Charlie decides to breed pigs. In pigs, hair color is either black, white, or tan. Tan hair coloring is a condition that results from being heterozygous. HINT: assume black is the dominant color.

  1. Isabel, Charlie’s black pig (i.e. BB) escapes from her pen one night. Sometime later, she gives birth to a tan piglet (i.e. Bb) and two black piglets (i.e. BB). The color of what piglet tells the father’s color?
  2. Charlies mates Matty, who is tan, with Butch, who is white? What color piglets can he expect?
  3. Matty refuses to mate with Butch, so Charlies brings in Bas, who is tan. Matty ends up having four piglets, two black and two white. What are the expected piglets in this cross?

9. Piebald spotting is a condition found in humans in which there are patches of skin that lack pigmentation. The condition results from the inability of pigment-producing cells to migrate properly during development. Two adults with piebald spotting have one child who has this trait. Their second child has normal pigmentation.

a. Is the piebald spotting trait dominant or recessive?

b. What are the genotypes of the parents?

c. The first child with piebald spotting has a child with someone who has no history of the trait in their family (i.e homozygous recessive). The second child has children with someone whose two parents have the trait ((i.e heterozygous or homozygous dominant). What are the phenotypes and genotypes of these “grandchildren”?

10. Albinism is a condition in which pigmentation is lacking. In humans, the result is white hair, non-pigmented skin and pink eyes. The trait in humans is caused by a recessive allele. Two normal parents have an albino child. What are the parent’s genotypes? What is the probability that the next child will be:

a. an albino =

b. a normal girl =

c. an albino boy =

11. The common grandfather of two first cousins has hereditary hemochromatosis – a recessive condition causing an abnormal buildup of iron in the body. Neither of the cousins has the disease, nor do any of their relatives.

a. If the first cousins mate with each other and had a child, what is the chance that the child would have the disease? Assume that the unrelated parents of these cousins are not carriers–

b. How would your calculation change if you knew that 1 out of every 10 unaffected people in the population (including the unrelated parents above) were carriers?–

12. Polycystic kidney disease is a dominant trait that causes the growth of numerous cysts on the kidneys. The condition eventually leads to kidney failure. A child with the disease is born to a couple – neither of which show the disease. What possibilities might explain this outcome?

Dihybrid Problems:

1. In horses, black color (B), dominates chestnut (b). The trotting gait (T) dominates the pacing gate (t). A cross is made between a horse homozygous for black and pacing gait (i.e. BBtt) and a horse homozygous for chestnut and trotting gait (i.e. bbTT).

a. List the probable genotypes and phenotypes from offspring resulting from this cross.

b. List the probable phenotypes of offspring that would result if the offspring from the original cross were crossed amongst themselves.

2. The following chart show the result of different matings between jimsonweed plants that either had purple or white flowers and spiny or smooth pods. Determine dominant allele for these two traits and indicate the genotypes of each of the parents in the crosses a through f

Parents / Offspring Phenotypes
purple
spiny / white
spiny / purple
smooth / white
smooth
a. purple spiny X purple spiny / 94 / 32 / 28 / 11
b. purple spiny X purple smooth / 40 / 0 / 38 / 0
c. purple spiny X white spiny / 34 / 30 / 0 / 0
d. purple spiny X white spiny / 89 / 92 / 31 / 27
e. purple smooth X purple smooth / 0 / 0 / 36 / 11
f. white spiny X white spiny / 0 / 45 / 0 / 16

3. A third grader decides to breed guinea pigs for her school science project. She goes to a pet store and buys a male with smooth black fur and a female with rough white fur. She wants to study the inheritance of these traits and breeds them. She gets 8 pups that are all rough black animals. She breeds the parents again and gets 7 rough black pups. The first F1 litter breeds among themselves and starts to produce offspring. These F2 offspring have a variety of coat colors. Before long, the child has 125 F2 offspring. Eight of them have smooth white coats, 25 have smooth black coats, 23 were rough and white and 69 were rough and black (i.e. a 9:3:3:1 ratio).

a. How are coat color and texture inherited?

b. What phenotypes and proportions should the girl expect if she mates one of the smooth white F2 females to an F1 male?

4. How many genetically different eggs could be formed by women with the following genotypes?

a. Aa bb CC DD =

b. AA Bb Cc dd=

c. Aa Bb cc Dd =

d. Aa Bb Cc Dd =

5. A pea plant heterozygous for plant height, pod shape and flower color was “selfed”. The progeny consisted of 272 tall, inflated pods with purple flowers; 92 tall, inflated pods with white flowers; 88, tall flat pods with purple flowers; 93 dwarf, inflated, purple; 35, tall, flat, white; 31 dwarf, inflated white; 29 dwarf, flat, purple; 11 dwarf, flat, white. Which alleles are dominant?

6. In dogs, black coloring is dominant and red color is recessive; solid coloring is dominant while white spotting is recessive.

a. A homozygous black and white spotted male is crossed with a red and white spotted female. What is the probability of them producing a solid black puppy?

b. This black and white spotted male is mated with a solid black female. Can this mating produce solid colored puppies? Why or why not?

Pedigree and X-linked Problems

For Questions 1-9, use the pedigree chart shown below. Some of the labels may be used more than once.

1. A male

2. A female

3. A “marriage”

4. A person who expresses the trait

5. A person who does not express the trait

6. A connection between parents and offspring

7. How many generations are shown on this chart?

Assuming the chart above is tracing the autosomal dominant trait of "White Forelock (F)" through the family. F is a tuft of white hair on the forehead.

8. What is the most likely genotype of individual “A”? (FF, Ff or ff?)

9. What is the most likely genotype of individual “C”? (FF, Ff or ff?)

Complete the following problems. If necessary, draw a pedigree chart to help you work through these problems

10. In humans, Hemophilia is a blood clotting disorder in which one of the proteins needed to form blood clots is missing or reduced. Individuals have difficulty forming blood clots following injury and may suffer significant blood loss from even minor cuts and bruises. The key clotting factor in hemophilia is called Factor VIII. The gene for Factor VIII is found on the X chromosome. Hemophilia is caused by a lack of Factor VIII and results from a recessive allele (h) found on the X chromosome. The condition for normal blood clotting dominates over non-clotting. A hemophiliac male has a child with a woman who is a carrier for this condition. Using the letter H for normal Factor VIII and h for abnormal Factor VIII, what are the chances that they have a male child who clots normally?

11. In humans, the condition for normal vision dominates color blindness. Both are linked to the X chromosome. Using C for normal vision and c for the color-blind disorder, what are the chances that a color-blind female and color-blind male will have a daughter with normal vision?

12. Remember that because hemophilia is an X-linked disorder, when you identify genotypes in this pedigree, you must use the XX/XY notation and use superscripts with each X chromosome to indicate whether the “H” (normal) or “h” (hemophilia) allele is present. (Ex. XHY = normal male).

Hemophilia became known as the “Royal disease” after it suddenly cropped up in some of the descendants of Great Britain’s Queen Victoria and spread through the royal families of Europe. Queen Victoria and her husband Prince Albert had 9 children – 5 girls (Beatrice, Victoria, Alice, Helena, and Louise – none of whom were hemophiliacs) and 4 boys (Edward, Alfred and Arthur had normal blood clotting; their son Leopold, however was a hemophiliac). Beatrice married a man named Henry and they had four children (sons Leopold and Maurice who were hemophiliacs, daughter Eugenie who was not a hemophiliac, and another son who was also not a hemophiliac). Eugenie married Alfonso XIII of Spain (non-hemophiliac) and they had 6 children (2 normal sons, 2 normal daughters and 2 hemophiliac sons). One of those normal sons married a non-hemophiliac woman and gave birth to one son – a non-hemophiliac they named Juan Carlos (the reigning King of Spain).

Using this information, draw the pedigree chart for this Royal family

A little bit more info – for fun

Another of Victoria and Albert’s daughters was Alice (XHXh ) who married Louis (XHY). Their daughter Alexandria (XHXh ) married Csar Nicholas of Russia (XHY). They had one hemophiliac son (Alexander= XhY) and what we think were normal daughters. We don’t know since they along with their entire families were murdered during the Bolshevik revolution.

One of Victoria and Albert’s sons, Edward Louis (XHY) married and had a son names George V (XHY). George V married Mary and had a son, George VI. George the VI married Elizabeth and had the current Queen Elizabeth II. Because George V was normal and married a non-hemophiliac women who wasn’t a carrier, the current Royal family of Britain is now hemophilia free

Another child of Alice and Louis was the grandmother of Prince Philip, the current consort of Queen Elizabeth II

Dominance Problems

1. In four o-clocks, the allele for red flowers is incompletely dominant over the allele for white flowers, so that heterozygotes have pink flowers. What ratios of flower colors would you expect among the offspring of the following crosses?

a. pink x pink=

b. white x pink=

c. red x red=

d. red x pink=

e. white x white=

f. red x white=

g. If you wanted to produce pink flowers, which of these crosses would be most efficient?

2. A cross between two plants that both have yellow flowers produces 80 offspring plants of which 38 have yellow flowers, 22 have red flowers and 20 have white flowers. If one assumes that this variation in color is due to a single gene, what is the genotype associated with each flower color? How is this flower color inherited?

Multi-Allelic and Gene Interaction Problems

Complete the following. Use a Punnett square or a Pedigree chart to help you determine your answers.

  1. In humans, the trait for type A blood and type B blood show incomplete dominance, so that a person with both alleles as blood type AB. Both A and B are dominant over the O allele. Therefore type A blood can have two genotypes: AA and AO. A person with type A blood has a child with a person with type O blood. List the types of offspring they could have and the probability for each blood type.
  1. There are several genes in humans in addition to the ABO gene that give rise to antigens on the surface of an RBC. The MN and Rh genes are two such examples. The Rh locus can either contain a positive or a negative allele, with positive being completely dominant over the negative allele. M and N are actually co-dominant alleles for the MN gene. The following chart shows several mothers and their children. For each mother-child pair, choose the father of the child from among those listed in the right column. Assume one child per father.

Mother / Child / Father
a. O M Rh+ / B MN Rh- / O M Rh-
b. B MN Rh- / O N Rh- / A M Rh+
c. O M Rh+ / A M Rh- / O MN Rh+
d. AB N Rh- / B MN Rh - / B MN Rh +
  1. In radishes, the shape may be long, round or oval. Crosses between long and oval gives 159 oval and 156 long. Crosses between oval and round produce 203 oval and 199 round. Crosses between long and round give 576 oval. Crosses between oval and oval give 121 long, 243 oval and 119 round. Which of the shapes are defined by a homozygous dominant genotype? Homozygous recessive? Heterozygous?

For this problem, use the letters L and l

4. Alleles of the gene that determines seed coat patterns in lentils can be organized in a dominance series: marbled > spotted = dotted (co-dominant) > clear. A lentil plant homozygous for the marbled seed pattern allele was crossed to one homozygous for the spotted pattern allele. In another cross, a homozygous dotted lentil plant was crossed to one homozygous for clear. An F1 plant from the first cross was then mated to an F1 plant from the second.

a. What phenotypes and in what proportions are expected?