Please answer these following questions on the blank worksheets provided in this week’s class.
In pea plants, yellow peas are dominant over green peas.
Use a Punnett square to predict the genetic outcome (offspring) of a cross between two plants for yellow peas that yield a small amount of green peas.
The long hair of persian cats is recessive to the short hair of siamese cats. Complete a Punnett Square when a a purebred persian is mated with a purebred siamese cat.
The black coat of persian cat is dominant to the brown and tan coat of siamese. Complete a Punnett Square when a a purebred black persian is mated with a purebred brown siamese cat.
In four o’clock flowers, red plants are purebred for the dominant allele (R) of the gene for flower color. Plants with white flowers are purebred for the recessive (r) allele of the same gene. Plants with pink flowers have one of each of the two alleles. Complete a Punnett square that is expected when plants with pink flowers are intercrossed.
In humans, brown eyes (B) are dominant over blue (b). A brown-eyed man marries a blue-eyed woman and they have three children, two of whom are brown-eyed and one of whom is blue-eyed. Draw the Punnett square that illustrates this marriage.
Suppose one of the brown-eyed children marries someone with blue eyes. Use the second Punnett square to predict their offspring.
Queen Victoria’s Bloodline
First, let’s take a look at Queen Victoria’s son Leopold’s family. His daughter, Alice of Athlone, had one hemophilic son (Rupert) and two other children—a boy and a girl—whose status is unknown.
(a) What is the probability that her other son was hemophilic?
(b) What is the probability that her daughter was a carrier? Hemophilic?
(c) What is the probability that both children were normal?
Now for the Spanish connection: Victoria’s youngest child, Beatrice, gave birth to one daughter, one normal son, and two hemophilic sons.
(a) Looking at the pedigree of the royal family, identify which of Beatrice’s children received the hemophilic gene; why can you make this conclusion?
(b) Notice that Beatrice’s daughter, Eugenie, married King Alfonso XIII of Spain and had six children, one of whom was the father of Juan Carlos, the current King of Spain. Would you predict that Juan Carlos was normal, a carrier, or a hemophilic?
Queen Victoria’s third child, Alice, passed hemophilia to the German and Russian imperial families (see Figure 4, next page). Of Alice’s six children, three were afflicted with hemophilia. At the age of three, her son Frederick bled for three agonizing days from a cut on the ear. Eventually, the flow of blood was stanched. But a few months later, while playing boisterously in his mother’s room, the boy charged headlong through an open window and fell to the terrace below. By the evening he was dead from the internal bleeding. Alice’s daughter Irene, a carrier, married her first cousin, Prince Henry of Prussia, and gave birth to two hemophilic sons. Every attempt was made to conceal the fact that the dreaded disease had shown itself in the German imperial family, but, at the age of four, Waldemar, the youngest of the princes, bled to death. The other prince, Henry, died at the age of fifty-six. Alice’s other daughter, Alix, was also a carrier. Had she accepted the offer of marriage from Prince Eddy, or his brother George, hemophilia would have been re-introduced into the reigning branch of the British royal family. But Alexandra (Alix) married Tsar Nikolas II instead and carried the disease into the Russian imperial family. She had four daughters, Olga, Tatiana, Marie, and Anastasia, before giving birth to the long-awaited son, Alexis, heir to the Russian throne. These children, along with their parents, were eventually murdered during the Russian Revolution. Within a few months of his birth, his parents realized that their precious and only son, Alexis, had hemophilia. The first sign had been some unexpected bleeding from the navel, which had stopped after a few days. Much more serious, however, were the dark swellings that appeared each time the child bumped an arm or a leg. And worst of all was the bleeding into the joints. This meant a crippling of the affected limbs in addition to excruciating pain. As the boy grew older, he was obliged to spend weeks in bed, and after he was up, to wear a heavy iron brace.
(a) What are the probabilities that all four of the girls were carriers of the allele hemophilia?
(b) Supposing Alexis had lived and married a normal woman, what are the chances that his daughter would be a hemophiliac?
(c) What are the chances his daughters would be carriers? (d)What are the chances that his sons would be hemophiliacs?
In 1995, a sixty-three-year-old man named Eugene Romanov, a resident of the former Soviet Union, turned up. He shared both the disease and his last name with the royal family of czarist Russia. He proclaimed himself a grandson of Nikolas II’s youngest daughter, Anastasia, whose body had at that time not been recovered, and who was believed by some to have managed to survive the revolution. Eugene Romanov claimed Anastasia was raised by a farmer, and later she married a nephew of her adopted parents and had a daughter, Eugene’s mother.
(a) According to Eugene’s argument, what was the likely hemophilic status of Eugene’s mother and grandmother? What about his father and grandfather? Is this argument plausible?
(b) How plausible is it that Eugene inherited both hemophilia and the last name from the royal family? (Hint: Look how each of them is passed from generation to generation.)
5. Prince Charles is the designated next king of England. His well publicized marriage to Princess Diana produced two sons before it ended in an acrimonious divorce.
If you learned that one of the two sons was a hemophiliac, what are the possible explanations for this event?
Here are some good Punnett practice problem sites. In fact, the problems above (and likely the questions on the midterm) come from these sites.
The Association for Biology Laboratory Education has a really good .pdf handout on the step by step procedure to solving Punnett square problems.Here is my own list:
- Genetics Practice Problems
- Soterios Lallas’ Website – at Westby, Wisconsin!
- The Biology Project – Good multiple choice problems (not on our midterm, though…)
- Glencoe Online – more multiple choice questions
- Palomar College – yet more multiple choice questions
- Middle Tennessee State University – don’t worry about sex-linked crosses.
- Texas A&M – Only Problems #1-5, avoid incomplete dominance and dihybrids…
- Anthro, Limited – only work on monohybrid crosses
- Clermont College, University of Cincinnati – again, don’t worry about incomplete dominance
So practice, practice, practice… Bring any problems you have difficulty with to class, and we’ll work them out together.