Gene

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Locus

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Allele

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Trait

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True-breeding

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Parental Strain

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Hybrid

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Dominant

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Recessive

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Monohybrid

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Dihybrid

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P Generation

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F₁ Generation

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F₂ Generation

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Generation Test

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Reciprocal Cross

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Cross Heterozygote

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Punnett Square

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Terminology

Monohybrid Punnett Square

(F1xF1=F2)

Dihybrid Punnett Square

(one big: 16 squares)

Dihybrid Punnett Squares

(two small 4 and 4 )

Dihybrid Branching Diagram

(using GENOtypes)

Dihybrid Branching Diagram

(using PHENOtypes)

Autosomal Dominant characteristics of inheritance, examples

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Autosomal Recessive characteristics of inheritance, examples

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Tumor Suppressors: Dominance or Recessiveness - both

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Chromosome Numbers, arms p/q

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See syllabus for reading pages in Chapter 3.

There are a lot of practice questions here This is to give you lots of practice with questions. Do them until they feel the punnet squares and predicted offspring are second nature, or 'easy.' Hit each section of questions to be sure you can do problems of each type.

• Branching Diagram (to make gametes)
• Branching Diagram (to make genotypes in a dihybrid cross)

Basic Comprehension Questions

1. Who was Gregor Mendel?

• A hungarian botanist who first discovered independent assortment and recombination using quantitative methods.

2. What does 'antagonistic' traits mean?

• ? 3. What does a 'selfing' or self-cross mean, in plants?
• Selfing is the act of crossing a monoecious plant with itself.

3. What's the easy way to do and F1 x F1 in plants?

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3. How would one set up an F1 x F1 mating in animals?

• ? 4. What is the difference between phenotype and genotype?
• Genotype is the combination of alleles received from the parents.
• Phenotype is the expressed trait derived from the combination of alleles.

5. What is the principle of dominance? Why are there more genotypes than phenotypes?

• Dominance causes certain alleles to overwrite other alleles. This makes it so some combinations of alleles don't matter if the dominant allele exists.

6. What is the principle of allele segregation? When does this happen in the M-phase (what sub-phase)?

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7. What is the principle of independent assortment? When does that actually happen in the the M-phase (what sub-phase)? This refers to 2 or more genes - what types of genes does this apply.

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8. What phenotypic ratio was observed in the F1 generation in Mendel's monohybrid crosses? What was the genotypic ratio?

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9. What ratio was observed in the F2 generation in Mendel's monohybrid crosses?

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10. What is the definition of Dominance according to Mendel? What type of individual shows this?

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11. What is the definition of recessive according to Mendel? What type of individual shows this?

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12. Why do we say that the allele is dominant or recessive and not the gene?

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13. Why can we use the multiplication rule to predict the outcome of dihybrid crosses? What is the assumption made for this to be true?

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13. What is a test cross? What can it determine? Are you testing an organism with a dominant or recessive phenotype? What are you testing for? What is the phenotype of the organism you bring into the cross to do the test ← the "tester strain"?

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14. What is a reciprocal cross? What is the expected outcome?

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Formation of gametes

15. Kelp, a large, multicellular type of algae, has air bladders in the blades to help them float near the surface of the ocean where they can get more sunlight. Assume that having many air bladders (k) is a recessive trait. What gametes would be produced by a heterozygous individual?

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16. In humans, sickle cell anemia is a recessive disease caused by a mutation of a single gene or 'locus' which codes for an important blood protein. The allele for the normal protein (S) is dominant to that for the one causing sickle cell anemia, s. What gametes would be produced by an individual who suffers from sickle cell anemia?

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17. In areas of the very deep and damp southeastern United States lives what is essentially a giant flying cockroach known as a Palmetto bug. Assume that long antennae (L) are dominant to short antennae and that normal wings (N) are dominant to bent ones. What gametes will be produced by an individual that is homozygous dominant for antennae and heterozygous for wings?

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18. Suppose you are designing a new Jurassic Park and you would like to have the crowd drawing presence of Velociraptor without the danger of having your crowds eaten. You have managed to come up with two varieties, very aggressive (A), which is apparently a dominant trait in Velociraptors, and non-aggressive. They also come in two colors, red (R), which is dominant, and green. At the moment you have a green female that is homozygous dominant for aggression and a non-aggressive male that is homozygous dominant for color. What gametes will be produced by the male and female?

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Monohybrid Crosses

19. In sheep white is due to a dominant gene (W), black to its recessive allele (w). A white ewe mated to a white ram produces a black lamb. If they produce another offspring, could it be white? If so, what are the chances of it being white? List the genotypes of all animals mentioned in this problem.

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20. In tomatoes the texture of the skin may be smooth or peach (hairy). The Ponderosa variety has fruits with smooth texture. The red peach variety has fruits with peach texture. Crosses between the two varieties produce all smooth fruits. Crosses between these smooth fruited F₁ plants produced 174 peach textured fruits and 520 smooth textured fruits. How are these skin textures inherited? (complete or incomplete dominance, dominant trait, recessive trait?)

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21. In armadillos, green snouts (G) are dominant to red snouts (g). Domingo is homozygous dominant and Louisa has a red snout. What proportion of Domingo and Louisa's offspring will have green snouts? What proportion of Domingo and Louisa's offspring will have red snouts?

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22. In humans, being neat (N) is dominant to being messy (n). Ricky is neat, and his wife, Lucy is messy. They have a child who is messy. What is the probability that the next child will also be messy? What is the probability that the next child will be neat?

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23. In purple people eaters, one-horn is dominant and no horns is recessive. Draw a punnet square showing the cross of a purple people eater that is hybrid for horns with a purple people eater that does not have horns. Summarize the genotypes and phenotypes of possible offspring.

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24. A green-leafed luboplant is crossed with a luboplant with yellow-striped leaves. The cross produces 185 green leafed luboplants.
    • a. Which allele is dominant?
    • b. What are the genotypes of each parent?
    • c. What are the genotypes of the F1 offspring?
    • d. Summarize the genotypes and phenotypes of the F2 offspring that would be produced by crossing two of the green leafed luboplants obtained from this cross.
25. Mendel found that crossing wrinkle-seeded plants with pure round-seeded plants produced only round-seeded plants. What genotypic and phenotypic ratios can be expected from a cross of a wrinkle-seeded plant and a plant heterozygous for this trait (seed shape)?

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26. In 1986, National Geographic magazine conducted a survey of its readers' abilities to detect odors. About 7% of Caucasians in the United States could not smell the odor of musk. If both parents could not smell musk, then none of their children were able to smell it. On the other hand, two parents who could smell musk generally had children who could smell it, too, but a few of the children in those families were unable to smell it. If a single pair of alleles governs this trait, is the ability to smell musk best explained as an example of dominant or recessive inheritance?

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27. What would be the best genotype to use in a test cross determine if your tall plant (TT or Tt) were pure breeding?
    • a. TT
    • b. Tt
    • c. tt
28. In a certain plant, purple flowers are dominant to red flowers. If the cross of two purple flowered plants produces some purple flowers and some red flowered-plants, what is the genotype of the parent plants?

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29. A man has six fingers on each hand and six toes on each foot. His wife and their daughter have the normal number of digits. Extra digits is a dominant trait. What fraction of this couple's children would be expected to have extra digits?

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30. In sheep, lustrous fleece (L) results from an allele that is dominant over an allele for normal fleece (l). A ewe (adult female) with lustrous fleece is mated with a ram (adult male) with normal fleece. The ewe then gives birth to a single lamb with normal fleece. From this single offspring, is it possible to determine the genotypes of the two parents? If so, what are their genotypes? If not, why not?

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31. Joe has a white cat named Sam. When Joe crosses Sam to a black cat, the litter has ½ white kittens and ½ black kittens. He decides to interbreed the black kittens and when he does all the kittens are black. On the basis of these two matings (Sam x black cat, and the black x black kittens) would you conclude that white or black coat color is a recessive trait? Explain your reasoning.

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32. In cats, blood-type A results from an allele (A) that is dominant over an allele (a) that produces blood type B. There is no O type in cats. The blood types of male and female cats that were mated and the blood types of their kittens follow. Give the most likely genotypes for the parents of each litter.

    	Father	Mother	Offspring (kittens)
    a.	A	B	4 type A, 3 type B
    b.	B	B	6 type B
    c.	B	A	8 type A
    d.	A	A	7 type A, 2 type B
    e.	A	A	10 type A
    f.	A	B	4 type A, 1 type B

33. Suppose you are raising Mongolian gerbils. You notice that some of your gerbils have white spots, while others have solid coats. What types of crosses could you carry out to determine if white spots are due to a recessive or dominant allele?

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34. Hairlessness in American rat terriers is recessive to the presence of hair. Suppose you have a rat terrier with hair. How can you determine whether your dog is a homozygous or heterozygous for the hairy trait?

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35. Dwarfism is a recessive trait in Hereford cattle. A rancher discovers that several of calves in his herd are dwarves and he wants to eliminate this undesirable trait from the herd as rapidly as possible. The rancher has hired you as a genetic consultant to advise him on how to breed dwarfism out of his herd. What crosses would you advise him to conduct to ensure that the allele causing dwarfism is eliminated from his herd?

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Dihybrid Cross:

36. Wolves are sometimes observed to have black coats and blue eyes. Assume that these traits are controlled by single locus genes and are located on different chromosomes. Assume further that normal coat color (N) is dominant to black (n) and brown eyes (B) are dominant to blue (b). Suppose the alpha male and alpha female of a pack (these are the dominant individuals who do most of the breeding) are black with blue eyes and normal colored with brown eyes, respectively. The female is also heterozygous for both traits. What are the possible genotypes of the offspring? How many of the offspring (assume 16) living in the pack will have each of these genotypes?

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General

1. What's the difference between mono- and di- hybrid crosses? Which has an expected ratio of different classes of phenotypes = 9:3:3:1? Which has an expected ratio of different classes of phenotypes = 3:1? Are those ratios referring to the F1 or F2 generations?

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2. Alleles: define wildtype, define mutant.

• Wildtype is the most common version of an allele.
• Mutant is a rare variant of an allele.

2. Can wildtype be recessive?

• Yes, wildtype can be recessive.

3. What law of inheritance do Monohybrid experiments test?

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4. What law of inheritance do Dihybrids test?

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5. If two genes' alleles assort independently, are they on different chromosomes relative to each other, or are they on the same chromosome.

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6. What determines if a disorder due to a genetic mutation/variant is heritable?

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7. What do we name arms of the chromosomes that are are short? long?

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8. Which genetic inheritance almost every generation in a family: dominant or recessive disorders?

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9. Name 4 differences between dominant and recessive inheritance.

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10. Name some Autosomal dominant disorders.

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11. Name some Autosomal recessive disorders.

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12. What class of disorders act in both dominant + recessive ways?

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Dihybrid Crosses

1. Wolves are sometimes observed to have black coats and blue eyes. Assume that these traits are controlled by single locus genes and are located on different chromosomes. Assume further that normal coat color (N) is dominant to black (n) and brown eyes (B) are dominant to blue (b). Suppose the alpha male and alpha female of a pack (these are the dominant individuals who do most of the breeding) are black with blue eyes and normal colored with brown eyes, respectively. The female is also heterozygous for both traits. What are the possible genotypes of the offspring? How many of the offspring (assume 16) living in the pack will have each of these genotypes?

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2. Snails have either two or three eyes and green or blue slime. Both of these characters are controlled by single, independent loci. Teddy has a pair of snails that give rise to the following offspring: 29 three eyed, blue slimers; 8 three eyed, green slimers; 9 two eyed, blue slimers; and 2 two eyed, green slimers. What are the genotypes of the parents and which traits are dominant?

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3. In humans, black hair (B) is dominant over red hair (b) and having six fingers (F) is dominant over having five fingers (f). Sally has black hair and five fingers. Her father has red hair. Sally marries Bill who has red hair and six fingers. Bill's mother had five fingers. Sally & Bill have children. What are the expected genotypic and phenotypic ratios of their children?

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4. In sesame plants, the one-pod condition (P) is dominant to the three-pod condition (p), and normal leaf (L) is dominant to wrinkled leaf (l). Pod type and leaf type are inherited independently. Determine the genotypes for the two parents each of the following matings producing the following offspring:

   • i. 318 one-pod normal, 98 one-pod wrinkled
   • ii. 323 three-pod normal, 106 three-pod wrinkled
   • iii. 401 one-pod normal
   • iv. 150 one-pod normal, 147 one-pod wrinkled, 51 three-pod normal, 48 three-pod wrinkled
   • v. 223 one-pod normal, 72 one-pod wrinkled, 76 three-pod normal, 27 three-pod wrinkled

   ... for (i.) and for (iii.) there are three legitimate 'correct' answers.

5. The genotype of F₁ individuals in a tetrahybrid cross is AaBbCcDd. Assuming independent assortment of these four genes, what are the probabilities that F₂ offspring would have the following genotypes?

   • i. aabbccdd
   • ii. AaBbCcDd
   • iii. AABBCCDD
   • iv. AaBBccDd
   • v. AaBBCCdd

6. The mating of two curly-haired brown guinea pigs results in some offspring with brown curly hair, some with brown straight hair, some with white curly hair and some with white straight hair. Which of Mendel's laws does this mating illustrate?

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Probability

7. Albinism is a recessive condition in humans; two carriers for albinism alleles mate and have three children: What is the probability that they will have one child with albinism, and two without? How many different paths to that outcome are there?

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8. Explain the significance of Sickle Cell, PKU and CF (know those disorders, the mutations, phenotypes, and selections) for balanced polymorphisms. How do disease alleles persist in humans?

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9. How can Tumor Suppressor genetic disorders be classified as both Dominant, and Recessive? Explain. What type of disease is caused by mutated tumor suppressor genes? Name 3 examples.

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10. Name two databases that hold information about human genetic disorders. Visit them.

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