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H Biology

Genetics Basics Packet

PART ONE: TERMINOLOGY

Like any other language, the language of genetics consists of symbols and rules for using these symbols. When a trait being studied shows dominance, it is observed in nature much more frequently than if it is a recessive form. The capitalized letter of the dominant form becomes its symbol (ex: R stands for round seeds.) For the recessive form of the same trait (the recessive allele), the symbol remains the same but is not capitalized (ex: r stands for wrinkled seeds). Complete the following chart using these rules of symbols.

| |Plant Trait |

| |Height |Coats |Pods |Seed Color |Shape |Flower |

|Dominant |T (tall) |___ (colored) |G (green) |___ (yellow) |R (round) |___ (axial) |

|Recessive |___ (short) |c (white) |___ (yellow) |y (green) |___ (wrinkled) |a (terminal) |

1. Using the symbols from the above chart, write the allele symbols that would be present in the following homozygotes. Next, indicate whether they are going to express the dominant or recessive trait.

| |Allele Symbol |Expressed Trait (dom or rec) |

|a. tall, stemmed plants | | |

|b. terminal flowers | | |

|c. white seed coats | | |

|d. yellow seeds | | |

|e. yellow pods | | |

2. Write the symbols for the following heterozygotes.

a. yellow seeded peas ______

b. axial flowers ______

c. green podded peas ______

d. colored seed coats ______

e. round seeds ______

f. tall stemmed plants ______

3. The following letters represent pairs of alleles. Indicate whether each pair is a heterozygotse or homozygote. Then indicate whether each pair would display a dominant or recessive phenotype.

| |Homo or Hetero |Phenotype (dom or rec) |

|a. DD | | |

|b. ss | | |

|c. Tt | | |

|d. Dd | | |

|e. Rr | | |

|f. yy | | |

4. What percentage of the alleles does each parent contribute to their offspring? _____%

5. What are the phenotypes for each of the following dihybrids?

a. TtCc _______________

b. GgYy _______________

c. AaRr _______________

d. TtAa _______________

6. PART TWO: SINGLE TRAIT CROSSES (MONOHYBRID)

7. Tall pea plants are dominant over short pea plants. If two homozygous tall parents are crossed, then:

a. Show parental cross and punnet square ( ___ x ____

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b. How many tall plants would be expected?

c. How many dwarf plans would be expected?

d. How many hybrid plants would be expected?

8. If two heterozygous tall pea plants are crossed, then:

a. Show parental cross and punnet square ( ___ x ____

| | |

| | |

b. How many tall plants would be expected?

c. How many dwarf plans would be expected?

d. How many hybrid plants would be expected?

9. If two homozygous recessive plants are crossed, then:

a. Show parental cross and punnet square ( ___ x ____

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b. How many tall plants would be expected?

c. How many dwarf plans would be expected?

d. How many hybrid plants would be expected?

10. If a tall hybrid plant is crossed with a dwarf plant, then:

a. Show parental cross and punnet square ( ___ x ____

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| | |

b. How many tall plants would be expected?

c. How many dwarf plans would be expected?

d. How many hybrid plants would be expected?

11. If a purebred tall plant is crossed with a dwarf, then:

a. Show parental cross and punnet square ( ___ x ____

| | |

| | |

b. How many tall plants would be expected?

c. How many dwarf plans would be expected?

d. How many hybrid plants would be expected?

In a certain species of rats, black color is dominant to white. Show parental cross and punnett square for each question!

12. Cross two hybrid black rats.

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| | |

a. Parental genotypes = ___ x ____

b. F1 genotypes = _______________________

c. F1 phenotypes = ______________________

13. Cross a heterozygous black rat with a white one.

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a. Parental genotypes = ___ x ____

b. F1 genotypes = _______________________

c. F1 phenotypes = ______________________

14. Short fur in rabbits is dominant to long fur. What phenotypic ratio would you expect from a heterozygous female and a male with long fur?

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| | |

Parental genotypes = ___ x ____

Genotypic Ratio:

Phenotypic Ratio:

15. If black fur is dominant to white fur in rabbits, what would be the genotypic and phenotypic ratios resulting from the following crosses?

| |Genotypic Ratio |Phenotypic Ratio |

|a. Homozygous black and white | | |

|b. Two heterozygous blacks | | |

|c. A heterozygous black and white | | |

Show your work(

16. The polled (hornless) trait in cattle is dominant. The horned trait is recessive. A certain polled bull is mated to three cows. Cow A, which is horned, gives birth to a polled calf. Cow B, also horned, also produces a horned calf. Cow C, which is polled, produces a horned calf. Name the genotypes of all parents and show the Punnett squares and possible gentoypes of each offpring resulting from the cross.

| |Genotype |Possible Genotypes of Offspring Resulting from Cross |

|Cow A | | |

|Cow B | | |

|Cow C | | |

Show your work (

17. Persons with sickle cell anemia have a problem with the blockage of capillaries due to a mutation in the hemoglobin gene. This usually causes death before reproductive age. This trait is produced by the homozygous recessive nn. Two heterozygous individuals are planning a family and have asked you to tell them their chances of having a sickle cell child. What would you tell them?

PART THREE: TEST CROSS

In the case of a gene whose alleles exhibit dominance and recessiveness, it is not possible to determine from appearance alone if an individual with the dominant phenotype is homozygous or heterozygous. The method used to determine if a particular individual with a dominant phenotype is heterozygous or homozygous is to cross it with an individual that is homozygous recessive. This is called a test cross.

17. A tall pea plant is crossed with a short pea plant. All 55 of the offspring are tall. What is the genotype of the tall parent?

18. In squash, white fruit color is dominant to yellow fruit color. If a cross between a white-fruited plant and a yellow-fruited plant yielded 43 white and 37 yellow progeny, what is the white parent’s genotype?

19. A blonde haired man marries a brown haired woman. They have 4 children all of whom have brown hair. (a) What is the genotype of their mother? (b) If the mother is heterozygous, what is the probability that the couple will have a blonde child?

20. In watermelon, the allele for short fruit (S) is dominant to the allele for long fruit (s), and the allele for green fruit color (G) is dominant to the allele for mottled fruit color (g). Each of four short green plants was crossed with a different long mottled plant. The results of the crosses are shown below.

|Plant |Short green |Short mottled |Long green |Long mottled |

|1 |28 |30 |33 |31 |

|2 |71 |X |60 |X |

|3 |109 |X |X |X |

|4 |49 |56 |X |X |

What are the genotypes of plants 1-4?

Test

PART FOUR: TWO-TRAIT CROSSES (DIHYBRID)

21. Some dogs bark when trailing, others are silent. The barking trait is due to a dominant allele. Erect ears are dominant to drooping ears. What kind of pups would you expect from a heterozygous, erect-eared barker mated to a droop-eared silent trailer?

Parental Cross ( ______ x ______

22. In snap dragons, if purple is dominant over yellow seed coat color, and smooth is dominant over a wrinkled seed coat, what would be the expected phenotypic ratio of the offspring of a cross between two parents that are heterozygous for both alleles?

Parental Cross ( ______ x ______

23. In snapdragons, tall stems are dominant to short stems. Red is incompletely dominant to white flower color, the heterozygous condition being pink. A tall pink plant is crossed with a short red plant. If tall is heterozygous in this case, what will be the phenotypes of the offspring?

Parental Cross ( ______ x ______

PART FIVE: INCOMPLETE DOMINANCE

24. In Japanese four o’clock plants, the flowers may be red or white in the purebred form. But in the hybrid form, the flowers are pink and therefore show incomplete dominance. Write the correct genotype symbols for the following three plants.

a. red flowered plants _____

b. pink flowered plants _____

c. white flowered plants _____

25. What would be the possible genotypes and phenotypes resulting from a cross between a pink parent and red parent four o’clock plant?

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a. Parental genotypes = _____

b. F1 genotypes = _______________________

c. F1 phenotypes = ______________________

26. In short horned cattle, genes for red and white coats occur. Crosses between a red (RR) and a white (rr) produce an offspring whose coat appears a reddish-gray or roan color. A roan cow mates with a white bull. What will be the phenotypes of the offspring?

Parental Cross ( ___ x ___

Phenotypic Ratio of Offspring: __________

27. In radishes, when a plant homozygous for red radishes is crossed with a plant for homozygous white radishes, plants bearing purple radishes are produced.

a. What would the offspring look like in a cross between a purple and a white?

b. A red and a white?

c. A red and a purple?

28. Radishes may be long, oval or round. Long is dominant, round recessive and oval is a mixture of the two. If a farmer has all oval plants in his garden, what will be the phenotypes of the F1 generation?

a. Parental Cross ( ___ x ___

b. F1 gentoypes:

PART SIX: SEX-LINKED PROBLEMS:

29. In Drosophila, the allele for red eyes, R, is dominant over the allele for white eyes, r; this is sex-linked. Determine the possible genotype and phenotype ratios expected from a cross between:

|Cross |Genotype Ratio |Phenotype Ratio |

|a. Heterozygous female x red-eyed male | | |

|b. Heterozygous female x white-eyed male | | |

|c. Homozygous dominant female x red-eyed male | | |

|d. Homozygous dominant female x white-eyed male | | |

30. In humans, the gene for normal blood clotting, H, is dominant over the gene for hemophilia, h. This is a sex-linked trait found on the X chromosome. A woman with normal blood clotting and a man who has normal blood clotting have four children (see below). Determine the probable genotype for each member of the family.

Parental Genotypes _____ x _____

Normal son __________

Hemophiliac son __________

Normal daughter __________

Normal daughter __________

31. In humans, the gene for normal color vision, N, is dominant to the gene for red-green colorblindness, n; this trait is sex-linked and found on the X chromosome. The gene for brown eyes, B, is dominant to the gene for blue eyes, b. Calculate the probable genotype and phenotype of the children born to a blue-eyed woman who is heterozygous for color vision and a heterozygous brown-eyed man who is colorblind. (THIS IS TRICKY)

Parental Genotypes ( __________ x ___________

Genotype Probabilities:

Phenotype Probabilities:

32. In cats, black color is due to the gene, B, and yellow color is due to allele b. Yellow is incompletely dominant to black and with the heterozygous condition results in a color known as calico (black, yellow and white spotted). These genes are sex-linked. What kinds of offspring would you expect from a cross between a black male and a calico female?

Parental Cross ( _____ x _____

Types of offspring expected:

PART SEVEN: MULTIPLE ALLELES:

33. Assume that blood type is inherited as A and B dominant over O, but A and B incompletely dominant over each other. Genotypes AA and AO are then phenotypically type A, genotypes BB and BO are type B, genotype AB is type AB and genotype OO is type O blood. A man with type A blood marries a woman with type A blood. They have their first child as type O blood. What are the genotypes of the father, mother and baby?

Show work here (

|Individual |Genotype |

|Father | |

|Mother | |

|Baby | |

34. A man with type AB blood marries a woman with type O blood, but whose father was type A blood. What genotypic ratios would you expect for their children?

Parental Cross ( _____ x _____

35. A man with type B blood marries a woman with type A blood. They have six type AB children. What are the most probable genotypes of the father, mother and children?

Show work here (

|Individual |Genotype |

|Father | |

|Mother | |

|Children | |

36. A man whose father is type B and whose mother is type A has type A blood. He marries a type A woman whose parents had the same blood types as his parents. What are the genotypes of the man and woman and what is the probability that their first child will be blood type A?

Show work here (

|Individual |Genotype |

|Man | |

|Woman | |

Probability that 1st child will be type A blood?

37. A man with type A blood marries a woman with type B blood. They have a type O child. What is the probability of their 15th child have type O blood?

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