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Genetics Chapter 3 Study Guide



Modified True/False
Indicate whether the sentence or statement is true or false.  If false, change the identified word or phrase to make the sentence or statement true.
 

1. 

When Mendel crossed purebred short plants with purebred tall plants, all of the offspring were short. _________________________

 

2. 

A hybrid is the offspring of parents that have different alleles for a trait. _________________________

 

3. 

A pea plant that is heterozygous for tall stems has the alleles Tt. _________________________

 

4. 

A Punnett square shows all the possible combinations of alleles in parents. _________________________

 

5. 

An organism’s physical appearance is its phenotype. _________________________

 

6. 

The sex cells produced by meiosis have twice the number of chromosomes as the parent cells. _________________________

 

7. 

Chromosomes carry genes from parents to offspring. _________________________

 

8. 

The number of DNA bases forms a genetic code. _________________________

 

9. 

A mutation in a sex cell can be passed to offspring. _________________________

 

Multiple Choice
Identify the letter of the choice that best completes the statement or answers the question.
 

10. 

What did Gregor Mendel do to study different characteristics in his genetics experiments?
a.
He studied only asexual animals.
b.
He studied only self-pollinating plants.
c.
He cross-pollinated plants.
d.
He cross-pollinated animals.
 

11. 

In Mendel’s experiments, what proportion of the plants in the F2 generation had a trait that had been absent in the F1 generation?
a.
none
b.
one fourth
c.
half
d.
three fourths
 

12. 

Factors that control traits are called
a.
genes.
b.
purebreds.
c.
recessives.
d.
parents.
 

13. 

Scientists call an organism that has two different alleles for a trait a
a.
hybrid.
b.
trait.
c.
purebred.
d.
factor.
 

14. 

What does the notation TT mean to geneticists?
a.
two dominant alleles
b.
two recessive alleles
c.
at least one dominant allele
d.
one dominant and one recessive allelle
 

15. 

What does the notation Tt mean to geneticists?
a.
two dominant alleles
b.
two recessive alleles
c.
at least one recessive allele
d.
one dominant allele and one recessive allelle
 

16. 

What is probability?
a.
the actual results from a series of events
b.
the likelihood that a particular event will occur
c.
the way the results of one event affect the next event
d.
the number of times a coin lands heads up
 

17. 

What did Mendel predict was the probability of producing a tall plant from a genetic cross of two hybrid tall plants?
a.
one in four
b.
two in four
c.
three in four
d.
four in four
 

18. 

What does a Punnett square show?
a.
all the possible outcomes of a genetic cross
b.
only the dominant alleles in a genetic cross
c.
only the recessive alleles in a genetic cross
d.
all of Mendel’s discoveries about genetic crosses
 

19. 

If a homozygous black guinea pig (BB) is crossed with a homozygous white guinea pig (bb), what is the probability that an offspring will have black fur?
a.
25 percent
b.
50 percent
c.
75 percent
d.
100 percent
 

20. 

An organism’s physical appearance is its
a.
genotype.
b.
phenotype.
c.
codominance.
d.
heterozygous.
 

21. 

What does codominance mean in genetics?
a.
Both alleles are dominant.
b.
Both alleles are recessive.
c.
The alleles are neither dominant nor recessive.
d.
Each allele is both dominant and recessive.
 

22. 

What is the chromosome theory of inheritance?
a.
Chromosomes are carried from parents to offspring on hybrids.
b.
Genes are carried from parents to offspring on chromosomes.
c.
Hybrid pairs of chromosomes combine to form offspring.
d.
Codominant genes combine to form new hybrids.
 

23. 

Walter Sutton discovered that the sex cells of grasshoppers have exactly
a.
12 times the number of chromosomes found in the body cells.
b.
twice the number of chromosomes found in the body cells.
c.
the same number of chromosomes found in the body cells.
d.
half the number of chromosomes found in the body cells.
 

24. 

What happens during meiosis?
a.
Each sex cell loses half of its chromosomes.
b.
Chromosome pairs separate to form new sex cells.
c.
Each sex cell copies itself to form four new chromosomes.
d.
Chromosome pairs remain together when new sex cells are formed.
 

25. 

When sex cells combine to produce offspring, each sex cell will contribute
a.
one fourth of the normal number of chromosomes.
b.
half the normal number of chromosomes.
c.
the normal number of chromosomes.
d.
twice the normal number of chromosomes.
 

26. 

What is the genetic code?
a.
the order of nitrogen bases along a gene
b.
the number of nitrogen bases in a DNA molecule
c.
the order of amino acids in a protein
d.
the number of guanine and cytosine bases in a chromosome
 

27. 

What is a mutation?
a.
any change that is harmful to an organism
b.
any change in a gene or chromosome
c.
any change that is helpful to an organism
d.
any change in the phenotype of a cell
 

28. 

A mutation is harmful to an organism if it
a.
changes the DNA of the organism.
b.
changes the phenotype of the organism.
c.
reduces the organism’s chances for survival and reproduction.
d.
makes the organism better able to avoid predators.
 

29. 

Which term refers to physical characteristics that are studied in genetics?
a.
traits
b.
offspring
c.
generations
d.
hybrids
 

30. 

The different forms of a gene are called
a.
alleles.
b.
factors.
c.
masks.
d.
traits.
 

31. 

What does the notation tt mean to geneticists?
a.
two dominant alleles
b.
two recessive alleles
c.
at least one dominant allele
d.
one dominant and one recessive allelle
 

32. 

An organism’s genotype is its
a.
genetic makeup
b.
feather color
c.
physical appearance
d.
stem height
 

33. 

An organism that has two identical alleles for a trait is
a.
codominant.
b.
tall.
c.
homozygous.
d.
heterozygous.
 

34. 

A heterozygous organism has
a.
three different alleles for a trait.
b.
two identical alleles for a trait.
c.
only one allele for a trait.
d.
two different alleles for a trait.
 

Completion
Complete each sentence or statement.
 

35. 

The offspring of a ____________________ plant will always have the same alleles for a trait as the parent.
 

 

36. 

Mendel used ____________________-pollination to produce purebred plants.
 

 

37. 

If a ____________________ allele is present, its trait will appear in the organism.
 

 

38. 

In pea plants, the tall-stem allele and the short-stem allele are different forms of the same ____________________.
 

 

39. 

If D represents the dominant allele of a gene, then ____________________ represents the recessive allele.
 

 

40. 

Mendel used the principles of ____________________ to predict what percent of offspring would show a particular trait.
 

 

41. 

If each of ten events is equally likely to occur, the probability of each individual event occurring is ____________________ percent.
 

 

42. 

A chart used to predict results of genetic crosses is known as a(n) ____________________.
 

 

43. 

In a cross between two hybrid Tt pea plants, ____________________ percent of the offspring will be Tt.
 

 

44. 

An organism that has two dominant or two recessive alleles is said to be ____________________ for that trait.
 

 

45. 

Alleles that are neither dominant nor recessive produce an inheritance pattern known as ____________________.
 

 

46. 

Genes are located on structures called ____________________.
 

 

47. 

The process in which a parent cell divides twice to produce sex cells is called ____________________.
 

 

48. 

If all of the sex cells of an organism have the T allele, the genotype of that organism must be ____________________.
 

 

Essay
 

49. 

In pea plants, green pod color is controlled by a dominant allele. Yellow is controlled by a recessive allele. Explain why a plant with yellow pods can never be a hybrid.
 

50. 

A woman gives birth to a son. Two years later, she gives birth to another son. What is the probability that her third child will be a girl? Explain your reasoning.
 

51. 

Some clover plants have leaves with a white stripe. Other clover plants have leaves with a white spot. When these two types of plants are crossed, the leaves of the offspring have a white stripe and a white spot. Explain how this inheritance pattern occurs.
 

52. 

Explain the function of meiosis.
 

53. 

Explain why Mendel’s cross of purebred tall and short pea plants resulted in only tall plants.
 

54. 

In pea plants, the allele for smooth pods (S) is dominant over the allele for pinched pods (s). Construct a Punnett square that shows a cross between an SS plant and an Ss plant. Predict what percent of the offspring are likely to have smooth pods.
 



 
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