CH. 14 & 15 STUDY GUIDE: GENETICS
***Note: If you are not absolutely sure what happens to chromosomes during meiosis you should
review that before you begin this section on genetics.
KEY TERMS
1. F1 generation
22. multiple alleles
2. F2 generation
23. sex linked
42. Drosophila
melanogaster
43. mutant phenotypes
3. P generation
24. autosome (=somatic
chromosome)
4. Mendel's Laws
44. chromosomal
mutations
25. sex chromosome
45. giant chromosomes
5. Laws of Probability
26. X chromosome
46. nondisjunction
6. gene
27. Y chromosome
28. Barr body
47. autosomal
abnormalities
29. sex influenced traits
48. trisomy
30. epistasis
49. polyploid
31. pleiotropy
50. Down's syndrome
32. penetrance
51. sex chromosome
disorders
7. dominant
8. recessive
9. locus
10. allele
11. homozygous
12. heterozygous
33. expressivity
13. genotype
34. pedigree
14. phenotype
35. sickle-cell disease
15. Punnett square
36. carrier
16. monohybrid cross
37. Huntington's disease
17. dihybrid cross
52. hemophilia
53. Barr body
54. sex-linked trait
55. sex-influenced trait
56. Kleinfelter's syndrome
18. trihybrid cross
38. consanguineous
mating
57. Turner's syndrome
19. test cross
39. amniocentesis
58. super females
20. incomplete dominance
40. polygenetic inheritance
59. Nature vs. nurture
21. codominance
41. wild type
60. Linkage
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WORD ROOTS
co - = together (codominance: phenotype in which both dominant alleles are expressed in the
heterozygote)
- centesis = a puncture (amniocentesis: a technique for determining genetic abnormalities in a
fetus by the presence of certain chemicals or defective fetal cells in the amniotic fluid, obtained by
aspiration from a needle inserted into the uterus)
di - = two (dihybrid cross: a breeding experiment in which parental varieties differing in two traits
are mated)
epi - = beside; - stasis = standing (epistasis: a phenomenon in which one gene alters the
expression of another gene that is independently inherited)
geno - = offspring (genotype: the genetic make up of an organism)
hetero - = different (heterozygous: having two different alleles for a trait)
homo - = alike (homozygous: having two identical alleles for a trait)
pedi - = a child (pedigree: a family tree describing the occurrence of heritable characters in
parents and offspring across as many generations as possible)
pheno - = appear (phenotype: the physical and physiological traits of an organism)
pleio - = more (pleiotropy: when a single gene impacts more than one characteristic)
poly - = many; gene - = produce (polygenic: an additive effect of two or more gene loci on a
single phenotypic character)
aneu - = without (aneuploidy: a chromosomal aberration in which certain chromosomes are
present in extra copies or are deficient in number)
cyto - = cell (cytological maps: charts of chromosomes that locate genes with respect to
chromosomal features)
hemo - = blood (hemophiliac: a human genetic disease caused by a sex-linked recessive allele,
characterized by excessive bleeding following injury)
mono - = one (monosomic: a chromosomal condition in which a particular cell has only one copy
of a chromosome, instead of the normal two; the cell is said to be monosomic for that
chromosome)
non - = not; dis - = separate (nondisjunction: an accident of meiosis, in which both members of a
pair of homologous chromosomes or both sister chromatids fail to move apart properly)
poly - = many (polyploidy: a chromosomal alteration in which the organism possesses more than
two complete chromosome sets)
re - = again; com - = together; bin - = two at a time (recombinant: an offspring whose phenotype
differs from that of the parent)
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trans - = three; soma - = body (trisomic: a chromosomal condition in which a particular cell has
an extra copy of one chromosome, instead of the normal two; the cell is said to be trisomic for
that chromosome)
QUESTIONS
1. Discuss Mendel's conclusions and relate them to the chromosomal theory
of inheritance. Include comments on each of the following: Law of
segregation, Law of independent assortment
2. Differentiate between: dominant-recessive; allele-gene; homozygousheterozygous; phenotype-genotype; monohybrid-dihybrid-trihybrid-etc.
3. What does it mean when we say a strain of organisms is "true breeding"?
4. What is a test cross?
5. Explain the inheritance of human ABO blood groups.
6. Describe and give an example of the following: pleiotropy, penetrance,
expressivity and epistasis.
7. What are polygenetic traits?
8. Give two examples of dominant human genetic disorders.
9. Who is T.H. Morgan? What were his major contributions to genetics?
10. What does it mean if we say genes are linked? Which of Mendel's "laws"
do linked genes break?
11. Explain linkage and show how crossover frequencies are used to make
chromosome maps.
12. What kind of information is shown on chromosome maps?
13. Explain how sex is determined in humans.
14. Describe the X-Y, W-Z and haplo-diploidy systems of sex determination
and give examples of each.
15. Discuss sex-linked inheritance in terms of X and Y chromosomes.
16. Explain gene dosage in terms of human female X chromosomes. Include
in your description an explanation of what Barr bodies are.
17. What is aneuploidy(think about roots and prefixes- an, eu and ploidy)?
Describe triploidy, and polyploidy.
18. Explain nondisjunction and tell how it affects chromosomal composition of
cells.
19. Discuss chromosomal aberrations, including changes in individual
chromosomes and alterations in chromosome number. Include in your
discussion causes of these aberrations.
20. Explain how translocations, deletions, duplications and inversions alter
chromosomal composition.
21. Describe the cause of Down syndrome.
22. Give five examples of human genetic diseases.
23. Distinguish between Turner's, Kleinfelter's and super female (metafemale)
syndromes.
24. Explain why statistics is a useful genetic(or scientific) tool.
25. Explain why a large sample is more statistically reliable than a small
sample?
26. Why is Drosophila such a good organism in which to study genetics?
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A METHOD FOR DOING MENDELIAN CROSSES
1. Know the traits to be used.
2. Know how the alleles are expressed. Which is dominant, which is recessive,
which is incomplete.
3. Establish a letter symbol for each trait. Use capital letters for dominant traits
and small letters for the recessive allele.
4. Determine the genotypes of the parents. Keep in mind which traits are
dominant and which are recessive when you do this.
5. Determine the gametes which are produced by the parents.
6. Combine the gametes. A Punnett square can be used.
7. Determine the genotype and phenotype ratios of the offspring.
TIPS FOR SOLVING GENETICS PROBLEMS
1. Only homozygous recessive genotypes express the recessive trait.
2. If an individual expresses a dominant trait that individual has AT LEAST one
dominant gene.
3. If an intermediate condition or blending of traits is observed, expect
codominance.
4. If a trait expresses itself mainly in males, suspect sex-linkage.
5. Monohybrid heterozygous crosses result in 3:1 phenotype ratios.
6. Dihybrid heterozygous crosses result in 9:3:3:1 phenotype ratios.
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