Chap 20

Question 1

1) Genes are?.

Answer 1

1. located on chromosomes, inherited in the same way as chromosomes, arranged in linear sequence on chromosomes, may be exchanged between homologous chromosomes.

Question 2

2) What concept helps to explain why close relatives have a varied mix of genetic traits?

Answer 2

2. independent assortment

Question 3

3) Describe homologous chromosomes.

Answer 3

3. There are two of each kind, Each parent contributes one of each homologous pair, Most homologous chromosomes carry the same genes for the same traits, Homologous chromosomes pair up during early meiosis

Question 4

4) DNA coding regions that affect the same trait are called????..

Answer 4

4. alleles

Question 5

5) The location of a gene on a chromosome is its????????.

Answer 5

5. locus

Question 6

6) True or False? The closer together genes are found on a chromosome, the greater the chance that crossing over will occur between them.

Answer 6

6. False

Question 7

7) What is a karyotype?

Answer 7

7. is a visual display of chromosomes arranged according to size.

Question 8

8) In karyotyping, what distinguishes individual chromosomes from each other?

Answer 8

8. a comparison of chromosome lengths, bands produced on chromosomes by differential staining, the position of centromeres, the relative lengths of the “arms.”

Question 9

9) Karyotyping is usually done using what kind of cells?

Answer 9

9. blood

Question 10

10) What can Karyotype analysis be used in?

Answer 10

10. prenatal diagnosis to detect chromosomal mutations and genetic disorders in embryos.

Question 11

11) With respect to chromosomes how is the difference between normal human males and females defined

Answer 11

11. In males, an X is replaced by a Y.

Question 12

12) Describe sex chromosomes.

Answer 12

12. determine gender, vary from one sex to another, carry some genes that have nothing to do with sex, appear in a diploid cell as either XX or XY

Question 13

13) True or false, for the sex chromosomes: The Y chromosome carries a greater number of nonsexual traits.

Answer 13

13. False

Question 14

14) True or false, for the sex chromosomes: X and Y are different in size but carry nearly equal numbers of genes.

Answer 14

14. False

Question 15

15) True or false, for the sex chromosomes: The X chromosome carries more genes for nonsexual traits.

Answer 15

15. True

Question 16

16) True or false, for the sex chromosomes: The X chromosome carries only gender-related genes.

Answer 16

16. False

Question 17

17) In human females, one of the sex chromosomes is switched off during early development. What is this called?

Answer 17

17. X inactivation

Question 18

18) When does X inactivation occur?

Answer 18

18. after the first cleavages of the zygote

Question 19

19) What is a condensed, female X chromosome called?

Answer 19

19. Barr body

Question 20

20) Because geneticists can’t use human subjects for experimentation, a ____ is used to obtain an analysis of a genetic family history.

Answer 20

20. pedigree chart

Question 21

21) Which term could be used to describe a person with one normal gene and one gene for a recessive disease?

Answer 21

21. carrier

Question 22

22) A carrier is a person who???

Answer 22

22. carries a recessive gene for a genetic disorder but shows no signs or symptoms

Question 23

23) Chromosomes other than those involved in sex determination are known as

Answer 23

23. autosomes

Question 24

24) An autosomal recessive disorder ??.

Answer 24

24. can appear only in children of parents who both carry the gene

Question 25

25) The probability of producing a phenotypically normal child by two parents who are carriers for an autosomal recessive disorder is

Answer 25

25. 75 percent

Question 26

26) The probability of producing a child who suffers from cystic fibrosis by two parents who are carriers for the autosomal recessive disorder is

Answer 26

26. 25 percent

Question 27

27) If a study of several pedigrees demonstrated that two parents are normal but their children express a trait, then the trait is controlled by a

Answer 27

27. recessive gene

Question 28

28) A woman is diagnosed as having the genetic disease known as Huntington’s disease. It is a rare defect caused by an autosomal dominant allele. The chance for any one of her eggs to carry the gene is

Answer 28

28. dependent on the genotype of the woman

Question 29

29) In an autosomal dominant disorder such as Huntington’s, two heterozygous parents have the probability of passing the gene on to ____ percent of their children.

Answer 29

29. 75

Question 30

30) A color-blind man and a woman with normal vision whose father was color blind have a son. Color blindness, in this case, is caused by an X-linked recessive gene. If only the male offspring are considered, the probability that their son is color-blind is

Answer 30

30. 50 percent

Question 31

31) Red-green color blindness is an X-linked recessive trait in humans. A color-blind woman and a man with normal vision have a son. What is the probability that the son is color-blind?

Answer 31

31. 100 percent

Question 32

32) Red-green color blindness is an X-linked recessive trait in humans. What is the probability that a color-blind woman and a man with normal vision will have a color-blind daughter?

Answer 32

32. 0 percent

Question 33

33) If a daughter expresses an X-linked recessive gene, she inherited the trait from

Answer 33

33. both parents

Question 34

34) Where is a human X-linked gene found?

Answer 34

34. found on the X chromosome

Question 35

35) Color blindness is an X-linked trait in humans. If a color-blind woman marries a man with normal vision, the children will be

Answer 35

35. all color-blind sons, but carrier daughters.

Question 36

36) A woman heterozygous for color blindness (an X-linked recessive allele) marries a man with normal color vision. What is the probability that their first child will be color-blind?

Answer 36

36. 25 percent

Question 37

37) Why do males tend to be affected in greater numbers by X-linked recessive genetic disorders than are females?

Answer 37

37. males receive only one recessive gene for the disorder

Question 38

38) An affected father with faulty enamel trait, a sex-linked dominant trait, will pass the condition on to

Answer 38

38. all of his daughters

Question 39

39) Give at least four examples of chromosomal aberrations.

Answer 39

39. Deletion, extra chromosomes, translocation (exchange of parts between nonhomologs), fewer chromosomes

Question 40

40) If a chromosome’s gene sequence is represented by the letters A B C D E F G before modification and A B C D L M N O P afterward, this would be an example of what kind of mutation?

Answer 40

40. translocation.

Question 41

41) If a chromosome’s gene sequence is represented by the letters A B C D E F G before modification and A B C D C D E F G afterward, this would be an example of what kind of mutation?

Answer 41

41. duplication.

Question 42

42) A chromosome’s gene sequence that was A B C D E F before damage and A B C F G after is an example of

Answer 42

42. deletion

Question 43

43) What is the genotype of a normal human female?

Answer 43

43. XX

Question 44

44) What is the genotype of a normal human male?

Answer 44

44. XY

Question 45

45) In cats, the allele B produces black, while b produces yellow. Neither gene is dominant, and in the heterozygous state, the phenotype is a combination of yellow and black spots called tortoiseshell. The alleles B and b are X-linked. If a tortoiseshell cat has three tortoiseshell kittens and two black kittens, give the genotype and phenotype of the tomcat that produced them, and give the sex of the kittens.

Answer 45

45. BY black, tortoiseshell female, black males

Question 46

48) White eyes in Drosophila is a mutation that turned out to be X-linked recessive. Would you expect that the white eye was discovered the first time in a male or female?

Answer 46

48. Male