1. Chromosomes and Human Inheritance
Chapter 12

2. Strange Genes, Richly Tortured Minds
Impacts, Issues Video
Strange Genes, Richly Tortured Minds

3. Genes Units of information about heritable traits
In eukaryotes, distributed among chromosomes
Each has a particular locus
Location on a chromosome

4. Homologous Chromosomes
Homologous autosomes are identical in length, size, shape, and gene sequence
Sex chromosomes are nonidentical but still homologous
Homologous chromosomes interact, then segregate from one another during meiosis

5. Alleles Different molecular forms of a gene Arise through mutation
Diploid cell has a pair of alleles at each locus
Alleles on homologous chromosomes may be same or different

6. Karyotype Preparation

7. Karyotypes
Karyotypes are used to identify defects in the chromosomes like:
Missing chromosomes
Multiple chromosomes

8. Karyotype Preparation

9. Autosomal Dominant Inheritance
Trait typically appears in every generation

10. Autosomal Dominant Inheritance

11. Huntington Disorder Autosomal dominant allele
Causes involuntary movements, nervous system deterioration, death
Symptoms don’t usually show up until person is past age 30
People often pass allele on before they know they have it

12. Hutchinson-Gilford Progeria
Mutation causes accelerated aging
No evidence of it running in families
Appears to be dominant
Seems to arise as spontaneous mutation
Usually causes death in early teens

13. Hutchinson-Gilford Progeria

14. The Y Chromosome Fewer than two dozen genes identified
One is the master gene for male sex determination
SRY gene (sex-determining region of Y)
SRY present, testes form
SRY absent, ovaries form

15. The X Chromosome Carries more than 2,300 genes
Most genes deal with nonsexual traits
Genes on X chromosome can be expressed in both males and females

17. X-Linked Recessive Inheritance
Males show disorder more than females
Son cannot inherit disorder from his father

18. Color Blindness

19. Color Blindness

20. Hemophilia

21. Fragile X Syndrome An X-linked recessive disorder
Causes mental retardation
Mutant allele for gene that specifies a protein required for brain development
Allele has repeated segments of DNA

22. Chromosomal Mutations
involve a change in the structure of a chromosome

23. Alterations of Chromosome Structure
Breakage of a chromosome can lead to four types of changes in chromosome structure
Deletion removes a chromosomal segment
Duplication repeats a segment
Inversion reverses orientation of a segment within a chromosome
Translocation moves a segment from one chromosome to another non homologous chromosome 23

24. Chromosomal Mutations24

25. Duplications and translocations also tend to be harmful
A diploid embryo that is homozygous for a large deletion is likely missing a number of essential genes; such a condition is generally lethal
Duplications and translocations also tend to be harmful
In inversions, the balance of genes is normal but phenotype may be influenced if the expression of genes is altered 25

26. Deletion
Cru-Du-Chat
Cru-Da-Chat Cry

27. Translocation
A piece of one chromosome becomes attached to another nonhomologous chromosome
Most are reciprocal
Philadelphia chromosome arose from a reciprocal translocation between chromosomes 9 and 22

28. Abnormal Chromosome Number
Large-scale chromosomal alterations in humans and other mammals often lead to spontaneous abortions (miscarriages) or cause a variety of developmental disorders
Plants tolerate such genetic changes better than animals do 28

29. NONDISJUNCTION Nondisjunction
pairs of homologous chromosomes do not separate normally during meiosis
as a result, one gamete receives two of the same type of chromosome, and another gamete receives no copy 29

30. Meiosis I Nondisjunction
Figure Meiotic nondisjunction (step 1) 30

31. Meiosis I Nondisjunction Meiosis II Non- disjunction
Figure Meiotic nondisjunction (step 2) 31

32. Nondisjunction of homo- logous chromosomes in meiosis I (b)
Meiosis II
Non-
disjunction
Gametes
Figure Meiotic nondisjunction (step 3)
n  1
n  1
n − 1
n − 1
n  1
n − 1 n n
Number of chromosomes
(a)
Nondisjunction of homo-
logous chromosomes in
meiosis I
(b)
Nondisjunction of sister
chromatids in meiosis II 32

33. only one copy of a particular chromosome Trisomic zygote
Aneuploidy
results from the fertilization of gametes in which nondisjunction occurred
offspring with this condition have an abnormal number of a particular chromosome
Monosomic zygote
only one copy of a particular chromosome
Trisomic zygote
three copies of a particular chromosome 33

34. Aneuploidy Individuals have one extra or less chromosome
(2n + 1 or 2n - 1)
Major cause of human reproductive failure
Most human miscarriages are aneuploids

35. Polyploidy
Individuals have three or more of each type of chromosome (3n, 4n)
Common in flowering plants
Lethal for humans
99% die before birth
Newborns die soon after birth

36. Down Syndrome Trisomy of chromosome 21
Mental impairment and a variety of additional defects
Can be detected before birth
Risk of Down syndrome increases dramatically in mothers over age 35

39. Down Syndrome

40. Patau Syndrome Trisomy 13
Serious eye, brain, circulatory defects as well as cleft palate
1:5000 live births

42. Edwards Syndrome Trisomy 18 Every organ is affected 1:10,000 births
Life expectancy few months (full trisomy 18)

44. Turner Syndrome Inheritance of only one X (XO)
98% spontaneously aborted
Survivors are short, infertile females
No functional ovaries
Secondary sexual traits reduced
May be treated with hormones, surgery

47. Klinefelter Syndrome XXY condition
Results mainly from nondisjunction in mother (67%)
Phenotype is tall males
Sterile or nearly so
Feminized traits (sparse facial hair, somewhat enlarged breasts)
Treated with testosterone injections

49. XYY Condition Taller than average males
Most otherwise phenotypically normal
Some mentally impaired
Once thought to be predisposed to criminal behavior, but studies now discredit

51. Genetic Disorders and Genetic Abnormalities

52. Prenatal Diagnosis
Amniocentesis

53. CVS - Chorionic villus sampling

54. Pedigree Analysis

55. Pedigree Analysis
In humans, pedigree analysis is an important tool for studying inherited diseases
Pedigree analysis uses family trees and information about affected individuals to:
figure out the genetic basis of a disease or trait from its inheritance pattern
predict the risk of disease in future offspring in a family (genetic counseling)

56. Pedigree Analysis I II Mating Normal Normal Female Male 1st born
Affected
Siblings

57. Pedigree’s How to read pedigrees Basic patterns of inheritance
autosomal, recessive
autosomal, dominant
X-linked, recessive
X-linked, dominant (very rare)

58. Autosomal Recessive Trait is rare in a pedigree
Trait often skips generations (hidden in heterozygous carriers)
Trait affects males and females equally
Most common Autosomal Recessive disorders
Cystic fibrosis
Sickle cell anemia
Phenylketonuria (PKU)
Tay-Sachs disease

59. Autosomal Recessive

60. (parents, aunts, and uncles) FF or Ff ff ff Ff Ff ff
Figure 11.14b
Key
Male
Affected
male
Mating
Offspring, in
birth order
(first-born on left)
Female
Affected
female
1st generation
(grandparents) Ff Ff ff Ff
2nd generation
(parents, aunts, and uncles)
FF or Ff ff ff Ff Ff ff
3rd generation
(two sisters)
Figure 11.14b Pedigree analysis (part 2: attached earlobe) ff FF or Ff
Attached earlobe
Free earlobe
(b) Is an attached earlobe a dominant or recessive trait? 60

61. Autosomal Dominant Trait is common in the pedigree
Trait is found in every generation
Affected individuals transmit the trait to approximately 1/2 of their children (regardless of sex)

62. Autosomal Dominant

63. (parents, aunts, and uncles)
Key
Male
Affected
male
Mating
Offspring, in
birth order
(first-born on left)
Female
Affected
female
1st generation
(grandparents) Ww ww ww Ww
2nd generation
(parents, aunts, and uncles) Ww ww ww Ww Ww ww
3rd generation
(two sisters)
Figure 11.14a Pedigree analysis (part 1: widow’s peak) WW or Ww ww
Widow’s peak
No widow’s peak
(a) Is a widow’s peak a dominant or recessive trait? 63

64. X-Linked Recessive Trait is rare in pedigree Trait skips generations
Affected fathers DO NOT pass to their sons,
Males are more often affected than females

65. X-Linked Recessive

67. X-Linked Dominant Trait is common in pedigree
Affected fathers pass to ALL of their daughters
Males and females are equally likely to be affected
X-linked dominant diseases are extremely unusual
Often, they are lethal (before birth) in males and only seen in females
ex. incontinentia pigmenti (skin lesions)
ex. X-linked rickets (bone lesions)

68. X-Linked Dominant