1. Chapter 14
Human Heredity

2. Section 14-1 Human Chromosomes

3. Human Genome
A genome is the full set of genetic information that an organism carries in its DNA.
Scientists study chromosomes to understand an organisms genome.

4. Karyotype
A karyotype shows the complete diploid set of chromosomes grouped together in pairs, arranged in order of decreasing size.

5. Karyotype How is a Karyotype made?
Chromosomes are photographed during mitosis.
Chromosomes are cut out of the photograph.
They are grouped into similar pairs and arranged in decreasing size.

7. HUMAN CHROMOSOMES THERE ARE 46 CHROMOSOMES IN OUR BODY CELLS.
THEY ARE ARRANGED INTO 23 PAIRS.
THE 23RD PAIR IS CALLED THE SEX CHROMOSOMES.
THE REMAINING 22 PAIRS ARE CALLED AUTOSOMES.
Total number of chromosomes:
female – 46,XX
male – 46, XY

8. Sex Chromosomes
autosomal chromosomes
sex chromosomes

9. Sex Chromosomes
Humans have two sex chromosomes or one pair (the 23rd).
Determine an individuals sex.
Females: XX
Males: XY

10. Sex Chromosomes Each egg cell carries one X chromosome. (23 X).
Half the sperm carry an X chromosome (23 X) and half carry a Y chromosome (23 Y).
Therefore, males determine the sex of the child.

11. Autosomal Chromosomes
Autosomal chromosomes or autosomes are the other 44 human chromosomes or 22 pairs.

12. Transmission of Human Traits
Human genes follow the same Mendelian patterns of inheritance as the genes of other organisms.

13. Dominant and Recessive Alleles
Many human traits follow a pattern of simple dominance.
Ex. Recessive alleles produce red hair.

14. Albinism is recessive
albino Africans

15. Prevalence of dominance
Because an allele is dominant does not mean it is better or more common.
Polydactyly:
dominant allele

16. Polydactyly individuals are born with extra fingers or toes
dominant to the recessive allele for 5 digits
recessive allele far more common than dominant
 399 individuals out of have only 5 digits
 most people are homozygous recessive (aa)

17. Hound Dog Taylor

18. Codominant and Multiple Alleles
The alleles for many human genes display codominant inheritance.
Ex. ABO blood group.
genotype
phenotype
status
IA IA IA i
type A
type A oligosaccharides on surface of RBC __
IB IB IB i
type B
type B oligosaccharides on surface of RBC
IA IB
type AB
both type A & type B oligosaccharides on surface of RBC
universal recipient
i i
type O
no oligosaccharides on surface of RBC
universal donor

19. Blood compatibility Matching compatible blood groups.
critical for blood transfusions
A person produces antibodies against oligosaccharides in foreign blood.
wrong blood type
Donor’s blood has A or B oligosaccharide that is foreign to recipient.
Antibodies in recipient’s blood bind to foreign molecules.
Cause donated blood cells to clump together.
Can kill the recipient.
Karl Landsteiner
( )

20. Blood donation

21. Sex-Linked Inheritance
Genes located on the X and Y chromosomes show a pattern of inheritance called sex-linkage.
A sex linked gene is a gene located on a sex chromosome.
Males have just one X chromosome. Thus, all X-linked alleles are expressed in males, even if they are recessive.

22. Sex-linked Traits X-linked follow the X chromosomes.
males get their X from their mother.
trait is never passed from father to son because the father’s X chromosome is not passed.
Y-linked
very few traits.
only 26 genes.
trait is only passed from father to son.
females cannot inherit trait.

23. Genes on Sex Chromosomes
Y chromosome
SRY: sex-determining region
master regulator for maleness
turns on genes for production of male hormones
Pleiotropy – a single gene affects many!
X chromosome
other traits beyond sex determination
hemophilia
Duchenne muscular dystrophy
color-blind
Duchenne muscular dystrophy affects one in 3,500 males born in the United States.
Affected individuals rarely live past their early 20s.
This disorder is due to the absence of an X-linked gene for a key muscle protein, called dystrophin.
The disease is characterized by a progressive weakening of the muscles and loss of coordination.

24. Map of human X chromosome
Sex-linked
usually X-linked
more than 60 diseases traced to genes on X chromosome

25. Map of Human Y chromosome?
< 30 genes on Y chromosome

26. Sex-linked traits XHXh XHY XHXh XH Xh XH Y XHXH XHXH XHY XHY XH Xh XHY
sex-linked recessive
XHXh
XHY
XHXh XH Xh XH Y
male / sperm
XHXH
XHXH
XHY
XHY XH Xh
female / eggs
XHY Y XH
XHXh
XHXh
XhY
XhY

27. SEX-LINKED RECESSIVE DISORDERS
Colorblindness
unable to distinguish some colors
mostly red green
XCXC = NORMAL FEMALE
XC Xc = CARRIER FEMALE
Xc Xc = COLORBLIND FEMALE
XCY = NORMAL MALE
XcY = COLORBLIND MALE

28. SEX-LINKED RECESSIVE DISORDERS
Hemophilia
A protein necessary for normal blood clotting is missing.
1 in 10,000 males.
People with hemophilia can bleed to death from minor cuts and may suffer from internal bleeding.
Treated with normal clotting factors.

29. Hemophilia

31. X-Chromosome Inactivation
Females have two X chromosomes, but males have only one.
Females can inactivate parts of an X chromosome and use the same genetic information from the corresponding chromosome.
The inactivated X chromosome forms a dense region in the nucleus called a Barr Body.

32. Polygenic inheritance
Some phenotypes determined by additive effects of 2 or more genes on a single character.
phenotypes on a continuum
human traits
skin color
height
weight
eye color
intelligence
behaviors

33. Human Pedigrees
A pedigree is a chart that shows the presence or absence of a trait according to the relationships between parents, siblings, and offspring.
The information gained from pedigree analysis makes it possible to determine the nature of genes and alleles associated with inherited human traits.

34. Human Pedigrees
Draw and label the pedigree chart and symbols on the next slide. Include alleles for the recessive disease being traced.

35. A Pedigree A circle represents a female. A square represents a male.
A horizontal line connecting a male and female represents a marriage.
A vertical line and a bracket connect the parents to their children.
A half-shaded circle or square indicates that a person is a carrier of the trait.
A circle or square that is not shaded indicates that a person neither expresses the trait nor is a carrier of the trait.
A completely shaded circle or square indicates that a person expresses the trait.

36. Section 14-2 Human Genetic Disorders

37. Molecule to Phenotype
Changes in a gene’s DNA sequence can change proteins by altering their amino acid sequences, which may directly affect one’s phenotype.

38. Sickle Cell Disease
Characterized by the bent and twisted shape of the red blood cell.
Sickle shaped red blood cell tend to get stuck in the capillaries.
Produce physical weakness and damage to the brain, heart and spleen.
Sometimes fatal.
Change in just one DNA base.
This change inserts amino acid valine in place of glutamic acid.
Hemoglobin molecules stick together and form long chains that produce the characteristic shape of sickled cells.

41. Q: Why do so many African Americans carry the sickle cell allele?
Many African Americans have West Central African ancestry where malaria is a serious problem.
People who are heterozygous for the sickle cell allele don’t get sickle cell and they don’t get malaria. These people survive to pass on the hetero alleles so they become more prominent in the gene pool.

42. Where malaria is common
Where sickle cell is common

43. Cystic Fibrosis (CF)
Most common among people whose ancestors come from northern Europe.
Caused by a recessive allele on chromosome 7.
Produce a thick heavy mucus that clogs their lungs and breathing passageways.
Serious digestive problems.
Only half survive into their 20’s.

45. Huntington's
Progressive loss of muscle control and mental function until death occurs.
People with disease show no symptoms until they are in their 30’s and 40’s.

46. Huntington's affect on the brain

47. Nondisjunction
When homologous chromosomes fail to separate in meiosis.
Most common error in meiosis.

48. If nondisjunction occurs, abnormal numbers of chromosomes may find their way into gametes.

50. Down Syndrome
When nondisjunction happens and a baby is born with 3 copies of chromosome 21.
Trisomy 21.
1 in 800 in U.S.
Mild to severe retardation.
Susceptible to many diseases.
Increased frequency of birth defects.

53. Turners Syndrome (female)
Only inherit one X chromosome, and no Y.
Genotype = XO
Women with Turner syndrome are sterile, their sex organs don’t properly develop at puberty.

55. Klinefelters Syndrome (males)
Inherit extra X chromosomes.
Genotype = XXY
The extra X interferes with meiosis and usually prevents them from reproducing.
Some cases XXXY or XXXXY.
These abnormalities show us the role of Y in sex determination.
Even in combination with several X’s, the Y makes them male.
But if this Y is absent, the embryo develops into a female.

57. XYY (males) Inherit extra Y chromosomes. Genotype = XYY
The extra Y chromosome has been linked to violent offenders.
Many lawyers are using the disorder as a defense tactic.

58. Pleiotropy Most genes are pleiotropic.
one gene affects more than one phenotypic character.
wide-ranging effects due to a single gene:
dwarfism (achondroplasia)
gigantism (acromegaly)
The genes that we have covered so far affect only one phenotypic character, but most genes are pleiotropic

59. Acromegaly: André the Giant

60. Achondroplasia - dwarfism
Never reach 4 feet 4 inches.
Cartilage forms in such a way that the arms and legs end up being disproportionately short.
1 in every 10,000 is affected.

61. Tay Sachs Autosomal recessive.
Found mostly in Jewish families of central and eastern European ancestry.
Results in nervous system breakdown and death in the first few years of life.
There is no treatment, but there is a test prospective parents can take.

62. PKU – phenylketonuria Lack enzyme needed to break down phenylalanine.
Found in milk and other foods.
If newborn has PKU, phenylalanine may build up in the tissues during severe mental retardation.
If newborns are tested early, they can be placed on a low phenylalanine diet which prevents most of the affects.
PKU is caused by a recessive allele carried on chromosome 12.

63. PKU

64. Section 14-3 Studying the Human Genome

65. Human DNA Analysis Way too much DNA to search through.
Biologists search the volumes of the human genome using DNA sequences.

66. Manipulating DNA
By using tools that cut, separate, and replicated DNA base by base, scientists can now read the base sequences in DNA from any cell.

67. Cutting DNA
Restriction enzymes are used to cut a DNA molecule into precise pieces called restriction fragments.

68. Separating DNA
Once DNA is cut by restriction enzymes, scientists can use a technique known as gel electrophoresis to separate and analyze the differently sized fragments of the DNA.

69. Reading DNA
DNA sequencing machines read color coded bases that are made by adding chemical dye, DNA polymerase, and A, G, C, T to a test tube containing the separated DNA.

72. The Human Genome Project
The Human Genome Project was a 13-year, international effort with the main goals of sequencing all 3 billion base pairs of human DNA and identifying all human genes.

73. The Human Genome Project
Advances in DNA sequencing technologies at the close of the twentieth century made it possible to begin sequencing entire genomes.
At first, biologists worked on small genomes of viruses and bacteria.
In 1990, scientists in the United States and other countries began the Human Genome Project.
In 2000 scientists announced that the DNA sequence of the human genome was essentially complete.
Now the task is to figure out how so few genes make an organism as complex as us.

74. Bioinformatics
Data from the human genome project is posted on the internet on a daily basis.

75. The Human Genome Project
The Human Genome Project pinpointed genes and associated particular sequences in those genes with numerous diseases and disorders.