1. Chapter 14
Human Heredity

2. 14-1 Human Heredity

3. • Scientists once knew much less
about humans then about other
“model” organisms such as fruit flies
and mice
• With the completion of the Human
Genome Project scientists are on
verge of understanding human
genetics at least as well as they
understand that of some other
organisms

4. Human Chromosomes
• To analyze chromosomes, cell
biologists photograph cells in
mitosis
• Chromosomes are fully
condensed and easiest to see
during metaphase

5. Karyotype
• A picture of chromosomes
arranged in order

6. • We all began life when a haploid
sperm fertilized a haploid egg
23
carrying just ________
chromosomes each.
• The
Diploid
_________________________
zygote or fertilized egg contained
the full complement of
__________ chromosomes
46

7. Sex Chromosomes
• Determine an individuals sex
Females: XX
Males: XY
• The regular 44 chromosomes are
known as autosomes

8. Q: Why are males & females born
in a roughly 50:50 ratio?
A: All egg cells carry a single
X
_______ chromosome. However,
X
half of all sperm carry an _______
chromosome, the other half carry
Y
a ________ chromosome

10. Human Traits
• In order to apply Mendelian
genetics to humans, biologists
must identify an inherited trait
controlled by a single gene
• Then, they have to study how the
trait is passed from one
generation to the next

11. Pedigree
• A chart which shows the
relationship within a family

13. • Most human traits are not
coded for by single genes
• Also, many traits are strongly
influenced by environmental
factors
–Ex.) average height has
increased 10cm in the United
States and Europe since 1800’s

14. Polygenic Traits
• Traits coded for by many genes
• Ex.) skin color, hair color

15. The Human Genome
• Our complete set of genetic
information
• Includes tens of thousands of
genes
• Until recently the identification of
a human gene took years of work

16. Humans aren’t easy test subjects
• Long generation times
• Complex life cycle
• Produce few offspring

17. Blood Group Genes
• A number of genes are responsible
for human blood groups, but the best
known are the ABO and Rh blood
groups
• Rh blood groups
• Rh+ (dominant)
• Rh- (recessive)

18. Q: How do scientists identify recessive
alleles that cause these disorders
A: Compare affected persons genotype
to normal persons

19. 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

20. PKU

21. 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

22. 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

23. 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

24. Huntington's affect on the brain

25. Codominant
• Sickle cell disease
• Affects 1 in 500 African
Americans

26. From Gene to Molecule

27. 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

29. 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

32. Q: Why do so many African Americans
carry the sickle cell allele?
• A: 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

33. Where malaria is common Where sickle cell is common

34. Dominant or Recessive
• It all depends on the nature of a
genes protein product and its role in
the cell
• Ex.) In CF, one copy of the normal
allele can supply cells with enough
chloride channel proteins to function
therefore the normal CF allele is
considered ____________________
Dominant

36. 14-2 Human Chromosomes

37. • A human diploid cell contains more than
6 billion nucleiotide pairs of DNA
• Despite its size, all of this information is
neatly packed into the 46 chromosomes
present in every diploid cell
• Each chromosome is like a library
containing hundreds or even thousands of
books
• Biologists are many decades away from
mastering the contents of these books, but
they are learning just how many books
there are and what they deal with

38. Sex Linked Genes
• Genes located on the
sex chromosomes
• Most found on the
X
________ chromosome

39. Colorblindness
• Gene associated with color vision
are located on the X chromosome
• Affects 1 in 10 males
• Affects 1 in 100 females

40. Q: Why the difference between the
sexes?
A: Males have
just one
____________________________ X
chromosome. Thus, all X-linked
alleles are expressed in males, even
if they are recessive
• In order for a woman to be affected,
there must be
__________________________ of
Two copies
the allele

41. 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

42. Duchenne Muscular Dystrophy
• Results in progressive weakening and
loss of skeletal muscle
• Rarely live past early adulthood
• In the U.S. 1 in 3000 males is born
with Duchenne muscular dystrophy
• Caused by a defective version of the
gene that codes for a muscle protein

43. X-Chromosome Inactivation
Q: If all you need is one X
chromosome, what happens to
the extra X chromosome in
females?
A: one chromosome is randomly
switched off
• Forms a barr body – dense region
in the nucleus

44. Calico Cats
• Fur color is on the X chromosome. Some
areas have one color switched on, and
others its switched off

45. nondisjunction
• When homologous chromosomes
fail to separate – most common
error in meiosis

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

48. 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

49. Down Syndrome

50. 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

52. 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

54. 14-3 Human Molecular
Genetics

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

56. Testing for alleles
• If two prospective parents suspect
they might be carrying recessive
alleles for a genetic disorder they can
now get a test to determine the risk of
passing that trait on to their children
– Use labeled DNA probes to detect
specific sequences found in disease
causing alleles
– Looking at changes in restrictive
enzyme cutting sites
– Looking at differences in lengths of

57. DNA fingerprinting
• Analyzes sections of DNA that
have little or no known function
but vary widely from one
individual to another
• Used to settle paternity disputes
• Convict criminals and overturn
convictions

58. 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
– An attempt to sequence all human DNA
• In 2000 scientists announced that the DNA sequence of
the human genome was essentially complete
• We estimate as little as 31,000 genes
– Fruit fly – 14,000
– C. elegans worm 20,000
• Now the task is to figure out how so few genes make an
organism as complex as us

59. Promoter
• Section of DNA that signals the start
of a gene
• Researchers are looking for genes
that provide useful clues to some of
the basic properties of life
• Also looking for genetic information
that may be useful in developing new
drugs and treatment of disease

60. A Breakthrough for Everyone
• Data from the human genome project is
posted on the internet on a daily basis
• www.genome.gov

61. Gene Therapy
• Replacing an absent or faulty
gene by a normal working gene

62. Ethical Issues in Human Genetics
• There are many questions which science
will rapidly force society to come to grips
with
• If it’s just as easy to manipulate genes for
personal preference then it is to cure a
disease should we do it?
• Our society will have to develop a
thoughtful and ethical conscious of what
should and shouldn’t be done with the
human genome