FROM LAGUNA UNIVERSITY

2. MULTIPLE
ALLELES
--Genes that have
more than two alleles

3. Genes and their alleles
•About 30% of the genes in
humans are di-allelic
They exist in two forms,
(they have two alleles)

4. Genes and their alleles
•About 70% are mono-
allelic, they only exist in
one form and they show no
variation
•A few are poly-allelic
having more than two
forms.

5. Combinations
•Di-allelic genes can
generate 3 genotypes
AA, Aa and aa
•Genes with 3 alleles can
generate 6 genotypes
(3+2+1)

6. Combinations
•Genes with 4 alleles can
generate 10 genotypes
(4+3+2+1)
•Genes with 8 alleles can
generate 36 genotypes.

7. Genes and the immune
system
•Poly-allelic genes
associated with tissue
types
•Genes so varied they
provide us with our genetic
finger print

8. Genes and the immune
system
•Important for our immune
system
•self and non-self.

9. The ABO blood system
•Controlled by a tri-allelic
gene
•6 genotypes

10. The ABO blood system
•The alleles for antigens
on the surface of the red
blood cells
•Two of the alleles are
codominant to one
another and both are
dominant over the third

11. The ABO blood system
•Allele IA produces antigen
A
•Allele IB produces antigen
B
•Allele i produces no
antigen.

12. The ABO blood system
Genotypes Phenotypes
IA IA A
IA IB AB
IAi A

13. The ABO blood system
Genotypes Phenotypes
IB IB B
IBi B
ii O

14. Blood types and
transfusions
•Blood types vary and your
immune system recognises
your own blood type = self
•Other blood types = non-
self

15. •If a blood, which is
incompatible with your
body, is transfused it will
result in the agglutination
of the foreign red blood
cells.

16. Blood types and
transfusions
•Other blood types = non-
self

17. Antigens

18. Antigens

19. www.vet-lyon.fr/.../ENV_immuno_1A/immun1-04.htm.
© 2016 Paul Billiet ODWS
Agglutination

20. Blood types & transfusions
•Type A people produce
antibodies to agglutinate
cells which carry Type B
antigens
Recognised as non-self

21. Blood types & transfusions
•The opposite is true for
people who are Type B
•Neither of these people
will agglutinate blood cells
which are Type O

22. •Type O cells do not carry
any antigens for the ABO
system
Type O cells pass
incognito
•What about type AB
people?
Blood types & transfusions

24. = Agglutination
= Safe transfusion

25. Type A B AB O
A
B
AB
O
RecipientsDonor

26. Note:
•Type O blood may be
transfused into all the
other types = the
universal donor

27. Note:
•Type AB blood can
receive blood from all the
other blood types = the
universal recipient.

28. Sex Linkage
Sex linkage applies to
genes that are located on
the sex chromosomes.

29. These genes are
considered sex-linked
because their expression
and inheritance patterns
differ between males and
females.

30. Sex chromosomes
determine whether an
individual is male or
female. In humans and
mammals, the sex
chromosomes are X and
Y.

31. Females have two X
chromosomes, and males
have an X and a Y.

32. Non-sex chromosomes are
also called autosomes.
Autosomes come in pairs
of homologous
chromosomes.

33. Homologous chromo-
somes have the same
genes arranged in the
same order. So for all of
the genes on the auto-
somes, both males and
females have two copies.

34. A female’s two X
chromosomes also have
the same genes arranged
in the same order. So
females have two copies
of every gene, including
the genes on sex
chromosomes.

35. The X &Y chromosomes,
however, have different
genes. So, for the genes
on the sex chromosomes,
males have just one copy.

36. The Y chromosome has
few genes, but the X
chromosome has more
than 1,000. Well-known
examples in people include
genes that control color
blindness and male pattern
baldness. (sex-linked)

39. Inheritence of
Sex Chromosomes

40. Meiosis is the process of
making gametes, also
known as eggs and sperm
in most animals.

41. During meiosis, the
number of chromosomes
is reduced by half, so that
each gamete gets just one
of each autosome and one
sex chromosome.

42. Egg and sperm join to
make a zygote, which
develops into a new
offspring.

43. An egg plus an X-
containing sperm will
make a female offspring,
and an egg plus a Y-
containing sperm will
make a male offspring.

44. Female offspring get an
X chromsome from each
parent
Males get an X from their
mother and a Y from their
father

45. X chromosomes never
pass from father to son
Y chromosomes always
pass from father to son

46. X-Linked Traits
Insects also follow an XY
sex-determination pattern
and like humans,
Drosophila males have an
XY chromosome pair and
females are XX.

47. Eye color in Drosophila
was one of the first X-
linked traits to be
identified, and Thomas
Hunt Morgan mapped this
trait to the X chromosome
in 1910.

48. In fruit flies, the wild-type
eye color is red (XW) and is
dominant to white eye
color (Xw).

50. Because this eye-color
gene is located on the X
chromosome only,
reciprocal crosses do not
produce the same offspring
ratios.

51. Males are said to be
hemizygous, because they
have only one allele for
any X-linked characteristic.

52. Hemizygosity makes the
descriptions of dominance
and recessiveness
irrelevant for XY males
because each male only
has one copy of the gene.

53. Drosophila males lack a
second allele copy on the Y
chromosome; their
genotype can only be XWY
or XwY. In contrast, females
have two allele copies of
this gene and can be
XWXW, XWXw, or XwXw.

55. X-Linked Recessive
Disorders in Humans

56. Sex-linkage studies
provided the fundamentals
for understanding X-linked
recessive disorders in
humans, which include
red-green color blindness
and Types A and B
hemophilia.

57. Because human males
need to inherit only one
recessive mutant X allele
to be affected, X-linked
disorders are
disproportionately
observed in males.

58. Females must inherit
recessive X-linked alleles
from both of their parents
in order to express the
trait.

60. Recessive Carriers
When they inherit one
recessive X-linked mutant
allele and one dominant
X-linked wild-type allele,
they are carriers of the
trait and are typically
unaffected.

61. Carrier females can
manifest mild forms of the
trait due to the inactivation
of the dominant allele
located on one of the X
chromosomes.

62. However, female carriers
can contribute the trait to
their sons, resulting in the
son exhibiting the trait, or
they can contribute the
recessive allele to their
daughters.

66. Y linkage, also known
as sex linkage, or
Holandric Inheritance,
describes traits that are
produced by genes
located on the Y
chromosome.

67. For a trait to be considered
Y linkage, it must exhibit
these characteristics:
 occurs only in males
 appears in all sons of
males who exhibit that
trait

68.  is absent from
daughters of trait
carriers; instead the
daughters that
are phenotypically
normal and do not have
affected offspring.