This document discusses patterns of non-Mendelian inheritance in genetics. It describes several patterns such as incomplete dominance where a hybrid phenotype results from two alleles, codominance where both alleles are fully expressed at the same time, and multiple alleles where more than two alleles determine a trait like blood types. It also covers sex-linked inheritance determined by alleles on the X chromosome and sex-influenced traits where expression depends on sex hormones. Examples are provided to illustrate each non-Mendelian inheritance pattern.

1. PATTERNS OF NON-
MENDELIAN INHERITANCE

5. GENETICS
• Genetics is a branch of biology
that studies hereditary
information.
• Heredity refers to the passing
of characteristics from the
parents to offspring.

6. GENETICS
• The study of genetics also
examines and explains
similarities and differences
between or among organisms.
• Inherited characteristics are
the causes of similarities.

7. GENETICS
• Each individual does
posses unique traits that
differentiate him/her from
others called variation.

8. DIVISIONS OF
GENETICS

9. DIVISIONS OF GENETICS
• Genetics can be divided
into three divisions:
• Mendelian Genetics
• Molecular Genetics
• Population Genetics
• Non-Mendelian Genetics

10. DIVISIONS OF GENETICS
• Mendelian Genetics
reviews the basic laws of
inheritance that were
described by Gregor
Mendel.

11. DIVISIONS OF GENETICS
• Molecular Genetics deals
with the chemical nature of
the gene, the mechanisms
of transmission, and its
varied transmission.

12. DIVISIONS OF GENETICS
• Population Genetics
focuses on the behavior of
a particular gene in group
of organisms and how gene
frequency is affected by
environmental factors.

13. IT ALL BEGAN WITH
GARDEN PEAS

14. GREGOR JOHANN MENDEL
• Gregor Johann Mendel is an
Austrian Priest who began the
scientific study of heredity with
his experiment on Pisium
sativum (garden peas).

15. GREGOR JOHANN MENDEL
• Mendel was the first scientist to
give a satisfactory explanation of
the mechanisms of heredity and
still the basis of the study of
genetics.

16. THE START OF MENDELIAN GENETICS
• Mendel bred different
varieties of garden peas and
cross-pollinated flowers that
had clearly different forms of
traits.
• Such contrasting expressions
or alternative forms of a trait
are called alleles.

17. THE START OF MENDELIAN GENETICS

18. GENOTYPE AND PHENOTYPE
• A genotype is the gene that
is responsible for the
observed trait.
• The observable expression
expressions of the trait is
called the phenotype.

19. ALLELE
• An allele is an alternative form
of a gene (one member of a
pair) that is located at a specific
position on a specific
chromosome.
• These DNA codings determine
distinct traits that can be passed
on from parents to offspring
through sexual reproduction.

20. NON-MENDELIAN
INHERITANCE

21. WHAT IS NON-MENDELIAN INHERITANCE?
• Non-Mendelian inheritance is a
general term that refers to any
pattern of inheritance in which
traits do not segregate in
accordance with Mendel’s laws.
• These laws describe the
inheritance of traits linked to
single genes on chromosomes in
the nucleus.

22. NON-MENDELIAN INHERITANCE
• Incomplete dominance
• Codominance
• Multiple alleles
• Sex-Linked Genes
• Sex-Influenced Traits

23. INCOMPLETE DOMINANCE

24. INCOMPLETE DOMINANCE
• Incomplete dominance is a form
of intermediate inheritance in
which one allele for a specific
trait is not completely dominant
over the other allele.
• This results in a third phenotype
in which the expressed physical
trait is a combination of the
dominant and the recessive.

25. INCOMPLETE DOMINANCE

26. INCOMPLETE DOMINANCE

27. ANALYSIS

28. ANALYSIS

29. CODOMINANCE

30. CODOMINANCE
• Codominance happens when
two dominant alleles of a
contrasting pair fully
expressed at the same time in
the heterozygous individual.
• This results when one allele is
not dominant over the other.

31. CODOMINANCE

32. ANALYSIS

33. ANALYSIS

34. MULTIPLE ALLELES
• Multiple Alleles are present
that create a unique mode of
inheritance.
• Three or more alleles of the
same gene are found.
• can be studied only in
populations

35. MULTIPLE ALLELES
• Example: ABO Blood
Group
• In humans, there are four
blood types (phenotypes): A,
B, AB, O
• Blood type is controlled by
three alleles A, B, O
• O is recessive, two O alleles
must be present to a person to
have type O blood.

36. MULTIPLE ALLELES

37. MULTIPLE ALLELES

38. ANALYSIS

39. MULTIPLE ALLELES
Mother’s Blood
Type
Father’s Blood
Type
Child’s Blood
Type
A A, B, AB, or O A
B A or AB AB
AB A, B, AB, or O B
O A, B, or O O

40. SEX-LINKED GENES
• Sex-linked traits are inherited through the X
chromosomes.
BODY
CHROMOSOMES
SEX
CHROMOSOMES
MALE 44 XY
FEMALE 44 XX

41. SEX-LINKED GENES

42. SEX-LINKED GENES

43. SEX-LINKED GENES
• Males (XY) have only one X
chromosome thus, if they
inherit the affected X, they
will have the disorder.
• Females (XX) have two X
chromosomes therefore, they
can inherit /carry the trait
without being affected if it
acts in a recessive manner.

44. SEX-LINKED GENES
• Aneuploidy where there is an
excess or lack of X or Y
chromosome and genital
development during
conception, and the social
interactions after birth may
contribute to a certain degree
to the expression of human
sexuality.

45. ANALYSIS

46. ANALYSIS

47. SEX-INFLUENCED TRAITS

48. SEX-INFLUENCED TRAITS
• A sex-influenced trait is a trait controlled by a pair
of alleles found on the autosomal chromosomes
(pairs 1 through 22) but its phenotypic expression is
influenced by the presence of certain hormones.
• Estrogen, Progesterone, Testosterone, etc.
• It can be seen in BOTH sexes, but will vary in
frequency between the sexes, or in the degree of the
phenotypic expression.

49. SEX-INFLUENCED TRAITS
Genotype Phenotype
Females Males
BB Bald Bald
Bb Not Bald Bald
bb Not Bald Not bald

50. SEX-LIMITED TRAITS
• Sex-limited traits are
those that are
expressed exclusively
in one sex.
Genotype Phenotype
Females Males
HH Hen-feathered Hen-feathered
Hh Hen-feathered Hen-feathered
hh Hen-feathered Rooster-feathered