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GENETICS
Genes - factors of heredity that controls
inherited traits; what are passed on to
offspring by parents
Kinds of Inherited Characters
1
...
Physiological - functions of parts
3
...
Sexual - association with sex
Gregor Mendel - Father of Classical
Genetics
• Alleles - two alternate forms of a gene
• Locus - position of a gene in a
chromosome
• Phenotype vs Genotype
• Heterozygous vs Homozygous
MENDELIAN Mode of Inheritance
1
...
Law of Dominance (LD)
- The gene physically expressed
is dominant while the other
one masked/hidden is
recessive
...
Law of Segregation (LS)
o Gametogenesis
§ Product: Sperm/Egg
§ Two genes of a pair
segregate so that only one
gene of a pair is carried by
each gamete
...
Law Independent Assortment of
Genes (LIAG)
o Inheritance of genes will never
influence inheritance of
another gene pair
o Ladies first in gene pairs

MONOHYBRID CROSS
Dominant Recessive Conditions
100%
0%
At least one
parent is
homozygous
dominant
75%
25%
Both parents are
heterozygous
50%
50%
Parents have
different
phenotypes;
dominant one is
heterozygous
0%
100%
Both parents are
homozygous
recessive
GENETIC VARIABILITY
- shows marked differences of
individuals, no matter how close they
are
- may be attributed to mode of
reproduction (sexual reproduction)
ENVIRONMENTAL EFFECTS
- may affect gene expressions
o temperature
o light
o maternal relations
o nutrition
o substrate
o age
o sex
- may also be a source of mutagens
(factors that may cause drastic
heritable changes in the gene)
o UV radiation
o benzopyrene (cigarette smoke)
o extremes of temperature
o microbial infection
- Examples of undesirable products of
mutation:
o Albinism
o Sickle cell anemia
o Polydactyly - more than 5 digits
on hand/foot
o Mental retardation phenylketonuria

NONMENDELIAN Mode of Inheritance
1
...
Polygenic/Quantitative Inheritance
- traits are controlled by two or
more gene pairs
o Violates 1 gene pair controls 1
inherited character
o Examples:
Human skin color
GENOTYPE
AABB
AABb, AaBB
AAbb, aaBB, aaBb
Aabb, aaBb
aabb
Human intelligence
AABBCCDDEE
AaBbCcDdEe,
AABBCcddee
aabbccddee

PHENOTYPE
Black
Dark brown
Medium brown
Light brown
Fair

Genius
Average
Idiot

3
...
Codominance - all genes are
expressed
o Violates LD
o Roan: R1XR2 = R1R2 (red &
white)
o AB blood type (IA & IB)

5
...
g
...
g
...


Female bald
Female not
bald
Female not
bald

o Sex-linked (X-linked)
Expression of red-green color-vision in
humans
Femal Female P Male
Male
eG
G
phenotype
s
C C
C
Female,
Male,
X X
X Y
normal
normal
color
color
vision
vision
C c
c
Female,
X X
X Y Male, color
normal
blind
color
vision
c c
Female, color blind
XX
§ There are more colorblind males
than colorblind females because
they only need 1 Xc to express
colorblindness while females need
2
...
g
...
Chromosomes and DNA
• DNA - contains the blueprint for the
synthesis of all proteins
• proteins - determine what characters
are expressed by the organism
• nitrogenous bases - determine the
kinds of proteins our cells synthesize
•

Chromatid - each strand of a
chromosome
- made up of deoxyribonucleic acid
(DNA) molecules tightly coiled
around histones
• Nucleosome - basic unit of a
chromosome
• Chromosome - made up of:
1) histones - basic proteins
2) DNA - nucleic acid
• Nucleic acids - polynucleotides
1) deoxyribose - 5-C sugar
2) phosphate group
3) nitrogenous base
• Nitrogenous bases
Purine
Pyrimidine
Guanine
Cytosine
Adenine
Thymine

2
...
2 billion
nitrogenous base pairs
3
...
The Central Dogma
DNA - replicated, copied to RNA to
provide instructions in protein synthesis
Proteins - express structural and functional
characteristics
- building blocks of the body
- hemoglobin
- melanin
- insulin
- functional enzymes
protein synthesis - basis of expression of
hereditary characteristics in both structure
and function
5
...
Mutation
• mutation - permanent, heritable
change in a DNA
• mutagens - agents that cause
mutation
1) radiation
2) chemicals
3) extremes of temperatures
4) microbial infections



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