Chapter 11 Notes
Introduction to Genetics
Genetics – Study of heredity
Heredity – How things or
characteristics (traits) are passed on
from parent to offspring
Gregor Mendel ( 1822-1884 )
1. “Father of Genetics”
2. Austrian Monk in the 1800’s –
worked with pea plants
3. Why garden peas?
- Reproduced by self-pollination
- Have seven different traits (ex.
Tall vs. short,
round vs. wrinkled)
4. His experiments led to 4 Laws
Fundamental Laws of Heredity

Law of Unit Characters


Traits are controlled by factors called genes
For every trait you have 2 genes


1 from each parent
Law of Dominance



One of the gene pair can mask the other
The gene which appears or does the
masking is called the dominant gene
The gene being masked is called recessive

Law of Segregation
- During the formation of gametes (meiosis)
each gamete only receives one gene from the
pair. (The chromatids separate and go to
separate cells)

Law of Independent Assortment
- Chance is involved in determining
which gene a gamete will receive
Genetic Terms and Abbreviations:
Dominant Gene – (the masker)
- Symbolized by a capital letter
Recessive Gene – (the masked)
- Symbolized by a small letter
Homozygous – Alleles/genes are the same
- Purebred  (TT, tt)
Heterozygous – Alleles/genes are different
- Hybrid  (Tt)
 Genotype – The genetic make-up of an
individual
-Letters (TT, Tt, tt)
Phenotype – The individuals physical
appearance
- Words (tall, short, straight hair, green eyes, etc.)
Punnett Square – Resembles a checker board
and shows the possible gene combinations of
offspring
Abbreviations and Generations
P1 – Pure breeding parent generation
F1 – (1st Fillial) Offspring generation; cross
between members of the P generation
F2 – (2nd Fillial) Offspring of crosses
between members of F1 generation
Ratios for MONOHYBRID CROSSES
Phenotypic Ratio – Shows the ratio of physical
traits
How many dominant : How many recessive
Ex. 3 Tall : 1 Short
Genotypic Ratio – Shows the ratio of different
genotypes
Homozygous dominant: Heterozygous dominant: Homozygous recessive
Ex. 1TT : 2Tt : 1tt
Example Monohybrid Cross
 In humans, being a tongue roller (R) is dominant over nonroller (r). A man who is a non-roller marries a woman who is
heterozygous for tongue rolling.
Father’s phenotype _____
Father’s genotype _____
Mother’s phenotype _____
Mother’s genotype _____
What is the probability of this couple having a child who is a
tongue roller? ________
Example Monohybrid Cross
 In humans, being a tongue roller (R) is dominant over non-roller (r). A
man who is a non-roller marries a woman who is heterozygous for
tongue rolling.
Father’s phenotype :non-roller
Father’s genotype : rr
r
r
Mother’s phenotype: roller
Mother’s genotype : Rr
R
r
Rr
rr
Rr
rr
What is the probability of this couple having a child who is a tongue
roller? 2/4 = 50%