GENETICS
 Genetics
is the study of heredity
GREGOR MENDEL (1822 – 1884)
Recognized as the “Father of Genetics”
 An Austrian monk

Tended to the gardens at the monastery
 Observed plant growth and researched hereditary
characteristics

 Mendel
 Why?


experimented on pea plants.
They were easy to grow
Could produce a large number of offspring
in a short amount of time.
MENDEL’S OBSERVATIONS
Noticed that some traits are passed on from
one generation to the next.
 Noticed that traits exist in two possible forms.
 Noticed that for each trait, one form
dominates the other.

GENES
Paired
units which transmit
hereditary traits.
GENES
Occur
in pairs in the nucleus.
GENES
 Separation
of homologous
chromosomes during meiosis determines
which genes the offspring will get.
 Law

LAWS OF HEREDITY
of Dominance
The dominant form of the trait
prevents the expression of the
recessive form.
LAWS OF HEREDITY
 Law

of Segregation
The pair of genes responsible for each
trait separate so that each gamete
contains only one gene for each trait.
LAWS OF HEREDITY
 Law

of Independent Assortment
Genes for different traits are inherited
independently of each other.
GENETIC TERMINOLOGY
Allele
 The
possible form a gene may take
GENETIC TERMINOLOGY
Dominant
 Prevents
trait
the expression of a
recessive trait
 Represented by a capital letter (T)
GENETIC TERMINOLOGY
Recessive
 Form
Trait
of a trait that can be hidden.
 Represented by a lower case letter (t).
GENETIC TERMINOLOGY
Homozygous
 Having
two identical alleles
GENETIC TERMINOLOGY
Heterozygous
 Contains
one of each allele
GENETIC TERMINOLOGY
Genotype
 The
combination of alleles (type of genes)
Homozygous Dominant =

Heterozygous Dominant =

Homozygous Recessive =

GENETIC TERMINOLOGY

Phenotype
 The
physical expression of the
trait (how it looks).
 Example:
Blue eyed, right
handed, tall, curly, etc.
GENETIC TERMINOLOGY
Punnett
 Shows
Square
the possible outcomes
from the cross of a trait.
GENETIC CROSSES
MONOHYBRID CROSSES
Dominant/Recessive

Cross
Offspring show either the dominant or
the recessive phenotype
Example 1: Cross a homozygous right handed mom with
a left handed dad.
Parents Genotype: _____________ X ______________
Genotypic Ratio:
Phenotypic Ratio:
Example 2: Cross a heterozygous right handed mom with
a left handed dad.
Parents Genotypes: ___________ X ____________
Genotypic Ratio:
Phenotypic Ratio:
Example 3: Cross two heterozygous right handed parents.
Parents Genotypes: ___________ X ____________
Genotypic Ratio:
Phenotypic Ratio:
MONOHYBRID CROSSES
Incomplete

Dominance
The heterozygous genotype creates a
new, blended phenotype.
Example: Cross a red flower with a white flower.
Parents Genotype: _____________ X ______________
Genotypic Ratio:
Phenotypic Ratio:
MONOHYBRID CROSSES
Co-Dominance

Both traits are expressed equally
Example: Cross a black chicken with a white chicken.
Parents Genotype: _____________ X ______________
Genotypic Ratio:
Phenotypic Ratio:
MONOHYBRID CROSSES
Sex-Linked

Traits
Sex chromosomes: X and Y chromosomes
(all other chromosomes are called autosomes)

Females: have 2 X chromosomes (XX)
(only one type of allele)

Males: have 1 X and 1 Y chromosome
(one of each allele)

Sex-Linked Traits: traits inherited on sex
chromosomes



Genes for some traits are on sex
chromosomes
Some traits are determined by only one
gene (the X or the Y, not both)
Some genes are only found on the Y
chromosome
(adam’s apple, hairy ears)

Example: In a certain animal, the gene for black color coat
(B) is dominant to the gene for orange coat color (b). The
characteristic is sex-linked.
Parents:
• Female Genotype ____________
Gametes _______ & _______
Male Genotype_______________
Gametes _______ & _______
•
Genotypic Ratio:
Phenotypic Ratio:
MONOHYBRID CROSSES

Multiple Alleles

One trait is controlled by more than
one allele

Genetic Example: Blood type

Alleles
IA
B
I
O
 I or i

 IA
and IB are dominant to i
 Neither IA
or IB is dominant over the
other; they are co-dominant
 This
results in the 4 possible blood types
A
 B
 AB
 O


Example: Cross a heterozygous type A parent with a
heterozygous type B parent.
Parents ______________ X ______________
Genotypic Ratio:
Phenotypic Ratio:
DIHYBRID CROSSES

A cross involving two traits
 When setting up your Punnett square
use the foil method to determine your
gametes.
Example: Cross a heterozygous tall, heterozygous round
pea plant with a short, wrinkled pea plant.
Parents: ___________________ X _____________________
Genotypic Ratio:
Phenotypic Ratio: