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Genetics is the study of inheritance
Parents send information about traits
(characteristics) to their offspring.
This information is what we refer to as genes.
Genes are located on chromosomes which are made
of DNA.
Each individual has two copies of a gene, one from
each parent.(one from egg, one from sperm).
The two copies of each gene may or may not have
the same information (or ALLELES) for each trait
For example both of your parents gave you an
ALLELE for tongue rolling.
Allele = form of a trait
Your mom might have given you the gene that says
you can roll your tongue. While your dad might
have given you the gene that says you cannot roll
your tongue.
Dominant - represented by capital
letters it is the overpowering trait
Recessive - represented by lowercase
letters it is the trait that is
sometimes hidden by the dominant
trait
The ability to roll your tongue is a dominant trait,
so it would be represented with a T
Not being able to roll your tongue would be a
recessive trait represented with a t
If they are the same genes the individual is
said to be homozygous for that trait. DD or
dd
If they have different information the
individual is said to be heterozygous for
that trait. Dd
Remember homo means the same
And
Hetero means different
Let’s Practice!
Determine if each is Homozygous or
Heterozygous.
AA
Aa
aa
Phenotype of an organism is its physical
appearance (what it is going to look like)
Example: Acne or No Acne, Big Eyes or
Small Eyes
The genotype of an organism is the genes or
letters that organism has for a trait.
Ex. AA, Aa, or aa
Hybrid vs. Purebred?
If you have a Hybrid dog breed vs. a
Purebred Dog breed, what does that mean?
The ability to roll your tongue is a dominant trait,
so it would be represented with a T
Not being able to roll your tongue would be a
recessive trait represented with a t
If the dad cannot roll his tongue his
genotype is tt
If the mom can roll her tongue her genotype
is either TT or Tt
Let’s say the mom is heterozygous for the
tongue rolling trait which would make her
genotype Tt
In flowers red petal color is dominant to
white petal color. Cross a heterozygous red
petaled flower with a white petaled flower
Rr x
rr
Phenotype
50% Red
50% White
Genotype
50% Rr
50% rr
HOW TO SUCCEED IN
GENETICS PROBLEMSOLVING
LEGEND
PARENTS
CROSS IT
RESULTS
Rr x Rr
Phenotype
Genotype
75% Red
25% RR
25% White
50% Rr
25% rr
RR x Rr
Phenotype
Genotype
100% Red
50% RR
0% White
50% Rr
In Quaker Parrots, green feathers (F) are dominant to
blue feathers (f). If a homozygous dominant male mates
with a homozygous recessive female, what are the
chances that they would have a blue feathered
offspring?
Legend
Parents
F = Green feathers
f = blue feathers
FF x ff
Cross
Results
F
f
f
F
Ff
Ff
Ff
Ff
Phenotype:
Green : blue
4: 0
Genotype
FF: Ff: ff
0 : 4: 0
Intermediate Inheritance (aka Incomplete
Dominance)
Sometimes the dominant and the recessive trait
blend together.
For example, in snapdragons a red flower crossed
with a white flower = all pink flowers!
Intermediate Inheritance: THE RULES ARE GOING TO CHANGE
in how we write the GENOTYPE!!!!
Example: When you cross a Red(FRFR) flower with a White
flower(FWFW) all offspring are pink (FRFW)
Legend
______= Red
_______=White
FRFW=_______
Parents
Cross it
Genotypic Ratio
FRFR: FWFW: FRFW
Phenotypic Ratio
Red: White: PINK
Dihybrid Cross
 Monohybrid = 1 trait
 Dihybrid = 2 traits
Dihybrid Cross in Pea Plants
 Round (R) is Dominant, wrinkled (r) is recessive
 Yellow (Y) is Dominant, green (y) is recessive
RrYy x RrYy
Phenoype:
9:3:3:1
9 round & yellow, 3 round & green,
3
wrinkled & yellow, 1 wrinkled & green
Your 23rd pair of chromosomes are called your “sex
chromosomes”
These chromosomes have the genes that determine if you
are male XY or female XX.
Who determines the sex of the child the mom or the dad?
The dad is the only one that can give a Y chromosome so
he is the one that determines the sex of the child.
Some traits are sex linked traits like: colorblindness,
hemophilia (a blood disorder), and certain types of
baldness.
Sex linked traits are traits that are on the X chromosome
Cross a male who does not have hemophilia with a female
carries hemophilia, but does not have it.
Some traits are controlled by genes that have more
than two alleles this is called a multiple allele.
An example of multiple alleles is blood types.
Blood Type
Genotype
(Phenotype)
A
IAIA or IAi
B
IBIB or IBi
AB
I AI B
O
ii
Phenotypic Ratio
25% AB
25% A
25% B
25% O
Phenotypic Ratio
50% A
50% O
Polygenic Traits
Poly – many
Genic – genes
Polygenic Traits are traits that are controlled by
many genes.
Skin, hair, and eye color are all influenced by the
effects from three to six genes.
Each of these genes control the amount of a
pigment called melanin. The more of the genes
that are expressed, the darker the color
produced.