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Genetics
The study of heredity
Father of Genetics: Gregor Mendel (mid 1800’s)
Developed set of laws that explain how
heredity works
Father of Genetics: Gregor Mendel
original pea plant (input)
offspring (output)
What happened here??
Mendel’s subjects: pea plants
How To Read A Punnett
Square
What is the P Generation?
What is the F1 Generation?
What must parents undergo to
produce haploid gametes?
What is phenotype?
What is genotype?
Does genotype largely determine
phenotype?
Monohybrid Crosses: parents differ by one
characteristic
Was the heritable factor of green
peas lost?
Mendel’s Conclusions
1. How many forms of genes
(alleles) does each
individual have for each
trait?
2. How does an individual
get these genes (alleles)?
3. How many alleles for each
trait does each gamete
(sperm or egg) contain?
Mendel’s Conclusions
4. What must the alleles do
in order to only have one
allele for each trait in
each gamete?
5. How many alleles for each
trait are present in the
embryo when fertilization
occurs (the union of
sperm and egg)?
Law of Separation
Pairs of alleles separate during
egg & sperm formation
(meiosis) & fusion of egg &
sperm at fertilization creates
allele pairs again.
8. What do we call an allele
when it masks the expression
of the other allele? Example?
9. What do we call an allele
whose trait is being masked?
Example?
Alleles on Homologous Chromosomes
1 chromosome comes from mother & other from
father
Homologous chromosomes may have either same
or different alleles at a location.
Alleles on Homologous Chromosomes
Homozygous?
When organism has a pair of identical alleles for a
gene (__ or __) (homozygous dominant or
homozygous recessive)
Alleles on Homologous Chromosomes
Heterozygous?
When organism has two different alleles for a
gene (__)
Pairs of alleles separate during egg
& sperm formation (meiosis) &
fusion of egg & sperm at
fertilization creates allele pairs
again = Law of Segregation
Phenotypes &
genotypes of
parents?
Eggs & sperm of
parents?
Male
Female
Sperm
Phenotypes &
genotypes of
offspring?
Phenotypic ratio?
Genotypic ratio?
F1 Generation
Eggs
Phenotypes &
genotypes of
parents?
Male
Sperm
Eggs & sperm of
parents?
Phenotypes &
genotypes of
offspring?
Phenotypic ratio?
Female
Eggs
t
t
T
Tt
Tall
Tt
Tall
T
Tt
Tall
Tt
Tall
Genotypic ratio?
F1 Generation
Phenotypes F1 Generation
&
genotypes
of parents?
Eggs & sperm of
parents?
Phenotypes &
genotypes of
offspring?
Phenotypic ratio?
Genotypic ratio?
X
Practice this one on your own
PP
pp
1. Phenotypes &
genotypes of
parents?
2. Eggs & sperm of
parents?
3. Phenotypes &
genotypes of
offspring?
3. Phenotypic &
genotypic ratios?
Is this article true or false? Why?
Recessive alleles don’t get wiped out. They get
passed on and retain potential to have effect but
must be paired with another recessive allele.
Fraternal twins whose parents are both mixed race (blackwhite unions). One twin inherited alleles passed on from her
black grandparents while other inherited alleles passed on
from white grandparents.
Dihybrid Crosses: parents differ by two
characteristics
smooth
& yellow
wrinkled
& green
smooth & yellow
Mendel’s Conclusions
1. Do all possible combinations
of traits occur in the
gametes?
2. Does each pair of traits
separate independently of
the other pairs?
Law of Independent
Assortment
Each pair of alleles separates
independently of the other pairs
during gamete formation.
Inheritance of one characteristic
has no effect on inheritance of
another.
Tall & green
pods
male
F1 generation
Phenotypic
ratio?
Genotypic
ratio?
Short &
yellow pods
female
Tall & green
pods
Short &
yellow pods
male
tg
female
tg
tg
tg
TG TtGg TtGg TtGg TtGg
F1 generation
Phenotypic ratio?
Genotypic ratio?
TG TtGg TtGg TtGg TtGg
TG TtGg TtGg TtGg TtGg
TG TtGg TtGg TtGg TtGg
Tall & green
pods
Phenotypic ratio?
X
Practice this one on your own
Mendel’s Principles &
Human Inheritance
Mendel’s principles apply
to the inheritance of some
human traits
Human Disorders Controlled by a Single Gene
Genes involved in these disorders are located on
autosomes = chromosomes other than sex
chromosomes X & Y
Autosomal Recessive Disorders
Person w/ a single properly functioning allele
will not suffer from disorder; recessive
Parents are heterozygous & are carriers of
recessive allele for disorder but are
phenotypically normal
Can they produce a
child that exhibits the
condition?
What is the probability
of this happening?
Sickle-Cell Anemia
Autosomal Recessive Disorders
Autosomal Dominant Disorders
A single faulty allele can cause a disorder even
when a properly functioning allele exists.
Parent need only pass on a single allele for
offspring to suffer from condition.
Usually individuals w/ disorder are heterozygous
(Dd) for the disorder.
Autosomal Dominant Disorders
Ex. Huntington disease
Probability that child will
exhibit condition?
Autosomal Dominant Disorders
Ex. Huntington disease
Probability that child will
exhibit condition?
Autosomal Dominant Disorders
Pedigrees are used to determine inheritance of
characteristics that follow Mendel’s principles in
humans.
?
d
d
?
?
d
Is deafness a
dominant or
recessive disorder?
You can tell who are heterozygous carriers of
the recessive condition. How so?
?
d
d
?
?
d
Is deafness a
dominant or
recessive disorder?
1. Fill in known genotypes first.
2. Use that info to determine the unknown genotypes.
?
d
d
?
?
d
Is deafness a
dominant or
recessive disorder?
Incomplete
Dominance
Neither allele is dominant
Heterozygote phenotype is
intermediate between either
of the homozygous
phenotypes
One red allele produces only
enough pigment to yield pink
color
Multiple Alleles
When more than 2 possible alleles exist in a
population.
Each individual carries, at most, 2 different alleles
for a particular gene, however, more than 2
possible alleles exist in a population.
Multiple Alleles
Human blood
types: 3 alleles for
blood type A, B & O
which can produce
4 phenotypes (A, B,
O or AB)
Multiple Alleles
Human blood types: 3 alleles for blood type A, B &
O which can produce 4 phenotypes (A, B, O or AB)
Codominance
Both alleles are
dominant so both are
displayed
What alleles are
both dominant?
Who do we receive
these alleles from?
Polygenic Inheritance
Inheritance determined by
interaction of multiple
genes, with each gene
having additive effect on
trait
Height, weight, eye color,
skin color are controlled by
several genes working
together
Sex Determination
Who contributes what?
Sex linked genes – any gene located on a sex
chromosome
Eye color in fruit flies
Is white eye color
dominant or
recessive?
Is the eye color allele
on the X or Y
chromosome?
X-linked trait
Eye color in fruit flies
What alleles does this
female carry?
Will she be red or white
eyed?
What allele does the male
carry?
Will he be red or white
eyed?
Can white eyed males be
produced from this cross?
How would a female get
white eyes?
Eye color in fruit flies
How would a female get
white eyes?
Red-Green Color Blindness
Color blindness
Is color blindness on
the X or Y
chromosome?
Is color blindness a
dominant or
recessive?
Which child will be
color blind?
Color blindness
How would a daughter be color blind??
Sex (X) Linked Disorders
Genes & Environment
Effects of genes
vary according to
environment in
which genes are
expressed
Organism’s
genotype &
environment
interact to produce
organism’s
phenotype
Effects of genes vary according to environment in
which genes are expressed
Organism’s genotype & environment interact to
produce organism’s phenotype
Effects of genes vary
according to
environment in which
genes are expressed
Organism’s genotype
& environment
interact to produce
organism’s phenotype
Our lifestyles and environment can change the way our genes are
expressed, leading even identical twins to become distinct as
they age.
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