Download Heredity

Heredity
The passing on of characteristics
from parents to offspring.
What characteristics do you share
with your parents?
Hair color
Eye color
Inheritance Terms

Genes – unit of information on your DNA
passed down from parents to offspring
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Diploid cells (somatic cells) have one gene for
a trait on each homologous chromosome.
2 total
These different forms of a gene are called
alleles.
Genotypes
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The actual combination of
alleles that an organism
has
Always arranged in
this order:
Homozygous
dominant
2. Heterozygous
3. Homozygous
recessive
TT : Tt : tt
1.
Phenotypes
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The physical expression of the
genotype
What we look like
Always arranged in this
order:
Homozygous dominant trait
2. Heterozygous trait (If there
is one)
3. Homozygous recessive trait
#Tall : # Short
# Tall : # Medium : # Short
1.
Punnet Squares and Ratios
Remember!
Your phenotypic ratio depends on the
number of phenotype options
 Not all crosses are complete!

Practice crosses
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Flower
Red is dominant
White is recessive
Cross a homozygous
dominant with a
heterozygous
What is the genotypic
and phenotypic ratios?
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Seeds
Green is dominant
Yellow is recessive
Cross a homozygous
recessive with a
homozygous dominant
What is the genotypic
and phenotypic ratios?
Who is Gregor Mendel and Why Did He Have
a Funny Name?
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Lived 1822-1884
He had a funny name because he was
Austrian
He was a monk who liked to play in the
garden.
He became a monk in order to get an
education
He wanted to be a science teacher
Mendel: Not a Pea Brain

He was the first
person to be able to
predict how traits
were transmitted
through generations
Mendel looked at several
characteristics of his pea plants
Mendel and Cross Pollination

Mendel used cross-pollination in order to
study his plants
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Cross pollination – pollination in which pollen
is transferred between flowers of two different
plants
Plants were bred for several generations that
were true-breeding for specific traits (have
the same versions of an allele) and called
those the “P generation”.

Pure strain
Monohybrid
Cross

The purple traits was
dominate
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The white trait was
recessive
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Covers up the other
trait in a complete
dominance cross
Only shows up
physically when there
are 2 recessive genes
First generation = F1

Hybrids – have nonidentical alleles
How traits show up
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P generation = tt * TT
First generation of
offspring are called F1
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Hybrids = Tt
Offspring of the F1
generation were called
F2.

TT – Tt - tt
Second Generation
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F2
Three-fourths purple
One-fourth white

Where did the white
come from?

A trait must have
passed down from the
parental generation.
Law of Dominance
Mendel concluded that inherited
characteristics are controlled by factors that
occur in pairs
 He found that one factor in the pair
masked the other.
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Dominant – the trait that could be observed
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The trait that covers up the other trait in the F1 generation
is dominant
Dominant traits are indicated by capital letters
Recessive – the trait that was masked
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The trait that disappeared is recessive
Recessive traits are indicated by lower case letters
Law of Segregation

Every individual has two
alleles of each gene and when
gametes (sex cells) are made,
each gamete receives one of
these alleles.
Law of Independent Assortment
Genes for individual characteristics are
distributed to gametes independent of one
another
 The genes can not be on the same
chromosome
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Types of Crosses
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Complete – Dominant and recessive alleles
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Incomplete – Intermediate, a blending of
both traits
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R = Red
r = White
RR = Red
Rr = Pink
rr = White
Codominance – Both traits show
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RR = Red
Rr = Red and white stripes
rr = White
Incomplete Dominance
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Long water melon (LL) * Round
watermelon (ll)
Do the cross
 What is the genotypic ratio?
 What is the phenotypic ratio?
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Remember – The phenotype in the case has 3
possibilities – homozygous dominant trait,
heterozygous trait, and homozygous recessive
trait.
Codominance Crosses
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Horse with red coat (RR) * horse with
white coat (rr)
Do the cross
 What is the genotypic ratio?
 What is the phenotypic ratio?
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Remember that both traits will show equally in
a heterozygous individual
You have 3 options for phenotype
Multiple alleles
Most genes only have 2 alleles, some have
more than 2
 Ex: blood types – A, B, O
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Blood types A and B are codominant
Type O is recessive to A and B
Human Blood Types and Genotypes
Blood Type
A
A
B
B
AB
O
Genotype
Homozygous A
Hybrid A
Homozygous B
Hybrid B
AB
ii
IA IA
I Ai
IB IB
I Bi
I AI B
ii
Punnet Square For Blood Types
IA
i
i
IB
Test Crosses
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An individual of unknown genotype X
homozygous recessive individual
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It is used to determine the genotype of the unknown
individual
?
?
t
? t
? t
t
? t
? t
t
t
?
?
Tt
tt
t
Tt
tt
t
T
t
Tt
tt
Tt
tt
Law of Independent Assortment
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Genes from different traits are inherited
independently of each other.
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If an organism has an allele for height
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And color
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Y = Yellow
y = Green
Their genotype is TtYy
They can pass on combinations of these alleles
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T = Tall
t = Short
TY
Ty
tY
Ty
Some genes are linked and so will not independently assort
Dihybrid Cross
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A cross involving
two different traits
instead of just
one.
Shows the law of
independent
assortment
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Genotype RrTt
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Possible combinations
of genes donated to a
gamete
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RT
Rt
rT
rt
Do the cross!
RrTt * RRtt
RT
Rt
Rt
Rt
Rt
Rt
rT
rt
Environmental influence on Gene
Expression
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The ability for one single gene to affect an
organism in several or many ways
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Ex:
Polygenic inheritance
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When a characteristic, such as eye color, is
controlled by two or more genes
Sex-Linked Genes
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Sex linked
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Genes found on the X chromosome are “Xlinked genes”.
A sex-linked trait is a trait whose allele is
located on the sex chromosome.
Males have only 1 X chromosome. So, a male
who carries a recessive allele on the x
chromosome will exhibit the sex linked trait.
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Ex. colorblindness
Sex Influenced Genes
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A trait that is expressed differently in men
than in women, even if the gene is on an
autosome and both sexes have the same
genotype
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Hormones dictate expression
Ex. Male pattern baldness
Pedigree
A diagram that reveals inheritance
patterns of genes
 Geneticists use pedigrees to trace
diseases or traits through families
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Examples of some Genetic Diseases
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Autosomal Dominant
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Huntington’s disease
Caused by a single
dominant allele
Onset in 30’s and 40’s
Causes loss of muscle
control and severe
mental illness. Results
in death.
Carrier genotype
HH, Hh
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Autosomal Recessive
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Cystic Fibrosis
Tay-Sachs disease
Phenylketonuria (PKU)
Sickle cell anemia
All are caused by
inheriting two recessive
alleles.
Carrier genotype
dd
Autosomal Recessive Diseases
continued…
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Phenylketonuria (PKU)
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Autosomal recessive
Failure of the brain to
develop in infancy and can
cause death if untreated
Defective form of an
enzyme need to digest the
amino acid phenylalanine
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Cystic fibrosis
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Autosomal recessive
Thick mucus clogs the
lungs, liver and pancreas
More common in white
population
Sickle Cell Anemia
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Autosomal recessive
Impaired blood circulation
causes damage to organs
Caused by a point
mutation making the
hemoglobin molecules
abnormal
Common in African
Americans
Tay-Sachs disease
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Autosomal recessive
Deterioration of the
central nervous system in
infancy; death occurs in
early childhood.
More common in Jews of
European descent
Sex-linked diseases….
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Hemophilia
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Recessive X-linked trait
Defective form of bloodclotting factor causing
failure of blood to clot
Muscular dystrophy
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Recessive X-linked trait
Muscle fibers
degenerate; shortened
life expectancy
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Colorblindness
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Recessive X-linked trait
Inability to distinguish
between certain colors
8% of males are
colorblind
Hemophilia – Offspring of Queen
Victoria