Download Genetics and Heredity

Mendelian Genetics
Fig. 11.20, p. 190
How is genetic information
passed?


Thought 1- The Homunculus- tiny,
complete person inside a sperm that grows
into a full grown person
Thought 2- Blended Heredity-
Then comes Mendel…..

Gregor Mendel1860’s - Austrian
monk
 Worked with Pisum
sativum (pea plants)interested in statistics
of inheritance
 Never knew of genes
or DNA
 Just lucky!!
Why peas?
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Small
Easy to grow
many offspring
mature quickly
7 identifiable traits
can be self- and crossfertilized
What is a trait?

TRAIT: the physical effects of the
expression of a gene
• the hair is blonde
• the bunny has spots
• The cat has white feet
Traits Mendel Chose to
observe
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1.)Flower color
2.)Seed Color
3.) Seed shape
4.) Pod Color
5.) Pod shape
6.) Flower position
7.)Plant height

Each trait shows as 1
thing or another
 i.e.- flowers either
purple or white
 pods either inflated or
wrinkled
Mendel’s Experiment

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3 Steps
Step 1- Create purebred parental generation
PUREBRED: organism which has the same traits as
both parents
Yorkshire Terriers, Dalmatians, etc.

Allows self-fertilization for many
generations to get purebred white and
purebred purple flowering plants
PARENTAL (P) Generation
STEP 2

Creates the F1 generation- First filial- latin
for son or daughter
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Crosses Purple plant x White Plant
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ResultsAll had purple flowers!!!!!
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STEP 3
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F2 Generation
Crosses 2 F1 plants
F1 x F1 (purple x
purple)
Results--3:1 ratio of purple to white!
What’s an allele?

ALLELE: a version of the expression
of a gene
• all genes have 2 alleles for their
expression
• a brown eyed person may have 2 “brown”
alleles or 1 “brown” and one “blue” allele
Mendel Summarizes Data

1) parents must transmit a “factor” containing
information- we know these as genes now

2) Different forms of “factors”= ALLELES
• Genetic makeup of all alleles= genotype
• Physical appearance due to alleles= phenotype

3)Dominant alleles mask recessive alleles
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4) Everyone has two factors-1 from each parentif they are the same= homozygous, if they are
different= heterozygous

DOMINANT: gene that is fully
expressed when two alleles are paired

RECESSIVE: gene that is not
expressed when paired with a
dominant gene or that produces a
different version of the trait than
the dominant
Which one is dominant? Brown eyes
or blue?
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a person with 2 “brown” alleles has
brown eyes
a person with 1 “brown” and 1 “blue”
has brown eyes
or a person with 2 “blue” alleles has
blue eyes

LAW OF DOMINANCE - the
dominant allele is expressed and the
recessive allele is hidden, if a
dominant allele is not present, the
recessive will be expressed
MENDELS LAWS/modernized

LAW OF SEGREGATION- during
meiosis, gene pairs separate and end
up in individual gametes
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LAW OF INDEPENDENT
ASSORTMENT - during meiosis,
traits will sort independently of each
other
Revisiting Law of Segregation
Homozygous
dominant parent
Homozygous
recessive parent
A
a
A
a
(chromosomes
duplicated
before meiosis)
A
a
AA
aa
A
a
meiosis
I
A
A
A
a
A
a
a
a
meiosis
II
A
A
A
A
a
a
a
a
gametes
gametes
A
a
Fertilization
produces
heterozygous
offspring
Fig. 11.4, p. 178
Revisiting Law of Independent Assortment
Chromosome Theory of Heredity

the material of inheritance is carried by
genes on chromosomes, and the genes
occur in pairs on homologous chromosomes

the gene pairs can be found in different
types called alleles and are found at the
same place on each chromosome, called the
LOCUS
A pair of homologous chromosomes,
each in the unduplicated state (most
often, one from a male parent and its
partner from a female parent)
A gene locus (plural, loci), the
location for a specific gene on
a specific type of chromosome
A pair of alleles (each being a
certain molecular form of a gene)
at corresponding loci on a pair of
homologous chromosomes
Three pairs of genes (at three
loci on this pair of homologous
chromosomes); same thing as
three pairs of alleles
Fig. 11.3, p. 177
BASIC GENETIC SHORTHAND

in working with genes, scientists have
found that assigning alphabetical letters to
each trait makes the traits easy to follow
through generations
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Rules:
Dominant alleles are written as
CAPITAL letters
Recessive alleles are written as lower
case letters
Traits are expressed in pairs, so the
diploid condition will always have 2 of
the same letters representing the
trait
examples include BB, Bb, bb
REVIEW
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GENOTYPE - the types of genes an
organism has, expressed in letters
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PHENOTYPE - the physical
expression(appearance) of the gene
pair
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HOMOZYGOUS - a genotype
description of a gene pair with both
dominant or both recessive alleles

HETEROZYGOUS - a genotype
description of a gene pair with 1
dominant and 1 recessive allele in the
gene pair
Example of Genetic Law

In peas, yellow pea color is dominant over
green pea color.

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Just because it is more commonly seen,
does not mean that trait will be the
dominant trait
Phenotype
Genotype
Genotypic
Expression
Yellow Pea
BB
Homozygous
dominant
Yellow Pea
Bb
Heterozygous
Green Pea
bb
Homozygous
recessive
Ideas to Keep In Mind…
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it is simpler to discuss one gene pair at a time
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an organism will have many traits expressed at the
same time
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not all genes are expressed by 2 alleles, some may
be expressed by multiple alleles, like blood type
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not all traits are expressed by just one gene, some
may involve many genes like skin color-determined
by the expression of 21 different gene pairs
MAKING PREDICTIONS
USING GENES
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To improve crops
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To help produce an improved product
people will buy
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To predict possibility of genetic
disorders
Paternity Tests
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HOW TO PREDICT
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use of PUNNETT SQUARES
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MONOHYBRID CROSSES
• one trait being crossed
• use 4 squares
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DIHYBRID CROSSES
• two traits being crossed
• use 16 squares
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In the Hairy Apeloideus, blue ears
are dominant to red ears. If a
heterozygous individual is crossed
with an red eared individual, what is
the probability that the offspring will
have red ears?
DIHYBRID CROSSES
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2 Factors
 Example
In Humans curly hair (C ) is dominant to
straight hair (c) and freckles (F) are dominant
to not having freckles (f). If a man who is
heterozygous for curly hair and doesn’t have
freckles marries a woman who has straight hair
& is homozygous dominant for freckles, and
they have babies, what could the possible
phenotypes in their offspring be??
Completing the Cross
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1- Figure out gametes- use the FOIL
method- SEE BOARD
2- Write gametes above and on side of
boxes- use 16 squares this time
3- Letter pairs go back together in offspring
Completing the Cross
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1. Determine the letter you’ll use
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2. Determine the gametes of the parents
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3.Make your punnett square
DIFFICULT PREDICTIONS

Mendel was lucky because his
“factors” behaved in a predictable
fashion and there were only 2
phenotypes per trait
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Not all traits are so orderly
Incomplete Dominance
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the genes in the pair are not
necessarily dominant or recessive,
but become “BLENDED” in the
offspring
heterozygotes show the blending,
homozygotes show one of 2
expressions
Examples in Humans
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Familial Hypercholesterimia- caused
by defective proteins that cannot
remove LDL from blood- leads to
atherosclerosis-
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Sickle Cell Anemia
CODOMINANCE
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both genes become expressed, but
are individually recognizable
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may involve multiple alleles
ROAN Animal Coats
Red haired parent + White haired
parent = red and white haired
offspring
(Roan- horses and cattle)
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Examples in humans
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Tay-Sachs disease- in children- fat
buildup on brain
Gene is recessive but heterozygotes
have good and bad enzymes presentbut they’re normal
Blood Types A, B, AB, O- different
antibodies present on RBCs
Other Influences
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Polygenic traits have more than one
gene pair controlling expression
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Pleiotropy occurs when a single gene
affects more than one trait
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Multiple Alleles have more than 2
phenotypes expressed
Blood Type Genetics
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Blood is …
• 1. Plasma
• 2. Cells
• a. Platelets
• b. white blood cells
• c. Red blood cells
Blood Type genetics
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Genes involved
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I = dominant
i = recessive
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Rather than just 2 alleles, there are
many
Blood Type Genetics
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Blood Types
•
•
•
•
A
B
AB
O
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Genotypes
IAIA or IAi
IBIB or IBi
IAIB
ii
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http://anthro.palomar.edu/blood/table_of_A
BO_and_Rh_blood_type_frequencies_in_U
S.htm
Blood Type Genetics
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Red Blood cells contain surface antibodies(like
little flags)- marker proteins
A blood contains A proteins and anti- B antibodies
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B blood contains B proteins and anti- A antibodies
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O blood contains no proteins and anti- A and antiB antibodies
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AB contains A and B proteins but no antibodies
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http://learn.genetics.utah.edu/units/basics/blood/types.cfm
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Blood Type genetics
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Antibodies recognize foreign blood
and cause agglutination (clumping)
Transfusions- example- person with
Type A blood must be matched with A
or O ; otherwise Anti B antibodies will
recognize B blood and reject it
Type 0 = universal donor
Type AB = universal receiver
PROBLEM
 If
a man with O blood type marries
a woman with type AB blood, what
blood types are possible in their
children?
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X or Sex Linked Traits
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The X Chromosome is bigger when
compared with the Y chromosome
Females= XX
Males = XY
Some traits are only carried by Genes on the
X chromosome
Men need only 1 copy, women need 2 to
exhibit the trait
Example
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Hemophilia- failure of blood to clot
XH = normal
Xh= hemophilia
Women need 2 copies of Xh
Men only need 1 copy
See example on board
Other sex linked traits
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Red-Green Color Blindness
Congenital Night Blindness
Duchenne Muscular Dystrophy
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Environmental Influences such as
weather may affect the phenotypic
expression of the organism (will have
multiple alleles)
PEDIGREES
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allows you to show how a trait and the
genes that control it are inherited within a
family or group
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used to study familial inheritance
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could be used for genetic counseling for
parents who are afraid of passing on a
devastating genetic disorder