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Mendelian
Genetics
Artificial Selection
Inherited variations in traits
Mendelian
Genetics
Mendelian Genetics
• Heredity – The
passing of traits from
parents to offspring
through generations.
– Genetics – The study
of genes. “Genesis” to
be born
• Genes – Individual bits
of information made of
DNA and located on
chromosomes
Mendelian Genetics
• Gregor Mendel –
• Father of Genetics
• Austrian
monk/mathemetician
• Experimented with
pea plants
• Mid 1800’s – work
was not accepted
• Work rediscovered in
1900’s
Pea plants
Advantages:
1. Grow quick in a
small plot.
2. Easy to cross (mate)
3. Dioecious – both
sexes on same plant.
4. Many viable
offspring from a
variety of crosses
Pea plants
Advantages:
1. Grow quick in a
small plot.
2. Easy to cross (mate)
3. Dioecious – both
sexes on same plant.
4. Many viable
offspring from a
variety of crosses
Pea plants
Advantages:
1. Grow quick in a
small plot.
2. Easy to cross (mate)
3. Dioecious – both
sexes on same plant.
4. Many viable
offspring from a
variety of crosses
male
-female
Pea plants
Advantages:
1. Grow quick in a
small plot.
2. Easy to cross (mate)
3. Dioecious – both
sexes on same plant.
4. Many viable
offspring from a
variety of crosses
Pea plants
Advantages:
1. Grow quick in a
small plot.
2. Easy to cross (mate)
3. Dioecious – both
sexes on same plant.
4. Many viable
offspring from a
variety of crosses
Pea plants
Advantages:
1. Grow quick in a
small plot.
2. Easy to cross (mate)
3. Dioecious – both
sexes on same plant.
4. Many viable
offspring from a
variety of crosses
Pea plants
Advantages:
1. Grow quick in a
small plot.
2. Easy to cross (mate)
3. Dioecious – both
sexes on same plant.
4. Many viable
offspring from a
variety of crosses
Differences in Mendel’s study
1. Repeated results
2. Large numbers (in a
small space)
3. Limited traits
4. Used readily
identified traits and
pure varieties
Probability
• Dealing with chance
• The determination of
what is most likely to
happen
• Only works for large
numbers
• Each event is
independent over
another
Probability
• Dealing with chance
• The determination of
what is most likely to
happen
• Only works for large
numbers
• Each event is
independent over
another
Probability
• Dealing with chance
• The determination of what
is most likely to happen
• Only works for large
numbers
• Each event is independent
over another
• Deviation – the difference
between the results you
expect and the results you
actually get.
Mendel’s studies
• Pure varieties –
Always produce same
results and same traits
• Bred for 10
generations to ensure
viability
X
6 feet tall
=
6 feet tall
X
1 foot tall
=
1 foot tall
Pure variety cross
Pure Tall
x
Pure dwarf
Pure variety cross
Pure Tall
x
All Tall
Pure dwarf
Pure variety cross
Pure Tall
x
All Tall
Pure dwarf
x
Tall
Pure variety cross
Pure Tall
x
All Tall
Pure dwarf
x
Tall :
Tall
Dwarf
Pure variety cross
Pure Tall
x
Pure dwarf
All Tall
x
Tall :
Tall
Dwarf
3:1
75% : 25%
Genetic terms
Hybrid – Contains both
dominant and recessive
genes or traits
Dominant – Always
appears in a hybrid.
Capital letter denotes the
dominant trait
T = Tall
Recessive – Never
appears in a hybrid.
Lower case denotes the
recessive trait.
t = dwarf
Genetic terms
Phenotype– How the genes
appear.
Ex. Tall, dwarf, Green,
yellow
Genotype – Shows the
gene combinations
present.
Ex.
TT , Tt , tt
Tt = tT
(capital 1st)
Genetic terms
Genotype – Shows the
gene combinations
present.
Ex.
TT , Tt , tt
Tt = tT
(capital 1st)
Allele – Refers to
one of the two forms
of a gene.
Ex. “T” or “t”
locus – the location
of an allele on a
chromosome
Genetic terms
Genotype – Shows the
gene combinations
present.
Ex.
TT , Tt , tt
Tt = tT
(capital 1st)
Allele – Refers to
one of the two forms
of a gene.
Ex. “T” or “t”
locus – the location
of an allele on a
chromosome
Genetic terms
Genotype – Shows the
gene combinations
present.
Ex.
TT , Tt , tt
Tt = tT
(capital 1st)
Allele – Refers to
one of the two forms
of a gene.
Ex. “T” or “t”
locus – the location
of an allele on a
chromosome
Genetic Crosses
• Law of Complete
Dominance – When a
dominant and
recessive trait appear
in a hybrid. The
dominant trait always
appears.
• Capital = Dominant,
lower case = recessive
• Homozygous –
Organisms which have
the same 2 genes (alleles
– letters) for a trait. TT
or tt (purebred)
• Heterozygous –
Organisms which have 2
different genes (allelesletters) for a trait. Tt
(hybrid)
Genetic Crosses
• Calculating
phenotypes and
genotypes
• P1 = parent generation
• F1 = first offspring
(filial)
• F2 = 2nd offspring
from F1 cross.
• Punnett Square – Diagram
used to calculate probabilities,
genotype, and phenotype from
genetic crosses.
• Right side – father’s alleles –
letters
• Left side – mother’s alleles –
letters
• Each square = offspring (4)
= 25%
Genotype
Offspring
Gametes
Phenotype = Tall
25%
25%
Phenotype = Tall
Phenotype = Tall
25%
25%
Phenotype = Short
Haploid - 23
Diploid-46
Law of segregation:
• Law of segregation –
the 2 alleles for each Haploid - 23
trait separate when
gametes form
Diploid-46
25%
Genotype
Offspring
Gametes
Phenotype = Tall
25%
25%
Phenotype = Tall
Phenotype = Tall
25%
25%
Phenotype = Short
Sample Genetic Problems
Solve on Punnett Square
Sample # 1 and 2
Tall (T) is dominant over short (t)
(recessive) pea plants. Mate a
homozygous tall with a
homozygous recessive and
calculate the genotypes and
phenotypes per cents and ratios
for the F1 and F2 generations.
#3
Round ( R ) seeds are dominant
over wrinkled ( r ) seeds. Mate a
heterozygous round seed plant
with a homozygous wrinkled.
Calculate the genotypes,
phenotypes, and % and ratios for
the F1 generation.
Sample # 4
Green (G) is the dominant color
for pods in pea plants. Yellow (g)
is recessive. Calculate the F1
generation genotypes, phenotypes,
% and ratios from a cross between
two heterozygous Green podded
plants.
4 Chromosomes
2 Chromosomes
1 Diploid Cell
4 Haploid Cells
Crossing over and
Independent assortment
Haploid - 23
Diploid-46
Genotype
Offspring
Gametes
Phenotype = Tall
25%
25%
Phenotype = Tall
Phenotype = Tall
25%
25%
Phenotype = Short
Test cross
• To determine an
unknown genotype. A
known genotype
(homozygous
recessive) is mated
with an unknown
(pure or hybrid?) to
determine from the
results
Test cross
Tall = TT or Tt
dwarf = tt
A tall plant of
unknown genotype is
crossed with a dwarf.
2 possible choices
Dihybrid Cross
2 differents characters with two
different traits on different
chromosomes
Dihybrid Cross
2 differents characters with two different
traits on different chromosomes
Law of Independent Assortment – States
that alleles of each gene segregate into
gametes independently of alleles of other
genes, as shown in a dihybrid cross
Human Genetics and Exceptions
to Mendel’s Studies
Exceptions to Mendel’s studies
• Mendel – Traits
showed complete
dominance
(autosomal) with traits
on separate
homologous
chromosomes
Exceptions to Mendel’s studies
1) Incomplete or Codominance – Neither
gene is hidden in a
hybrid
Causes a blending of
traits or both traits
appear
Exceptions to Mendel’s studies
1) Incomplete or Codominance – Neither
gene is hidden in a
hybrid
Causes a blending of
traits or both traits
appear
Ex. 4 o’clock flower,
carnations, shorthorn
cattle
Incomplete Dominance
Two different traits. Neither is dominant,
so there is a blending of the traits.
X
Codominance
Two different traits, both are
dominant and both appear
Sample Problem #1
• Shorthorn cattle –
Red fur = R
White fur = R’
RR x R’R’ = RR’
= Roan (pink)
Cross two Roan cattle
2) Multiple Alleles
More than two alleles possible to
choose for a trait , but only two
alleles present
Multiple alleles
• Rabbit fur • 4 possible alleles
C = normal
c = albino
Cch = chinchilla
ch = himalayan
Multiple alleles
• Rabbit fur CC =
Cc =
cc =
CCch =
ch c =
Cch ch =
Multiple Alleles – Blood type
• Human blood
• Antigens - Foreign
clotting factor
• 3 alleles –
IA, IB, i (no antigen)
Phenotypes:
Type A = IA IA or IA I
Type B = IB IB or IBi
Type AB = IA IB
Type O = i i
OO
AA
or
AO
BB
or
BO
AB
Sample # 2
• Blood type –
A woman who is hybrid
for type B blood
marries a man with
type O blood. What
type of blood could
their children NOT
have?
Chromosomes and Sex
determination
44 Autosomes
2 Sex
Chromosomes
Male
Genotype
44 Autosomes
2 Sex
Chromosomes
Female
Genotype
Probability of
Boy vs. Girl?
50:50
3) Sex-linked Traits
Sets of alleles found only on the X
chromosome. Females have two alleles
X+X, males have only one X+Y
3) Sex-linked traits
• Some traits are found
on the alleles of only
X chromosomes and
not on the Y.
• (Females = XX and
Males = XY)
• First discovered in
fruit flies
Fruit Flies
Drosophila melanogaster
3) Sex-linked traits
• 1910 – Thomas Morgan
• Drosophila (fruit flies)
white eyed flies – recessive
mutation (r) 3/1000
Red eyes = dominant (R)
Homozygous cross – all red
Hybrid cross = 3:1 ?
Results = 3,470:782 with all
white eyes being male
Traits on X but not Y
chromosome
3) Sex-linked traits
• 1910 – Thomas Morgan
• Drosophila (fruit flies)
white eyed flies – recessive
mutation (r) 3/1000
Red eyes = dominant (R)
Homozygous cross – all red
Hybrid cross = 3:1 ?
Results = 3,470:782 with all
white eyes being male
Traits on X but not Y
chromosome
Drosophila Fruit Fly Cultures Wild Type (+)- Genetics
Drosophila Fruit Fly Cultures Chromosome 1, White
Sample # 3
XR = Red eyes
Xr = white eyes
Cross 2 Hybrid red-eyed
flies. Calculate the
genotypes and
phenotypes for male and
female offspring
Sample # 4
Red-Green or Green-Red
Colorblindness,
Hemophilia
N=
X Normal trait
Xn = colorblind
A colorblind female
marries a normal eyed
male. Which offspring
will be colorblind?
Everyone should see a 12.
Normal visioned people should see 45.
Colorblind people won't see any numbers.
Normal visioned people should see 29. Colorblind
people should see 70.
Normal visioned
people won't
readily see any
number, but
colorblind
people will
easily see a
number 5.
Normal visioned
people will see 26. If
you are red-blind,
you should only
clearly see the 6. If
you are green-blind,
you should only see
the 2. A totally
colorblind person
won't see any number
in this plate.
only
or
XBXB and XBY
or
XOXO and XOY
XBXO
This is illustrated by calico cats. Coat color in cats is an X-linked gene, with
alleles for black and orange-brown, so XBXB and XBY cats will have a black
coat, while XOXO and XOY will have an orange-brown coat. Another possible
combination for female cats would be XBXO. Both of the color alleles would
be expressed, so the cat would end up being partially brown and partially
black.
Hemophilia Family Tree
4) Sex influenced traits
Gene present plus the proper
hormone required
Examples: Male pattern baldness,
hairy pinna (ears), horns in sheep.
5) Polygenic traits
More than two alleles on more than two
chromosomes, with more than two alleles
appearing at once.
Polygenic traits in humans
•
•
•
•
Non – Blue Eye color
Skin color
Hair color
Height
Light Green eyes
Dark skin
Dark Brown eyes
Light skin
Short
Tall
Hair color
Non – Blue Eye color
Skin color
Genes and the Environment
• The environment
influences the phenotype
for some genotypic traits.
• The norm of reaction is
the phenotypic range of a
genotype influenced by
the environment
• For example, hydrangea
flowers of the same
genotype range from blueviolet to pink, depending
on soil acidity
Genes are what an organism
may become not will become
Ex. Genes for chlorophyll – no
sunlight = no chlorophyll
Human behavior – identical
twins - differences
Acidic soil
Basic or alkali soil
Genes and the Environment
• Norms of reaction are
generally broadest for
polygenic characters
• Such characters are
called multifactorial
because genetic and
environmental factors
collectively influence
phenotype
Genetic disorders
Pedigree : Chart used to trace family
histories of genetic traits
Hemophilia Family Tree
Sickle
Cell
Anemia
Polydactyly
PKU
Phenylketonuria
PKU - 1 in 15,000 Americans.
• A non-food source of phenylalanine is the
artificial sweetener Aspartame. This
compound, sold under the trade names
"Equal" and "NutraSweet", is
metabolized by the body into several
chemical byproducts including
phenylalanine.
Porphyry ?