Transcript genetics notes

Mendel
• Austrian monk
and plant
breeder
• Studied the
inheritance of
pea plants
• Pea plants are
self fertilizing
• But can be cross
pollinated
• Mendel cross
bred male yellow
pea plants and
female green pea
plants
Inheritance
• How did Mendel know the plants
were true green and true yellow?
• He self pollinated the plants for a
few generations to make sure that
the plants were only one color.
• He called these true plants the P
generation or Parental generation
The inheritance of the pea plant
• Then Mendel cross
pollinated the P
generation to get the
first filial generation
or F1
• Mendel noticed that
the offspring were all
green; the yellow
trait was not in the
F1 and wanted he to
know why
• He took two F1 plants and cross
pollinated them.
• This new group is called the F2
generation
• The yellow trail reappeared in
the F2 generation but there were
very few of them. (6022 green
and 2001 yellow) A 3:1 ration
Genes come in pairs
• The two colors in the pea plant
meant that there were two factors
involved in pea color
• These factors are called alleles
(different versions of the same gene)
• But what determined which gene
would show?
Law of Segregation
• The alleles for a character
separate during Meiosis
• During fertilization one allele
from each parent unite creating
the new genotype
Questions
1.Why are pea plants good subjects for
genetic experiments?
2. What was the ratio obtained by
Mendel’s experiments? How did he
explain them?
3. Do you think the results would
differ if Mendel used squash plants
instead of peas, which usually do not
self-pollinate?
Dominant and Recessive Genes
• Mendel concluded that some gene
alleles were dominant while others
were recessive
• In the case of pod color, Green is
dominant, because it was the only
color in the F1 generation.
• While the yellow allele is recessive.
• Dominance is represented by a
capital letter
• Recessive alleles is represented
by a lower case letter
Homozygous vs Heterozygous
• Homozygous means two of the
same alleles for a trait
–LL or ll
• Heterozygous means two
different alleles for the same
trait
–Ll
Genotype and Phenotype
• The appearance of an organism does not
indicate what the alleles of the organism
are.
– For example: a yellow pea plant can
be either YY or Yy because the yellow
is dominant and masks the other color.
• The genotype is the organism’s alleles
(YY)
• The phenotype is the visible trait (yellow)
Mendel had another question
• If you have purple
flowers are you
always a tall plant?
• That is, will the
inheritance of one
character influence
the inheritance of
another character?
How to determine possible
gametes
Dihybrid cross
Monohybrid cross vs Dihybrid cross
• A monohybrid cross involves only a single trait
– For example – determining color of a pea
plant
• A dihybrid cross involves the heredity of two
traits
– For example – determining the color and
shape of a pea
• Based on Mendel’s study of dihybrid
crosses he discovered the law of
independent assortment which states
that there is a random distribution of
alleles during meiosis
• They separate independently
Genetic variation
• Genetic recombination occurs during
meiosis
– What stage?
– What process?
Gene linkage
• Because genes are so close on the
chromosome they tend to move together
during crossing over
Chromosome mapping
• Map the relative position of genes on a
chromosome
• First map of fruit flies in 1913
• Human genome is currently being
mapped
Probability and statistics
• Calculations are used to predict
outcomes.
• Three mathematical calculations are used
to predict the outcome of crosses.
• Sum rule
• Product rule
• Binomial expansion equation
Sum Rule
• The probability that one of two or more
mutually exclusive events will occur is
equal to the sum of the individual
probabilities of t
• he events.
• Ex. Pea plant heterozygous for flower
color and height. (PpTt) the results will
be 9:3:3:1.
• The four phenotypes are mutually
exclusive
• This means a plant with purple flowers
and tall can not be white and short.
• The sum rule allows us to determine
What is the probability that we will
obtain any one or more different types of
offspring.
• What is the probability that an offspring
will have purple flowers and tall or have
white flowers and short?
• Investigator wants to predict whether
one of two mutually exclusive events will
occur.
Calculate
•
•
•
•
•
•
cross: PpTt x PpTt =9:3:3:1
Calculate individuals probabilities
Purple and tall 9/16
White and short is 1/16
Now add 10/16 or .625 x100=62.5%
That offspring will be either of the two.
Product Rule (or)
• This is used to predict the probability of
independent events
• That is the occurrence of one does not
affect the probability of another.
• Can be used to predict outcome of a
cross involving two or more genes that
sort independently.
Ex.
• Cross TT Pp RR xTt pp Rr
• What is the probability of Tt PpRr?
Probability
• Probability= # of times an event
occurs/total # of events.
• Pheads=1/heads/(1heads + 1 tails)=1/2=50
• If you flip a coin three times in a row
what is the probability that it will land on
heads?
• ½ x ½ x ½ x=1/8
• Do Now: Albinism (lack of pigment) is a
recessive disease. If a heterozygous
normal parent and an albino parent have
3 children, what is the probability their 3
children will be will all be carriers
(heterozygous)?
• Objective: Practice complex genetic
problems.
• HW: Finish packet. Study for test.
Tuesday.
Do Now: Left- handedness is recessive to
right- handedness. A left-handed woman
and a right- handed man have a lefthanded child what is the probability their
second child will also be left- handed?
Objective: Practice complex genetic
problems.
HW: Finish packet and study for test.
• Using the same parents from previous
question, what would be the probability
of having two dimpled, non-tongue
rolling children in a row?
Do Now: Set up a Punnett Square
– Long fur is dominant to short fur. The
parental male is homozygous for long fur
and the parental female is homozygous
for short fur. Using a Punnett Square
determine what the F1 generation will
look like.
– Objective: Perform test cross and
calculate probability of offspring.
– H.W. Read 8.1, key terms, and study for
quiz.
Do Now
• Wrinkled peas are dominant
• Round peas are recessive
• Cross a male heterozygous with a
female homozygous recessive
• Give the percentages for:
– Heterozygous
– Homozygous dominant
– Homozygous recessive
• DO NOW: Rolling your tongue is
dominant to not rolling your tongue
and dimples are dominant to no
dimples. If a heterozygous dimpled
mother who can not roll her tongue
has children with a man who is
heterozygous for both dimpled and
tongue rolling, what is the
probability of them having a child
who has no dimples and can roll his
or her tongue?
• Cross RdYy x RrYy
• What is the probability that an offspring
will be round and yellow or wrinkled and
green?
•
•
•
•
•
Jane is sample 1
Mike is sample 2
John is sample 3
Baby is sample 4
Can you tell who the father is from your
results? How?
• Do Now: Purple flower color is dominant
to white.
• The first pea plant is homozygous
dominant.
• The second is homozygous recessive.
• Create the Punnett square and give ratios
for the offspring genotype and
phenotype.
• Do Now: Create a dihybrid test cross for
the traits of flower color and tallness in
pea plants.
• Objective: Practice dihybrid cross and
describe polygenetic traits and multiple
alleles.
• HW:
Do Now:
• A woman with type B blood has a child with
type O blood. What are the possible genotypes
of the mother and of the father? Use the
Punnett square to answer.
• Objective: Practice Punnett Squares and
introduce complex heredity patterns.
• Complex genetic packet.
Polygenic Inheritance
When several genes influence a
character.
The genes may be located on one
chromosome or scattered along
different chromosomes.
Ex. Eye color, height, weight, hair
and skin color.
Multiple alleles
• Genes that have more than two alleles.
• Ex. Color coat for rabbits
• Ex. Blood type for humans
• C = full color
• Cch = chinchilli partial defect in
pigmentation
• Ch= Himalayan color in certain parts
• c= albino= no color
Incomplete Dominance
• When offspring display a character
that is intermediate between the
two parents.
• Ex. A snapdragon with red flowers
is cross with a snapdragon with
white flower, a snapdragon with
pink flowers is produced.
Incomplete Dominance
Snapdragon
Characters Influenced by
Environment
• Hydrangea- Acidic soil bloom blue
flowers.
• Neutral to basic soil bloom pink.
• Arctic fox – Fur is white in winter and
brown in summer.
Hydrangea
Arctic Fox
Codominance
• When both alleles contribute to
phenotype.
• Ex. Cattle (roan) red and white
• Ex. Speckled chicken feathers (black and
white)
Speckled Chicken
Roan Cattle
Sex-linked genes
• Genes located on the X or Y
chromosomes. Most are located on the
X.
• In many cases sex-linked disorder will
affect males more because they only
have one X. Females have another X to
compensate for the mutation.
• Females must have a mutation in both
X’s to be affected.
Sex-linked
• Ex. Hemophilia- a mutation is the
persons ability to produce
clotting factor.
• Ex. Color-blindness- inability to
see difference between certain
colors.
What is a pedigree chart?
• Pedigree charts show a record of the
family of an individual
• They can be used by a genetic counsellor
to study the transmission of a hereditary
condition
• They are particularly useful when there
are large families and a good family
record over several generations.
© 2007 Paul Billiet ODWS
Symbols used in pedigree
charts
•
•
•
•
•
Normal male
Affected male
Normal female
Affected female
Marriage
A marriage with five children, two
daughters and three sons. The eldest
son is affected by the condition.
Eldest child  Youngest child
© 2007 Paul Billiet ODWS
Basic Symbols
Connecting Pedigree Symbols
Examples of connected symbols:
• Married Couple
• Siblings
Connecting Pedigree Symbols
Examples of connected symbols:
• Fraternal twins
• Identical twins
More Symbols
Organizing the pedigree chart
• A pedigree chart of a family showing 20
individuals
© 2007 Paul Billiet ODWS
Organising the pedigree chart
– Generations are identified by Roman numerals
I
II
III
IV
© 2007 Paul Billiet ODWS
Organising the pedigree chart
• Individuals in each generation are identified by Arabic numerals
numbered from the left
• Therefore the affected individuals are II3, IV2 and IV3
I
II
III
IV
© 2007 Paul Billiet ODWS
Dominant Autosomal Pedigree
I
2
1
II
1
2
3
4
5
6
III
1
2
3
4
5
6
7
8
9
10
Recessive Autosomal Pedigree
Pedigree Chart -Cystic Fibrosis