Transcript Unit 8 - Genetics

Unit 8 - Genetics
Probability
- The likelihood of a particular event
occurring.
- The chance of something happening
- It can be expressed as a Fraction ( ¼ ),
Percent ( 25 % ), or Decimal ( .25 )
- Probability is a mathematical way of making
a prediction
How to Determine or Calculate Probability
Probability =
# of Desired Outcomes
# of All Possibilities
To determine the odds of rolling an even # on a die:
# of Even Numbers (3)
# of All Numbers (6)
= ½ or 50% or .50
Rules of Probability
1) Probability suggests what is Likely to happen, NOT
what will Definitely happen.
Ex Not all females have half male and half female
kids
2) Previous outcomes DO NOT affect future outcome
Ex A coin will not come up heads just because it was
tails the time before
3) In order for Probability to be accurate, the sample
size must be large.
Ex This class is not 50% male and 50% female, but
the school population is
Calculating Probability for Multiple Events
• Multiply the probability of each event by each other
Ex The odds of flipping 3 coins & they all land
tails up.
½ x ½ x ½ = 1/8
.50 x .50 x .50 = .125
50% x 50% x 50% =12.5%
Ex The odds of rolling a 6 three times in a row
1/6 x 1/6 x 1/6 = 1/216
.166 x .166 x .166 = .0045 or 0.45%
Probabilities Role in Genetics
• Each parent has two sets of DNA
• Only one set can be passed to the offspring.
• What are the odds certain traits being passed
on based on the combinations.
Ex
MOM
set “A” set “B”
1-23
1-23
Mom A & Dad A or
Mom B & Dad A or
DAD
set “A” set “B”
1-23
1-23
Mom A & Dad B or
Mom B & Dad B
Mother’s DNA Strand # 1
1
Gene
2
Gene
R
c
Purebred
Homozygous
R
Dominant
Father’s DNA Strand # 2
TRAITS
Tongue
Rolling
r
p
PH-NO
Purebred
Homozygous
c
Recessive
Purebred
Homozygous
c
Recessive
Cleft
c
Purebred
Homozygous
p
Recessive
PH-NO
Polydactyl
P
PH-5
4
Gene
t
r
PH-Roll
PH-NO
3
Gene
Purebred
Homozygous
Recessive
Hybrid
Heterozygous T
PH- Medium
Hybrid
Heterozygous p
PH-6
Height
T
Purebred
Homozygous
Dominant
PH- Tall
T
• Each parent possesses 2 strands of 23 different
types of DNA
• 1 strand came from their Mom & 1 strand came
from their Dad
• Each parent can only give one strand to their child
• Each strand has hundred/thousands of segments
called Genes
• Each gene is the information needed to develop a
Trait or Characterisitic
• Some traits have many different types or forms that
can show up called Alleles
Ex Trait: Eye Color
Alleles: Gray Brown Blue Green
Unit 8 – Genetics
• The basic rules of Heredity were first discovered by
Gregor Mendel, who conducted his experiments on
garden peas (pg 256)
• He was the first to determine that genes (factors)
are the carriers of traits and that it takes two genes
to cause a characteristic to develop
Guidelines Used By Mendel
1)Concentrated on one trait at a time
2)Used large numbers organisms (trails)
3)Used rules of probability to check his work
• The original Parents (P1)
were Purebred Tall
crossed with Purebred
Short
• The 1st generation
offspring (F1) were all
Tall
• The 2nd generation
offspring (F2) had some
tall and some short
plants
Law of Dominance
**When two different alleles are crossed and one
masks over the other
Dominant
- The allele that is expressed in a hybrid
- Symbolized by a Capitol Letter
Recessive
- The allele that is masked over in a hybrid
- Symbolized by a lower case letter
Purebred Dominant x Purebred Recessive = Hybrid
RR
x
rr
= Rr
• Parents Phenotype
Tall & Short
• Parents Genotype
TT & tt
• Cross parents (find all
the possible offspring
genotypes &
phenotypes by using a
Punnett Square)
• 1st generation offspring
phenotype Tall
• Genotype Tt
Indicate whether it is heterozygous or
homozygous:
AA ______
dd _______
Bb ______
EE _______
Cc ______
Ff _______
For each genotype below determine the
phenotype:
(purple is dominant to white)
PP ______
Pp ______
pp ______
B = Blue b = gold
Genotype Phenotype
Homozygous dominant
Purebred recessive
Heterozgous
Hybrid
Homozygous recessive
1. A tall plant (TT) is crossed with a short plant
(tt). Show the cross. What % will be tall?
2. A Tt plant is crossed with a Tt plant. What is
the phenotypic and genotypic ratio?
3. A heterozygous round seeded plant is
crossed with a homozygous round seeded
plant. Round is dominant to wrinkled.
Show the cross.
(Use letter R)
Unit 8 - Genetics
• Each individual has two alleles/genes for each trait,
but only has the ability to pass on one of them to its
offspring
Law of Segregation
- The random passing of only one of an organism’s
two alleles to its offspring
** The alleles/genes segregate or separate because of
Synapsis in Anaphase I of Meiosis I
**The new offspring must also have 2 alleles for each
trait and it will receive only one from each parent. This
results in 4 diff. possible combinations instead of 2
Pedigree Charts
**A chart that is used in human genetics to analyze
Mendelian inheritance of certain traits, especially
diseases.
Pedigree Chart Rules:
Males: Are represented by a square shape
Females: Are represented by a circle shape
Husband & Wife: Are represented by a line between
a square and a circle
Children: Are represented by lines
coming down from the line between
husband & wife
Which color is dominant?
RED
PINK
WHITE
Law of Incomplete Dominance Traits
Definition When neither of the two genes are
dominant or recessive, there is a blending of the
two traits where they meet in the middle
Example: When red colored petunias are crossed with
white petunias some pink petunias show up in the
offspring.
** We use the same capital letter for both since
neither is dominant or recessive to each other.
A prime ‘ or apostrophe is used to
differentiate the letters.
Genotype
RR
=
R’R’
=
R’R or RR’ =
Phenotype
red
white
pink
Parents:
R
R
Red
RR
x
x
White
R’R’
R’
R’
RR’
RR’
RR’
RR’
Results:
100% Pink Phenotype
100% RR’ Genotype
** Now do a cross between 2 pink flowers
Human Blood Types & Co-Dominance
• The human blood gene has three different alleles;
2 dominant & 1 recessive. More alleles mean more
combinations, which results in more phenotypes.
• The three alleles are; IA , IB , and i
• They result in four blood types: A, B, AB, & O
Law of Co-Dominance:
Where two different alleles are paired and
BOTH are dominant. Both phenotypes show
up independently without blending
• Both the IA and IB alleles are dominant over
the i allele.
• Neither the IA nor the IB alleles are dominant
over each other.
The blood gene cause Antigens (Protein Tags)
to form on the red blood cells (RBC). The type
of antigen determines the type of blood
(phenotype).
• Allele IA produces A antigens, IB produces B
antigens, and i does not produce any antigens.
• Chemicals called antibodies are also found in
blood in the liquid plasma part. Antibodies
react with antigens by clotting all RBC’s that
have the improper antigen together.
Blood Type
Alleles
(Phenotype) (Genotype)
Antigens
Antibodies
A
IAIA or IAi
A
Anti-B
B
IBIB or IBi
B
Anti-A
AB
IAIB
A&B
None
None
Anti-A &
Anti-B
O
ii
• In blood transfusions we must consider the
receivers antibodies & the donors antigens (do
they conflict?)
According to the chart:
Type A blood can receive blood from . . .
Type B blood can receive blood from . . .
Type AB blood can receive blood from . . .
Type O blood can receive blood from . . .
Universal Donor = Type O
Universal Receiver = Type AB
IT TAKES ALL TYPES
• The myth that, “my blood type is common, so there
are plenty of donors,” is just that, a myth. The more
people there are in your blood group, the more that
will need your donation. The reverse is also false.
“My blood type is so rare, no one will need a
donation.” The truth of the matter is, your
community blood bank needs all types. From the
most common O+’s to the rarest AB-’s. So help save a
life today, give the gift of life, GIVE BLOOD!
O+
A+
B+
AB+
...
...
...
...
37%
33%
11%
3.4%
O- . . .
A- . . .
B- . . .
AB- . . .
7%
6%
2%
.6%
Blood Typing Problems
1. Mom is heterozygous type A blood. Dad is
heterozygous type B blood. What % of their kids
would be type A? Type B? Type AB? Type O?
2. Mom is genotype AB. Dad is genotype Ai. What %
of their kids would be type A? Type B? Type AB?
Type O?
3. Mom is heterozygous type B blood. She had a
baby with type A blood. She thinks the father is
Mr. Y. He is type AB. Could Mr. Y be the father?
4. A mom who is genotype Ai had a baby who is type
A blood. What are the potential genotypes of the
father?
Sex-Linked Traits
Are you Colorblind?
Sex-Linked Traits
Definition A gene/trait that is found on the sex
chromosomes (X or Y)
Example Hemophilia and Red-Green Colorblindness
are recessive traits found on the “X” chromosome
Male’s
Genotype
Male’s
Phenotype
Female’s
Genotype
Female’s
Phenotype
XY
XCY
Normal
Colorblind
XX
XCX
Normal
Carrier (but
is normal
XcXc
Colorblind
Sample Dad is colorblind and Mom is totally
normal. What is the probability of having a
colorblind child?
XC
Y
X
XC X
XY
X
XC X
XY
Sample Mom is colorblind and Dad is totally
normal
A) What is the probability of having a
colorblind child?
B) What is the probability of their son being
colorblind?
C) What is the probability of their daughter
being colorblind?
• In the recessive sex-linked traits females can be
“carriers.” They do not have the trait, but they carry
it on their X chromosome and can pass it on to their
offspring.
• This is possible because females have two “X”
chromosomes. The normal X chromosome is
dominant to the defective X C or H chromosome and
masks the defective trait.
• Males are more likely to get sex-linked traits
because they either have the trait or they don’t.
Males do not have another X chromosome to mask
over the defective X C or H. Their other chromosome
is the Y chromosome.
1) Mom is carrier for colorblindness and Dad is
colorblind. What would be the phenotypic
ratio of the offspring?
XC
X
XC
X CXC
XC X
Y
XC Y
XY
2 Colorblind : 2 Normal
2) Mom is a carrier for Hemophilia and Dad is
normal. What are the chances of them having
a child who is a Hemophiliac?
A male who is a Hemophiliac?
A female who is a Hemophiiac?
X
Xh
X
X hX
XX
25% Hemophilia
50% Male Hemophilia
Y
X hY
XY
0% Female Hemophilia