Download Genetics Notes

Genetics
 Alleles-alternate forms of a gene for a trait.
Ex. Trait=height
Genes=tall or short
 Genetics is the study of heredity
o Heredity is the transmission of characteristics from parents to
offspring.
Greger Mendel came up with two principles of genetics from studying pea
plants.
1. Law of segregation-alleles separate when gametes are formed.
2. Law of independent assortment-2 or more pairs of alleles
segregate independently of one another
Punnett Squares
 A model used to predict patterns of inheritance.
-Monohybrid, dihybrid and trihybrid crosses can be used. This refers to
the amount of traits you are looking at.
 Homozygous-when 2 alleles are the same (pure) ex. TT or tt
 Heterozygous-when 2 alleles are different (hybrid) ex. Tt
 Genotype-the genetic make up of an organism ex. Tt (indicated by
letters)
 Phenotype-Physical appearance of the organism ex Tall (indicated
by the word)
 Dominant-the allele that shows up (capital letter) ex. Tt organism is
tall b/c T=tall and t=short
 Recessive-allele is present but not seen ex. Tt- t is the recessive trait
 F1 (filial)-offspring of the parents
Monohybrid Cross
 Cross between individuals involving one trait ex. Height
1. Determine what is dominant and recessive ex. Tall or short
2. Assign genotypes to parents ex. T=tall t=short TT x tt
3. Segregate gametes
TT x tt
T T
t t
4. Put gametes in punnett square
T
T
t
t
5. Bring letters down into box (capital letter goes 1st)
6. Interpret results
a. Genotype=
b. Phenotype=
7. Cross f1’s if problem asks you to: Tt X Tt
T
t
T TT
Phenotype: 3 tall: 1 short or 75% tall, 25%
Tt
short
tt
t Tt
Genotype : 1 TT: 2Tt: 1tt or 25% TT, 50%
Tt, 25% tt
Example:
a. Cross a homozygous red plant with a homozygous yellow plant.
What is the phenotype ratio? And what is the genotype ratio? R=red
r=yellow
r
r
RR x rr
R
Rr
Rr
Rr
R
Rr
Phenotype:
100% red; 4 red: 0yellow
Genotype: 100% Rr; 4Rr: 0
b. Cross the F1 generation and state the phenotype percent and genotype
percent.
Rr x Rr
R
r
R RR
Phenotype: 75% red, 25% yellow
Rr
Genotype: 25% RR, 50% Rr, 25% rr
Rr
rr
r
c. Cross homozygous tall plant with a heterozygous tall plant. What is
the genotype and
phenotype percentage? T=tall
t=short
TT x Tt
T
T
T TT
Phenotype: 100% tall
TT
Genotype: 50% TT, 50% Tt
t
Tt
Tt
T
Dihybrid Cross
 Cross between individuals with 2 traits.
1. Determine dominant/recessive traits
1st trait=Pea shape
Trait 2= color
R=round
Y=yellow
r=wrinkled
y=green
2. Assign parents genotypes
Homoz. Round yellow x homoz. Wrinkled green
RRYY x rryy
3. Segregate gametes
RRYY x rryy
RY, RY, RY, RY x ry, ry, ry, ry
4. Fill in Punnett Square
Or
RY
ry RrYy
RrYy
RY
RrYy
RrYy
ry
5. Interpret Results
a. Genotype= 100 % RrYy
b. Phenotype=100% Round, yellow
6. Cross F1’s if asked
RrYy X RrYy
RY
ry RrYy
7. Segregate gametes
RY, Ry, rY, ry x RY, Ry, rY, ry
8. Fill in punnett Square
RY
Ry
RY
RRYY
Ry
RRYy
rY
RrYY
ry
RrYy
RRYy
RRyy
RrYy
Rryy
RrYY
RrYy
rrYY
rrYy
RrYy
Rryy
rrYy
rryy
rY
ry
9. Interpret results: 9 round yellow: 3 round green: 3 wrinkled yellow: 1
wrinkled green
Test Cross
 Crossing of an individual of unknown dominant genotype with a
homozygous recessive.
Ex. TT x tt
or Tt x tt
Crosses aren’t always simple!
1. Incomplete Dominance (codominance)
a. When 2 traits blend
b. Occurs in heterozygous condition
Example: RR=red
RR x rr
R
R
r
Rr
Rr
r
Rr
Rr
Cross F1’s: Rr x Rr
R
R
rr=white Rr=pink
Genotype: all Rr
Phenotype: all pink
r
RR
Rr
Genotype: 1RR: 2Rr: 1rr
Rr
rr
Phenotype: 1 Red: 2 pink: 1 white
r
Phenotype:
2. Multiple Alleles-3 or more alleles of the same gene code for one trait.
3. ex. Blood type
Blood Typing
Types: A, B, AB, and O
-The type of blood you are is determined by which protein you have on
your blood cell.
 If you are A you have an A protein
-Not all blood types can donate to all other blood types
-Antibodies can form which fight off foreign material
So…if you have A blood, you can receive blood only from A and O
** O is a universal donor! Gives to everyone.
**AB is a universal recipient-can get from everyone!
RH Factor-where + and – come in
 If you are RH+ you have RH factors on blood cells
 If you are RH- you DON’T have the RH factor present
 So you can be A+ or A-, B+ or B- etc…
 If A+ you can get blood from A+ or A- or O
 If A- you can only get blood from A- or OBlood Types
A
B
AB
O
Genotypes
AA or AO
BB or BO
AB
OO
A and B are both dominant→they dominate O
Cross Type AO x AB
A
A
B
O
AA
AO
AB
BO
Types: A, AB, B
Sex-Determination
Male: XY male determines sex of child
Female: XX
XX x XY
X
X
X
XX
XY
*Everytime you have a child 50%
XX or XY
XX
XY
Y
Sex-Linked Traits
-carried on X chromosomes; can be dominant or recessive
ex. Colorblindness=sex-linked recessive
Cross normal male with a carrier female
XCY x XCXc
XC
C
X
Y
XCXC
XCXc
XCY
XcY
Xc
Phenotype: 1 normal female; 1 carrier female; 1 normal male; 1
colorblind male
Ex 2 Hemophilia (blood doesn’t clot)-sex linked recessive Xh Xh
XHY
Xh
H
X
Y
XH Xh
Xh Y
x
Xh
XH Xh
Xh Y
Phenotype: 2 carrier females; 2 hemophiliac males
Human Genetics
 Pedigrees-shows a pattern of inheritance in a family for a trait.
Ex. Hemophilia, tongue rolling etc.
 Represented as follows
= male
= female
 Each generation is represented by a roman numeral
 Each person in a generation is numbered
Childrens line Marriage line
*Can predict genotype of each person
-assign recessive trait to shaded box or circle.
-Assign one dominant gene to non-shaded
-Do punnett squares to figure out genotypes.
 In 1st generation what are the parents genotypes? What are the
childrens?
DNA Fingerprinting
Lets look at the activity on the website below:
http://www.pbs.org/wgbh/nova/sheppard/analyze.html