Download Genetics Notes! - Biology By Ruiz

Genetics
• Is the science of heredity.
• Heredity is the transmission of genetic
or physical traits from parent to
offspring.
Gregor Mendel
• Austrian Monk – born 1822
• Considered the “Father of Heredity”
• He conducted plant breeding
experiments in their monastery garden
using peas.
• Developed the Laws of Inheritance.
Particulate Inheritance
Mendel stated that
physical traits are inherited
as “particles”
Mendel did not know that
the “particles” were actually
Chromosomes & DNA
4
What would Gregor Mendel have
said if he knew he’d been named
the “Father of Genetics”?
“WHOO-PEA!”
Do chromosome numbers increase as
species become more advanced?
Common Name
Diploid Number
Monkey
42
Dog
78
Human
46
Mouse
40
Frog
26
Flatworm
16
Corn
20
Yeast
32
Potato
48
Green Algae
20
Fruit Fly
8
Sex Determination
• Female can contribute only an X chromosome
towards the sex of their offspring.
• Male can contribute an X or a Y chromosome
toward the sex of their offspring.
• Absence of a Y chromosome results in a the
embryo developing into a female.
• Presence of a Y chromosome results in the
embryo developing into a male.
• So, what is the genotype of a FEMALE?
MALE?
Genes
• Some traits are inherited directly from
one set of genes.
• Some traits are inherited through
several sets of genes.
Terms to know
• Homozygous- contains 2 identical alleles
for the same trait, AA, BB, cc (Purebred)
• Heterozygous- contains 2 different alleles
for the same trait, Aa, bB, Cc (Hybrid)
• Phenotype- Outward appearance of a trait,
coat color, polled, horned. description
• Genotype- Genetic makeup for gene, AA,
Aa, aa. letters
• Allele- Specific gene for specific trait.
• F-one = First cross offspring mating.
• F-two = Second cross offspring
Let’s practice . . .
• Are these homozygous or heterozygous?
•
•
•
•
•
•
•
•
•
EE
AA
Cc
dd
tt
Bb
LL
Pp
jj
What are dominant genes?
• The gene that expresses itself
• These hide the recessive gene if there is
complete dominance.
• Some examples of dominant traits in
humans are:
–
–
–
–
–
–
Broad lips (BB or Bb)
Second toe longer (TT or Tt)
Brown eyes (BB or Bb)
Freckles (FF or Ff)
Rolling tongue (RR or Rr)
Detached earlobe (EE or Ee)
What are Recessive Genes?
• The gene that is overshadowed by a
dominant gene – hidden by dominant
• Recessive genes can only express
themselves when there are two
• Some examples of dominant traits in
humans are:
–
–
–
–
–
Thin lips (bb)
Color blindness (cc)
Near sightedness (nn)
No dimples (dd)
Attached earlobes (ee)
Let’s practice . . .
• Are these homozygous or heterozygous
and dominant or recessive?
•
•
•
•
•
•
•
•
•
EE
AA
Cc
dd
tt
Bb
LL
Pp
jj
More Terms to know –
you will need to add these to your notes
• Codominance Alleles are equally expressed,
there is no dominance. Results in BOTH
phenotypes being visible.
• Incomplete Dominance Neither allele is
dominant, heterozygotes show a BLEND,
there is no dominance.
• Gene A segment of DNA that codes for a
trait.
• Heredity Transmission of genes from
parent to offspring.
Vocabulary Practice
• Pair up with your neighbor and match
the term with the correct definition.
Mendel’s Laws
• Law of Dominance
– In a cross of parents that are pure for
contrasting traits only one form of the
trait will appear in the next generation.
(If one parent is HH and the other is hh,
all offspring will show dominant trait)
– All the offspring will be heterozygous and
express only the dominant trait.
Mendel’s Laws
• Law of Segregation
– During meiosis, the formation of gametes
(eggs or sperm), the two alleles responsible
for a trait separate from each other.
– Alleles for a trait are then "recombined" at
fertilization, producing the genotype for
the traits of the offspring.
Mendel’s Laws
• Law of Independent Assortment
– Alleles for different traits are distributed to
sex cells (& offspring) independently of one
another.
– Offspring may look different from parents
and each other!
– This law can be illustrated using dihybrid
crosses.
– Red hair and freckles does not travel
together!
Punnet Square
• Angus- Black coat color is dominant over red.
Cross a heterozygous with a homozygous recessive
cow.
Make a KEY:
• BB = Homozygous Dominant and black
• Bb = Heterozygous and black
• bb = Homozygous recessive and red
Write the Parent Cross _________X__________
Punnet Square
B
b
b
Bb
bb
b
Bb
bb
Punnet Square
B
b
b
Bb
bb
b
Bb
bb
•
•
•
•
•
Results
2 heterozygous = Bb
2 Homozygous Recessive = bb
50% Black, 50% Red
Genotypic ratio = 2:2 = 1:1
Phenotypic ratio = 2 Black: 2 Red = 1:1
B
b
b
Bb
bb
b
Bb
bb
Take out a sheet of paper
• Title – “Types of Monohybrid Problems”
1. Dominance
2. Incomplete Dominance
3. Co-Dominance
4. Sex Linked
5. Multiple Alleles
1. Dominance
• Brown bunnies are dominant over
white bunnies. Cross two
heterozygous brown bunnies. What is
the chance there will be a white
bunny born?
• Make a key:
– BB –
– Bb –
– bb -
Parent Cross:
________X________
1. Dominance
• Brown bunnies are dominant over
white bunnies. Cross two
heterozygous brown bunnies. What is
the chance there will be a white
bunny born?
• Make a key:
– BB – Brown
– Bb - Brown
– bb – white
Parent Cross:
__Bb__ X __Bb__
Work the punnet square . . .
1. Dominance
• Make a key:
– BB – Brown
– Bb - Brown
– bb – white
Parent Cross:
__Bb__ X __Bb__
Work the punnet square . . .
B
B
bb
b
B
BB
Bb
bb
Bb
bb
Bb
Bb
bb
bb
1. Dominance
• Make a key:
– BB – Brown
– Bb - Brown
– bb – white
Chance of a
white bunny?
1 in 4 or
25% chance
Parent Cross:
__Bb__ X __Bb__
Work the punnet square . . .
B
B
bb
b
B
Bb
BB
bb
Bb
bb
Bb
Bb
bb
bb
2. Incomplete Dominance
• Red roses and white roses result in
pink roses. Cross a red rose with a
pink rose. What is the genotypic ratio
and phenotypic ratio of the offspring?
• Make a key:
– RR
– RW
– WW
2. Incomplete Dominance
• Red roses and white roses result in
pink roses. Cross a red rose with a
pink rose. What is the genotypic ratio
and phenotypic ratio of the offspring?
• Make a key:
– RR – red
– RW – pink
– WW - white
What is the
Parent Cross?
________X________
2. Incomplete Dominance
• Red roses and white roses result in
pink roses. Cross a red rose with a
pink rose. What is the genotypic ratio
and phenotypic ratio of the offspring?
• Make a key:
What is the
– RR – red
Parent Cross?
– RW – pink
__RR__X__RW__
– WW – white
Work a Punnett Square . . .
2. Incomplete Dominance
Make a key:
What is the
– RR – red
Parent Cross?
– RW – pink
__RR__X__RW__
– WW – white
Work a Punnett Square . . .
B
R
bR
b
R
Bb
bb
W
b
Bb
bb
2. Incomplete Dominance
Make a key:
What is the
– RR – red
Parent Cross?
– RW – pink
__RR__X__RW__
– WW – white
Work a Punnett Square . . .
B
R
bR
b
R
RR
Bb
RR
bb
W
b
RW
Bb
RW
bb
Genotypic ratio:
Phenotypic ratio:
3. Co-Dominance
Make a key:
• BB - Red
• BW – Red and White spots
• WW - White
3. Co-Dominance
• Black chupacabras and white
chupacabras make black and white
stripped chupacabras. Cross a black
chup and a white chup. What is the
genotypic ratio what will the offspring
look like?
Make a key:
• BB • BW • WW -
3. Co-Dominance
• Black chupacabras and white
chupacabras make black and white
stripped chupacabras. Cross a black
chup and a white chup. What is the
genotypic ratio what will the
offspring look like?
• Make a key:
– BB – black
– BW – stripped
– WW - white
What is the
Parent Cross?
_____X_____
3. Co-Dominance
• Black chupacabras and white
chupacabras make black and white
stripped chupacabras. Cross a black
chup and a white chup. What is the
genotypic ratio what will the offspring
look like?
• Make a key:
What is the
– BB – black
– BW – stripped
– WW - white
Work a Punnett Square . . .
Parent Cross?
_BB_X_WW_
3. Co-Dominance
• Make a key:
What is the
– BB – black
Parent Cross?
– BW – striped blk/white _BB_X_WW_
– WW - white
Work a Punnett Square . . .
B
B
bB
b
W
Bb
bb
W
b
Bb
bb
3. Co-Dominance
• Make a key:
What is the
– BB – black
Parent Cross?
– BW – stripped
_BB_X_WW_
– WW - white
Work a Punnett Square . . .
B
B
bB
b
W
BW
Bb
BW
bb
W
b
BW
Bb
BW
bb
Genotypic ratio:
Phenotypes:
4. Sex-Linked
• Color blindness is a sex linked
recessive trait carried on the X
chromosome. Cross a colorblind male
with a female carrier. What is the
chance of a colorblind child?
• Make a key:
Parent Cross:
______X______
4. Sex-Linked
• Color blindness is a sex linked
recessive trait carried on the X
chromosome. Cross a colorblind male
with a female carrier.
• Make a key:
Parent Cross:
XCXC – Normal vision
XcY X XCXc
XCXc – Normal but carrier
XcXc – Colorblind
XCY – Normal vision
XcY – Colorblind
Work a punnet square
4. Sex-Linked
• Make a key:
Parent Cross:
XcY X XCXc
XCXC – Normal vision
XCXc – Normal but carrier
XcXc – Colorblind
XCY – Normal vision
XcY – Colorblind
Work a punnet square
Bc Y
b
X
Chance of colorblind
child? 2 out of 4
50% chance
X X
XbC Bb
C
b
c
X
bb
c
XCY
Bb
bb
XcXc
XcY
5. Multiple Allele
Blood Types have 3 alleles!
A, B and O (O is recessive to A and B)
AA, AO = Type A blood
BB, BO = Type B blood
AB = Type AB blood
OO = Type O blood
SIX possible combinations for parents
Cross a Type O mom with a Type AB dad.
What are the possible phenotypes of the offspring?
5. Multiple Allele
• Cross a Type O mom with a Type AB
dad. What are the phenotypes of the
offspring?
• Parent Cross: OO x AB
Offspring phenotypes:
Type A and Type B
50% chance of either
B
A
bB
b
O
AO
Bb
bb
BO
O
b
AO
Bb
BO
bb
Dihybrid Cross
• What about crossing more than one trait?
Let’s look at traits for Seed shape & color
• Alleles:
–
–
–
–
•
R round
r wrinkled
Y yellow
y green RrYy
RY Ry rY ry
x
RrYy
RY Ry rY ry
Use “FOIL” to find all possible gamete
combinations
45
Dihybrid Cross
RY
Ry
rY
ry
RY
Ry
rY
ry
46
Dihybrid Cross
RY
RY RRYY
Ry RRYy
rY RrYY
ry RrYy
Ry
RRYy
RRyy
RrYy
Rryy
rY
RrYY
RrYy
rrYY
rrYy
ry
RrYy
Rryy
rrYy
rryy
Round/Yellow:
Round/green:
9
3
wrinkled/Yellow: 3
wrinkled/green:
1
9:3:3:1 phenotypic
ratio
47
Are there any shortcuts?
• YES!!!
• Cross AaBB with AaBb
• Cross AAbb with aaBB
• Cross AABb with AABB
Heterozygous to Heterozygous
(AaBb x AaBb)
is ALWAYS 9:3:3:1 phenotypic ratio.