Transcript Genetics

GENETICS
DNA-What makes you YOU?
• DNA is a system of codes that controls every
aspect of your life (how you look, how you act,
etc.)
• DNA is like the instruction manual to keep you
working.
DNA
• DNA
What are sections of DNA known as?
 (Hint-they
gene code for a protein)
• Gene = one section of DNA that controls one
specific trait. (Ex. Hairline gene, earlobe gene, etc.)
DNA
• Chromosome = 1 strand of DNA that is
condensed/squeezed into a rod shape
Essential Question:
“How can 2 brown rabbits have a white fur baby?”
Genetics is the scientific study of how traits are
inherited from one generation to next.
Heredity = biological inheritance
Gregor Mendel - “Father of Genetics”
• Mendel was a monk
in the 1800’s
• He was in charge of
the monastery
garden.
• He performed
experiments
breeding pea
plants.
Mendel knew an important fact of his pea plants:
The flowers of plea plants have both male and female
reproductive parts.
Pea plants have the
ability to:
• #1 Self Pollinate=
the sperm cells in
the pollen fertilize
the egg cells in the
same flower.
• Aka TRUE
Breeding- creates
identical versions
of parents.
•
#2 Cross-pollinate= fertilization between 2 plants
(1 plant’s egg cells & another plant’s pollen (sperm).
• Mendel grew garden peas to
see how characteristics were
inherited.
• He looked at 7 traits that are
easily recognized and only
occur in 1 of 2 traits.
Mendel’s 1st Experiment
• Mendel crossed 2 plants with contrasting traits together.
– Round pea plant x a wrinkled pea plant
• These plants are called the Parental or “P” generation
Mendel’s Experiment: Results
RR
• The result of the
cross= the “F1”
(filial 1
generation).
• These offspring=
hybrids
rr
???
Hybrids- a mix of the 2 characteristics
Questions:
• #1 What were the F1 generation like?
• #2 Did the characteristics of the P generation blend?
Mendel’s Experiment: Results
RR
• He observed
that ALL the
offspring in
the F1
generation
had the trait
of only 1 of
the two
parents.
rr
Rr
Question:
• #1 What happened to the characteristics that "disappeared”?
Mendel’s Experiments
• Mendel
allowed the
“F1” hybrid
generation to
self pollinate
and produce
an F2
generation
(second
filial).
rr
RR
Rr
• He found that in the F2 offspring of this mating the recessive
alleles reappeared.
Mendel’s Experiment
• Mendel mated a
PURE purple
with a PURE
white flower=
cross fertilization.
• P generation=
• F1 generation=
• F2 generation=
What do you think
offspring (F1) look
like??
Mendel’s Experiments
What do you think
offspring (F2) look like??
Thank you Mendel!
• Based on his experiments we found:
1. There are alternative forms of genes he called factors
(today we call these alleles)
Alleles- alternative form of a gene
GENE
ALLELES
Height
Tall (T) or Short (t)
Flower Color
Purple (P) or White (p)
Seed Shape
Round (R) or Wrinkled (r)
Alleles:
PHENOTYPE: The physical trait that you actually see
on the person.
example: Tall, Purple, Round
GENOTYPE: The alleles (letters) on the gene
example: Tt, Pp, RR
GENE
ALLELE
from MOM
ALLELE
From DAD
Phenotype?
Height
Tall (T)
Short (t)
Tall
Flower Color
White (p)
Purple (P)
Purple
Seed Shape
Round (R)
Round (R)
Round
Thank you Mendel!
2. For each characteristic an organism
has 2 alleles – one from each parent
– If these 2 alleles are the same we
call it homozygous
– If these 2 alleles are different we call it heterozygous
GENE
ALLELE
from MOM
ALLELE
From DAD
Genotype?
Height
Tall (T)
Tall (T)
(TT) Homozygous
Flower Color
White (p)
Purple (P)
(Pp) Heterozygous
Seed Shape
Round (R)
Round (R)
(RR) Homozygous
Homozygous- both pairs of genes for a specific trait are the same.
Heterozygous- both pairs of genes are different
Thank you Mendel!
3. When 2 alleles are different, the 1 that is expressed
is dominant, while the one that is hidden is
recessive.
GENE
ALLELE
from MOM
ALLELE
From DAD
Phenotype?
Height
Tall (T)
Short (t)
Tall
Flower Color
White (p)
Purple (P)
Purple
Seed Shape
Round (R)
Round (R)
Round
Dominant Allele- mask/hides the other allele.
Recessive Allele- the allele is hidden unless there are 2 copies of the
recessive allele.
Thank you Mendel!
4. Law of Segregation= Independent Assortment during Meiosis I
(Metaphase I)
– Genes are segregated/separated from each other when
gametes are formed.
Probability & Punnett Squares
• Probability- the likelihood that a particular
event will occur.
• The way alleles segregate in an organism is
completely random- like a coin flip so the
principles of probability apply
If we flip a penny 20 times How
many times should you get heads?
How many times should you get
tails?
Let’s see if you are correct!!
TAKE OUT A COIN!!!
Probability & Punnett Squares
• Punnett Square is used to determine the
possible gene combinations that could
result from a genetic cross.
P
U
N
N
E
T
T
VID
Making a Punnett Square
BABY STEPS:
1. determine the genotypes of the parent organisms
2. write down your "cross" (mating)
3. draw a p-square
4. "split" the letters of the genotype for each parent & put them
"outside" the p-square
5. determine the possible genotypes of the offspring by filling in
the p-square
6. summarize results (genotypes & phenotypes of offspring)
7. bask in the glow of your accomplishment !
Punnett Squares
• Monohybrid Crosses- A cross between individuals
that involves 1 pair of contrasting traits
Punnett Squares
What pattern do you see?
Genotype:
100% Xx
Phenotype:
100% Dominant Trait
Punnett Squares
What pattern do you see?
Genotype:
25% XX, 50% Xx 25% xx
Phenotype:
75% Dominant trait 25% Recessive trait
Trait
Seed coat shape
Pod color
Seed Coat Color
Height of plant
Dominant
Round R
Green G
Brown B
Tall
T
Genotype:
25% TT, 50%
Tt,
25% tt
Phenotype:
75% Tall plant
25% short plant
Genotype:
100% bb
Phenotype:
100% white
seed coat
Recessive
Wrinkled
Yellow
White
Short
T
t
Punnett Squares
r
g
b
t
T
R
t
R
b
b
b
r
b
w
R
R
r
w
Determine
Genotype:
the
100% RR
Genotype
&
Phenotype:
Phenotype
100% Round
seed
coat shape
for #1,#2,#3
& just the
genotype
Genotype: for
25%
#4 rr, 50% rw,
25% ww
Phenotype:
Can’t determine
w/ the table
sorry!!
Trait
Seed coat shape
Pod color
Seed Coat Color
Height of plant
G
G
Dominant
Round R
Green G
Brown B
Tall
T
Recessive
Wrinkled
Yellow
White
Short
g
r
g
b
t
Punnett Squares
g
__g
G
g
G__
__g
G
Gg
Determine the
Genotype &
Phenotype
Genotype:
100% Gg
Phenotype:
100% Green
pod color
Punnett Squares
Continuing Mendelian Genetics
Question:
• Do genes segregate together or separately?
– Mendel conducted an experiment which followed 2
traits at a time:
• Crossed a homozygous yellow/round pea plant (YYRR) with
a homozygous green/wrinkled pea plant (yyrr)
• The F1 generation produced ALL yellow/round pea plants
(YyRr)
Dihybrid Crosses
__
__
__
__
__
__
__
__
PLEASE
FILL IN YOUR
PUNNET SQAURE!
RRYY
Dihybrid Crosses
PLEASE
FILL IN YOUR
PUNNET SQAURE!
Continuing Mendelian Genetics
Question:
• Do genes segregate together or separately?
– Mendel then used the F1 plants and self pollinated RrYy x
RrYy:
– He found that alleles segregated independently – use the
FOIL (first-outer-inner-last) method to figure out all of the
possible combinations of alleles from one parent:
• RY
• Ry
• rY
• ry
RrYy= RY Ry rY ry
This is known as a…..
• Dihybrid Crosses- A cross between individuals that
involves TWO pairs of contrasting traits.
Black fur?
Black eyes?
Red eyes?
Black fur & black eyes?
Black fur & red eyes?
Monohybrids
(one trait)
Dihybrids
(two traits)
& means
multiply!
P Generation= AaBb vs. AaBb
Dihybrid Crosses
AaBb= AB Ab aB ab
FOIL your
gametes to
figure out
what goes in
the columns
and rows
Dihybrid Crosses
ssyy= sy sy sy sy
SsYy= SY Sy sY sy
Dihybrid Crosses
P Generation= EeTt
vs. EeTt
P Generation= AaBb vs. AaBb
Dihybrid Crosses
AaBb= AB Ab aB ab
FOIL your
gametes to
figure out
what goes in
the columns
and rows
Dihybrid Crosses
ssyy= sy sy sy sy
SsYy= SY Sy sY sy
Dihybrid Crosses
P Generation= EeTt
vs. EeTt
Exceptions to Mendel’s Rules
Beyond Dominant and Recessive Alleles
1)
2)
3)
4)
5)
6)
Complete Dominance
Incomplete Dominance
Codominance
Multiple Alleles
Polygenic
Sex Linked
Exceptions to Mendel’s Rules
Beyond Dominant and Recessive Alleles
1)
2)
3)
4)
5)
6)
Complete Dominance
Incomplete Dominance
Codominance
Multiple Alleles
Polygenic
Sex Linked
1. Complete Dominance
• One allele can completely hide the other
• Mendel traits
2. Incomplete Dominance
• When 2 or more alleles influence the
phenotype and the heterozygous
phenotype is a blend of both homozygous
phenotypes.
• BOTH alleles affect the Phenotype
• BLEND
Incomplete Dominance Example:
The trait for fur color in mice is controlled by two
alleles. W for white and w for black. The
intermediate phenotype is grey. Cross a grey mouse
with a white mouse.
What is the probability the offspring will be white?
W
w
W
WW
Ww
W
WW
Ww
3. Codominance
• When both alleles for
a gene are expressed
in a heterozygous
offspring the trait.
• No Blending.
• BOTH traits are
expressed.
Codominance Example:
• Two tulip plants are mated one has yellow
petals and the other has red. All the
offspring of these flowers have both red
and yellow petals.
What are the genotypes of the parents and the offspring?
4. Multiple Alleles
• A trait that is
controlled by
three or more
alleles that can
fit into one
gene.
Multiple Alleles Example
Example Problem:
ABO blood type
Phenotype
Genotype(s)
A type
IAIA or IAi
B type
IBIB or IBi
AB type
O type
A man heterozygous for blood
type B marries a woman
heterozygous for blood type A.
What is the chance that their first
offspring will have type O?
IAIB
ii
IB
i
IA
IAIB
IAi
i
IBi
ii
5. Polygenic
• A trait controlled
by many genes
combined
together.
6. Sex Linkage
• Refers to genes that exist
only on the X chromosome.
• Males have only one allele
for these traits females have
two alleles.
• Usually passed from mother
to son.
Sex Linked Examples:
COLOR BLINDNESS is a recessive trait
XB= not colorblind
Xb=colorblind
The Parent Genotypes:
• – Male= XB Y
• – Female=XB Xb
Determine probability of having a color blind daughter? Colorblind son?
XB
Xb
XB
X BX B
X BX b
Y
X BY
XbY
Exceptions to Mendel’s Rules
Beyond Dominant and Recessive Alleles
1)
2)
3)
4)
5)
6)
Complete Dominance
Incomplete Dominance
Codominance
Multiple Alleles
Polygenic
Sex Linked
Pedigrees
Using your textbook and 1 BioBuddy, please complete the
Pedigree notes that you picked up when you came in today.
Goals:
1. To learn what a Pedigree is.
2. To understand how to read a Pedigree.
3. To learn how to construct a Pedigree.
4. To learn how to identify Genotypes for individuals on a
Pedigree.
What is a pedigree?
A chart showing the inheritance of a
trait over several generations
It shows the phenotypes of each
generation
What do the symbols on the chart
mean?
A circle represents a female
A square represents a male
A line connecting a male and a female
represents a marriage
What do the symbols on the chart
mean?
• Fully shaded circle or square =
person shows the trait
• This could mean homozygous or
heterozygous, dominant or
recessive.
What do the symbols on the chart
mean?
• Empty circle or square = person does
not show that trait
• It may mean the person is a carrier
for the trait (if the trait is recessive)
What can a pedigree be used for?
• Track any inherited trait:
dimples, widows peaks, ear lobe
attachment, etc
• Track the incidence of a
disease in a family
• Determine inheritance
pattern:
– Autosomal/sex-linked trait
– Recessive/dominant