Transcript Genetics - Monroe County Schools

Genetics
Clifton L. Hamilton
Biology
Concepts
 Instructions for specifying characteristics
are carried in nucleic acids.
 Mulitcellular organisms, including
humans, form from cells that contain two
copies of each chromosome. This explains
many features of heredity.
History
 Genetics: Study of inherited traits
 Heredity: Passing of traits from parents to
offspring.
 Gregor Mendel: Given credit for what we
know about genetics/heredity.
 Mendel studied garden peas and came up
with a model for inheritance.
How does the environment influence
traits we have?
Students will…
 Construct Punnett squares in order to determine
phenotype of offspring.
 Predict what genes individuals carry based on traits they
have.
 Identify mechanisms of change that influence evolution
 Distinguish between mechanisms of change influencing
traits of organisms.
 Compare conditions necessary for populations to be in
Hardy-Weinberg equilibrium.
 Design animal with adaptations to help them survive.
Who was Gregor Mendel?
• An Austrian monk: he was known as the
“FATHER OF GENETICS”
• He discovered how traits were inherited
GENETICS –is the
scientific study of
heredity.
HEREDITY – the
passing of traits from
parents to offspring
(This is what makes
each species unique)
Mendel’s Peas
• Mendel did his study on pea plants
• Pea plants have many traits
(tall/short, purple flowers/white
flowers)
• Pea plants can be
self-fertilized (selfpollinated) or
cross-fertilized.
Mendel’s Work
• Mendel used true-breeding plants which
means if they were left to breed with
themselves they would produce offspring
identical to themselves.
• Mendel studied 7 different traits in pea
plants (Pod Shape, Pod Color, Seed Coat,
Flower Color, Plant Height, etc.)
• Trait: is a specific characteristic that varies
from one individual to another.
Types of Plants He Used…
1.True-Breeding - these plants
always create plants that look
like themselves
2.Hybrids – offspring of two
different “true-breeding” plants
Tall x Short = Hybrid
(TT)
(tt)
(Tt)
Dominance
Some traits are dominant over
others.
Tall x Short = all tall offspring
(hybrids)
*Tall is the dominant trait (T_)
*Short is recessive (tt)
Mendel’s Model
 For each trait, we have two copies of the gene—
one from the mother and one from the father.
 There are alternative forms of genes. These are
called alleles. For example, we possess two alleles
for freckles. Their combination determines
whether we will have freckles or not.
 These alleles can be dominant or recessive.
Dominant alleles, when present, will be expressed.
Recessive alleles can be masked by dominant
alleles. In order for recessive alleles to be
expressed both must be recessive.
 Gametes carry only one allele for each
inherited trait. At fertilization each gamete
contributes one allele.
 If a person is carrying two alleles for a trait
that are the same—they are homozygous
for that trait. If the alleles are different they
are heterozygous.
 The genes we are carrying for traits is our
genotype (Ex. AA, Aa, aa, BB, Bb, bb, etc.)
The outward expression of those genes is
our phenotype (Tall, Short, Hair Color, Eye
Color, etc.).
If Tall is dominant in pea plants and
short is recessive. Which would
represent the genotype of a heterozygous
plant
TT
Tt
tt
ST
Response Grid
0%
ST
0%
tt
0%
Tt
0%
TT
A.
B.
C.
D.
20
Countdown
Which would represent the
genotype of a short pea plant?
TT
Tt
tt
ST
0%
ST
0%
tt
0%
Tt
0%
TT
A.
B.
C.
D.
Response Grid
20
Countdown
How many plants would be tall if
you cross a heterozygous parent
with a short parent?
0%Response Grid
ta
l
20
ll
w
ou
ld
be
l
0%
A
0%
½
0%
¾
¼
½
¾
All would be tall
¼
A.
B.
C.
D.
Countdown
Monohybrid vs. Dihybrid
Crosses
 Monohybrid cross:
 Dihybrid cross:
– Looks at only one trait
– Looks at two traits at one
at a time.
– Ex. AA X aa  All Aa
time (Ex. Eye Color and
Height)
– Each trait gets a different
letter (A: Eye & B:Height)
– Letters on Punnett Square
are determined from all
possible combinations of
parent alleles.
A
A
a
Aa Aa
a
Aa Aa
 Example: If black fur and long whiskers are
dominant in rabbits.
 First, a rabbit would need two letters to
represent each trait.
 Homozygous Dominant for color and
Homozygous Recessive for whisker length
would be [BBll] this means the rabbit
would be black with short whiskers.
 Question: What would a rabbit look like if it
were heterozygous for both traits? [BbLl]
What would the following rabbits
look like?
 BbLl
– Black with long whiskers
 bbLL
– Grey with long whiskers
 BBll
– Black with short whiskers
 Bbll
– Black with short whiskers
Example: Dihybrid Cross
*When
crossing
parents that
are both
heterozygous
for two traits,
you will
ALWAYS end
up with a
9:3:3:1 ratio.
(R & Y)
(rr & Y)
(R & yy)
(rr & yy)
Predicting offspring
 In your notes, Cross two parents
heterozygous for both traits.
 Remember: Black is dominant to Grey and
Long Whiskers is Dominant to Short
Whiskers.
BbLl X BbLl
If Black is dominant and Long whiskers is
dominant. What would the genotype of a
rabbit that is grey and heterozygous for
whisker length be?
A. BBLL
B. Bbll
C. bbll
D. bbLl
0%
B
B
LL
B
0%
0%
l
bl
bb
ll
0%
bb
Response Grid
Ll
20
Countdown
What would the rabbits look like if you crossed
one that is homozygous dominant for color and
whisker length with a rabbit who is grey with
short whiskers?
A. ¼ black long, ¼ black
short, ½ grey short.
B. ¼ black long, ¼ black
short, ¼ grey long, ¼
grey short
C. All grey short
D. All black long
0% 0% 0% 0%
lo
n
la
ck
A
ll
b
re
y
ll
g
A
g
rt
sh
o
...
bl
ac
¼
ng
,
lo
k
bl
ac
20
¼
¼
bl
ac
k
lo
ng
,
¼
bl
ac
...
Response Grid
Countdown
Additional Practice w/ Dihybrid Crosses:
Complete All Problems in Your Notes!
In pea plants being tall is dominant over short and
green is dominant over yellow (T-Tall, G-Green).
1. Cross two pea plants heterozygous for both traits.
[TtGg X TtGg]
2. Cross a pea plant heterozygous for both traits
with one that is short and yellow.[TtGg X ttgg]
3. Cross a homozygous dominant pea plant with one
heterozygous for both traits. [TTGG X TtGg]
4. Cross a plant homozygous recessive for height
and heterozygous for color with one heterozygous
for height and homozygous dominant for color.
[ttGg X TtGG]
Other Traits
 Multiple Allele: Determines blood type.
A & B are dominant—O is recessive.
 Codominance: When two dominant alleles
are expressed together. (Ex: Black Fur X
White Fur Black and White Fur).
 Incomplete dominance: Intermediate trait
is expressed in heterozygous individuals.
Ex: In snapdragons a red (RR) and white
(rr) cross makes pink flowers (Rr).
What color would the flowers be if you
cross a red flower with a pink flower?
A. Red & Pink
B. Red, Pink &
White
C. All Red
D. All White
0%
0%
0%
0%
R
ed
R
,P
in
k
te
ll
W
hi
ed
ll
R
A
A
ed
&
&
Pi
nk
W
hi
te
Response Grid
20
Countdown
If a woman has type O blood, and a
man has type A blood, what could the
children have?
Only Type O
Only Type A
Type A or Type B
Type A or Type O
0%
0%
0%
0%
O
B
or
or
T
Ty
p
yp
e
e
pe
Ty
pe
Ty
pe
Ty
A
A
nl
y
O
nl
y
Ty
pe
A
O
Response Grid
O
A.
B.
C.
D.
20
Countdown
Inherited diseases
 Genetic predisposition: Having an
increased chance of a disease due to
inheritance. Ex: Heart disease & Diabetes
 Genetic disorder: If you have the genes for
the disorder, you will definitely have the
disease. Ex: Colorblindness & albinism
Autosomal Disorders
 Autosomal traits mean that the genes are
carried on one of the 22 autosomes.
– BOTH male and females can be carriers of
autosomal disorders.
– A carrier can pass on the genes but does not
have the disorder.
– Some include: albinism, cystic fibrosis, and
sickle cell anemia
Sex-linked Traits
 Sex-linked traits are carried on the X
chromosome.
– ONLY females can be carriers of sex-linked
disorders.
– Some of these include: Colorblindness,
Muscular Dystrophy & Hemophilia.
– Because males only have one X, they are more
likely to have sex-linked diseases than
females.
If a man with MD marries a carrier,
could they have a child with MD?
A. Yes, but only a girl
B. Yes, but only a boy
C. Yes, could be a boy
or girl
D. No
o
N
or
...
y
bo
be
d
co
ul
s,
Ye
Response Grid
a
bu
to
s,
Ye
Ye
s,
bu
to
nl
y
nl
y
a
a
bo
y
gi
rl
0% 0% 0% 0%
20
Countdown
Pedigrees
 Chart showing how a trait is inherited over
several generations.
 Males are squares—females are circles.
 Children are listed in order of birth.
 Shapes are colored completely if they
express the trait. Only half shaded if they
are heterozygous for trait.