Download Genetics - Monroe County Schools

Genetics
Melissa T. Emberton
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.
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 determine 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. The expression of those genes is
our phenotype.
If Tall is dominant in pea plants and
short is recessive. Which would
represent the genotype of a heterozygous
plant
20
TT
Tt
tt
ST
3
4
5
6
7
8
9
10
11
21
22
23
24
25
26
27
28
29
30
31
12
13
0%
14
0%
15
ST
2
0%
tt
1
TT
0%
Tt
A.
B.
C.
D.
16
17
18
19
20
Which would represent the
genotype of a short pea plant?
TT
Tt
tt
ST
20
0%
0%
1
2
3
4
5
6
7
8
9
10
11
21
22
23
24
25
26
27
28
29
30
31
12
0%
13
14
ST
TT
Tt
0%
tt
A.
B.
C.
D.
15
16
17
18
19
20
How many plants would be tall if
you cross a heterozygous parent
with a short parent?
20
¼
½
¾
All would be tall
0%
0%
l
0%
3
4
5
6
7
8
9
10
11
21
22
23
24
25
26
27
28
29
30
31
12
13
14
15
16
ta
l
17
ll
w
2
A
1
ou
ld
be
½
¼
0%
¾
A.
B.
C.
D.
18
19
20
 Monohybrid cross:
– Looks at only one
trait at a time.
 Dihybrid cross:
– Looks at two traits at
one time.
– Each trait gets a
different letter
– Letters on Punnett
Square are determined
from all possible
combinations of parent
alleles.
 If black fur and long whiskers are
dominant in rabbits.
 A rabbit would need two letters for each
trait.
 homozygous dominant for color and
homozygous recessive for whisker length
 BBll—the rabbit would be black with short
whiskers.
 What about a rabbit who is 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
Predicting offspring
 Cross two parents heterozygous for both
traits.
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?
20
A. BBLL
B. Bbll
C. bbll
D. bbLl
0%
B
B
LL
B
1
2
3
4
5
6
7
8
9
10
11
21
22
23
24
25
26
27
28
29
30
31
0%
0%
l
bl
bb
12
13
0%
ll
14
L
bb
15
l
16
17
18
19
20
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?
20
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
4
5
6
7
8
9
10
21
22
23
24
25
26
27
28
29
30
g
la
ck
A
ll
b
re
y
ll
g
A
lo
n
rt
sh
o
...
bl
ac
¼
ng
,
lo
k
bl
ac
3
11
12
31
¼
2
¼
1
bl
ac
k
lo
ng
,
¼
bl
ac
...
0% 0% 0% 0%
13
14
15
16
17
18
19
20
Other Traits
 Multiple Allele: Determine blood type. A
& B are dominant—O is recessive.
 Codominance: When two dominant alleles
are expressed together. Ex: Roan coat.
 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
53%
47%
R
ed
R
,P
in
k
te
ll
W
hi
A
ll
R
ed
0%
A
ed
&
&
Pi
nk
W
hi
te
0%
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
76%
18%
O
B
A
pe
Ty
Ty
pe
O
A
nl
y
or
or
T
Ty
p
yp
e
e
pe
Ty
pe
Ty
nl
y
0%
A
O
6%
O
A.
B.
C.
D.
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
67%
20%
13%
s,
Ye
o
N
or
...
y
bo
co
ul
d
be
a
bu
to
s,
Ye
Ye
s,
bu
to
nl
y
nl
y
a
a
bo
y
gi
rl
0%
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
carry are heterozygous for trait.