genetics melissa t. emberton biology. concepts instructions for specifying characteristics are...
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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
TT T
t tt ST
0% 0%0%0%
A. TT
B. Tt
C. tt
D. ST
20
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Which would represent the genotype of a short pea plant?
TT T
t tt ST
0% 0%0%0%
20A. TT
B. Tt
C. tt
D. ST
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How many plants would be tall if you cross a heterozygous parent
with a short parent?
¼ ½ ¾
All
woul
d be
tall
0% 0%0%0%
20A. ¼
B. ½
C. ¾
D. All would be tall
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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?
BBLL
Bbll
bbll
bbLl
0% 0%0%0%
A. BBLL
B. Bbll
C. bbll
D. bbLl
20
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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?
¼ b
lack
long
, ¼ b
lac.
..
¼ b
lack
long
, ¼ b
lac.
..
All
grey
short
All
black
long
0% 0%0%0%
20A. 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 shortD. All black long
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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?
Red
& P
ink
Red
, Pin
k & W
hite
All
Red
All
White
53%
0%
47%
0%
A. Red & Pink
B. Red, Pink & White
C. All Red
D. All White
If a woman has type O blood, and a man has type A blood, what could the
children have?
Only
Typ
e O
Only
Typ
e A
Typ
e A o
r Typ
e B
Typ
e A o
r Typ
e O
18%
76%
0%6%
A. Only Type O
B. Only Type A
C. Type A or Type B
D. Type A or Type O
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?
Yes
, but
only
a g
irl
Yes
, but
only
a b
oy
Yes
, cou
ld b
e a
boy or..
. N
o
0%
20%
67%
13%
A. Yes, but only a girl
B. Yes, but only a boy
C. Yes, could be a boy or girl
D. No
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.