Transcript NOTES Incomplete Dom Test & Traceback

I.
Introduction
A.
Genes are not always dominant or recessive in their
relationship.
II. Incomplete dominance
A. Also called blending inheritance.
B. The heterozygous is a blend of the two alleles.
Red x White = Pink Black x White = Grey
Examples
A.
Incomplete dominance – Four o’clock flowers
1. Genes:
a.
b.
2.
R = Red
R’ = white
Genotypes/Phenotypes
a.
b.
c.
RR = Red
RR’ = Pink
R’R’ = white
B. Cross two pink four o’clocks
RR’
Pink
R
F1 cross
RR’
Pink
R’
G =RR : RR’ : R’R’
1 : 2 : 1
R
RR
R’
RR’ R’R’ P =Red : Pink : White
1 : 2 : 1
RR’
III. Co-dominance
A. Both of the contrasting alleles are expressed.
B. Red x White = red with white patches.
EXAMPLES
A. Co-dominance – Shorthorn cattle
1. Genes:
a. R = red
b. W = white
2. Genotypes/Phenotypes
a. RR = red
b. RW = red & white
c. WW = white
B. Can you get a red & white calf by crossing two
red cows?
NO
RR x RR = RR
C. Cross a red & white bull with a white.
F2 cross
RW
Red&white
WW
White
R
W
W
RW
WW
W
RW
WW
G=
RW:WW
2 : 2
P = Red : White
&White
2 : 2
IV. Traceback
• TRACEBACK- When you know some of the
“families” genotypes/phenotypes, you can
determine the other family member’s genetics
using a traceback.
• Step 1: Read the information given.
• Step 2: List each family member on its given
level (i.e. grandparents at top, parents on next
level, children on next, etc)
• Step 3: Write in the given knowledge
(genotypes/phenotypes).
• Step 4: Use deductive reasoning to figure out
the rest of the family members
genotypes/phenotypes.
EXAMPLE:
• Sarah has a BROWN male German
Shepard and a tan female German
Shepard that recently had 6 puppies.
BROWN (B) is dominant to tan (b). Four
of the puppies where BROWN (B) and the
other two were tan (b). The female’s
mother and father were both PUREBRED
tan (b). The male’s mother was BROWN
and the father was tan. What are all of
the genotypes of the family?
Male’s Mother Male’s Father
Father
BB or Bb
Father
Bb
Female’s Mother Female’s
bb
bb
X
Mother
bb
Brown puppies
Bb
Tan puppies
bb
bb
V. Test Cross
1. test cross- used to determine if an individual
exhibiting a DOMINANT TRAIT is homozygous or
heterozygous for that trait.
2. Test crosses involve breeding the individual in
question with another individual that expresses a
RECESSIVE version of the same trait.
3. If all offspring display the dominant phenotype,
the individual in question is homozygous
dominant; if the offspring display both dominant
and recessive phenotypes, then the individual is
heterozygous.
EXAMPLE:
In chinchillas, brown fur (b) is recessive to
BLACK fur (B). A farmer wants to produce
purebred BLACK chinchillas. He purchases
a BLACK chinchilla from a pet store. How
can he determine if the chinchilla he
purchased is purebred?
ANSWER! MEMORIZE WORDING!!
1. The farmer breed his black chinchilla
with a brown chinchilla.
2. If ALL of the offspring are BLACK, the
chinchilla is most likely HOMOZYGOUS,
PUREBRED.
3. If ANYof the offspring are brown, the
chinchilla is HETEROZYGOUS, HYBRID.
Let’s work the problems on the back using the
overhead projector.