I.I. IntroductionIntroductionA.A. Genes are not always dominant or recessive in their Genes are not always dominant or recessive in their

relationship.relationship.

II. Incomplete dominanceII. Incomplete dominanceA. Also called blending inheritance.A. Also called blending inheritance.B. The heterozygous is a blend of the two alleles.B. The heterozygous is a blend of the two alleles.

Red x White = PinkRed x White = Pink Black x White = GreyBlack x White = Grey

ExamplesExamplesA.A. Incomplete dominanceIncomplete dominance – Four o – Four o’’clock flowersclock flowers

1.1. Genes:Genes:a.a. R = RedR = Redb.b. RR ’’ = white = white

2.2. Genotypes/PhenotypesGenotypes/Phenotypes• RR = RedRR = Red• RRRR’’ = Pink = Pink• RR ’’RR ’’ = white = white

B. Cross two B. Cross two pinkpink four o four o’’clocksclocks

R RR R’’

RR

RR’’

RRRR RRRR’’

RRRR’’ RR ’’RR’’

G =G =RR : RRRR : RR’’ : R : R’’RR’’ 1 : 2 : 11 : 2 : 1

P =P =Red : Pink : WhiteRed : Pink : White 1 : 2 : 11 : 2 : 1

F1 cross

RRRR’’ RRRR’’Pink PinkPink Pink

III. Co-dominanceIII. Co-dominanceA. Both of the contrasting alleles are expressed.A. Both of the contrasting alleles are expressed.B. Red x White = red with white patches.B. Red x White = red with white patches.

EXAMPLESEXAMPLESA. Co-dominance – Shorthorn cattleA. Co-dominance – Shorthorn cattle

1. Genes:1. Genes:a.a. R = redR = redb.b. W = whiteW = white

2. Genotypes/Phenotypes2. Genotypes/Phenotypesa.a. RR = redRR = redb.b. RW = red & white RW = red & white c.c. WW = whiteWW = white

B. Can you get a red & white calf by crossing two B. Can you get a red & white calf by crossing two red cows?red cows?

Red&whiteRed&white White

R WR W

RWRW WWWWWW

WW

F2 crossRWRW WWWW

RWRW WWWW

G = RW:WWG = RW:WW 2 : 2 2 : 2 P = Red : WhiteP = Red : White &White &White 2 : 2 2 : 2

C. Cross a red & white bull with a white.C. Cross a red & white bull with a white.

NO RR x RR = RR

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 Female’s Mother Female’s Father

BB or Bb bb bb bb

Father X Mother Bb bb

Brown puppies BbTan puppies 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.

LetLet’’s work the problems on the back using the s work the problems on the back using the overhead projector.overhead projector.