Complete dominance occurs when the dominant allele completely masks the recessive allele in heter0zyg0us individuals. 1) 100% / 2) no chance / 3) 50% / 4) no chance / 5) 1:2:1.
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Available data:
→ Six diallelic genes code for six different traits.
→ All genes express complete dominance, meaning that the dominant allele hides the expression of the recessive one.
→ Beyonce ⇒ ee ww Dd Hh cc Bb
→ Bruno Mars ⇒ ee ww dd Hh CC Bb
→ Cross: Beyonce x Bruno Mars
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1) Earlobes
Parentals) ee x ee
Gametes) e e e e
Punnett square) e e
e ee ee
e ee ee
F1) 100% of the progeny is expected to have unattached earlobes, ee.
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2) hairline
Parentals) ww x ww
Gametes) w w w w
Punnett square) w w
w ww ww
w ww ww
F1) 100% of the progeny is expected to have straight hairline, ww.
There is no chance for their children to have widow’s peak because both of them are h0m0zyg0us recessive for the trait.
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3) Dimples
Parentals) Dd x dd
Gametes) D d d d
Punnett square) D d
d Dd dd
d Dd dd
F1) 2/4 = 1/2 = 50% of the progeny is expected to have dimples, dd
2/4 = 1/2 = 50% of the progeny is expected to have no dimples, Dd.
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4) Chin
Parentals) CC x cc
Gametes) C C c c
Punnett square) C C
c Cc Cc
c Cc Cc
F1) 100% of the progeny is expected to have cleft chin, Cc
There is no chance for their children to have smooth chin because one of them is h0m0zyg0us dominant and the other one is h0m0zyg0us recessive for the trait. C hides the expression of c.
The whole porgeny is expected to be heter0zyg0us, Cc, expressing cleft chin.
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5) Eyes
Parentals) Bb x Bb
Gametes) B b B b
Punnett square) B b
B BB Bb
b Bb bb
F1) 3/4 = 75% of the progeny is expected to have brown eyes, BB + Bb
1/4 = 25% of the progeny is expected to have blue eyes, bb
- Genotypic ratio ⇒ 1:2:1
- Phenotypic ratio ⇒ 3:1
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