Chapter04_ExtensionMendelianGenetics

What is the genotypic ratio (ratio of genotypes) for monohybrid (one character) crosses for heterozygous individuals (Pp x Pp) under Mendelian inheritance?

• 1:2:1

  1(HoDo)

  2(Het)

  1(HoRec)

• 3:1

  3(HoDo)

  1(HoRec)

• 1

  (All are Het)

Answer explanation

Aa x Aa cross makes 1 HoDo, 2Het, and 1 HoRec

What is the phenotypic ratio (ratio of phenotypes) for monohybrid (one character) crosses for heterozygous individuals (Pp x Pp) under Mendelian inheritance?

• 1:1 (one dominant, one recessive)

• 3:1

  (3 dominant phenotypes, one recessive)

• 1:2:1

  (one dominant, two intermediates, one recessive)

Answer explanation

Aa x Aa cross under Mendelian inheritance results in a genotypic ratio of 1 (HoDo), 2(Het), 1 (HoRec).

Phenotypically, those are 3 dominant, 1 recessive.

What is the genotypic ratio (ratio of phonotypes) for dihybrid (two character) crosses for heterozygous individuals under Mendelian inheritance?

• 9:3:3:1

  9 (Both Dominant)

  3 (1 Dominant, one recessive)

  3 (1 Dominant, one recessive)

  1 (both

• 3:1:3:1

• 9:5:2

What is the genotypic ratio (ratio of genotypes) for monohybrid (one character) crosses for heterozygous individuals (R1R2 x R1R2) under incomplete dominance?

• 1:2:1

  1(HoDo)

  2(Het)

  1(HoRec)

• 3:1

  3(HoDo)

  1(HoRec)

• 1

  (All are Het)

What is the phenotypic ratio (ratio of phenotypes) for monohybrid (one character) crosses for heterozygous individuals (R1R2 x R1R2) under incomplete dominance?

• 1:2:1

  (one dominant, two intermediates, one recessive)

• 1:1:1

  1:1 (one dominant, one intermediate, one recessive)

• 3:1

  (3 dominant phenotypes, one recessive)

Answer explanation

Expected ratios under incomplete  dominance:

•Genotypic: 1(HoR1):2(He):1(HoR2)

•Phenotypic: 1(red):2 (pink):1 (white)

What is the phenotypic ratio for a monohybrid cross between heterozygous under codominance

• 1:2:1

• 1:1

• 2:1