Question

1. dihybrid cross - take the traits of ear shape and length. what are the odds that an offspring would have long and droopy ears if both parents were heterozygous for both traits? do the dihybrid cross and highlight the boxes with the trait mentioned above. give genotype and phenotype ratios.

Explanation:

Step1: Define trait alleles

Let \(L =\) long ears (dominant), \(l =\) short ears (recessive); \(D =\) droopy ears (dominant), \(d =\) non-droopy ears (recessive). Heterozygous parents have genotype \(LlDd\).

Step2: Identify parent gametes

Each parent produces 4 gamete types: \(LD, Ld, lD, ld\)

Step3: Build dihybrid Punnett square

	\(LD\)	\(Ld\)	\(lD\)	\(ld\)
\(Ld\)	\(LLDd\)	\(LLdd\)	\(LlDd\)	\(Lldd\)
\(lD\)	\(LlDD\)	\(LlDd\)	\(llDD\)	\(llDd\)
\(ld\)	\(LlDd\)	\(Lldd\)	\(llDd\)	\(lldd\)

Highlighted boxes (long, droopy ears: \(L\_D\_\)): \(LLDD, LLDd, LlDD, LlDd, LLDd, LlDd, LlDD, LlDd, LlDd\)

Step4: Calculate odds & ratios

Total offspring squares = 16. Number of long/droopy offspring = 9.
Odds of long/droopy: \(\frac{9}{16}\)

Genotype Ratios:

\(LLDD: 1, LLDd: 2, LlDD: 2, LlDd: 4, LLdd: 1, Lldd: 2, llDD:1, llDd:2, lldd:1\)
Simplified: \(1:2:2:4:1:2:1:2:1\)

Phenotype Ratios:

Long droopy : Long non-droopy : Short droopy : Short non-droopy = \(9:3:3:1\)

Answer:

• Odds of offspring with long and droopy ears: $\frac{9}{16}$
• Highlighted Punnett square cells: $LLDD, LLDd, LlDD, LlDd, LLDd, LlDd, LlDD, LlDd, LlDd$
• Genotype Ratio: $1:2:2:4:1:2:1:2:1$ (for $LLDD:LLDd:LlDD:LlDd:LLdd:Lldd:llDD:llDd:lldd$)
• Phenotype Ratio: $9:3:3:1$ (for long droopy : long non-droopy : short droopy : short non-droopy)