In pea plants, the allele for tall stems (T) is dominant over the allele for short stems (… — Armed Services Vocational Aptitude Battery (ASVAB)

In pea plants, the allele for tall stems ( $T$ ) is dominant over the allele for short stems ( $t$ ). If a homozygous dominant ( $TT$ ) plant is crossed with a heterozygous ( $Tt$ ) plant, what percentage of the resulting offspring will be tall?

A
$50\%$
B
$75\%$
$100\%$ Answer
D
$25\%$

Answer

100% of the offspring will be tall.

The homozygous dominant parent (

TT

) contributes a dominant allele (

T

) to every single offspring. Since the presence of just one dominant allele (

T

) is sufficient to produce the tall phenotype, 100% of the resulting offspring will be tall (50%

TT

and 50%

Tt

Step-by-Step Solution

Determine the alleles contributed by each parent's gametes.

The homozygous dominant parent (

TT

) produces only gametes with

T

. The heterozygous parent (

Tt

) produces 50% gametes with

T

and 50% gametes with

t

During meiosis, alleles segregate so each gamete carries one allele per gene.

Construct a Punnett square to find offspring genotypes.

Possible offspring combinations are

TT

(50%) and

Tt

(50%).

Combining the gametes (

T \times T \rightarrow TT

and

T \times t \rightarrow Tt

) yields the genotypic distribution.

Determine the phenotypic expression of the genotypes.

Both

TT

and

Tt

genotypes result in the tall phenotype, giving a total of

100\%

tall offspring.

The dominant allele (

T

) completely masks the recessive allele (

t

) whenever present.

Key Concept

Monohybrid cross with complete dominance where a homozygous dominant parent ensures all offspring exhibit the dominant phenotype.

Estimated Time:1m 0s

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Answer

Step-by-Step Solution

Key Concept

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