When two unaffected individuals have an affected offspring, it is a classic sign of a recessive inheritance pattern. The parents must both be heterozygous carriers of the recessive allele. If the trait were dominant, at least one parent would have to be affected to pass the allele to the child.

In a cross of $$TtRr \times TtRr$$, the probability of a tall offspring ($$T-$$) is $$3/4$$, and the probability of a white-flowered offspring ($$rr$$) is $$1/4$$. Using the product rule for independent events, the probability of an offspring being tall and white is $$(3/4) \times(1/4) = 3/16$$.

This is a dihybrid test cross ($$RrTt \times rrtt$$). The heterozygous parent produces four types of gametes ($$RT, Rt, rT, rt$$) in equal proportion. The homozygous recessive parent produces only one type of gamete ($$rt$$). The resulting offspring will have four different genotypes ($$RrTt, Rrtt, rrTt, rrtt$$) and four corresponding phenotypes, each in equal proportion, leading to a 1:1:1:1 ratio.

A test cross is used to determine an unknown genotype of an organism showing the dominant phenotype. This is done by crossing the organism with a homozygous recessive individual. The phenotypes of the offspring will reveal the unknown genotype.

Because red is dominant, the red-flowered phenotype can be produced by both the homozygous dominant ($$RR$$) and heterozygous ($$Rr$$) genotypes. Therefore, the population of red-flowered plants can contain individuals with two different genotypes while exhibiting only one phenotype.

For each gene, the cross is between two heterozygotes. The probability of short ($$tt$$) is $$1/4$$. The probability of purple flowers ($$P-$$) is $$3/4$$. The probability of wrinkled seeds ($$rr$$) is $$1/4$$. Since the genes are unlinked, the probabilities are multiplied: $$(1/4) \times(3/4) \times(1/4) = 3/64$$.

This question tests Mendelian inheritance analysis, requiring inference of parental genotype from self-cross offspring ratios. The 3:1 smooth-to-wrinkled ratio indicates the parent is heterozygous Kk, as self-fertilization (Kk x Kk) produces KK, Kk, and kk genotypes. Alleles segregate equally into gametes, yielding 1/4 KK, 1/2 Kk (smooth), and 1/4 kk (wrinkled), for a 3:1 phenotypic ratio. This fits because only a heterozygote can produce both dominant and recessive phenotypes in that proportion. A tempting distractor is KK or Kk, which might stem from thinking homozygotes could yield recessives, ignoring that KK self-cross gives all smooth. For inheritance questions, work backward from ratios to parental genotypes using standard Mendelian patterns like 3:1 for heterozygote self-crosses.

This question tests the skill of analyzing Mendelian inheritance patterns. The cross between a tall snapdragon of unknown genotype and a short one (tt) yields approximately equal numbers of tall and short offspring, indicating a 1:1 phenotypic ratio. This ratio suggests the tall parent is heterozygous (Tt), as it produces gametes with 1/2 T and 1/2 t, combining with the t gametes from the short parent to give Tt and tt equally. If the tall parent were homozygous (TT), all offspring would be tall, but the observed data matches the segregation expected from a heterozygous parent. A tempting distractor is TT, which might arise from the misconception that dominant phenotypes always indicate homozygous genotypes without considering test cross results. To solve similar inheritance questions, use test crosses with recessive individuals to reveal unknown genotypes through offspring ratios.

This question tests the skill of analyzing Mendelian inheritance patterns. In the cross between two heterozygous red-eyed fruit flies (Rr × Rr), each parent produces gametes with 1/2 R and 1/2 r alleles due to independent segregation. The Punnett square reveals offspring genotypes of RR, Rr, and rr in a 1:2:1 ratio, directly reflecting the combination of alleles from random fertilization. This classic monohybrid ratio confirms the expected genotypic distribution. A tempting distractor is 3 RR : 1 rr, which might stem from the misconception of equating genotypic ratios with phenotypic ones by ignoring the heterozygous category. To solve similar inheritance questions, calculate genotypic ratios using Punnett squares and distinguish them from phenotypic ratios based on dominance.

This question tests the skill of analyzing Mendelian inheritance patterns. In the cross between a homozygous dominant long-eared rabbit (LL) and a heterozygous one (Ll), the LL parent produces only L gametes, while the Ll parent produces 1/2 L and 1/2 l. Offspring genotypes are LL from L + L combinations and Ll from L + l, each occurring with 1/2 probability due to segregation. Therefore, half of the offspring are expected to be heterozygous (Ll), as the recessive allele appears in half the gametes from the heterozygous parent. A tempting distractor is 3/4, which could arise from the misconception of applying a monohybrid ratio without accounting for one parent's homozygosity. To solve similar inheritance questions, identify gamete probabilities for each parent and use them to compute specific genotypic proportions.