Heredity and Variation

In garden pea plants (*Pisum sativum*), the allele for round seed shape ($R$) is completely dominant over the allele for wrinkled seed shape ($r$). Match each parental cross in the left column with its corresponding expected offspring phenotypic or genotypic ratio in the right column.

In tomato plants, the allele for red fruit ($R$) is completely dominant over the allele for yellow fruit ($r$). If two heterozygous red-fruited plants ($Rr$) are crossed, what is the expected genotypic ratio of their offspring?

In chickens, sex is determined by the ZZ-ZW mechanism, where males are ZZ and females are ZW. Barred plumage is controlled by a Z-linked dominant allele ($Z^B$), whereas non-barred plumage is controlled by the recessive allele ($Z^b$). A non-barred rooster ($Z^b Z^b$) is mated with a barred hen ($Z^B W$). If an $F_1$ male offspring is subsequently crossed with an $F_1$ female offspring, what is the probability that a female in the $F_2$ generation will have barred feathers?

During a cytogenetic investigation of a diploid organism, a researcher observes two distinct nucleotide sequence variations of a single gene located at identical positions on homologous chromosomes. Which genetics term specifically describes these alternative forms of a gene?

In a genetic study of human physical traits, researchers observed that certain characteristics show distinct, non-overlapping categories with no intermediate forms. Which of the following traits demonstrates this pattern of variation?

In a monohybrid cross between two heterozygous pea plants for flower position, $75\%$ of the $F_1$ offspring are expected to display the dominant phenotype.

In humans, hemophilia is an X-linked recessive disorder. If a carrier woman ($X^H X^h$) marries a hemophilic man ($X^h Y$), what is the probability that any daughter born to this couple will be a carrier of hemophilia?

In rabbits (*Oryctolagus cuniculus*), black fur color ($B$) is dominant over brown fur color ($b$), and short hair ($S$) is dominant over long hair ($s$). If a heterozygous black, short-haired rabbit ($BbSs$) is crossed with a homozygous recessive brown, long-haired rabbit ($bbss$), what proportion of the offspring is expected to possess brown fur and short hair?

In monohybrid crosses obeying Mendel's First Law (Law of Segregation) with complete dominance, match each parental genotype combination on the left with its corresponding expected offspring ratio on the right.

A biological study recorded a specific phenotypic trait across a large population of organisms. When the collected measurements were plotted on a frequency graph, the data formed a continuous, bell-shaped normal distribution curve. Which of the following traits was most likely being evaluated in this study?

In humans, Duchenne muscular dystrophy is inherited as an X-linked recessive disorder ($X^d$), while the normal allele is dominant ($X^D$). A phenotypically normal woman seeks genetic counseling. Her maternal grandfather had Duchenne muscular dystrophy, whereas her maternal grandmother was homozygous normal. Her father is phenotypically normal. If this woman marries a phenotypically normal man, what is the probability (expressed as a percentage) that their first male child will be affected by the disorder?

Which of the following characteristics is a defining feature of discontinuous variation in a biological population?

In maize (*Zea mays*), purple endosperm color ($P$) is dominant over yellow endosperm color ($p$), and starchy kernel texture ($S$) is dominant over waxy kernel texture ($s$). A plant heterozygous for both traits ($PpSs$) is allowed to self-pollinate, producing 480 kernels in the $F_2$ generation. How many of these kernels are expected to display the purple endosperm and waxy kernel texture phenotype?

In humans, red-green color blindness is an X-linked recessive trait ($X^c$), whereas normal vision is controlled by the dominant allele ($X^C$). Albinism is an autosomal recessive disorder ($a$), whereas normal skin pigmentation is controlled by the dominant allele ($A$). A woman with normal vision and normal skin pigmentation, whose father was both color-blind and albino, marries a man with normal vision who is a carrier for albinism. If this couple produces a male child (son), what is the percentage probability that the son will be both color-blind and albino?

A study conducted on a human population recorded two phenotypic traits: resting systolic blood pressure (Trait I) and the presence or absence of the Rhesus D antigen on red blood cells (Trait II). Trait I produced a smooth, bell-shaped frequency distribution curve across a continuous gradient of values, whereas Trait II resulted in two distinct, non-overlapping categories with no intermediate forms. Which of the following correctly explains the genetic mechanism and environmental susceptibility responsible for these observed patterns of variation?

In classic Mendelian genetics, a testcross is carried out by mating an organism exhibiting a dominant phenotype with an individual that is homozygous dominant for the trait in question.

A plant possesses two different alleles ($T$ and $t$) for the gene controlling stem height. Which of the following statements correctly identifies the genetic condition, genotype, and phenotype of this plant?

During a biology practical session, students recorded various inherited characteristics in their peer group. Which of the following traits demonstrates discontinuous variation?

Match each sex determination mechanism or sex-linked inheritance phenomenon on the left with its corresponding biological characteristic or inheritance pattern on the right.

In human ABO blood group inheritance, an individual carrying both the $I^A$ and $I^B$ alleles expresses both A and B antigens on the surface of their red blood cells, resulting in blood type AB. Which genetic phenomenon is directly demonstrated by the simultaneous, full expression of both alleles in the heterozygous state?