Heredity and Variation

In fruit flies (*Drosophila melanogaster*), the allele for normal wings ($V$) is completely dominant over the allele for vestigial wings ($v$). A monohybrid cross is carried out between two heterozygous normal-winged flies, producing a total of $320$ offspring in the $F_1$ generation. How many of these offspring are expected to be heterozygous normal-winged?

Match each human phenotypic trait on the left with its corresponding pattern of variation and underlying genetic mechanism on the right.

Glucose-6-phosphate dehydrogenase (G6PD) deficiency is an X-linked recessive metabolic condition in humans. If a man with normal enzyme activity ($X^G Y$) marries a heterozygous carrier woman ($X^G X^g$), what is the probability that any child born to them will be an affected male?

Human phenotypic traits exhibiting discontinuous variation, such as the ABO blood group system and tongue rolling ability, are governed by polygenic inheritance and can be significantly modified by environmental factors during an individual's lifetime.

In pea plants (*Pisum sativum*), the allele for green pod color ($G$) is completely dominant over the allele for yellow pod color ($g$). Which expected offspring phenotypic ratio corresponds to each parental cross?

Continuous variation in human morphological traits, such as adult height and body mass index, produces a smooth spectrum of intermediate phenotypes within a population because these traits are governed by polygenic inheritance and modified by environmental factors.

A Rhesus-negative ($Rh^-$) woman marries a Rhesus-positive ($Rh^+$) man whose father was Rhesus-negative ($Rh^-$). What is the probability that their second child will inherit the Rhesus-positive trait and be at risk of developing erythroblastosis fetalis?

Match each non-Mendelian genetic concept on the left with its correct phenotypic expression pattern or population characteristic on the right.

A cytogenetic analysis of a patient reveals a somatic cell chromosomal complement of $47$ chromosomes with an additional sex chromosome ($47, XXY$). Which mechanism is directly responsible for this structural or numerical chromosomal aberration, and what clinical condition does it produce?

A biological study recorded two distinct human characteristics across a high school population: Trait X (skin pigmentation shade measured by spectrophotometry, exhibiting a continuous bell-shaped distribution curve) and Trait Y (phenylthiocarbamide tasting ability, where individuals strictly belong to either the taster or non-taster phenotype). Based on these phenotypic distribution patterns, which of the following statements correctly contrasts the underlying genetic mechanisms and environmental influences governing both traits?

In genetic analysis of diploid organisms, the specific combination of alleles inherited by an individual for a particular gene (such as $Tt$) determines its observable physical characteristics. Which pair of terms correctly identifies the symbolic genetic makeup of the organism ($Tt$) and its state of having two different alleles for that gene, respectively?

A man with normal blood clotting marries a phenotypically normal woman whose father had hemophilia A, an X-linked recessive disorder. What is the probability that any child born to this couple will be a carrier of the hemophilia allele?

Down syndrome is a genetic disorder caused by a single nucleotide point mutation in a nuclear gene.

A color-blind man marries a phenotypically normal woman whose mother was color-blind. What is the probability that any female child born to this couple will be color-blind?

An agricultural breeder crosses two pure-breeding lines of oil palm: Line A, which produces high oil yield but is highly susceptible to fungal wilt, and Line B, which produces low oil yield but is completely resistant to fungal wilt. The resulting $F_1$ hybrids exhibit exceptional vigor, producing higher oil yields and stronger disease resistance than either parent. However, when these $F_1$ hybrid palms are self-pollinated, the $F_2$ generation displays wide phenotypic variation, with many individuals showing reduced yield and high disease susceptibility. Which of the following biological principles best explains the performance decline observed in the $F_2$ generation?

In rabbits, the allele for black coat color ($B$) is completely dominant over the allele for brown coat color ($b$). A black-furred rabbit mated with a brown-furred rabbit and produced 28 black-furred offspring and 26 brown-furred offspring over several litters. Which of the following represents the most likely genotypes of the parent rabbits?

A medical survey categorizes human traits according to their biological nature (morphological versus physiological) and their population distribution pattern (continuous versus discontinuous). Which of the following pairings correctly matches a physiological trait exhibiting discontinuous variation with a morphological trait exhibiting continuous variation?

Which of the following mutagenic agents primarily induces gene mutations by causing adjacent thymine bases on a single DNA strand to covalently bond and form pyrimidine dimers?

Nitrous acid ($\text{HNO}_2$) acts as a chemical mutagen by inducing the oxidative deamination of cytosine, converting it into uracil ($U$). If a double-stranded DNA molecule containing a newly formed uracil base undergoes two consecutive rounds of DNA replication without prior enzymatic repair, which specific base-pair substitution will ultimately be fixed in the mutant daughter DNA molecule?

Agricultural breeders often apply Mendelian genetics to select desirable traits in farm animals. A livestock breeder crosses two cattle that are both heterozygous for high milk production ($Mm$) and disease resistance ($Rr$). Assuming independent assortment of these dominant autosomal traits, what proportion of the offspring is expected to display both high milk production and disease resistance?