Genetics and Plant Breeding

Mirabilis jalapa (four o'clock plant) shows incomplete dominance - red x white gives pink F1. Pisum sativum shows complete dominance, Cajanus cajan and Saccharum officinarum are not standard examples. Note: Option A has typo 'psium' for 'pisum'.

Heredity is defined as the transmission of traits from one generation to the next through genetic material. Variation refers to differences between individuals, genetics is the study of heredity, and plant breeding is the application of genetic principles. Heredity directly matches the definition given in the question.

A back cross is defined as crossing a hybrid offspring with one of its pure-breeding parental types. While a test cross (crossing with homozygous recessive) is a specific type of back cross, the general term 'back cross' covers crossing with either parental type. Monohybrid and dihybrid crosses refer to the number of traits being studied, not the type of cross performed.

Germinal mutations occur in reproductive cells and are heritable, which can alter expected Mendelian ratios like the 9:3:3:1 dihybrid ratio in the F2 generation. Somatic mutations only affect body cells and are not inherited.

The 4'O clock plant (Mirabilis jalapa) is the classic example of incomplete dominance where heterozygotes show an intermediate phenotype between red and white flower colors. When red and white-flowered plants are crossed, the offspring have pink flowers, demonstrating that neither allele is completely dominant.

A large seeded mutant variety of Bengal gram is Cicer arietinum.

The 7:1:1:7 ratio is a classic example of gene linkage discovered by Bateson and Punnett in sweet pea (Lathyrus odoratus). This dihybrid ratio deviates from Mendel's expected 9:3:3:1 ratio because the two genes are linked on the same chromosome and do not assort independently. Options 12:3:1, 1:1:1:1, and 9:3:4 represent other genetic interactions (epistasis, test cross, and modified epistasis respectively) but are not the Bateson-Punnett linkage ratio.

Complementary genes (like in sweet pea flower color) produce a 9:7 phenotypic ratio, while various forms of epistasis produce ratios like 12:3:1, 9:3:4, or 15:1. All these ratios differ from Mendel's standard 9:3:3:1 dihybrid ratio, but the genes involved still assort independently and follow Mendel's second law. The deviation occurs due to gene interactions at the phenotypic level, not because genes fail to assort independently.

Mendel's monohybrid cross produces a 3:1 phenotypic ratio (dominant:recessive) and a 1:2:1 genotypic ratio (homozygous dominant:heterozygous:homozygous recessive). The dihybrid cross produces a 9:3:3:1 phenotypic ratio when genes assort independently. These ratios are fundamental to Mendelian genetics and result from the segregation and independent assortment of alleles during gamete formation.

In sweet peas, flower color is controlled by complementary gene interaction where both genes C (chromogen production) and P (enzyme to convert chromogen to anthocyanin) must be present in dominant form (C_P_) for purple color. The genotype CcPp has one dominant allele of each gene, so it produces purple flowers due to anthocyanin pigment. White flowers result when either gene is homozygous recessive.

The assertion is true: recessive traits only express phenotypically in homozygous recessive conditions (rr) because the dominant allele masks their effect. The reason is also true: alleles do segregate during gamete formation (Mendel's first law). However, the reason does NOT explain the assertion - segregation is about allele separation, not about why recessive traits are masked. The explanation for recessive expression relates to dominance relationships and protein function/dosage, not segregation mechanics.

A test cross involves crossing a hybrid (heterozygous) with a recessive (homozygous recessive) parent to determine the hybrid's genotype. A back cross involves crossing a hybrid with a pure breeding (homozygous) parent - which could be either dominant or recessive. Therefore, hybrid × recessive = test cross, and hybrid × pure breeding = back cross. Note that back cross is broader - test cross is a specific type of back cross.

Supplementary genes produce a 9:3:4 phenotypic ratio when two genes interact, where one gene's dominant allele supplements the other. In this ratio, 9 have both dominant traits, 3 show only one dominant trait, and 4 show recessive traits. This differs from complementary (9:7) or other gene interaction patterns.

Sorghum is the classic example of supplementary gene action, where glume color is controlled by two genes - one for pigment production and another for color presence. When either gene is recessive, the complementary effect is lost, producing the 9:3:4 ratio. Other options are important crop plants but not this specific genetic example.

Autotetraploids (4x) can form when two unreduced diploid gametes (2n each) fuse during fertilization, producing a 4x zygote. This is different from chromosome doubling in somatic tissues. The fusion of two abnormal diploid gametes is one documented pathway to autotetraploidy in plants.