Genetics and Plant Breeding

The F2 ratio (9:7) from complementary genes is a modification of dihybrid Mendelian ratio (9:3:3:1) because both ratios are based on 16 parts. Complementary genes require both dominant alleles together for trait expression, collapsing four phenotypes into two, but the fundamental 16-part proportion remains.

Mendel conducted his famous hybridization experiments on Pisum sativum (garden pea/field pea). He chose this plant because it has contrasting traits, short lifecycle, can be cross-pollinated manually, and produces many offspring.

In Mendel's monohybrid cross (F1 heterozygote × heterozygote), the phenotypic ratio is 3:1 (3 dominant phenotype : 1 recessive phenotype). 1:2:1 is the GENOTYPIC ratio. 1:3 and 1:1:2 are not standard Mendelian ratios.

A test cross is specifically designed to determine the genotype of an individual showing a dominant phenotype. By crossing it with a homozygous recessive individual, the appearance of recessive offspring reveals whether the dominant individual was heterozygous. This is a fundamental genetic diagnostic tool.

Carl Correns discovered incomplete dominance in Mirabilis jalapa (four o'clock plant). Red x white gave pink F1 - not pure red as Mendel expected. De Vries worked on mutation, Mendel on peas, Darwin on evolution.

Dihybrid test cross (AaBb x aabb) gives 1:1:1:1 ratio. Each gene segregates 1:1 in test cross, independent assortment gives four equal classes. Note: Duplicate of question 252873.

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.

Some plants never open to ensure complete self-pollination. This condition is called cleistogamy, e.g., Commelina bengalensis, Oxalis, Viola, etc.. The cleistogamous flowers are bisexual small, inconspicuous, colourless and do not secrete nectar.

An AB parent has both A and B alleles, while an O parent has two O alleles. Children inherit one allele from each parent, resulting in genotypes AO (blood type A) or BO (blood type B) - but not AB or O.

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.