BIO BOTANY [ 2 Marks Questions ]

(a) Dominance
(b) Incomplete dominance

(a) Supplementary genes – 9 : 3 : 4
(b) Complementary genes – 9 : 7
(c) Dominant epistasis -12 : 3 : 1

Observe the chart and mention the genetic phenomenon does it indicates.
Pleitrophy – A single gene affecting many traits. Here the single gene AA controls the traits – for flower colour, seed colour and leaf axil spot.

To identify the plant genotype whether homozygous or heterozygous Mala can perform test cross, where the individual is crossed with homozygous recessive for the trait. If the plant is heterozygous then the resultant progenies would be in the ratio 50:50

In Sorghum vulgare (Pearl maize), the gene located for the sterility pollens are located in the mitochondrial DNA. This phenomenon is called as cytoplasmic male sterility.

Extra nuclear inheritance is due to genes located on the cytoplasmic organelles such as chloroplast and mitochondrion hence it is called cytoplasmic inheritance.

Certain characters/traits are governed and inherited by genes located in cytoplasmic organelles (chloroplast or mitochondrion) other than nucleus. This is called extra nuclear inheritance.

Plasmogenes are independent, self-replicating, extra-chromosomal units located in cytoplasmic organelles, chloroplast and mitochondrion

(a) Chloroplast inheritance
(b) Mitrochondrial inheritance

Interlocus interactions take place between the alleles at different loci i.e. between alleles of different genes.
Eg: Dominant Epistasis

(a) Pleiotropism
(b) Poly genic inheritance

An allele which has the potential to cause the death of an organism is called a Lethal Allele.
E.g : Recessive lethality in Antirrhinum species.

Mirabilis Jalapa (4 o’ clock plant). Incomplete dominance ratio is 1 : 2 : 1

Interactions take place between the alleles of the same gene i.e., alleles at the same locus is called intragenic or intralocus gene interaction.

(a) Incomplete dominance
(b) Codominance
(c) Multiple alleles
(d) Pleiotropic genes are common examples for intragenic interaction.

The gene interactions may be
(a) Intragenic gene interaction. E.g.: Codominance
(b) Intergenic gene interaction. E.g.: Epistasis

A single phenotype is controlled by more than one set of genes, each of which has two or more alleles. This phenomenon is called Gene Interaction.

27 : 9 : 9 : 9 : 3 : 3 : 3 : 1

Four different gametes are produced by a dihybrid plant and on selfing, it yield 16 off springs.

Dihybrid test cross and the ratio is 1 : 1 : 1 : 1

(a) Dihybrid cross ratio = 9 : 3 : 3 : 1
(b) Dihybrid test cross ratio = 1 : 1 : 1 : 1

When two pairs of traits are combined in a hybrid, segregation of one pair of characters is independent to the other pair of characters. Genes that are located in different chromosomes assort independently during meiosis.

(a) Phenotypic ratio = 3:1.
(b) Genotypic ratio =1 : 2 : 1

genotype & phenotype

1. The term genotype is the genetic constitution of an individual.
2. The term phenotype refers to the observable characteristic of an organism.

Seed shape, flower color, flower position & pod color.

Gregor Mendel selected seven pairs of characters in Pisum sativum (garden pea)

Mendel’s theory of inheritance, known as the Particulate theory, establishes the existence of minute particles or hereditary units or factors, which are now called as genes.

Heredity : Heredity is the transmission of characters from parents to off springs.
Variations : The organisms belonging to the same natural population or species that shows a difference in the characteristics is called variation.

(a) Classical genetics
(b) Molecular genetics
(c) Population genetics
(d) Quantitative genetics

“Genetics” is the branch of biological science which deals with the mechanism of transmission of characters from parents to off springs. The term Genetics was introduced by W. Bateson in 1906.