Genetics and Plant Breeding

Incomplete dominance is a form of intermediate inheritance in which one allele for a specific trait is not completely expressed over its paired allele. In the early 1900s, German botanist Carl Correns (1864–1933) would conduct similar research on four o'clock plants. While Mendel's work laid a foundation, it isCorrens who is credited with the actual discovery of incomplete dominance. In his work, Correns observed a blend of colors in flower petals. So, the correct option is 'Law of incomplete dominance'.

Incomplete dominance is a type of intermediate inheritance in which one allele is not completely dominant over its paired allele. In this, the third phenotype is observed in heterozygous condition. In monohybrid cross with incomplete dominance, the phenotypic and genotypic ratio is 1:2:1, where one part is with dominant phenotype, 2 parts are with intermediate phenotype and 1 part is with recessive phenotype. For example, a snapdragon flower shows red (dominant), white (recessive) and pink (intermediate) flowers.

Mirabilis jalapa is a plant showing incomplete dominance which means that when in F$ _1$ generation intermediate phenotype appears instead of the two parent phenotypes. 

A.Heterozygotes – Organisms with a pairs of contrasting characters are called Heterozygotes.

B.Alleles - An alternative form of a character in a pair, controlled by a single gene is called Allele. It is dominant either in homozygous or heterozygous state.

C.Complementary gene – Two genes present on separate loci that interact together to produce a dominant phenotype is called Complementary gene. In the F₂ generation 9:7 ratio.

D.Supplementary gene – genes which include two pairs of non-allelic genes. Both of them are involved in affecting the same character. Out of the non-allelic genes, one gene is dominant and can express by itself. Second gene is also dominant but expresses only when it is supported by the presence of the first gene. In the F₂ geneartion 9:3:4 ratio.

So, the correct option is ‘Alleles’. 

class=A cross is made between pure yellow flowered  and round fruit(YYRR) with white flowered elongated fruit(yyrr). In the F1 generation 20 progeny with yellow flowered and round fruits(YyRr) are formed. When they are subjected to self pollination followed by self fertilization, in the F2 generation, 960 progeny are formed. In these 540 plants are yellow flowered round fruits, plants are yellow flowered elongated fruits, 180 fruits are white flowered round fruits and 60 plants are white flowered elongated fruits the correct option is 20, 540

This is a classic example of duplicate recessive epistasis in Summer Squash fruit shape. The F2 ratio for this type of interaction is 9:6:1, where 9 are discoid, 6 are circular, and 1 is long.

A.Supplementary genes – A pair of non allelic genes, one of which produces its effect independently in the dominant state while the dominant allele of the second gene is without any independent effect but is able to modify the effect of the former to produce to a new trait are called Supplemetary genes. Due to these genes in the F₂ generation, 9:3:4 ratio of progeny are obtained. It is a modified Mendel dihybrid ratio.

B.Complementary genes – Two genes present on separate loci that interact

together to produce dominant phenotypic character; neither of them if present alone can express itself are called complementary genes. Due to these genes in the F₂ generation, 9:7 ratio of progeny are obtained. It is a modified Mendel dihybrid ratio.

C.Lethal genes – A pair of genes present in the homozygous conditions, causes the death of the individual are called Lethal genes. Due to the genes, in F₂ generation 2:1 ratio of progeny are obtained.

D.Epistatic genes – A gene which masks the action of another gene is termed as epistatic gene and process is called epistasis. Due to these genes in the F2 generation, either 9:3:4  or 12.3.1 ratio of progeny are obtained. It is a modified Mendel dihybrid ratio.

So, the correct option is ‘supplementary genes’.     

The production of a new individual organism or offspring from the parents is the result of a process called reproduction which can be sexual or asexual. In the case of sexual reproduction, the offsprings tend to carry the genetic information from both the parents which are contained in genes carried by chromosomes. Sexual reproduction produces offspring that resemble their parents but are not identical to them but asexual reproduction does not involve mixing of genetic information and hence tend to give rise to genetically identical  progeny. In the case of human beings, this take place either due to natural cloning where there is the production of identical gametes.

Identical twins are also called as monozygotic twins. They are derived from a single zygote that splits at an early stage during development. They have same genetic make up and are of the same sex. Thus option A is the correct answer.

Identical twins are born when one ovum crosses with one sperm to form one zygote (monozygotic). This zygote later divides into two embryos. These embryos share the same womb. Non-identical twins are born when two ova crosses with two sperms at the same time to form two zygotes (dizygotic).

When one fertilized egg splits and develops into two embryos with the same genetic information is called as identical twins. It is also called as monozygotic as the single zygote is involved in the formation of two embryos. Whereas dizygotic twins are called as fraternal twins in which two zygotes are involved in the formation of two embryos. Thus, the correct answer is option B.

Fraternal or dizygotic twins develop when two separate eggs are fertilized by two separate sperm cells during the same ovulatory cycle, resulting in two distinct zygotes in the womb.

Fraternal twins are produced when two ovums are fertilized by two sperm cells simultaneously.

• There are two types of twins, Fraternal or dizygotic twins, and monozygotic twins.
  
• When the zygote, during the cleavage, separates and forms two different cells and both of them grow individually as embryos, they form the monozygotic twins.
  
• Monozygotic twins are of the same sex.
  
• When 2 zygotes are fertilized by two different sperms they form the dizygotic twins.
  
• They can be of different sex.