Genetics and Plant Breeding

The Principle of Independent Assortment states that two or more characters are inherited when the responsible gene separate independently from one another when reproductive cells develop. During meiosis, the pairs of homologous chromosome divide in half and form the haploid cell. This separation of chromosomes is random. After meiosis, each haploid cell of the offspring contain mixture of genes from the organism's mother and the father.

The principle of segregation is also called as the law of purity of gametes. A gamete may carry either the dominant or the recessive factor but not both as we find in F$ _1$ individuals. The gametes which are formed are always pure for a particular character. This is why it is called either as the principle of segregation or law of purity of gametes. Thus, the correct answer is option C.

DNA is the unit of heredity and determines the genetic traits of organisms. Inheritance of genetic traits from parent to offspring is ensured by processes of meiosis and syngamy. Meiosis is the process of cell division that reduces the number of chromosomes and thus, the DNA content to half in the resultant daughter cells i.e. gametes. Fusion of male and female gametes during syngamy restores the DNA content in the resultant offspring. Thus, each offspring consists of half paternal and half maternal DNA which in turn determines its traits. Thus, the correct answer is option C.

Mendel proposed the law of inheritance of traits from the first generation to the next generation. Law of inheritance is made up of three laws: Law of segregation, law of independent assortment and law of dominance. Therefore, (D) is the correct answer.

Mendel explained that one or more traits can be inherited from the parents individually and can be transmitted to the next generation. Mendels law of inheritance says that at least one trait is inherited by the progeny from the parent. Therefore, (a) is the correct answer.

 In experiments performed by Mendel all the genes showed independent assortment, in which genes separate from each other independently and there was no sign of any linked gene so he could not explain the concept of linkage, because he never observed it .

Law of segregation states that alleles for genes segregate from each other whether it is for tall (TT) or dwarf (tt) so that the gamete carries one allele for each gene, whereas law of dominance states that the phenotype which is expressed is the dominant character and other is recessive, since there are both tall & dwarf plants, this means that both characters are expressed . 

The identical twins are alike and they are produced from the same zygote. They have the same genome and so, the genes are alike. Due to these, the girls will have the same phenotypic appearance. There will be differences in the random repeats region which do not code for any protein. The mitochondrial DNA will be same as they have been inherited from the same mother. However, the mitochondrial genes are not involved in the phenotype expression. 

Law of segregation and Law of independent assortment are based on the mechanism of meiosis, because these principles show segregation of characters and independent movement of characters.

So, the correct option is ‘Meiosis’.

• Mendelian factors or genes, as well as chromosomes, are present in pairs.
• According to this Mendelian concept, inheritance of a trait depends on the passing-on of units. 
• For any given trait, an individual inherits one gene from each parent so that the individual has a pairing of two genes.

• The trait is a distinguishable feature of a character and its detectable variant. For example, tallness and dwarfness. 
• The hybrid plant possesses a heterozygous condition in which genotype have both contrasting alleles such as Tt in the hybrid plant. T represents tallness and t represents dwarfness.
•  Dominant character tallness (T) can be expressed in both conditions such as homozygous (TT) and heterozygous condition (Tt) but recessive character dwarfness (t) can be expressed only in homozygous (tt) condition and thus unable to express in hybrid plants.

• Segregation literally means separation. In Mendelian genetics, in a given plant or animal each character is governed by two alleles, one coming from the father and one coming from the mother.
•  At the time of gamete formation both the alleles, of each gene, separate from each other and go to separate gametes. 
• Thus, each gamete will be having only one allele from each pair of the allele, e.g., for tallness if we denote two alleles in a plant as Tt then that plant can form two possible gametes one having T and the other having t allele.

• Segregation means separation. In classical Mendelian genetics, it is assumed that each individual has two alleles which code for each character. 
• One allele comes from the father and the other from the mother. These two alleles separate from each other during gamete formation. 
• Thus, each gamete contributes a single allele for each character during zygote formation.

Mendel's law of genetics is applicable only in plants which reproduce sexually. In Mendelian genetics he explains about the independent assortment which results in the formation of gametes which has the contrasting characters from both male and female parents. It will be expressed according to its zygosity and dominant traits. if the recessive trait is present in its homozygous form, the character will be expressed. At the same time, dominant character will be expressed in both homozygous and heterozgous forms. Pisum sativum which Mendel chose was a sexually reproducing plant.