Genetics terminology - class-XII

In a monohybrid cross between two heterozygotes (Tt x Tt), the F1 genotypes are 1 TT, 2 Tt, and 1 tt. The homozygous individuals are TT and tt (1+1=2 out of 4), which is 50 percent.

A gamete may carry either the dominant or the recessive factor but not both as we find in F₁ individuals. This is why it is called either as 'principle of segregation' or as 'law of purity of gametes'. This concept of segregation is often called Mendel's first principle. The alleles of contrasting characters selected in the monohybrid cross will show exact Dominance and Recessive relationships. Monohybrid cross refers to  mating between two organisms with different variations at one genetic chromosome of interest. The character(s) being studied in a monohybrid cross are governed by two or multiple variations for a single locus.

A gene is a locus (or region) of DNA which is made up of nucleotides and is the molecular unit of heredity. It controls the development and function of all organs and all working systems in the body. Genes are passed from parent to offspring; the combination of these genes affects all aspects of the human body, from eye and hair colour to how well the liver can process toxins. 

Genes are the segment of DNA which carries information from parents to offsprings. It is the basic unit of heredity as they code for proteins which in turn determine the genetic traits. Genes are a continuous stretch of DNA and are linearly arranged on chromosomes. Chromatids are two identical parts of a duplicated chromosome. Nucleotides serve as a monomer of DNA. Codon is a base triplet of the gene that specifies specific amino acid. The correct answer is A.

Gregor Mendel is the father of genetics. When he explained about heredity for the first time ever, the term "Gene" which is now being used, was not given. After his demise only, most of his research studies came to lime light. According to his explanations, he called them as 'Factor' or determiner which was otherwise known as heredity units.

Genes are the functional hereditary units.  Gene is also defined as the functional unit of DNA which codes for a character. Genes are located on chromosomes, which are then carried to the next generation and thus plays a great role in heredity.

A gene is a sequence of nucleotides along a DNA strand - with 'start' and 'stop' codons and other regulatory elements - that specifies a sequence of amino acids that are linked together to form a protein.

• Genes are basic unit of heredity present on the chromosome.
  
• They are made up of DNA hence they are sequence of nucleotides.
  
• These orders of nucleotides in DNA later determine the sequence of polypeptide chain formed from them during translation. 
• So, the correct option is 'All of the above'.

In biology, a gene is a sequence of DNA or RNA that codes for a molecule that has a function. During gene expression, the DNA is first copied into RNA. The RNA can be directly functional or be the intermediate template for a protein that performs a function. However the inverse is incorrect. 

Gene is present in the coding region of the DNA. In eukaryotes, gene is made up of both introns and exons. So, the correct option is "Coding DNA".

• The ratio of long stem plants to short stem plants among the progeny is 165:54 which means it has a ratio of 3:1. This ratio is possible if the parents are heterozygous in nature which after the cross will produce homozygous tall, heterozygous tall and homozygous dwarf offsprings. 
• As the heterozygous offspring expresses the dominant allele, they will also be tall. This is a classic example of the monohybrid ratio that produces a ratio of 3:1 in the F2 generation of pure line parents.

• A Gene library or DNA library is a comprehensive collection of cloned DNA fragments from a cell, tissue, or organism.
• DNA libraries can be used to isolate a specific gene of interest as they generally include at least one fragment that contains the gene.
• Hence Gene library or DNA library has a collection of c DNA only.
• So, the correct answer is 'c DNA only'.

• The monohybrid cross-refers to inheritance of singe contrasting trait by two parents at a time. For example, a cross of tall (T) and dwarf (t) pea plants (TT x tt). Mendel observed that monohybrid cross between two pure breeding varieties yields $F _1$ generation which exhibits the dominant trait; although factor for a recessive trait is present in $F _1$ hybrids. Self-fertilization of $F _1$ generation obtains $F _2$ generation which exhibits both dominant and recessive traits in the 3:1 phenotypic ratio. This laid the foundation of the law of purity of gametes which states that the two factors for a trait, present together in a heterozygous individual, do not get mixed and are separated during gametogenesis. 

Monohybrid cross refers to inheritance of a single contrasting trait by two parents at a time. For example, a cross of tall (T) and dwarf (t) pea plants (TT xtt). Dihybrid cross refers to inheritance of two pairs of contrasting characters by two parents at the same time. For example, a cross of two pea plants, one with yellow and round seeds (YYRR) and other with green and wrinkled seeds (yyrr). The term “monozygous” represents twins being developed from a single zygote. The first division in zygote produces two identical cells that independently develop into two embryos; monozygotic twins are produced. The term “dizygous” represent twins being developed from individual zygotes. Fertilization of two eggs by separate sperms produces two zygotes that independently develop into two embryos. Thus, the correct answer is the option D.

Probability of their first (or any) daughter being colourblind is nil as the daughter of normal father can never be colourblind.

A.Genome – a set of chromosome in an organism in a body.

B.Chromosome – Dark coloured, small rod like structures, appear in the dividing nucleus is called Chromosome.

C.Genotype – It is the representation of an individual’s genetic constitution with respect to a single character or set of characters.

D.Gene - A gene is the basic physical and functional unit of heredity. Genes are made up of DNA. Some genes act as instructions to make molecules called proteins. However, many genes do not code for proteins. In humans, genes vary in size from a few hundred DNA bases to more than 2 million bases.

So,
the correct option is ‘Gene’.

• According to the modern concept, Mendel's factor is called a gene. Mendel believed that heredity is the result of discrete units of inheritance, and every single unit (or gene) was independent in its actions in an individual’s genome. According to this Mendelian concept, inheritance of a trait depends on the passing-on of these units. For any given trait, an individual inherits one gene from each parent so that the individual has a pairing of two genes.

A base pair (II) carries least information as at least three bases together (base triplet) make a codon (III) which in turn code for an amino acid. Genes (IV) are the stretch of DNA and each gene codes for a particular protein. Many genes are linearly arranged on a chromosome which means that chromosomes carry information for many proteins.

A tall plant was grown in nutrient deficient soil and remained dwarf .So , after crossed with dwarf plant then all hybrid plants are tall. Hybrid genotype is Tt.

The first cross between strain 1 and gg result in all wild-type offspring, it must have genotype GG. As in that case, all offspring will have Gg genotype hence showing wild-type character. Similarly, strain 3 must have genotype gg resulting in all ebony bodied offspring.