12-bio-botany-unit-III Cell Biology And Genetics

Explanation
The term "chromosome" was introduced by Waldeyer.

Explanation
Bridges is the correct answer because he was the first to provide experimental evidence that genes are carried by the chromosome.

Explanation
The given answer, 7:1:1:7, represents a coupling test cross ratio. This ratio indicates the relative frequencies of different genotypes in a test cross between two heterozygous individuals. The presence of the same alleles on opposite chromosomes (7:7) suggests that these alleles are tightly linked and likely to be inherited together. The presence of a different allele (1) in the middle suggests recombination has occurred. This ratio suggests that recombination is less likely to happen between the outer alleles (7) and more likely to occur between the middle allele (1) and the outer alleles.

Explanation
During the pachytene stage of prophase I of meiosis, recombination of chromosomes occurs. This is when homologous chromosomes pair up and exchange genetic material through a process called crossing over. This exchange of genetic material leads to genetic diversity in offspring. Therefore, pachytene is the correct stage for recombination to take place.

Explanation
Hugo de Vries first used the term mutation based on his observation on Oenothera lamarckiana.

Explanation
Neurospora is a genus of fungi that is commonly used in genetic research. Biochemical mutants of Neurospora have been extensively studied and it has been observed that these mutants are unable to synthesize certain amino acids. This suggests that Neurospora plays a crucial role in the biosynthesis of amino acids.

Explanation
Nullisomy is a type of aneuploidy where there is a loss of both homologous chromosomes of a pair, resulting in a total chromosome number that is two less than the diploid number (2n). Therefore, the correct answer is 2n - 2.

Explanation
Drosophila melanogaster, commonly known as fruit flies, have four chromosomes in their gametes. Chromosomes are the structures that contain the genetic material of an organism. In fruit flies, there are four distinct chromosomes that carry the genes responsible for various traits and characteristics. These chromosomes are passed on to the offspring through the gametes, which are the reproductive cells. Therefore, the correct answer is four chromosomes.

Explanation
Watson and Crick proposed the double helix DNA model. They are known for their discovery of the structure of DNA, which they published in 1953. Their model explained how DNA is composed of two strands that are twisted together in a helical shape, forming a double helix structure. This model revolutionized our understanding of genetics and laid the foundation for further research in the field.

Explanation
The width of a DNA molecule is 20 Å. This measurement refers to the distance between the two strands of the DNA double helix. The width of DNA is important because it determines the spacing between the nucleotide bases, which in turn affects the overall structure and stability of the molecule. The correct answer is 20 Å.

Explanation
RNA is universally present in all organisms except in DNA viruses. This is because DNA viruses replicate their genetic material using a DNA-dependent DNA polymerase, which means they do not require RNA for replication. In contrast, all other organisms, including bacteria, algae, and TMV (Tobacco mosaic virus), use RNA in various cellular processes such as protein synthesis and gene regulation.

Explanation
mRNA, or messenger RNA, is a type of RNA molecule that carries genetic information from the DNA to the ribosomes, where it is used as a template for protein synthesis. It is a relatively small portion of the total RNA content in the cell. Therefore, the correct answer is 3 - 5%, indicating that mRNA makes up only a small fraction of the RNA content in the cell.

Explanation
In bacterial cells, there are more than 70 tRNAs. These tRNAs are responsible for carrying specific amino acids to the ribosomes during protein synthesis. Each tRNA molecule has a specific anticodon sequence that matches with a specific codon on the mRNA. This allows the tRNA to bring the correct amino acid to the growing polypeptide chain. The large number of tRNAs in bacterial cells ensures that there is a wide range of amino acids available for protein synthesis, allowing for the production of diverse proteins necessary for the cell's functioning.