Which chromosome of man has the least number of genes?

DNAs are packaged into chromosomes and contains the genetic information. The Y chromosome is one of the smallest chromosomes in humans. It has the least number of genes that are approximately 55 genes and the X chromosome has about 900 genes.

Oswald Avery and others have continued Griffith' transforming principle to prove DNA as genetic material - Substantiate.

Frederick Griffith conducted a series of experiment with Streptococcus pneumoniae , a bacterium that commonly cause pneumonia in mammals including humans in 1928. He studied two strains of bacteria called S-strain and R-strain. S-strain was virulent. They have a mucopolysaccharide coat and produce smooth shiny colonies. R-strain was non-virulent. They do not possess coat and produces rough colonies when grown on culture plate. Griffith conducted a series of experiment on mice as shown in the figure. He observed that when a mixture of heat killed S-strain and live R bacteria are injected, the mice did not died. Further, the living S-strains can be recovered from the dead mice. He concluded that there was some factor in heat killed S-strain which transformed the live R-strains to S-strains and made the S-strain virulent. However, the biochemical nature of genetic material couldn't be revealed from his experiments. The first convincing evidence of the role of DNA in heredity came from the experiments of Avery, Macleod and McCarty, who showed that the genetic characteristics in bacteria would be altered from one type to another by treatment with purified DNA. In studies of Streptococcus pneumoniae , they transformed mutant cells which are unable to cause pneumonia into cell that could do so by treating with pure DNA of disease forms. From their experiment as showed in the figure, they concluded transformation cannot occur unless DNA is present thus, the molecule that carries heritable information is DNA. Hence, in this way Oswald Avery and others have continued Griffith's transforming principle to prove DNA as genetic material substantiate.

Explain the regulation of Lac operon in absence and presence of Lactose as an Inducer.

The promoter is a nucleotide sequence that helps a particular gene to be transcribed. The enzyme RNA polymerase recognizes the promoter and transcription is started. An operator is a segment of DNA which binds to a repressor. A repressor is a DNA or RNA binding protein that inhibits the expression of one or few genes and causes the transcription to stop. In order to start the process of transcription, a small molecule is introduced into the system which is known as the inducer. The inducer displaces the repressor molecule from the operator site and results in the operon to start transcription.Operons can be regulated by the action of the inducers and the repressors and this enables the organism to regulate the expression of various genes. In the negative control, the repressor binds with the operator site to stop the transcription. When an inducer is added, it causes to change the structural configuration of the repressor, and it cannot further bind with the operator. This type of negative control is found in lac operon. The lac operon is an operon required for the metabolism of lactose. It consists of three structural genes which are lacZ, lacY and lac A which codes for enzymes β-galactosidase, beta-galactoside permease and galactoside acetyltransferase. When no lactose is available, the lac repressor stops the production of enzymes and when lactose is available the transcription process begins. The absence of lactose causes the repressor to bind with the operator and transcription is stopped. However, the regulator gene for lac operon produces a protein that blocks RNA polymerase to bind to the operator. This binding of the regulator protein is prevented only when allolactose binds to it and causes inactivation of the repressor. Allolactose is formed from lactose and it acts as an inducer. It brings about conformational changes and decreases affinity of the repressor for the operator site and transcription can proceed.

E M B I B E

EMBIBE CHAPTER WISE PREVIOUS YEAR PAPERS FOR BIOLOGY>Chapter 6 - Molecular Basis of Inheritance>Karnataka Board-2019>Q 4

MEDIUM

12th Karnataka Board

IMPORTANT

Earn 100

DNA is the better genetic material than RNA. Justify the statement with three comparative reasons.

Important Questions on Molecular Basis of Inheritance

EASY

12th Karnataka Board

IMPORTANT

EMBIBE CHAPTER WISE PREVIOUS YEAR PAPERS FOR BIOLOGY>Chapter 6 - Molecular Basis of Inheritance>Karnataka Board-2019>Q 5

'DNA replication is said to be semiconservative'' Why? Describe the experimental proof of Messelson and Stahl to show DNA replication is semiconservative.