IGNOU MSc Zoology | Tutor Marked Assignment (TMA) | Detailed Solved Answers
Gregor Mendel used controlled crossbreeding experiments on pea plants to study inheritance of traits. By selecting true-breeding plants and controlling pollination, Mendel observed that certain traits appeared consistently in successive generations. He identified dominant traits that masked recessive traits in the F1 generation, while recessive traits reappeared in the F2 generation.
Based on these observations, Mendel proposed the laws of heredity. The Law of Dominance states that one allele can mask another. The Law of Segregation explains that alleles separate during gamete formation. The Law of Independent Assortment states that different traits are inherited independently when located on different chromosomes.
Epistasis is a genetic interaction in which one gene masks or modifies the expression of another gene at a different locus. It alters the expected Mendelian phenotypic ratios.
In dominant epistasis, a dominant allele of one gene suppresses the expression of another gene, as seen in fruit color of squash. In recessive epistasis, the homozygous recessive condition masks another gene, such as coat color inheritance in mice. Epistasis demonstrates that gene expression often involves interactions between multiple genes.
Mutations are heritable changes in DNA sequence. Types include point mutations (silent, missense, nonsense), frameshift mutations caused by insertions or deletions, and chromosomal mutations such as deletions, duplications, inversions, and translocations.
These mutations may alter the genetic code, affect protein synthesis, or change protein structure and function. Some mutations are harmful, some neutral, while others can be beneficial and contribute to evolution.
Transcription factors regulate gene expression by binding to promoter regions, while enhancers increase transcription efficiency by interacting with transcription machinery. These regulatory elements ensure tissue-specific and time-specific gene expression.
Epigenetic modifications such as DNA methylation and histone modification influence chromatin structure. DNA methylation generally suppresses gene expression, while histone acetylation promotes transcription. These changes regulate genes without altering DNA sequence.
In the X-Y sex determination system, males possess XY chromosomes and females XX, as seen in humans. The presence of the Y chromosome determines maleness.
In the Z-W system, females are heterogametic (ZW) and males homogametic (ZZ), as seen in birds and reptiles. Thus, sex determination depends on different chromosomal mechanisms in different organisms.
Karyotyping involves staining and arranging chromosomes to study their number and structure. It helps detect abnormalities such as trisomy and chromosomal deletions.
Fluorescence in situ hybridization (FISH) uses fluorescent probes to detect specific DNA sequences on chromosomes. It is useful for identifying gene deletions, duplications, and translocations with high precision.
Cloning vectors are DNA molecules used to carry foreign genes into host cells. They are essential tools in recombinant DNA technology.
Common cloning vectors include plasmids, bacteriophages, cosmids, and BACs. They possess features such as origin of replication, selectable markers, and restriction sites that enable gene insertion and expression.
A genomic library contains all DNA sequences of an organism, including introns and regulatory regions. A cDNA library is prepared from mRNA and represents only expressed genes.
cDNA libraries are preferred for studying gene expression because they reflect actively transcribed genes without non-coding sequences.
Transgenic animals are organisms that carry foreign genes introduced artificially. Techniques such as microinjection, viral vectors, and embryonic stem cell transfer are used to create them.
These animals contribute to advances in medicine, agriculture, and biotechnology by producing therapeutic proteins, improving livestock traits, and serving as disease models.
Gene therapy is a technique used to treat genetic disorders by introducing functional genes into a patient’s cells. It aims to correct defective genes at the molecular level.
Types include somatic gene therapy, germ line gene therapy, and ex vivo and in vivo approaches. Gene therapy has applications in treating inherited diseases, cancer, and immune disorders.