Chromosomal Basis of Inheritance: Summary

SUMMARY

Chromosomal theory of inheritance states that Mendelian factors have specific locus on chromosomes and they carry information from one generation to the next generation. Genes located close together on the same chromosome and inherited together are called linked genes the phenomenon is called Linkage. Two types of linkage are complete linkage and incomplete linkage. The groups of linearly arranged linked genes are called Linkage groups. Crossing over is biological a process that produces new combination of genes by inter-changing the corresponding segments between non-sister chromatids of homologous pair of chromosomes. In this segment of DNA are broken and recombined to produce new combinations of alleles a process is called Recombination. The diagrammatic representation of distances between the adjacent genes which is directly proportional to the frequency of recombination between them is called genetic mapping. When any of the three or more allelic forms of a gene occupy the same locus in a given pair of homologous chromosomes, they are said to be multiple alleles. Papaya sex determination is controlled by three alleles. They are m, M1 and M2 of a single gene. Mutational events that take place within individual genes are called gene mutations or point mutation, whereas the changes occur in structure and number of chromosomes is called chromosomal mutation. The agents which are responsible for mutation is called mutagens.

DNA metabolism includes replication, repair and recombination. Protein synthesis in eukaryotes is unique due to the capping, tailing and splicing. Transcription takes place in nucleus and translation in cytoplasm. AUG codes for methionine and it is monocistronic. Alternative splicing is a mechanism to overcome stress in plants. RNA editing takes place in chloroplast and mitochondria of plants which is of phylogenetic importance. Controlling elements gave a major shift in the gene organisation in plants to prove that DNA is not static but plastic entities. The first genome sequenced is Arabidopsis thaliana, which is a potential genetic tool to study the development and metabolism in plants.

Glossary

Antisense strand: It is also called Template strand. It is the strand of DNA that is used as template for RNA synthesis

Branch Migration: The process in which base pairs on homologous strands are consequently exchanged at a Holliday junction, moving the branch up or down the DNA sequence.

Cis configuration: The presence of dominant alleles of two or more pairs on one chromosome and the recessive alleles on the homologous chromosome.

Exons: A segment of DNA that is both transcribed into RNA and translated into protein.

Feminizing Masculinizing: To induce female characteristics in male To induce male characteristics in female

Heteroduplex: A double stranded molecule of nucleic acid originated through genetic recombination from different sources

Introns: Eukaryotes have non-amino acid coding sequences called Introns.

Monocistronic: Eukaryotic mRNAs contain amino acid coding information from just one gene.

Okazaki fragment: A short segment of DNA produced by discontinuous replication elongating in the 5’ → 3’ direction away from the replication.

Primase: It is a type of RNA polymerase an enzyme that catalyzes the polymerization of ribonucleotides to RNA. It creates a primer for DNA synthesis.

Promoter: A specific nucleotide sequence to which RNA polymerase attaches to initiate transcription of mRNA from a gene.

Self incompatibility: A genetic mechanism which prevent self fertilization thus encourage outcross.

Synapsis: The pairing of two homologous chromosomes that occurs during meiosis.

Tassel seed: Feminization of the tassel

Terminalisation: The movement of transverse bonds between paired chromosomes in meiosis from their points of origin toward the ends of the chromosomes.

Termination codon: A stop codon

Trans configuration: An arrangement in which the dominant allele of one pair of genes and the recessive allele of another pair are on the same chromosome

Transcript: The DNA is said to be transcribed into RNA and RNA is call as Transcript.

Transesterification: A reaction that breaks and makes chemical bonds in a coordinated transfer, so that no energy is required.

Transposon: A DNA sequence capable of transposition.

Vestigial: Rudimentary organ of body become functionless in the course of evolution