Question 17. A b c C B D Age F G H I From the over contour identify the sort of mutation and you may determine it. Answer: In reverse combination replication, the new recurring phase is found immediately following the standard phase however, the new gene series most other would-be stopped.
Matter 18. Answer: Sutton and you may Boveri (1903) by themselves advised the latest chromosome theory from genetics. Sutton joined the info regarding chromosomal segregation which have mendelian values and you may called they new chromosomal concept off inheritance.
These add a few similar categories of chromosomes. You to set is actually acquired out-of girls mother (maternal) plus the almost every other away from male father or mother (Parental)
These chromosomes constitute the homologous pair.
Chromosomes retain the structural individuality and you will identity regarding the lifetime course away from a system.
Per chromosome carries specific determiners out of mendalian factors which can be now referred to as genetics.
The fresh behavior away from chromosomes within the gamete formation (meiosis) will bring evidence that genes or factors are found toward chromosomes.
Concern 19. “Explain the process out of crossing-over. Answer: Crossing-over try an exact procedure that includes amounts instance synapsis, tetrad formation, cross-over and you may terminalization.
(i) Synapsis: Sexual pairing anywhere between one or two homologous chromosomes is established through the zygotene stage regarding prophase I from meiosis We. It’s off around three types:
Procentric synapsis: Combining initiate regarding center of chromosome.
(ii) Tetrad Creation: For each and every homologous chromosome away from a bivalent begin to mode several the same cousin chromatids, and therefore are nevertheless held together with her from the a centromere. At this stage for every bivalent keeps five chromatids. It stage is known as tetrad phase.
(iii) Cross-over: After tetrad formation, crossing-over takes place in pachytene stage. The brand new low-aunt chromatids away from homologous partners generate a message within one to or a whole lot more products. These points of get in touch with ranging from non¬sister chromatids from homologous chromosomes are called Chiasmata (singular-Chiasma).
In the chiasma, cross-shaped or X-molded formations try shaped, where cracking and you will rejoining from several chromatids exists. So it leads to mutual exchange of equivalent and you may related markets between them. Research conducted recently implies that synapsis and you can chiasma creation is actually facilitated by the an extremely organized construction out-of filaments entitled Synaptonemal Complex (SC). This synaptonemal state-of-the-art formation are absent in some types of male Drosophila, and therefore crossing over cannot happens.
So it combining sensation is known as synapsis otherwise syndesis
(iv) Terminalisation: Just after crossing over, chiasma begins to disperse for the terminal end out of chromatids. This really is known as terminalisation. Because of this, done separation of homologous chromosomes happens.
Homologous chromosomes is aimed side by side resulting in moobs out-of homologous chromosomes entitled bivalents
Question 21. How is Nicotiana exhibit self-incompatibility? Explain its mechanism. Answer: Self-sterility means that the pollen from a plant is unable to germinate on its own stigma and will not be able to bring about fertilization in the ovules of the same plant. East (1925) observed multiple alleles in Nicotiana which are responsible for self-incompatibility or self-sterility. The gene for self-incompatibility can be designated as S, which has allelic series S1 S2, S3, Scuatro and S5. The cross-fertilizing tobacco plants were not always homozygous as S1 S1 or S2 S2, but all plants were heterozygous as S1 S2, S3 S4 and S5 S6. When crosses were made between different S1 S2 plants, the pollen tube did not develop normally. But effective pollen tube development was observed when the crossing was made with other than S1S2 for example S3S 4 .
