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प्रश्न
Very Short Answer Question.
What is crossing over?
उत्तर
- Crossing over is a process that produces new combinations (recombinations) of genes by interchanging and exchanging of corresponding segments between non-sister chromatids of homologous chromosomes.
- It occurs during pachytene of prophase I of meiosis.
- The mechanism of crossing over consists of four sequential steps such as synapsis, tetrad formation, crossing over, and terminalisation.
- The phenomenon of crossing over is universal and it is necessary for the natural selection because it increases the chances of variation.
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संबंधित प्रश्न
Linkage and crossing-over of genes are alternatives of each other. Justify with the help of an example.
Define the following:
test cross.
Define complete linkage. Give an example of a cross, showing complete linkage.
British geneticist R.C. Punnett developed a graphical representation of a genetic cross called “Punnett Square”. Mention the possible result this representation predicts of the genetic cross carried.
Differentiate between complete and incomplete linkage.
Analyse the following statements with respect to complete sex linkage and select the correct option.
- It is exhibited by genes located on non-homologous regions of X and Y chromosomes
- Y-linked trait is hypertrichosis.
- X-linked traits are haemophilia, red-green colour blindness, myopia (near sightedness).
From the following disorders identify the ODD one.
Blue eye colour is recessive to brown eye colour. A brown-eyed man whose mother was blue-eyed marries a blue-eyed woman. The children shall be ______.
Which of the following is a test cross?
Mendal formulated the law of purity of gametes on the basis of ______.
