In this post, I am sharing the Class 12 Biology Chapter 20 Notes PDF for the students of Intermediate Part 2. This chapter’s name is Chromosomes and DNA. Students can download the Class 12 Biology Chapter 20 Notes PDF on their laptops or mobile. These Biology Notes are for all the boards working under the Punjab Board like Gujranwala Board, Lahore Board, Faisalabad Board, Multan Board, Rawalpindi Board, Sargodha Board, DG Kahn Board, and Sahiwal Board. Here are the complete FSC 2nd Year Biology Notes PDF chapters.
FSC Part 2 Biology Chapter 20 Notes – Chromosomes and DNA
CHROMOSOMES:
Chromosomes are thread like structure that appear inside the nucleus at the time O cell division.
Discovery:
They are first observed by the German embyologist Walther Fleming in 1882, when he was examining the rapidly dividing cells of salamandar larvae.
Number of Chromosomes in Different Organisms:
Chromosomes are found in the cells of all eukaryotes. Their number however varies from species to species. Pencicillium, a fungus, has only one pair of or 2 chromosomes, while some ferns have more than 500 pairs or 1000 chromosomes. A mosquito has 3N, honeybee 16 pairs, corn 10 pairs, sugarcane 40, frog 13 and a mouse has 20 chromosomes. Human cells have 46 chromosomes, consisting of 23 pairs.
Function of Chromosomes:
Each chromosomes contains hundreds or thousand of genes that play important roles in determing how a person’s body develops and functions. The possession of all chromosomes leads to serious consequences, and usually death occurs.
Structure of a typical chromosome:
Typically a chromosome is made of chromatids (two replies), centromere (primary constriction) and a secondary constriction.
How to Download 2nd year Biology Chapter 20 Notes
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