Recently in class X, Sushma was asked to identify which statement is correct, she replied correctly, what could be her answer:
(a)Genes are actually units of heredity which transfer characteristics from parents to their offspring during reproduction.
(b)Chromosome is a thread like structure in the nucleus of a cell formed of DNA which carries the genes
(c)A gene is a unit of DNA on a chromosome which governs the synthesis of one protein that controls a specific characteristic of an organism.
(d)All the above
Answers
Explanation:
Genes carry the information that determines your traits (say: trates), which are features or characteristics that are passed on to you — or inherited — from your parents. Each cell in the human body contains about 25,000 to 35,000 genes.
For example, if both of your parents have green eyes, you might inherit the trait for green eyes from them. Or if your mom has freckles, you might have freckles too because you inherited the trait for freckles. Genes aren't just found in humans — all animals and plants have genes, too.
Where are these important genes? Well, they are so small you can't see them. Genes are found on tiny spaghetti-like structures called chromosomes (say: KRO-moh-somes). And chromosomes are found inside cells. Your body is made of billions of cells. Cells are the very small units that make up all living things. A cell is so tiny that you can only see it using a strong microscope.
Chromosomes come in matching sets of two (or pairs) and there are hundreds — sometimes thousands — of genes in just one chromosome. The chromosomes and genes are made of DNA, which is short for deoxyribonucleic (say: dee-ox-see-ri-bo-nyoo-CLAY-ik) acid.
Most cells have one nucleus (say: NOO-clee-us). The nucleus is a small egg-shaped structure inside the cell which acts like the brain of the cell. It tells every part of the cell what to do. But, how does the nucleus know so much? It contains our chromosomes and genes. As tiny as it is, the nucleus has more information in it than the biggest dictionary you've ever seen.
In humans, a cell nucleus contains 46 individual chromosomes or 23 pairs of chromosomes (chromosomes come in pairs, remember? 23 x 2 = 46). Half of these chromosomes come from one parent and half come from the other parent.
Under the microscope, we can see that chromosomes come in different lengths and striping patterns. When they are lined up by size and similar striping pattern, the first twenty two of the pairs these are called autosomes; the final pair of chromosomes are called sex chromosomes, X and Y. The sex chromosomes determine whether you're a boy or a girl: females have two X chromosomes while males have one X and one Y.
But not every living thing has 46 chromosomes inside of its cells. For instance, a fruit fly cell only has four chromosomes!
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