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notes of genetics chapters to learn it

Answer 1

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Answer 2

A book of notes on Genetics



Genes, chromosomes and DNA

Gene:             A set of instructions that codes for 1 feature.  It is a small section of DNA.  It is usually regarded as the smallest unit of heredity and is located on a chromosome.

Chromosome:  a threadlike strand of DNA that carries genes.

DNA:                An instruction manual containing all the genetic codes for making an entire individual.  Full name deoxyribonucleic acid.



Humans have 46 chromosomes (23 pairs) in the nucleus of every cell except in the gametes (sex cells ie sperm and egg cells) which contain half of this amount ie 23 chromosomes.

Diagram to show how a chromosome is made of DNA



Genes, chromosomes and DNA

We all hear about genes, chromosomes and DNA, but many people don’t really know how these fit together.

All body cells contain chromosomes, contained in the control centre of the cell – the nucleus. There are 23 pairs of chromosomes in human cells, making 46 in all.



We inherit one of each of these pairs from our mother and one from our father. So we have two copies of each chromosome.

The chromosomes are made of DNA. This is the genetic code – the blueprint for a human being. DNA is a bit like an instruction manual for building the body and keeping it healthy.

Each strand of DNA is really a long string of genes.

Diagram of a gene on a chromosome

 



As we inherit a copy of each chromosome from each parent, we also inherit a copy of each gene from each parent. Scientists now think there are about 25,000 different human genes. Over 99% of the genetic code is identical in all of us. There are small variations in DNA between people. It is these small variations – having different genes - that make us all different from each other.

Cells in the body are constantly growing and dividing to replace old or damaged cells. Proteins in the cell control this process. They are the chemicals that do all the work in the cell. Each gene has the code to make one particular protein.