Genes

Genes:

Three of the main parts of the cells are the cell membrane, Cytoplasm and the Nucleus. In the nucleus there are long strands of a substance called DNA. Each strand forms chromosome.

The nucleus contains different chromosomes and there are usually two copies of each type of chromosome.

Chromosomes are divided into genes. With each chromosome carrying a large number of genes and each gene doing a particular job. Variation caused by genes is inherited variation as we inherit our genes from our parents.

To make it easier to think of chromosomes you should think of it as a set of books. Each book (chromosome) contains a set of sentences giving instructions (genes). All of the books together contain all of the instructions needed to produce a certain organism.

Alleles- Every gene comes in different types called alleles. So a gene for eye colour may come in a 'blue type' allele and a 'brown type' allele. Alleles are different forms of the same gene.

There are two copies of every chromosome in a nucleus so there are two copies of each gene. Every copy of a gene must be a different allele.

Different organisms have a different number of chromosomes. Humans have 23 pairs with 23 000 genes in total. Each different set of alleles that we inherit from our parents give each of us slightly different characteristics.


Key Words:

Cell membrane
Nucleus
Cytoplasm
DNA
Chromosome
Genes
Inherited Variation
Alleles


Questions:

1. Which part of the cells are chromosomes found?
2. Where are genes found?
3. What are alleles?
4. How does alleles explain the idea that we all look different?
5. Using you knowledge of science and genes how do you think a scientist would find out whether blood at a crime scene belongs to the victim or a suspect?


What you should've learnt:

The structure of the nucleus of the cell as containing chromosomes, on which genes are located.

An understanding that genes exist in alternative forms called alleles which give rise to differences in inherited characteristics.