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DNA and Chromosomes. What Is a Chromosome?. Chromo – means coloured. Some – means body. They are not really coloured, but they take up cell dyes easily so they look coloured. Chromosomes conists of a strand of DNA (Deoxyribose Nucleic Acid), wound around certain proteins.
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What Is a Chromosome? • Chromo – means coloured. • Some – means body. • They are not really coloured, but they take up cell dyes easily so they look coloured. • Chromosomes conists of a strand of DNA (Deoxyribose Nucleic Acid), wound around certain proteins.
What Is a Chromosome? • A strip of DNA is a gene. • Chromosomes carry your genes. • Genes determine your shape, height, certain behavioural characteristics, and even whether you will get certain diseases.
Homologous Pairs • Each of us has 2 sets of chromosomes, called Homologous pairs. • One set came from your mother and one from your father. • These homologous pairs: • Are the same size. • Have their centromere in the same place. • Have the same genes in the same places (the same locus).
Homologous Pairs • The actual expression of your genes depends on a combination of genetics working through your evolution, or family history. • If your ancestors lived in a desert area, you are likely to have a large nose, which can moisten the air before it hits the lungs. • If your ancestors lived in a cold, blizzard-swept area, you would probably have a small, squat nose.
Human Genome • Very soon we will know exactly which genes are on which chromosomes. • Teams of Scientists have worked out a map of the human genome. • Remember: a genome is the set of chromosomes in the nucleus of an organism).
Chromosome Number • A single set of chromosomes is called a Haploid number. It is given the symbol ‘n’. • A double set of chromosomes is called a Diploid Number. It is given the symbol ‘2n’. • Organisms can have more than 2 sets of chromosomes, this is called Polyploidy.
Human Chromosome Number • Humans have 46 Chromosomes: 23 from their mother and 23 from their father. • The human diploid number is 46 (body cells) and the haploid number is 23 (gametes).
Exception to the Rule • An exception to the rule that all homologous chromosomes are the same size are the sex chromosomes. • The females of most species are XX and the males of most species are XY. • All chromosomes other than the sex chromosomes are called Autosomes. • Human males have 22 autosomes + XY • Human Females have 22 autosomes + XX
Some Terms to Know • The total of an individual’s genetic material is called the Genome. • Organised into matching chromosomes, they are arranged into a Karyotype.
