25 June Genetics Variation and Change Introduction: DNA, alleles, genes and chromosones

All of our somatic cells contain DNA which is condensed into 46 chromosones. DNA is made up of nucleotides. A sequence of nucleotides contains information to make a specific protein. Variations of a gene are called alleles.

DNA: A molecule that carries genetic information, double helix structure

Chromosons: A strand of DNA and stabalizing proteins condensed into a threadlike structure found in a cell nucleus

Genes: A unit of heredity, codes for a protein

Allele: A variation of a gene

Structure of DNA

DNA is a double helix structure made up of two sands wrapped around each other. A strand of DNA is a polymer made up of monomers (neucleotides). Neucleotides are made up of sugar, phosphate and a base. There are four types of bases: Adenine, Thymine, Cytosine, Guanine. A pairs with T and C pairs with G. The phosphate bonds to sugar, forming a long chain (sugar-phosphate backbone). The bases pair up, connecting two strands.

Chromosomes

Chromosomes are condensed strands of DNA. We have two copies of each chromosome in a pair called homologous chromosomes. Each pair contributes to the pair. Both chromosomes in a pair contains the same collection of genes but the alleles that you receive from each parent may be different. Humans are diploid, meaning we have two sets of chromosomes (homologous). We have 23 pairs of chromosomes.

Genes and Alleles

Genes are the result of a sequence of nucleotides. We have the same genes on each chromosome in a pair but the alleles may be different. Alleles are a variation of a gene, so you could inherit blue eyes from your mom and brown eyes from your dad. That is heterozygous, different copies of a gene. Homozygous is when you have identical copies (blue eyes from both mom and dad). Homozygous can be dominant or recessive. Genes are found in the same position (locus) on each chromosome.