Genomes Genes and Alleles Nature of Biology 1 Chapter 13 pg 484 - 520

Three quick questions 1. Name one positive and one negative about sexual and asexual reproduction 2. Although independent assortment leads to a huge number of possible human variation in our sex cells crossing over brings that number up to nearly infinity. Explain this statement. 3. Name the five stages of the cell cycle denoted by the letters S, G2, G1, C, and M and place them in a logical order.

Study Design Unit 2, Area of Study 2 – Genomes, genes and alleles The distinction between a genome, gene and allele The genome as the sum total of an organism’s DNA measured in the number of base pairs contained in a haploid set of chromosomes

What makes you, you?

DNA revisited Deoxyribonucleic acid is a biomacromolecule which carries the genetic code for protein expression, dictating essentially all aspects of life. The nitrogenous base sequence of DNA is what results in the variety of living things in the world

What is a Gene? A gene is the basic functional unit of heredity. Made up of a specific strand of DNA and act as instructions to make a specific protein molecule. In humans, genes vary in size from a few hundred DNA base pairs to more than 2 million base pairs. Within a species such as humans 99.9% of our DNA is the same as the person next to us.

So where is the variation? It makes sense that we are so genetically alike… We are more similar to each other as a species than we are to other species Variation in genes come from changes in the nitrogenous base sequence of the DNA that makes up the gene Different variations of the same gene is termed an Allele.

Case Study – ABO Blood group alleles The ABO blood group gene codes for a type of protein which determines an individuals blood type. The gene is approximately 20 038 base pairs (bp) long and is found on chromosome 9. There are three allelic variations to the ABO gene The A allele develops the A marker on red blood cells The B allele develops the B marker on red blood cells The O allele results in a non-functional gene and develops no marker on red blood cells Let’s compare the nucleotide sequence of the three alleles

Case study – ABO Blood group alleles How many changes need to occur to change the allele? What proportion of the total gene is this?

Genome A genome is an organism’s complete set of DNA, including all of its genes. Each genome contains all of the information needed to build and maintain that organism. In Eukaryotes, a copy of the entire genome— more than 3 billion DNA base pairs—is found in all cells that have a nucleus. All of the genomic information of an organism is contained in one haploid set of chromosomes. With the exception of the sex chromosomes

Comparing Genomes The below table compares the genomes of various organisms What organism has the biggest genome? What organism has the most chromosomes? What organism has the most genes? Organism Base pairs Chromosome number (Haploid number) Number of genes Human 3 Billion 46 (23) 21 000 Mouse 2.5 Billion 40 (20) 23 000 Fruit Fly 150 Million 8 (4) 17 000 Arabidopsis (weed) 157 Million 10 (5) 25 000 Roundworm 97 Million 12 (6) 19 000 Yeast 13 Million 32 (16) 6 000 E. Coli (bacteria) 4.6 Million 1 3 200