Genes and Genomes

Learning Targets A gene is a heritable factor that consists of a length of DNA and influences a specific characteristic A gene occupies a specific position on a chromosome The various specific forms of a gene are alleles Alleles differ from each other by one or only a few bases New alleles are formed by mutation The genome is the whole of the genetic information of an organism The entire base sequence of human genes was sequenced in the Human Genome Project Sickle cell anemia can be caused by a base substitution mutation. This mutation in turn changes the resulting mRNA and polypeptide sequence in hemoglobin. Humans and other species have different numbers of genes Use of a database to determine differences in the base sequence of a gene in two species Comparison of genome size in T2 phage, Escherichia coli, Drosophila melanogaster, Homo sapiens and Paris japonica.

What are genes? A gene is a heritable factor that consists of a length of DNA and influences a specific characteristic A gene occupies a specific position on a chromosome, called its locus (plural loci) Basically, a gene is simply a specific segment of a DNA strand that codes for a specific trait or function

Comparing genes This is a comparison of the COX1 gene in a mouse, a human, a fly, and a yeast. This is just a snapshot of a comparison of bases 6640 to 6770 What do you notice?

Genomes An organism’s genome is the complete set of all of its genetic material It is often measured in basepairs

Human Genome Project Started in 1990, it was an international, publicly funded effort to map the entire human genome Set the stage for an unprecedented number of advances in genetics, with impacts in human health, biotechnology, evolution and many other fields Video

Human Chromosomes: Homologous Pairs Paternal Maternal Chromosomes are condensed segments of DNA that are composed of several hundred to a few thousand genes. Karyograms are pictures of chromosomes from late prophase. Each chromosome in the picture are in their duplicated state. The karyograms are organized from largest chromosomes to smallest. Homologous Pairs: many species have two sets of chromosomes, one from each parent - paternal and maternal. A cell that has homologous pairs is called a diploid cell. A cell that only has one set is called haploid. We have two of each type of chromosome because we receive one from our mother and one from our father. When we look at a human karyotype, the homologous chromosomes (one from mom and one from dad) are paired together and the chromosomes are further ordered by size. Remember that cells with two of each type of chromosomes are said to have a diploid (2n) number of chromosomes.

These are each duplicated chromosomes. Therefore, this individual has two duplicated “Number 16” chromosomes, with two sister chromatids each.

What is the genome size of the following organisms? Fill in the worksheet

Genes and Alleles Alleles are different forms of the same gene, inherited from each parent. For example, purple and white are two different forms of the flower color gene in some flowering plants. Alleles may differ from each other by only a few base pairs. Remember the rock pocket mice? 4:34. A locus is the actual physical location of an allele on its chromosome (pl. loci). Different versions of a gene are called alleles. Where the allele is found on the chromosome is called the locus (think location).

New Alleles form by mutation

Sickle Cell Anemia Most common genetic disease in the world Sickle cell anemia can be caused by a base substitution mutation in the gene that codes for the alpha- globin polypeptide in hemoglobin. Specifically, the sixth codon from changes GAG to GTG. When this is eventually translated, the sixth amino acid changes from glutamic acid to valine. This changes the shape of the red blood cells to a rigid sickle shape. The sickle shaped cells can get caught in capillaries and cause vascular damage as well as reducing circulation. HBB gene’s locus is on the short arm of chromosome 11 at position 15.5