How our genes are organized chromosomes

Genes A gene is an address – a location on the chromosome and in the DNA sequence where info for a specific trait is located.

Human Fertilization ZYGOTE – fertilized egg Gametes

Review of key terms: Gene Chromosome Chromatid Homologous chromosome

What are chromosomes? All eukaryotic cells store genetic information in chromosomes. Most eukaryotes have between 10 and 50 chromosomes in their body cells. Human cells have 46 chromosomes 23 pairs

Structure of chromosomes Complex of DNA and protein called chromatin Condenses during cell division DNA exists as a single, long, double-stranded fiber Organized in coils DNA is wrapped around proteins called histones

Sets of chromosomes Homologous chromosomes: chromosomes that are similar in size, shape and genetic content Each homolog (individual chromosome) in a pair come from one of the two parents

Chromosome replication (S phase) Each condensed chromosome consists of 2 identical chromatids joined by a centromere.

Types of chromosomes Autosomes: chromosomes that are not directly involved in determining the sex of an individual Sex chromosomes: pair of chromosomes directly involved in determining the sex of an individual

Types of chromosomes In humans: Autosomes: 22 pairs Sex chromosomes: 1 pair Referred to as X and Y chromosomes in humans

Karyotype: a snapshot of our chromosomes Arranged by size in in descending order Used to examine an individual’s chromosomes

Chromosomal mutations Changes in an organisms chromosome structure are called: MUTATIONS

Four types of chromosomal mutations: Deletion Duplication Inversion Translocation

Deletion mutation A piece of a chromosome breaks off completely: Consequence after cell division: new cell will lack a certain set of genes

Modeling deletion

Duplication mutation A piece of a chromosome breaks off and attaches to its homologous chromosome: Consequence after cell division: new cell will have an extra set of genes

Modeling duplication

Translocation mutation A piece of a chromosome breaks off and re-attaches to a non-homologous chromosome: Consequence after cell division: new cell will carry genes in the wrong location

Inversion mutation A piece of a chromosome breaks off and re-attaches to its original chromosome in REVERSE order: Consequence after cell division: new cell will carry genes that are in the wrong order – will code for the WRONG proteins

Modeling inversion

Wrong order = wrong proteins Changes in the order of genes on chromosomes has dire effects in the organism The wrong sequence will code for the wrong protein In some cases there is little effect, in others the result can be severe or even lethal to the organism.

References National Institutes of Health Carolina Biological Supply Biology Holt (4th Ed.)