Genes and Cell Division: Genes Chapter 5 Lesson 5A part 3

Objectives: I will be able explain the relationship between genes and chromosomes I will be able to differentiate between a haploid and diploid chromosome number.

What is a gene?

Genes Genes contain the information needed to build cells and cell products. Genes control thousands of traits. Specific sections of DNA that code for a specific protein (which develops a trait) The different forms of a gene are called alleles.

Genes & Chromosomes Genes are usually stored in chromosomes. Chromosomes are kept in the nucleus. Chromosomes consist of DNA and special proteins. Each chromosome has one allele for every gene on it. The two chromosomes in an offspring cell may have the same or different alleles.

Diploid cells In somatic cells (body cells) of most organisms, similar chromosomes occur in pairs. Diploid cells are cells that have pairs of homologous chromosomes.

Diploid cells

Diploid cells Pairs of chromosomes that have genes for the same traits arranged in the same order are called homologous chromosomes. Because one chromosome is inherited from each parent, the chromosomes are not identical. Different organisms have different numbers of chromosomes.

Homologous pair of chromosomes: have the same genes at the same loci (place on the chromosome)

Homologous chromosomes

Haploid cells Haploid cells are cells that have only one chromosome from each pair of homologous chromosomes. haploid from Greek haploeides, means “single”

Haploid vs Diploid

Human diploid number is 46 Normal human cells have 23 pairs of chromosomes which is a total of 46 chromosomes. Human diploid number is 46 Human haploid number is 23

Diploid & Haploid Examples Honey bee 16 32 Crayfish 100 200 Rabbit 22 44 Watermelon 11 Corn 10 20

"Some people find it hard to believe that the genes are capable of carrying enough information to produce all the physical traits you possess. Your DNA is tightly compressed. Al the DNA from all your cells would fit into a one-inch cube. If al the DNA in one human all were uncoiled and stretched out, it could form a thin string about 2 yards long. It has been estimated that the information found in the DNA of 1 human cell is equal to the information in 1,000 books containing 600 pages each. The nucleus of each of your cells is a good-sized chemical library."

The number of chromosomes in a cell is a species characteristic: human 46 fruit fly 8 goldfish 100 crayfish 200

The number of chromosomes does not determine the species. It is the genes on the chromosomes that make the organism.