Introduction

• Living organisms are distinguished by their ability to reproduce their own kind.

• Offspring resemble their parents more than they do less closely related individuals of the same species.

• The transmission of traits from one generation to the next is called heredity or inheritance.

• However, offspring differ somewhat from parents and siblings, demonstrating variation.

• Genetics is the study of heredity and variation.

1. Offspring acquire genes from parents by inheriting chromosomes

• Parents endow their offspring with coded information in the form of genes.

• Your genome is derived from the thousands of genes that you inherited from your mother and your father.

• Genes program specific traits that emerge as we develop from fertilized eggs into adults.

• Your genome may include a gene for freckles, which you inherited from your mother.

• Genes are segments of DNA.

• Genetic information is transmitted as specific sequences of the four deoxyribonucleotides in DNA.

• This is analogous to the symbolic information of letters in which words and sentences are translated into mental images.

• Cells translate genetic "sentences" into freckles and other features with no resemblance to genes.

• Most genes program cells to synthesize specific enzymes and other proteins that produce an organism's inherited traits.

• The transmission of hereditary traits has its molecular basis in the precise replication of DNA.

• This produces copies of genes that can be passed from parents to offspring.

• In plants and animals, sperm and ova (unfertilized eggs) transmit genes from one generation to the next.

• After fertilization (fusion) of a sperm cell with an ovum, genes from both parents are present in the nucleus of the fertilized egg.

• Almost all of the DNA in a eukaryotic cells is subdivided into chromosomes in the nucleus.

• Tiny amounts of DNA are found in mitochondria and chloroplasts.

• Every living species has a characteristic number of chromosomes.

• Humans have 46 in almost all of their cells.

• Each chromosome consists of a single DNA molecule in association with various proteins.

• Each chromosome has hundreds or thousands of genes, each at a specific location, it's locus.

2. Like begets like, more or less: a comparison of asexual and sexual reproduction

• In asexual reproduction, a single individual passes along copies of all its genes to its offspring.

• Single-celled eukaryotes reproduce asexually by mitotic cell division to produce two identical daughter cells.

• Even some multicellular eukaryotes, like hydra, can reproduce by budding cells produced by mitosis.

• Sexual reproduction results in greater variation among offspring than does asexual reproduction.

• Two parents give rise to offspring that have unique combinations of genes inherited from the parents.

• Offspring of sexualreproduction vary genetically from their

siblings and from both their parents.