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Genes

Genes. A gene is the entire sequence of DNA bases responsible for the synthesis of a protein. A mutation occurs when the sequence of bases in a gene is altered.

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Genes

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  1. Genes • A gene is the entire sequence of DNA bases responsible for the synthesis of a protein. • A mutation occurs when the sequence of bases in a gene is altered. • Mutations may interfere with the ability to produce vital protein and may lead to a new variety within the species, hence, evolution.

  2. Genes • Recently, geneticists have learned that only some parts of genes, called exons, are actually transcribed into mRNA (most of the nucleotide sequences in genes are not expressed during protein synthesis. • Some noncoding sequences, called introns, are initially transcribed into mRNA and then clipped out.

  3. Regulatory Genes • Genes that code for the production of proteins that can bind to DNA and modify the action of genes. • Many are active only during certain stages of development.

  4. Homeobox Genes (Hox genes) • An evolutionarily ancient family of regulatory genes (highly conserved) that directs the development of the overall body plan and the segmentation of body tissues. Homeobox mutation

  5. Cell Division • Cell division results in production of new cells. • During cell division: • Cells are involved with normal cellular and metabolic processes. • The cell’s DNA becomes tightly coiled. • DNA is visible under a microscope as chromosomes.

  6. Chromosome Structure • A chromosome is composed of a DNA molecule and associated proteins. • During normal cell functions, chromosomes exist as single-stranded structures. • During cell division, chromosomes consist of two strands of DNA joined at the centromere. • Since the DNA molecules have replicated, one strand of a chromosome is an exact copy of the other.

  7. Chromosomes and Genetics • Each species is characterized by a specific number of chromosomes (see chart on pg. 59). • Humans have 46 chromosomes. Housefly 12 Corn 20 Humans 46 Chicken 78

  8. Types of Chromosomes • Autosomes - govern all physical characteristics except sex determination. • Sex chromosomes - X and Y chromosome. • Mammal females have two X chromosomes. • Mammal males have one X and one Y chromosome.

  9. Mitosis • Mitosis is cell division in somatic cells. • Mitosis occurs during growth and repair/replacement of tissues. • The result of mitosis is two identical daughter cells that are genetically identical to the original cell. • Here’s the steps…

  10. Mitosis • The cell is involved in metabolic activities. • DNA replication occurs, but chromosomes are not visible.

  11. Mitosis • The nuclear membrane disappears, and double-stranded chromosomes are visible.

  12. Mitosis • The chromosomes align themselves at the center of the cell.

  13. Mitosis • The chromosomes split at the centromere, and the strands separate and move to opposite ends of the dividing cell.

  14. Mitosis • The cell membrane pinches in as the cell continues to divide. • The chromosomes begin to uncoil (below).

  15. Mitosis • After mitosis is complete, there are two identical daughter cells. • The nuclear membrane is present, and chromosomes are no longer visible.

  16. Meiosis • Cell division in specialized cells in ovaries and testes. • Meiosis involves two divisions and results in four daughter cells, each containing only half the original number of chromosomes. • These cells can develop into gametes.

  17. Problems with Meiosis • In order for fetal development to occur normally, the meiotic process needs to be exact • If chromosomes or chromosome strands do not separate during either of the two divisions, serious problems can develop • Failure to separate is called nondisjunction

  18. Recombination • Sometimes called crossing over; the exchange of genetic material between partner chromosomes during meiosis.

  19. Mitosis

  20. Meiosis

  21. Evolutionary Significance of Meiosis • Meiosis and sexual reproduction are highly important evolutionary innovations. • Meiosis increases genetic variation at a faster rate than mutation. • Offspring in sexually reproducing species represent the combination of genetic information from two parents.

  22. Recombinant DNA Technology • A process in which genes from the cell of one species are transferred to somatic cells or gametes of another species. • Human genes inserted into bacterium produce genetically-needed material like Insulin. • Genetic manipulation…

  23. Clones • Organisms that are genetically identical to another organism. • The term may also be used in referring to genetically identical DNA segments, molecules, and cells.

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