Introduction to Genetic Continuity

DNA (Deoxyribonucleic Acid) DNA is the hereditary material of the cell.

The Structure of DNA   DNA is a double helix that looks very much like a spiral ladder. Its components include a sugar-phosphate backbone that makes up the rails of the so called “ladder” and 4 nitrogenous bases that join the two rails and can be compared to the steps of the ladder.

Although there are four nitrogenous bases (Adenine, Guanine, Cytosine, & Thymine) they may only be joined in a specific pairing sequence. Adenine is always bound with Thymine (2 hydrogen bonds)

Guanine is always bound with Cytosine (3 hydrogen bonds)

Nitrogenous bases are joined to one another by Hydrogen Bonding. The Nucleotide is the structural unit of DNA; it includes a Deoxyribose sugar, a phosphate group and a nitrogenous base.

Because every nucleotide has each component, the only difference lies in the nitrogenous base; therefore there are only 4 types of nucleotides. Furthermore, each nucleotide can only bond to the specific nucleotide that contains its Complementary Base Pair. (i.e. A-T or G-C)

Cell Division Asexual Reproduction Sexual Reproduction The production of offspring from a single parent Offspring inherit the genes of that parent only Reproduction without sexual intercourse Sexual Reproduction The production of offspring from the union of 2 sex cells, one different from each parent Genetic make-up of offspring is different from that of either parent Reproduction with sexual intercourse

Cell Division Fertilization Possible advantages of reproducing: the union of male and female sex cells (egg & sperm) Possible advantages of reproducing: Asexually? Sexually?

Cell Theory Recap All living things are made up of 1 or more cells. Cells come from pre-existing cells by cell division.

Principles of Cell Division Early studies show that a single cell makes two cells by an equal split of nuclear contents in a process call Mitosis Cytokinesis refers to the equal split of cytoplasm and the organelles contained within it Parent Cell is the cell that divides Daughter or Sister Cells are the 2 cells that result from the division (they are genderless)

Principles of Cell Division A cells genetic information is contained in the DNA (deoxyribonucleic acid) molecules in the nucleus The DNA molecules are found in structures called chromosomes A human body cell contains 46 chromosomes To prepare for mitosis the cell makes a duplicate copy of each DNA molecule this causes each chromosome to be doubled Replication & separation of duplicate chromosomes ensure that the daughter cells are genetically identical to each other and the parent cell Replication ensures future cell divisions because each daughter cell is a potential parent cell for the next generation

Principles of Cell Division How many chromosomes result after the cell division? All body cells have the same genetic information because all cells in the body are made from the same fertilized egg Muscle, brain, and heart all contain the same chromosomes Not all cells in the body have the same shape or perform the same functions Why do different cells do different jobs? How do specialized cells know which genes to use? The million dollar question…

The Chromosome The Chromosome Chromosomes carry the genetic information that defines the development and appearance of each individual organism. They are made up of both DNA and proteins    The Chromosomal Theory of Inheritance Chromosomes carry genes, which are the units of heredity. Each chromosome carries different genes. During meiosis, homologous chromosomes are split and each sex cell receives half the number of chromosomes from that parent’s somatic cells. Chromosomes assort independently during meiosis, which further contributes to the diversity of offspring.

The sequencing of nitrogenous bases (adenine, guanine, cytosine, and thymine) is the code for our genetic information. There is obviously tremendous variation in the arrangement of the estimated 3.5 billion base pairs of DNA. Every species has its own particular chromosome number. (Humans have 23 pairs => 46 chromosomes)

Having more chromosomes is not a sign of higher organism standing. Within the human 46 chromosomes are an estimated 30,000 genes. Humans have 22 pairs of Autosomes and 1 pair of Sex Chromosomes.

The Cell Cycle Sequence of events from one cell division to another Cycle doesn’t pause after each phase, it is a continuous process Nuclear division makes up only a small part of the cell cycle Interphase makes up the larger remaining portion of the cell cycle

Interphase Chromatin Centromere Sister Chromatids Genetic material during interphase Tangled fibrous complex of DNA and protein with a eukaryotic nucleus Centromere The structure that holds the chromatids together Sister Chromatids Chromosome and its duplicate attached to one another by a centromere The pair remain attached until separated during mitosis

Prophase Early Prophase Late Prophase Chromosomes continue to condense Chromosomes condense becoming shorter and thicker Centrioles move to opposite poles of cell Spindle fibers start to form Centrioles are small protein bodies that are found in the cytoplasm of animal cells Spindle fibers are protein structures that guide chromosomes during cell division Late Prophase Chromosomes continue to condense Centrioles assemble and spindle fibers attach to centromeres of chromosomes Nuclear membrane starts to dissolve

Metaphase Chromosomes line up at the equatorial plate Nuclear membrane completely dissolves

Anaphase Centromeres divide forming chromosomes (before they were chromatids) Move to opposite poles of cells Identical set of chromosomes moves to each pole

Telophase Chromosomes lengthen again Spindle fibers disappear Nuclear membrane forms around chromosomes Human have 46 unique chromosomes in each new nucleus

Cytokinesis Cytoplasm starts to divide once chromosomes are at opposite poles of cell In animal cells, a furrow pinches off the cell into 2 parts In plant cells, a cell plate forms between the two chromatin masses. It eventually develops into a cell wall.