Unit 4: Genetics (part A) Ms. Whipple Brethren Christian High School

Genes, Chromosomes and Cell Division Within a species, there are many similar characteristics among the organisms. These similar traits (like hand shape, eye placement) are called Species Characteristics. Even though there many similar traits, organisms also have distinguishing features (hair color, body build, eye color) and these are called Individual Characteristics. Species and Individual Characteristics are controlled by Genes passed down from parents to children. The degree these genes are expressed depends on the environment (i.e. a person with the genetic potential to be 6 ft. may not actually be that tall if he/she had a poor diet from birth)

The Mechanism of Heredity Genetics: the study of heredity! It has been studied since ancient times but did not fully reach modern genetics until the discovery of the DNA molecule in 1953. Genes: A section of DNA that produces a protein (or part of a protein) that causes a particular trait. Humans have such a large amount of genes and DNA that if the DNA code from one human cell were put on paper, the info would take up 1000 books , each with 600 pages!!

DNA stands for deoxyribose nucleic acid 2 DNA stands for deoxyribose nucleic acid This chemical substance is present in the nucleus of all cells in all living organisms DNA controls all the chemical changes which take place in cells The kind of cell which is formed, (muscle, blood, nerve etc) is controlled by DNA The kind of organism which is produced (buttercup, giraffe, herring, human etc) is controlled by DNA

DNA is a very large molecule made up of a long chain of sub-units 3 DNA is a very large molecule made up of a long chain of sub-units The sub-units are called nucleotides Each nucleotide is made up of a sugar called deoxyribose a phosphate group -PO4 and an organic base

The most common organic bases are 5 The bases The most common organic bases are Adenine (A) Thymine (T) Cytosine (C) Guanine (G)

Brethren Christian High School 6 Nucleotides The deoxyribose, the phosphate and one of the bases Combine to form a nucleotide adenine deoxyribose PO4 It is the phosphate group which gives DNA its acidic properties Biology - Ms. Whipple

7 PO4 sugar-phosphate backbone + bases A molecule of DNA is formed by millions of nucleotides joined together in a long chain

In fact, the DNA usually consists of a double 8 In fact, the DNA usually consists of a double strand of nucleotides. These nucleotides are bonded loosely together with Hydrogen Bonds Review: What is a Hydrogen Bond? The sugar-phosphate chains are on the outside and the strands are held together by chemical bonds between the bases

The bases always pair up in the same way 10 The bases always pair up in the same way Adenine forms a Hydrogen bond with Thymine Adenine Thymine and Cytosine forms a Hydrogen bonds with Guanine Cytosine Guanine

The paired strands are coiled into a spiral called 13 The paired strands are coiled into a spiral called A DOUBLE HELIX

14 THE DOUBLE HELIX bases sugar-phosphate chain

5A-1 The Mechanism of Heredity Chromosomes: Long strands of DNA that contain genes. They are found in pairs (one from mother and one from the father). During non-dividing activity, they can be found as chromatin material tightly coiled around histones (proteins that support and hold DNA). Karyotype: a complete set of chromosomes for an individual

5A-1 The Mechanism of Heredity Structure of Chromosomes!!! Chromatid: when a chromosome is ready for division if duplicates itself into 2 identical halves. Each half is a Chromatid. Centromere: The area on the chromosome that joins the chromatids. Homologous Chromosomes: a pair of chromosomes. Humans have 23 Homologous pairs of chromosomes. Each chromosome in the pair is called a Homologue.

5A-1 The Mechanism of Heredity When a cell has homologous pairs of Chromosomes it is called Diploid and is abbreviated 2n. These are normal cells. When a cell does not have homologous pairs of chromosomes it is called Haploid and is abbreviated by n. These are sex cells as they carry half the genome of the individual.

5A-2 Cell Division The Cell Cycle: The repeating cycle of events in the life of a cell. It is divided into 3 major phases: Interphase: The cell spends most of its time in interphase and it is the major growth phase. The cell is increasing in size and making new organelles. This phase ends when the cell is fully mature. Mitosis: The division of nuclear material so that each new cell has a complete set of DNA. Cytokinesis: The division of the cytoplasmic contents – organelles, proteins, membranes, etc.

5A-2 Cell Division

5A-2 Cell Division MITOSIS!!! Mitosis is the division of the nuclear material into two complete sets for the two new cells. Mitosis occurs in 4 phases Prophase Metaphase Anaphase Telophase

5A-2 Cell Division Prophase: as the cell prepares to divide, the chromosomes become short and thick (they also become visible under a microscope).The nuclear membrane disintegrates and the nucleolus disappears. Also, microtubules begin to make a mitotic spindle. The spindle fibers then attach to the centromere of the chromosomes .

5A-2 Cell Division Metaphase: The chromosomes go the center of the cell. They line up along the equitorial plane bisecting the spindle.

5A-2 Cell Division Anaphase: Enzymes break down proteins in centromere and sister chromatids separate. They are then pulled to the opposite poles of the cell.

5A-2 Cell Division Telophase: A nucleus begins to form around the separate daughter nuclei. The mitotic spindle disappears. Mitosis is now over.

5A-2 Cell Division Cytokenesis: This is the final stage of the cell cycle. In animal cells, the cytoplasmic material is split and the membrane pinches off to form two daughter cells. In plant cells, a cell plate is formed that will become a new cell wall between the two daughter cells.

Metaphase

5A-2 Cell Division Uses of Mitosis!! Mitosis is used for growth, repair, and replacement of cells in most organisms. The average human has 10 trillion cells that are all the result of repeated Mitosis from the original one cell embryo. Mitosis can also be used for asexual reproduction in many organisms. There are a few forms of asexual reproduction: Fragmentation: Breaking a colony into two pieces and using mitosis to replace the missing cells. Colonial organisms, many algae, fungi, and bacteria reproduce this way. Budding: a new organism is formed on the side of the parent organism. Yeast reproduces this way. Spores: organisms use mitosis to make spores which are then spread around. These spores have a hard, protective covering and can remain alive for long periods of time in unfavorable conditions without dying or growing. Mosses, molds and fungi reproduce this way.