3.0 DNA is the Inherited Material Responsible for Variation

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1 2.2 Asexual and Sexual Reproduction Homework: p. 29 #1-3 p. 36 #1-6 Create a table that looks like this: Read pages and fill in your table. Asexual Reproduction Sexual Reproduction Advantages Disadvantages Why is it an advantage for some species to be able to reproduce asexually and sexually? 3.0 DNA is the Inherited Material Responsible for Variation What do DNA and a set of books or enclopedias have in common?

2 October 06, DNA - Transmitter of Genetic Code DNA - Deoxyribonucleic Acid - DNA is the molecule responsible for storing all the information that makes us who we are Oswald Avery - All living things contain DNA - The Genetic Code is made up of four different chemicals: (G = guanine, C = cytosine, A = adenine, T = thymine) - The same genetic code (or language) is used for all living things on earth James Watson and Francis Crick 3.1 DNA - Transmitter of Genetic Code In most organisms, DNA is found in the nucleus of the cell and it is highly organized. An encyclopedia analogy is useful when describing how DNA is organized: DNA DNA is written in the Genetic Code which uses 4 different chemicals (A, C, T, G) Encyclopedias Encyclopedias are written in the English Language which uses 26 letters

3 3.1 DNA - Transmitter of Genetic Code DNA Encyclopedias The Human genome is arranged into chromosomes. Each cell contains 23 pairs of chromosomes. (total = 46) One set of chromosomes came from each parent Different organisms have different numbers of chromosomes (not related to the complexity of the organism) Encyclopedias are arranged into volumes (usually about 23) different books) A person can own two sets of encyclopedias - the information will mostly be the same in both sets 3.1 DNA - Transmitter of Genetic Code DNA Encyclopedias Each chromosome is divided into genes. Humans have about 30,000 genes which works out to about 1,300 genes per chromosome Because organisms have two sets of chromosomes, they also have a pair of each gene. Each volume (book) is divided into sections If you have two sets of encyclopedias, you will have two copies of the same information

4 3.1 DNA - Transmitter of Genetic Code DNA Encyclopedias Organisms have two copies of each gene which may be the same or different. Different versions of a gene are called alleles If you have two sets of encylopedias, the information in each, although similar, may be slightly different. 3.1 DNA - Transmitter of Genetic Code For example: Widows Peak Widows Peak This chromosome has three genes on it for hairline, blood type, and eye colour. Type A Blood Type B Blood You can see there are different "versions" or alleles of each gene. Brown Eyes Blue Eyes Every individual has a pair of genes - they may be the same alleles as in hairline here, or they may be different alleles as in blood type and eye colour

5 Homework: p.45 #2-4, 8, Cell Division Why do cells divide? Cell Division Bean Germination Does growth mean the same thing for fish as it does for bacteria?

6 3.2 Cell Division 46 There are 2 types of cell division: Mitosis Purpose: Growth & Repair Daughter Cells: Identical to parent cells "92" Cell Division 46 There are 2 types of cell division: Meiosis Purpose: Produce gametes Daughter Cells: Half the number of chromosomes of the parent cell "92" Gametes:

7 3.2 Cell Division Organism Number of Number of Number of Number of pairs chromosomes in chromosomes in chromosomes in of chromosomes a body cell a gamete a zygote in a body cell Cabbage 18 Black Bear 76 Human 23 Tomato Cell Division What is Cancer: Cancer: Uncontrolled Cell Growth Cancer Cell Growth Henrietta Lacks Homework: p.48 #1-3, 6, 7, 8

8 October 06, 2011 The dobermann sub-species was bred in 1890 by Karl Friedrich Louis Dobermann to help protect him while he was collecting taxes. Purebred German Pinscher Purebred Beauceron What does purebred mean? What is a hybrid? Dobermann Pinscher Purebred: An organism that consistently produces offspring with the same characteristics Purebred organisms are homozygous (they have the same alleles) Ex. There are two alleles for the ability to roll your tongue: R = can roll your tongue r = can't roll your tounge Homozygous individuals would have either two copies of the R allele (RR) or two copies of the r allele (rr)

9 Hybrid: An organism that is the result of a cross between two different purebred parents. Hybrid organisms are usually heterozygous (they have two different alleles) Ex. RR (homozygous mom) x rr (homozygous dad) In sexual reproduction, offspring receive one allele from each parent (determined at random) Rr (heterozygous offspring) Do you think this person will be able to roll their tongue or not? Alleles may be considered 'dominant' or 'recessive'. The dominant allele is represented by an upper case letter and the recessive allele by a lower case letter. Dominant Allele Detached Earlobes in humans (E) White wool in sheep (W) Purple pea flowers (F) Recessive Allele Attached Earlobes in humans (e) Black wool in sheep (w) White pea flowers (f) Would an individual with EE have attached or detached ear lobes? Would a sheep with ww have white or black wool? Would a pea plant with Ff have purple or white flowers? Would an individual with Ee have attached or detached ear lobes?

10 Every organism has two copies of each gene and only one is passed on to their offspring. If a purebred purple flowered pea plant (FF) is cross-polinated with a purebred white flowered pea plant (ff), what will the offspring look like? F F f f What if two purple pea plants with different alleles (Ff) are cross-pollinated? What will the offspring look like? Ff Ff F or f F or f 3 Combinations are possible: FF Ff ff Are all of these possibilities equally likely?

11 A punnett square is a tool that can be used to determine the probabilities in the offspring. In the cross to the right, what fraction of the offspring will have purple flowers? Male: Ff Female: Ff What about white flowers? What fraction would be homozygous? What fraction would be considered heterozygous? Possible Female Gametes Gametes F f Possible Male Gametes F f Practice 1: Practice 2: Male: FF Female: Ff ff FF Gametes Possible Male Gametes Gametes Possible Female Gametes

12 Practice 3: More Practice: Assuming white wool is dominant to black wool, what will the offspring of a purebred white sheep and a black sheep look like? ff Ff Make your own punnett square! What percentage of the offspring will be: white? Assuming smooth pea seeds are dominant to wrinkled pea seeds, what would the seeds look like if two "hybrid" pea plants are crossed? purple? homozygous? heterozygous? Homework: Patterns of Inheritance Worksheet Not all traits follow patterns of dominance & recessiveness: Ex. Snapdragon flowers use something called "incomplete dominance" If it was a dominant / recessive trait, the offspring would be either red or white... but Incomplete dominance results in blended traits