1. Chapter 10: Patterns of Inheritance

2. Mendel’s Experimental Procedure Gregor Mendel is an Austrian Monk Observed and work with 22 varieties of garden pea plants, Pisum sativum True-breeding: when the flower self- pollinated The offspring will be like the parent plants and like each other. o Particulate theory of inheritance: characteristics are passed from one generation to the next through discrete particles (genes) that retain their ability to be expressed, even though they may not appear in every generation Inheritance involves the reshuffling of the same genes from generation to generation http://www.webref.org/anthropology/p/particulate_theory_of_inheritanc.htm

3. Trait

4. One-Trait Inheritance One trait was chosen to be observed In this case, height o P generation or the original parents are either tall (TT) or short (tt) o F 1 generation is the first-generation offspring o F 2 generation is the second-generation offspring o Punnet Square: shows every possible combination of gametes the offspring may inherit o A testcross between F 1 generation tall plants with true-breeding short plants resulted in a 1:1 ratio Indicating that the factors segregate when gametes are formed He arrived at the law of segregation, which states: Each individual has 2 factors for each trait The factors segregate during the formation of the gametes Each gamete contains only one factor from each pair of factors Fertilization gives each new individual 2 factors for each trait

5. Modern Genetics View Traits are controlled by alleles (alternate forms of a gene) that are found on the chromosome at the gene locus The dominant allele has the ability to mask the expression of the recessive allele What process that we have learned so far helps explain Mendel’s law of segregation? Genotype v phenotype Genotype refers to the alleles of an organism for a particular trait or traits - Homozygous refers to inheritance of 2 identical alleles - Heterozygous refers to inheritance of 2 different alleles Phenotype refers to the physical appearance of the individual

6. Two-Trait Inheritance Testcrossing of true-breeding plants that differed in two traits F 1 plants were crossed pollinated and F 2 generation was observed If the dominant factors (TG) always go together into the F 1 gametes and the recessive factors (tg) always stay together, then only 2 phenotypes will be observed in the F 2 plants If the 4 factors segregate into the F 1 gametes independently, then 4 phenotypes will be observed in the F 2 plants o Law of independent assortment: Each pair of factors segregates (assorts) independently of the other pairs All possible combinations of factors can occur in the gametes

7. Two-Trait Testcross Fruit flies Drosophila melanogaster are usually the favorite subject in studying genetics The wild type fly are crossed with a mutant fly An individual with dominate phenotype for both traits is cross with one having the recessive phenotype for both traits A dihybrid is an individual that is heterozygous for 2 traits (LlGg) When crossed with a homozygous recessive, it will give a phenotypic ratio of 1:1:1:1 What are the chances of an offspring with long wings and gray body? What are the chances of an offspring with short wings and gray body? o What will happen if the L_G_ fly is homozygous for both traits? o What will happen if the L_G_ fly is heterozygous for one trait but not the other? o The rule of multiplication: the chance of 2 (or more independent events occurring together is the product of their chances of occurring separately EX: coin toss

8. Mendel’s Laws and Meiosis Homologues separate independently so it does not matter which member of each pair goes into which gamete

9. Incomplete Dominance Incomplete dominance: inheritance pattern in which the offspring has an intermediate phenotype Ex: when a red-flowered plant and a white-flowered plant produce pink-flowered offspring When pink-flowered plants self-pollinate, ¼ is red, ¼ is white, and ½ pink o We can say that since only the dominant allele codes for a gene product, one allele of the product gives the intermediate result

10. Multiple-Allele Traits In ABO blood group, 3 alleles determine the presence or absence of antigens on RBCs Every individual has only 2 of the 3 alleles I A = A antigen on RBCs I B = B antigen on RBCs I = Neither A nor B antigen on RBCs I A and I B are dominant over I Type A blood (I A I A, I a i) Type B blood (I B I B, I B i) Type O blood (ii) o Codominance : Inheritance pattern in which both alleles of a gene are equally expressed in a heterozygote I A and I B are fully expressed in the presence of each other Type AB blood (I A I B)

11. Polygenic Inheritance A trait is governed by two or more sets of alleles Copies of allelic pairs are located on many different pairs of chromosomes Each dominant allele has a quantitative effect on the phenotype, and the effects are additive Multifactorial traits are those that are controlled by polygenes subject to environmental influences 1. white primroses above 32°C and red primroses at 24°C 2. Water buttercups have different appearance above and below water 3. Siamese and Himalayan rabbits have black fur only on the extremities where body heat is lost to the environment

12. Pleiotrophy A single gene has more than one effect Syndrome: a group of symptoms that appear together caused by a particular genetic mutation Marfan Syndrome Due to production of abnormal connective tissue Mutated gene (FBN1) on chromosome 15 that make functional protein, fibrillin Essential in the formation of elastic fibers in connective tissue Symptoms: - Disproportionately long arms, legs, hands, feet - Weakened aorta - Poor eyesight Porphyria Caused by a chemical insufficiency in the production of hemoglobin Hemoglobin is necessary for functional RBCs Symptoms: - Photosensitivity - Strong abdominal pain - Port-wine-colored urine - Paralysis Members of the British royal family suffered from this disorder

14. Sex-Linked Inheritance Y chromosome contains only 80 genes (most are concerned with sex difference) SRY is not present on the X chromosome o X chromosome contains nearly 2,000 genes (most not involving gender) o X-linked are genes that are carried on the X chromosome The Y chromosome is blank for these alleles Inheritance of a Y chromosome cannot offset the inheritance of an X-linked recessive allele Males always receive an X-linked recessive mutant allele from their female parent Heterozygous females are carriers (they do not exhibit a recessive trait, but can pass on the recessive allele) Males cannot be carriers What can you deduce from this?

15. Inheritance of Linked Genes Alleles that occur on the same chromosome form a linkage group and they are usually inherited together However, the daughter chromosomes would have recombined alleles if crossing-over occurs between 2 alleles Recombination occurs infrequently The closer the 2 genes are together, the less likely they are to cross over Scientist use linkage data to construct a chromosome map, which shows the relative distance between the gene loci on a chromosome 1% of crossing-over equals one map unit