BIOLOGY - CLUTCH CH.14 - MENDELIAN GENETICS.

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2 CONCEPT: MENDEL S EXPERIMENT Gregor Mendel designed an experiment to study inheritance in pea plants. Character a feature that can be inherited, and shows variation between individuals Trait each version of a character The pea plant was a great model organism, an organism that is studied to elucidate widely applicable phenomena. True breeding an organism that, through self-fertilization, always produces offspring with the same trait of interest Hybridize the cross-pollination of two true breeding organisms Page 2

3 CONCEPT: MENDEL S EXPERIMENT Parental Generation (P): true breeding parents are hybridized First Filial Generation (F1): the hybrid offspring of the parental generation, which are self-pollinated Second Filial Generation (F2): the offspring from self-fertilized F1 plants Mendel noticed that the F2 traits for the same character were always found in the same ratio. Allele a version gene Traits are determined by two alleles, one from each parent, at the same gene locus. Dominant Allele determines organisms appearance Recessive Allele has no notable influence on organisms appearance Page 3

4 CONCEPT: MENDEL S EXPERIMENT Phenotype the observable traits of an organism Genotype the genetic makeup of an organism (genotype Heterozygous two different alleles for the same gene Homozygous two of the same allele for a gene phenotype) Monohybrid Cross cross between monohybrids (heterozygous for one character), like those in F1 Punnett Suare a diagram representing the potential genetic outcomes of a cross Reciprocal Cross a cross used to determine the influence of parental sex on inheritance Law of Segregation two alleles for a given character separate during gamete formation, and go to different gametes Page 4

5 PRACTICE: 1. Phenotype ratio: Genotype ratio: 2. Phenotype ratio: Genotype ratio: Page 5

6 PRACTICE: 3. Phenotype ratio: Genotype ratio: 4. What did Mendel name the generations of plants in his experiments? The allele is to, the allele. 6. An organism that always produces offspring with the same trait of interest is said to be 7. What process accounts for Mendel s Law of Segregation? Page 6

7 CONCEPT: INDEPENDENT ASSORTMENT Mendel designed an experiment to examine the inheritance of two characters. Dihybrid Cross cross of a dihybrid (heterozygous for two characters) YR YR Yr yr yr Yr yr yr Independent Assortment alleles for different characters sort independently of each other during gamete formation. During meiosis, genes on different chromosomes will divide between daughter cells independently of each other. Test Cross a method to determine the genotype of a phenotypically dominant plant Page 7

8 CONCEPT: INDEPENDENT ASSORTMENT Multiplication Rule: to determine the probability of two events both happening, multiply their individual probabilities. Addition Rule: to determine the probability of either of two mutually exclusive events happening, add their probabilities. Dihybrid cross probability: Page 8

9 PRACTICE: 1. What is the probability that the offspring of a dihybrid cross (YyRr x YyRr) will be yellow? 2. What is the probability that the offspring of a dihybrid cross (YyRr x YyRr) will be green and wrinkled? 3. What is the probability that the offspring of a dihybrid cross (YyRr x YyRr) will be yellow or round? Page 9

10 CONCEPT: EXTENSIONS TO MENDEL Alleles can show varying degrees of dominance: Complete dominance the effect of one allele completely masks the other Incomplete dominance heterozygous phenotype is distinct from homozygous phenotypes, and is often intermediate Codominance the effect of both alleles is seen in the phenotype Page 10

11 CONCEPT: EXTENSIONS TO MENDEL Most genes have multiple alleles, like the ABO blood groups. Pleiotropy when one gene influences multiple phenotypic traits. Polygenic traits when multiple genes influence one trait The environment can have an impact on phenotype. Multifactorial character many factors influence phenotype, like genotype and environment Epistasis the expression of a gene at one locus alters the expression of a gene at another locus Page 11

12 PRACTICE: 1. A species of bird is known to have black beaks, yellow beaks, or spotted beaks, with patches of black and yellow. There is a single gene locus that determines beak pigment, and the most likely mode of inheritance is? a. Complete dominance b. Incomplete dominance c. Codominance d. Partial dominance 2. A species of fish have tails that vary in size. It is found that genes at 2 loci, as well as diet, influence tail size. This trait is an example of? a. Pleiotropy b. Polygenic inheritance c. Epistasis d. Multifactorial character 3. A ratio of 9:3:4 is produced during a heterozygote dihybrid cross when one gene pair interacts to control the expression of the second gene pair. This interaction is called? a. Dominance b. Epigenetics c. Epistasis d. Recessive Page 12

13 CONCEPT: GENETIC COUNSELING Pedigree a record of descent, mapping out inherited traits Mode of transmission whether a trait is autosomal or sex-linked, and the type of dominance of the allele Autosomal recessive pedigree: Carriers individuals who carries the recessive allele for a trait, but does not display the trait Page 13

14 CONCEPT: GENETIC COUNSELING Autosomal dominant pedigree: X-linked pedigree: Page 14

15 CONCEPT: GENETIC COUNSELING Genetic counseling relies on Mendel s rules for inheritance and probability to help parents avoid genetic disorders. Amniocentesis a type of fetal genetic testing that samples the amniotic fluid to test for markers of certain diseases Chorionic villus sampling (CVS) a type of fetal genetic testing that samples tissue from the placenta, which is derived from the fetus, and has the same genotype as the fetus Page 15