Genes & Traits  Gene – section of DNA that encodes a protein, resulting in/affecting a trait  Genetics – study of heredity, or how organisms inherit characteristics from parents  Trait – a characteristic of an organism; *genetic traits are inherited* Ex.: hair color, enzymes, size (potential), etc.

Genetics (ch. 9 & 12) There once was an Austrian monk who liked peas and was very good at math…

Gregor Mendel’s (1860s) Pea Plant Experiments Mendel crossed pea plants with different traits and observed the results in the offspring.

Mendel’s Pea Plant Experiments Dominant Recessive When two purebreds were crossed, recessive traits disappeared in the F1, reappeared in the F2. Mendel hypothesized that each trait was controlled by a “factor” and that there must be at least two forms of each “factor.” Why pea plants? short life cycle traits easily observed, no blending self-fertilize easily, easy to manipulate/fertilize Most genetic traits in nature are not so easy to distinguish.

Genes & Traits  Allele – one form of a gene Dominant allele – expressed whenever present, represented by a capital letter; ex.: B for brown hair color Recessive allele – only expressed when two copies are present; represented by a lower case letter; ex.: b for blonde hair color  A diploid organism inherits two alleles (one from each parent) for every genetic trait  Genotype - the set of alleles for a trait or all traits of an organism

Genotypes Purebred/Homozygous Organism that has only one form of a gene/trait (same allele received from both parents) Hybrid/Heterozygous Organism that has two forms of a gene/trait (different alleles received from each parent) BB – homozygous dominant genotype bb – homozygous recessive genotype Bb – heterozygous genotype

Phenotypes  Phenotype - the trait the organism actually expresses; ex.: having brown hair, or having blonde hair  The phenotype may show on the appearance of the organisms or not; ex.: being able to digest lactose is a phenotype that does not “show”  A phenotype results from the expression of a gene  a protein is made that affects the phenotype PhenotypePossible Genotypes Dominant Ex.: brown hair BB or Bb Recessive Ex.: blonde hair bb

When we look at the genotypes in each generation:

Check yourself: Discuss with your partner: –Can you find an example of a dominant trait in one of you? –Can you find an example of a recessive trait in one of you? –What is the phenotype for each trait? –What are the possible genotypes for each trait?

(not in notes) GGgg Gg GG or Gg gg

Mendel’s Laws (modern form)  Law of Segregation - Gene pairs separate when gametes form: Half of an organisms gametes contain one gene from a homologous pair, half contain the other gene  Law of Independent Assortment - Different traits are inherited independently: Genes for different traits segregate into gametes randomly and independently from each other  new combinations You can inherit your father’s eyes and your mother’s smile!  Law of Dominance - Dominant alleles are expressed, recessive alleles can be hidden: Hybrid pea plant: Py  P (purple flowers, dominant) is expressed, p (white flowers, recessive) is hidden

Walter Sutton’s (1903) Chromosome Theory of Heredity  Sutton (American) noticed that chromosomes behaved like Mendel’s factors  Sutton’s Chromosome Theory of Heredity states that the material of inheritance is carried by the genes in chromosomes  Theodor Boveri (German) reached the same conclusion independently

Predicting the Phenotype of Offspring: Using a Punnett Square for One Trait *Monohybrid cross * Genotypic Ratio: Phenotypic Ratio: YY : Yy : yy 1 : 2 : 1 Yellow : Green 3 : 1

Predicting the Phenotypes of Offspring: Using a Punnett Square for Two Traits *Dihybrid cross * Phenotypic Ratio: 9 : 3 : 3 : 1 Round & Yellow : Round & Green : Wrinkled & Yellow : Wrinkled & Green

Inheritance Pattern - Autosomal Recessive Trait Genotypes? 

Autosomal Recessive Traits in Humans (know all traits in bold print)  Albinism – skin, hair, eyes lack melanin (pigment), sensitive to sunlight  Tay-Sachs – fat deposits prevent normal development of brain in children  Cystic Fibrosis – lungs damaged from excessive mucous, respiratory problems  Sickle Cell Anemia – red blood cells misshaped, clog capillaries  circulation problems; many phenotypic effects, depending on where in the body the blockage occurs Click for Albino - pictures

Inheritance Pattern - Autosomal DominantTrait Genotypes?  (could also be DD)

Autosomal Dominant Traits in Humans (know all traits in bold print)  Dimples, freckles, widow’s peak, farsightedness, broad lips, polydactyly (extra fingers/toes)  Dominant disorders are less common than recessive disorders because carriers (heterozygotes) are affected and may die before reproducing Ex.: Huntington disease – deterioration of nervous system, especially brain

Inheritantce Pattern Autosomal Dominant (not in notes)  Variable Expression: Some people have milder / more severe symptoms than others -- Age of onset and organs affected may vary  Reduced Penetrance: Some people have the dominant gene but do not have any symptoms Ex.: autosomal dominant cancer susceptibility

Pedigrees Not always labeled

Pedigrees & Genetic Counseling People with PKU (phenylketonuria) lack an enzyme needed to break down the amino acid phenylalanine, which is found in milk and other foods. Accumulation of the amino acid in the body leads to developmental disabilities and death if not treated. Individual II-4 has PKU

From H. Genetics Lab : Pedigree -- Dominant or Recessive trait? Not always clear… Trait appears in every generation  More likely to be a dominant trait, but cannot be sure. * Notice that the hybrid individuals are not identified. *

Pedigree -- Dominant or Recessive trait? Not always obvious… Trait skips a generation or more  More likely to be a recessive trait, but cannot be sure. * Notice that the hybrid individuals are not identified. *

When can we tell for sure if the trait is dominant or recessive? Do the Pedigree Analysis to find out!

Pedigree A Parents have the trait, child does not. The trait is dominant: the “non-trait” phenotype is recessive. Xx xx Xx xx Xx Xx or XX MONOHYBRID CROSS

Pedigree B Parents don’t have the trait, child does. The trait is recessive: the allele is “hidden” in the parents. xx xx (all) xx MONOHYBRID CROSS XX or Xx Xx All Xx XX or Xx XX or Xx XX or Xx