Ch. 12 Mendel, Genes & Inheritance RUSSEL AP BIOLOGY RHODES

Why it Matters… DNA contains regions called genes Genes code for proteins or polypeptides If gene sequence is altered or incorrect then protein could also be ◦altered or ◦ineffective or ◦actually defective Sickle Cell Anemia (discovered microscopically early 1900) ◦Hemoglobin subunit (4) – one single amino acid difference ◦Cells misshaped ◦Can’t carry oxygen ◦Can lead to organ damage and death

12.1 The Beginning of Genetics – Mendel’s Garden Peas Gregor Mendel ◦Excellent (lucky) choice of research organism = Garden Peas ◦Easy to grow and house ◦Easy to observe traits ◦Cheap/ common Qualitative analysis ◦Professor of mathematics and Biology at University of Vienna; Statistics; Documentation Traits are passed from parents to offspring ◦Heritable factors now called genes and alleles Predictable ratios and combinations ◦All chosen trait were true breeding Mendel’s conclusions ◦1. pairs of traits in individual2. dominant and recessive ◦3. Segregate in gametes…. Didn’t know about DNA, genes, chromosomes or even gametes ! Test crosses Walter Sutton … Flies; noted similarities between “hereditary factors” and “chromosomes” and “meiosis” 200 years later

Gregor Mendel Mid 1800s – people believed in Blending Theory of Inheritance Monastary – gardens with peas; climate, generation time, protein, traits Math and science – professor at University of Vienna Pea plants – serendipitous choice; Pisum sativum ◦Good organism for genetics study because: ◦Easy to grow, self pollinate, true breeding, cross pollinated, observable traits, cheap/ common, ◦ short generation time, large number of offspring, “Father of Genetics” ◦Fundamental principles governing inheritance ◦Segregation of alleles ◦Independent assortment of homologous chromosomes

Mendel observed 7 pea plant traits turns out peas have 7 pairs of chromosomes and there was one trait on each chromosome and all were completely dominant- recessive

Initial Crosses Purple X white = all purple White X purple = all purple F2 cross = 3 purple: 1 white Idea of dominant/ recessive Idea of parents having 2 “factors” which we now call alleles Male Female

Important Vocabulary Self pollinating Cross pollination True breeding Reciprocal cross Male Female Gamete Zygote

Vocabulary P generation F1 generation F2 generation Alleles Principle of Segregation

Vocabulary Genotype/ Genotypic ratio Phenotype/ phenotypic ratio Homozygous/ homozygote Heterozygous/ heterozygote Monohybrid cross

Probability Rules PRODUCTSUM 2 or more different ways of obtaining the same results. Odds of a head and a tail ½ x ½ = ¼ head first then tail ½ x ½ = ¼ tail first then head ¼ + ¼ = ½ any combination of a head ◦ and a tail

Probability Rules ADDITION What is the chance of having 2 children and having a boy and a girl? (or flipping 2 coins and getting a head and a tail) HH, HT, TH, TT ¼ + ¼ = 2/4 = 1/2 What is the chance of having a boy or a girl? (what is the chance of flipping a head or a tail) ½ + ½ = 2/2 = 1 What is the chance of having 3 children and having all boys? (or flipping a coin 3 times and getting 3 heads) ½ X ½ X ½ = 1/8 If parents are AaBbCc X AaBbCc; (2 3 = 8 x 8) What is the chance of a child who is AABBCC? ¼ X ¼ X ¼ = 1/64 ( 1 of 64 boxes) A a B b C c A AA Aa B BB Bb C CC Cc a Aa aa b Bb bb c Cc cc MULTIPLICATION

Dihybrid Crosses Two traits (genes) simultaneously ** Law of Independent Assortment** Yellow seeds dominant to green (Y and y) Green pods dominant to yellow (G and g) Heterozygous yellow seeds in homozygous green pods X Heterozygous yellow seeds in yellow pods

12.2 Later Modifications and Additions to Mendel’s Principles The following are exceptions to Mendel’s Dominant – Recessive explanations ◦Incomplete dominance ◦Co-dominance ◦Multiple alleles ◦Epistasis ◦Polygenic inheritance ◦Pleiotropy

Incomplete dominance Trait expressed is part way between dominant and recessive Red X white flowers = PinkPink X Pink = ? RR X rr = RrRr X Rr = ….. R Rgenotypic ratio 4 Rr r Rr Rrphenotypic ratio 100% Pink r Rr Rr

Co – dominance (of Multiple Alleles) Both alleles of a gene are equally expressed Human ABO Blood Type A dominant to 0 (AA, A0) B dominant to 0 (BB, B0) 0 is recessive (00) And A and B are co dominant (AB)

Epistasis epi = on (like epidermis) and stasis = standing or steady (like homeostasis) ; “standing on” Genes interact ; 2 or more genes impact one phenotype The activity of one gene impacts the activity (expression) of another gene Coat color in Labrador retrievers = Black, Chocolate or Yellow B (BB, Bb and bb) = pigment color ◦Black dominant or chocolate recessive E (EE, Ee and ee) = deposition of pigment ◦Pigment (black or chocolate) or none (yellow)

Polygenic Inheritance “many genes” Several to many genes all contribute to a trait Bell curve distribution ( smooth or continuum) “quantitative traits” Human height Human skin color NOT blending Also impacted by environmental factors Tall vs not tall Tall, medium, short Bell curve distribution of many heights

Pleiotropy – single gene One single gene affects more than one characteristic of the organism Often related to a metabolic pathway disabilities PKU seizures skin and hair issues white fur Pigmentation blue eyes In cats deaf