Mendel & the Gene Idea

 Bred garden peas in monastery  Character – heritable feature  Trait – variant for a character  Cross-pollinated true-breeding varieties of pea plant (hybridization)  “Parents” – P generation  Offspring – F 1 generation  F 1 offspring – F 2 generation Gregor Mendel – Pea-rific!

 P: purple & white  F 1 : all purple  F 2 : 75% purple 25% white  How?  Hypothesis… Mendel’s Work

1.Alternative versions of genes (alleles) account for variations in inherited characteristics 2.For each character, you inherit one allele from each parent Mendel’s Work

3. If the two alleles differ…  Dominant allele - fully expressed  Recessive allele – no noticeable effect on appearance Mendel’s Work

4. Two alleles segregate (separate) during gamete production  Each gamete gets one  This is the Law of Segregation  Determined by Punnett square Mendel’s Work

 Homozygous – have two of same allele  Heterozygous – two different alleles  Phenotype – physical appearance & physiological makeup  Genotype – genetic makeup  Testcross – test unknown with homozygous recessive to determine unknown genotype Vocabulary to know

Test Cross

 Each different pair of alleles will segregate independent of any others during gamete formation  F 1 produced for single character – monohybrid  F 1 produced for two characters – dihybrid  Result of dihybrid cross - 9:3:3:1 Law of Independent Assortment

 Rule of Multiplication  Probability two independent events happen at same time – multiply each probability  Coin: H & H = ½ x ½ = ¼  F 1 is Pp – chance F 2 is pp?  Gamete has P = ½  Gamete has p = ½  ½ x ½ = ¼ Math Rules

 Dihybrid crosses  YyRr x YyRr  Probability of YYRR  Do a Punnett square for Yy x Yy  Get ¼  Do another for Rr x Rr  Get ¼  ¼ x ¼ = YY AND RR = 1/16 Math Rules

 Rule of Addition  Probability of event that can occur two or more different ways – add sum of separate probabilities  Example: cross two Heterozygous for flower color  probability that the offspring is heterozygous?  1)Mom’s recessive egg with dad’s dominant sperm – ¼  2)Dad’s recessive sperm with mom’s dominant egg – ¼  #1 OR #2  ¼ + ¼ = ½ Math Rules

 Incomplete Dominance  F 1 hybrids have intermediate characteristics  Ex: snapdragons  Not blending Mendel & Beyond

 Codominance  Two alleles in hybrid are BOTH expressed  Ex: blood types Mendel & Beyond

 Multiple Alleles  Blood type  A, B, AB, O  Three alleles – I a, I b, i  Presence or absence of carbo on surface  Wrong blood type – agglutination Mendel & Beyond

 Quantitative characters  Characters that vary along a continuum  Ex: human skin color  Indicates polygenic inheritance  Additive effect of two or more genes on single phenotypic character  Nature vs Nurture  Both often have an effect on gene expression Mendel & Beyond

 Chart with a pedigree Human Inheritance

 Recessively Inherited Disorders  Need homozygous recessive to have  Heterozygous are carriers & can pass on to offspring  Ex: Cystic fibrosis, Tay-Sachs, sickle-cell disease  Read details in text Human Inheritance

 Dominantly Inherited Disorders  Achondroplasia (dwarfism), cluster headaches  Affects homozygous dominant & heterozygous  If lethal, much less common – die before reproducing Human Inheritance

 If late-acting, can pass on dominant disorder  Ex: Huntington’s disease  Multifactorial Disorders  Genetics & environment play a role  Ex: diabetes, cancer, some mental illness Human Inheritance

 Fetal Testing  Amniocentesis  Chorionic villis sampling (CVS)  Ultrasound Technology