Biology Gregor Mendel & Genetics

Who is Gregor Mendel? An Austrian monk who loved to garden Through study and breeding of pea plants he unlocked mysteries of heredity What is heredity?

Pea Plants Have 7 different traits Traits are found on genes—genes are separated into alleles Example:  Height gene has 2 alleles: short & tall  Seed color gene has 2 alleles: yellow & green

Rules of Heredity The Rule of Dominance: one allele is dominant to the other recessive allele  Dominant trait will not allow recessive trait to be displayed  Example: height—tall (T) is dominant to short (t)  Dominant alleles capitalized  Recessive alleles lower case

Rules of Heredity The Law of Segregation: the alleles for the same gene are separate and are inherited independantly of each other Example: Tt Gene for height with 2 alleles T t During meiosis, 1 allele can go With one gamete, the other goes to a second gamete

How did he figure all this out? True-breeding and cross-breeding Phenotype: the trait that is displayed—what you see Genotype: the gene combination that displays the phenotype Homozygous: 2 alleles for same gene are identical  Example: TT or tt Heterozygous: 2 alleles for same gene are different  Example: Tt

Examples TT is a homozygous genotype for height  Phenotype: tall Tt is the heterozygous genotype for height  Phenotype: tall tt is a homozygous gentoype for height  Phenotype: short

Breeding Definitions P 1 : parent generation F 1 : 1 st generation son or daughter F 2 : 2 nd generation son or daughter Monohybrid Cross: breeding 1 trait only Dihybrid Cross: breeding 2 traits at same time

Monohybrid Cross Mendel cross pollinated 2 plants:  (P 1 ) 1 short X 1 tall = (F 1 ) all tall Then crossed all tall F1 generation  (F 1 ) 1 tall X 1 tall = (F 2 ) 3 tall and 1 short  A phenotypic ratio of 3:1 This led to his Rule of Dominance

Dihybrid Cross 2 traits: shape of seeds, color of seeds  (P 1 ) 1 round/yellow seed X 1 wrinkled/green = (F 1 ) all round/yellow Then crossed all round/yellow F1 generation  (F 1 ) 1 round/yellow X 1 round/yellow = (F 2 ) 9 round/yellow, 3 round/green, 3 wrinkled/yellow, 1 wrinkled/green  A 9:3:3:1 phenotypic ratio This led to the Law of Segregation

LET’S PRACTICE! PUNNETT SQUARES

Genetics Outside The Box Not all traits follow a simple dominance vs. recessive rule For Example: 1.Codominance Blood types 2.Incomplete Dominance 3.Multiple Alleles 4.Polygenic Traits 5.Sex-linked Genes

Codominance Both alleles contribute to the phenotype No blending of phenotypic traits—both traits are displayed For Example:  White Chicken (WW) X Black Chicken (BB)  Results in a Black AND White chicken (WB)

Codominance: blood types There are 4 human blood groups: A, B, AB, O The alleles that code for these types are: I A, I B, i Rh Factor is a single gene with 2 alleles  (+) is dominant, (-) is recessive

Codominance: blood types PhenotypeGenotypeAntigen on RBC Transfuse to Transfuse from AI A I A or I A iAA, ABA, O BI B I B or I B i BB, ABB, O ABI A I B A&BABA, B, AB, O OiiNONEA, B, AB, O O

Codominance: blood types AB = Universal Recipient  Can receive from everyone O = Universal Donor  Can donate to everyone Rh factor example:  AB (+) means you are positive for the Rh allele, either homozygous or heterozygous  AB(–) means you are negative for the allele, homozygous recessive

Incomplete Dominance No allele is dominant over another Heterozygous phenotype is a blending of the 2 homozygous phenotypes For Example:  Four O’Clock Flowers  Red (RR) X White (WW)  Results in pink flowers (RW)

Multiple Alleles Genes that have more than 2 alleles Does not occur in one person, but throughout a population For Example:  Rabbits hair color Full, chinchilla, himalayan or albino

Polygenic Traits Traits controlled by two or more genes Genes may be on the same or different chromosomes Has a wide range of phenotypes For Example: human skin color

Sex-Linked Genes Sex always determined by Dad To be a girl you must have XX chromosomes To be a boy, you must have XY chromosomes Mom will always give an X, the second chromosome is determined by Dad

Karyotype: picture of grouped chromosomes

Sex-Linked Genes Genes located on an X or Y chromosome only The X chromosome is bigger, therefore it holds more genes Because males only have 1 X chromosome, even recessive disorders are expressed in men Examples: color-blindness, hemophilia, Duchenne Muscular Dystrophy

Common Genetic Disorders Chromosomal Disorders  Down Syndrome Codominant Disorders  Sickle cell anemia Dominant Disorders  Huntingtons’s Disease Recessive Disorders:  Albinism  Cystic fibrosis  PKU  Tay-sachs disease

Trisomy 21: Down Syndrome