Chapter 10 Introduction to Genetics

Why Study Heredity ? Studying heredity allows us to figure out what our children may look like… Studying heredity allows us to figure out the possible blood types of our children. Such information can mean life or death for an unborn child…

Why Study Heredity ? Studying heredity helps explain why males tend to be red/green colorblind much more frequently than females Why do men have a distinct pattern of balding, when women don’t ? Studying heredity helps us explain this occurrence

Why Study Heredity ? Studying heredity allows us to identify how certain terrible diseases are passed on from parents to children Studying heredity allows us to look for certain traits throughout our family tree

Introduction to Genetics Chapter 10.2

Gregor Mendel 1842 – Entered a monastery in Austria Worked in the garden of the monastery Raised pea plants 1851 – Entered University of Vienna to studied Math and Science Explained trends in pea plant data Mendel’s Principles

Pea Plants Pea plants reproduce through sexual reproduction Contain both male (anthers) and female (stigma) reproductive structures Pollination: pollen uniting with egg Pea plants are able to self- pollinate (pollinate themselves) Mendel’s Principles

Pea Plants Self-pollination male structures fertilize the female structures of the same plant Cross-Pollination male structures of a plant fertilize the female structures of another plant Mendel’s Principles

Mendel’s Experiments Mendel wanted to study the plants traits over many generations. Mendel controlled which plants fertilized which Mendel’s Principles

Mendel’s Experiments Mendel obtained purebreed, true-breeding plants Looked at 7 traits Mendel’s Principles

Mendel’s Experiments Crossed true breeding plants with contrasting traits. Crossed true breeding plants with contrasting traits. The trait not present in the F 1 generation seemed to “re- appear” in the F 2 generation The trait not present in the F 1 generation seemed to “re- appear” in the F 2 generation Mendel concluded that “factors” or genes must come in pairs ! Mendel concluded that “factors” or genes must come in pairs ! We call these “factors” alleles We call these “factors” alleles Mendel’s Principles

Mendel’s Results and Conclusions Dominant factor, or gene can mask a more recessive gene trait that “re-appeared” was ¼ of the population 3 dominant traits for every 1 recessive trait Mendel’s Principles

Mendel’s Experiment Visual

Mendel’s Conclusions Visual

Predicting Genetic Crosses Probability Number of times an event is expected to happen Number of chances for that event to happen Probability = The probability of a coin landing heads up is: 1 2 What is the probability that a coin will land heads up, if the previous 5 tosses it landed tails up ? IT IS STILL….. 1/2 Each toss is independent, or unaffected by what came before it !!!

Predicting Genetic Crosses Probability What is the probability of tossing a coin heads up 5 times in a row ? This question asks us to figure out a series of events happening not simply the next event, unlike the last question In order to predict the probability of a series of events occurring together, we must use…. THE RULE OF MULTIPLICATION This rule states that you must multiply the likelihood of each separate event occuring ½ X ½ X ½ X ½ X ½ = 1/32 Is the answer to the question above

Probability Visual

Chromosomes and Genes Genes are small segments of DNA on chromosomes Information for different traits A chromosome can carry 100s to 1000s of genes The flower color gene in the diagram above has two forms: P-purple & p-white The different forms of genes are referred to as alleles Predicting Genetic Crosses

Genotype and Phenotype Pp Genotype The genes for a particular trait Phenotype Physical appearance of the trait Genotype: Pp In the diagram above, P=purple flowers p=white flowers Phenotype: Purple Pp = Purple flowers

Predicting Genetic Crosses Monohybrid Punnett Squares Punnett squares are charts used to predict the traits of offspring from a set of parents B b bbbb bb MOM DADDAD Capital letters are always written first within the grid of a punnett square The boxes within a punnett square represent the possible zygotes that a couple can make Monohybrid means that the punnett square is used to predict ONE trait

Monohybrid Cross Visual

Predicting Genetic Crosses Monohybrid Punnett Squares Setting up genetic word problems: I.Designate letter and what they represent T = Tall t = short The letter used is typically the first letter of the dominant trait II. Determine possible genotypes and the phenotype that each represents TT = Tall height Tt = Tall height tt = short height

Predicting Genetic Crosses Monohybrid Punnett Squares Setting up genetic word problems: III. Determine the genotypes of the parents being crossed Example: Homozygous dominant = TT Homozygous recessive = tt Hybrid = Tt Pure dominant = TT Pure recessive = tt Heterozygous = Tt TT x Tt shows that a Homozygous dominant is being crossed with a hybrid Hetero = different Homo = same

Predicting Genetic Crosses Monohybrid Punnett Squares Setting up genetic word problems: IV. Complete the punnett square to show possible gene combinations T t TTTT TTTt TTTt V. Determine the genotypic and phenotypic ratios Genotypic ratio - 2-TT:2-Tt gives a ratio of 1-TT:1-Tt Phenotypic ratio % Tall

Predicting Genetic Crosses Dihybrid Punnett Squares A dihybrid cross invloves using a punnett square to predict how offspring will inherit ________ traits The F.O.I.L. method of distribution needs to be used to show how each of the four alleles from each parent could combine Parent #1 (AaBb)X Parent #2 (AaBb) AB Ab aB ab Genes still segregate, so you never have two of the same letter in a given egg or sperm (this can’t read “aa”) AB Ab aB ab Keep the order of letters consistent, still always putting the capital letters first AABB AABb AaBB AaBb AABb AAbb AaBb Aabb AaBB AaBb aaBB aaBb AaBb Aabb aaBb aabb TWO

Predicting Genetic Crosses Dihybrid Punnett Squares Crossing two heterozygotes for one trait yielded a 3:1 ratio for Mendel’s peas Crossing two heterozygotes for two traits yields a 9:3:3:1 ratio 9 Dominant for both traits 3 dominant for first trait, recessive for the second 3 recessive for first trait, dominant for the second 1 recessive for both traits

Mendel’s Laws The Law of Segregation Two alleles which control a trait are separated Gametes Parent – Tt Eggs or sperm has either a T or t Not Both! The Law of Independent Assortment Random Distribution of alleles Flower color gene has no connection to plant height YyRr YR Yr yR yr Possible Gametes Produced during meiosis

Predicting Genetic Crosses Testcross While most phenotypes are visible, genotypes cannot be seen To determine the GENOTYPE of an organism with a dominant trait, you need to perform a TESTCROSS A testcross involves mating a homozygous recessive organism with the organism of unknown genotype If this mating produces any organisms with recessive traits, you can determine that the unknown genotype is heterozygous for the dominant trait B b bbbb The “testcross” homozygous recessive organism Bb bb

Test Cross Visual