Presentation on theme: "Monohybrid Crosses Objective"— Presentation transcript:
1Monohybrid Crosses Objective Use the punnett square method to determine the possible genotypes of different monohybrid crossesDetermine the phenotypic ratio of a monohybred cross.Explain how the process of meiosis and fertilization account for the transmission of inherited characteristics.
2Inheritance - MendelThe transfer of characteristics (traits) from one generation to anotherYour inherited characteristics (traits) are determined by the genes located on your chromosomes
3# of students with Dominant # of students with Recessive Ratio of Dominant TraitDescription# of students with Dominant# of students with RecessiveRatio ofDominant to RecessivePercentage with Recessive traitsClassEye colourHair colourHairlineFrecklesEarlobeFingersEar rimThumb jointFolded handsTongue rollingChin dimple
4Genea short segment of a chromosome coding for one trait
5Homologous chromosomes: chromosomes are found in pairsin humans, there are 46 chromosomes, made up of 23 pairs of homologous chromosomesa pair of chromosomes consists of two homologous chromosomes which look alike and carry genes for the same traitsyou receive one homologous chromosome of the pair from each parent, therefore you receive 2 genes for each trait
6PhenotypeThis term is used to describe the physical or visible appearance of an individual as determined by the gene combination you inherit from your parents.Example: in the case of eye colour, having brown eyes is the phenotype and is dominant
7Genotype the gene combination that produces the trait these genes may be the same or differentgenotypes are represented by upper and/or lower case letters e.g. Bbthere are three possibilities for genotypes for a single trait.e.g. BB or Bb or bb
8Allele alternate forms of a gene same location on a each chromosome of pairaffects the same trait but differentlyalleles are different forms of a gene that carry different instructionseg. Brown eyes or blue eyes
10Dominant Trait/Allele Characteristic that is always expressed its gene is presentonly one dominant allele needs to be present for the dominant trait to be expressedan upper case letter designates a dominant alleleeg. Tall is dominant. It is represented with a “T”
11Recessive Trait/Allele Characteristic that is only expressed when two genes for that trait are presenttwo recessive alleles need to be present for a recessive trait to be expressedif a dominant allele is present it “masks” the recessive alleleeg: Short is recessive. It is represented with a“t”
12Homozygous Genotype “homo” means the “same” the condition where both alleles for a trait are the samethere are two conditions for homozygous genotype:homozygous recessive genotype “aa”homozygous dominant genotype “AA”
13Heterozygous Genotype “hetero” means “different”the condition where both alleles for a trait are differentthe genetic information inherited for a trait from both parents is differentexample: heterozygous genotype “Aa”
15Pure breeding plants always produce identical offspring. Mendel’s ExperimentCrossed two purebred parents (One tall -T and one short -t)Pure breeding plants always produce identical offspring.All offspring were tall!!Mendel concluded that some traits were ___________ and some traits were ___________.
16Principal of dominance When individuals with different traits are crossed, the offspring (F1 generation) will express only the dominant trait.Parents: Tall x ShortF1 (Offspring): Tall Tall Tall TallWhat must the genotype of the offspring be if the parents were pure breeding?
17Hybrids have contrasting traits. What happened next??Mendel crossed the F1 generation.He crosses two hybrid pea plants.Hybrids have contrasting traits.F1: Tall plants x Tall plantsF2 (Offspring of F1): Tall Tall Tall ShortF2 generation = 3:1 ratioWhat must the genotype of these offspring be if the parents were hybrids (Tt and Tt)?
18Law of SegregationEach F1 parent starts with two hereditary factors (alleles); one is dominant and one is recessiveEach parent contributes only one factor (allele)Each offspring inherits one factor (allele) from each parentIf the dominant factor (allele) is present it will be expressed.If the recessive factor (allele) is present it will only be expressed if only recessive factors are present.
19Monohybrid Cross Mendel crossed two purebred plants TT – tall plant Tt – short plantMonohybrid cross – only one trait is being tested
20Punnett Squares Punnett Square Is a grid system resembling a checkerboard, used in computing possible results of various genetic combinationsSimply stated, it is a way of representing the possible combinations of genes when an egg and sperm unite in fertilization
21Predicting genotype and phenotype possibilities using Punnett Squares Characteristic hair texture –Dominant allele (gene) is curly hair - C.Recessive allele (gene) is straight hair - cMotherPhenotype – straight hairGenotype- homozygous recessive - ccFatherPhenotype – curly hairGenotype – homozygous dominant – CC
22Punnett Square Cc c C Egg Sperm All of their children will have curly hair. They all have a different genotype from their parents.
27Your Turn Bikini Bottom Genetics – Monohybrid Crosses HOMEWORK: Find out what the following words mean…HybridPure-breeding/PurebredWhy was it important that Mendel used purebred plants in his experiment?How does meiosis ensure that you inherit your mothers and fathers characteristics?
28Codominance, Incomplete dominance and Dihybrid Crosses Objectives:Explain what co dominance and incomplete dominance is. Give an example of each.Use a Punnett square to solve basic incomplete and co dominance crossesUse a Punnett square to solve basic dihybrid crosses.
29TermsIncomplete Dominance: When two alleles are equally dominant, they interact to produce a new phenotype.Codominance: When both alleles are dominant and are expressed at the same time.Pg 145 # 1-4
30Codominance When a red bull is crossed with a white cow, the offspring willbe roan.
31Incomplete Dominance When a red flower is crossed with a red flower, the resulting offspringwill be pink.
32Dihybrid CrossesA type of cross that involves two genes, each consisting of non identical alleles.
33What happened when Mendel crossed two pea plants that different in TWO traits? In his second experiment Mendel crossed a pea plant with round/yellow (RRYY) seeds with a pea plant with wrinkled/greed seed (rryy).RYryRrYyRYryGenotype: RrYy F1 - GenerationRatio 100%Phenotype: Round/YellowRatio 100%What genotypes resulted?What phenotypes resulted?
34Crossing F1(RrYy) x F1(RrYy) Genotype: RRYY RRYy Rryy RrYY RrYy rrYY rrYy rryyRatio:Phenotype: Round/Yellow Round/Green Wrinkled/Yellow Wrinkled/GreenRatio:In the resulting F2 – Generation, the phenotypic ratio will always be 9:3:3:1In other words, the likelihood of obtaining each of the above phenotypes from crossing two hybrid pea plants is 9:3:3:1.What genotypes resulted?What phenotypes resulted?
35Law of Independent Assortment The inheritance of alleles for one trait ________ (does/does not) affect the inheritance of alleles for another trait.