Presentation on theme: "WHAT IS GENETICS? GENETICS is the study of how traits are passed from parent to offspring in the form of Genes."— Presentation transcript:
1WHAT IS GENETICS?GENETICS is the study of how traits are passed from parent to offspring in the form of Genes.
2HISTORY! Gregor Mendel Born 1822 Austrian Monk Examined reproduction of pea plants
3Plants reproductive organs are called FLOWERSA flower has both male and female parts.The pea plants Mendel was working with were typically TRUE-BREEDING, meaning they self-pollinatedEX, TALL pea plants would always be pollinated by tall pea plants and produce tall offspring!
4WHAT WE KNOW (MENDEL DIDN’T) Genes – control a heritable feature (characteristic);Example: Hair color, seed shape, height;Allele – controls the variation of a feature (trait).Example: brown, blonde, black hair
8Mendel’s Idea Cross two pea plants with different contrasting traits! Ex:First cross : Crossed true breeding purple with true-breeding white plants.Called offspring F1 GenerationResults were that offspring were_100% PURPLE_Had the white allele disappeared????
10Mendel’s Law of Dominance some alleles over power others. So even if both alleles are present, we only “see” the dominant one.the “hidden” allele is called recessiveThis only applies to SOME genes, not all
11Second cross two of the purple F1 Offspring Called offspring the F2 GenerationResults75 % purple25 % were whiteWhite trait had reappeared!
13Mendel’s Law of Segregation during meiosis, the pair of alleles in a parent will separate.Only ONE allele for EACH TRAIT will pass from each parent to the offspring
14Ex. sugar beet preference. dominant allele (A) prefers sugar beetsrecessive allele (a) does not.Heterozygote produces gametes50% chanceGet AGet aQuestion: If a heterozygous sugar beet eater marries a non-sugar beet eater, what possible offspring could they have?
15Mendel’s Law of Independent Assortment Alleles for different genes are passed to offspring independently of each other.The result is that new combinations of genes present in neither parent is possible.How many allele combinations could the following genotype produce?RRYYRRYyRrYy
17Genetic Terms Diploid (2n)- Two sets of chromosomes. Somatic CellsHaploid (n)- One set of homologous Chromosomes(gametes)Egg- Female haploid gameteSperm- male haploid gamete
18Parent – Seriously, you should know this Meiosis – Cell division that produces haploid gametesTestes – Site of male meiosisGamete – Haploid sex cell (sperm, egg, pollen)
19Zygote- Single cell (result of sperm and egg) Progeny - OffspringOffspring – see aboveFertilization – gametes fuse into zygoteOvary- site of female meiosis - eggs
20Genotype: the alleles that an organism has. alleles are abbreviated using the first letter of the dominant trait.capital letter represents the dominant ex: P for purple flower allelelower case represents the recessive. ex: p for white flower allele
21All diploid organisms have two alleles for each trait: Can be two of the same alleles Ex: PP or pp called Pure or Homozygous.ORCan be two different alleles Ex: Pp described as Hybrid or Heterozygous
22Phenotype: physical appearance Examples: brown hair, widows peak, purple flowersthe trait that “wins” in the case of complete dominance;depends on the combination of alleles GENOTYPE
24P Generation: “parents;” MENDEL’S CROSSESP Generation: “parents;”F1 Generation offspring of P generationF2 Generation offspring of F1 generationPunnet Squares How we show allele combinations in crosses
25Allele in Egg 1 Allele in Egg 2 Allele in sperm 1 Allele in sperm 2 Zygote formed if sperm 1 fertilizes egg 1Allele in Egg 2Allele in sperm 1Allele in sperm 2Zygote formed if sperm 2 fertilizes egg 1Zygote formed if sperm 1 fertilizes egg 2Zygote formed if sperm 2 fertilizes egg 2
26Monohybrid Cross Tall vs. Short Example Tall allele T Short allele tP Cross TT x ttF1 GenerationGenotypesPhenotypesTTtt
27F2 Generation F1 Generations 100% Tt Tt x Tt F2 Generation Genotypes- Phenotypes-TtTt
30Sample Problems Homozygous Tall x Heterozygous Tall Heterozygous Tall x Homozygous Short
31Probability Probability is only the LIKELIHOOD of an event happening. It does not mean it is what HAS to happenEx. Coin Toss. Two tosses, always one heads and one tails?What happens when we look at very large samples?Ex. Male/female ratio of a family vs. the world!
32INHERITENCE PATTERNSEvery gene demonstrates a distinct phenotype when both alleles are combined (the heterozygote)Complete dominance is when both alleles are present, only the dominant trait is seen.Incomplete dominance - when both alleles are present, the two traits blend together and create an intermediate trait
34Inheritance Patterns: Co-dominance- when both alleles are present, both traits are visibleDifferent notation: Use first letter of the feature with a superscript for the trait.Example: CW or CR for white petals or red petals;
35Women have two X’s but men only have one. How do we deal with the genes on the X chromosome?
36ProbabilitiesQuestion 1: What is the probability of having a female offspring?Question 2: After having 4 sons in a row, what is the probability the next kid will be male?Question 3: What is the probability of having three daughters in a row?
37Sex-Linked TraitsRefers to traits coded by genes found on the X chromosomeFemales will have 2 copies of these genesMales will have 1 copy of these genesSignificance???If males get a bad (recessive) allele for a sex- linked trait, THEY WILL EXPRESS THE RECESSIVE TRAIT!
38Example – Color Blindness Seeing color (XC) is dominant to being color blind (Xc)Identify the sex and trait of the following:XCY XCXc XCXCXcXc XcY
39XC Xc XC XC Xc XC Xc Y Y XC Y Cross Number 1: What % chance of having color blind daughter?Son?XCXcXCXCXcXCXcYYXCY
40AFFLICTS 8% MALES AND 0.04% FEMALES. SEX-LINKED TRAITSCOLOR BLINDNESSAFFLICTS 8% MALES AND 0.04% FEMALES.
41Test cross: a cross that determines genotype of dominant parent - Cross unknown dominant parent (possibilities BB or BB) with a recessive parent then analyze the offspring.Ex. B- Black Hair b- white hairYou are given a black-haired guinea pig and need to determine whether homozygous dominant or heterozygous.
42Multiple AllelesGenes may have more than two alleles.
43Multiple alleles: Some genes have more than two variations that exist, although we still only inherit 2Example: Human blood typesThree alleles:IAIBiGenotypePhenotypeIAIAAIAiIBIBBIBiIAIBABii
48Multiple genes code for a trait each with 2 alleles Polygenic –Multiple genes code for a trait each with 2 allelesExamples in humans:Skin ColorEye ColorHeightWhy so many possibilities???SKIN PIGMENTATION
49Dihybrid cross:A cross that focuses on possibilities of inheriting two traits- two genes, 4 allelesBlack fur is dominant to brown furShort fur is dominant to long furWhat is the genotype of a guinea pig that is heterozygous for both black and short fur?
50Dihybrid cross:Parent phenotypes: BbSs x BbSsFigure out the possible gametes:Then set up punnett square
53Di-hybrid Cross Generalization Laws of probability indicate a 9:3:3:1 phenotypic ratio of F2 offspring resulting in the following:9/16 of the offspring are dominant for both traits3/16 of the offspring are dominant for one trait and recessive for the other trait3/16 of the offspring are dominant and recessive opposite of the previous proportions; and1/16 of the offspring are recessive for both traits.
54Linkage and Gene MapsWhen genes are one separate chromosomes, they independently assort.If on the same chromosome, they will rarely separate and be inherited together (gene linkage)Actually it is the chromosomes that assort independently, not the genes. Mendel was just lucky with the genes he was looking at!
55Crossing over in meiosis often separates linked genes. The distance between the two genes on the same chromosome are from each other affects the frequency of separation from each other during crossing-over.Further ApartCloser together
56The frequency of crossing over between genes is actually an indicator of how far apart different genes are located from each other on the same chromosome.Use the frequency rates to make gene maps that show relative locations of genes with respect to each other.