2 Do You Know These Words Heredity Passing on of characteristics from parent to offspringGeneticsPart of biology that studies heredityGenePiece of DNA that codes for a polypeptide (specify certain trait)TraitCharacteristic that is inheritedHomologous ChromosomesChromosome of the same type (pairs)LocusSpecific location of a gene on a chromosomeDiploid2 copies of each chromosome = 2nHaploid1 copy of each chromosome = 1n
3 Gregor Mendel Austrian monk A mathematician aware of probability The “father” of geneticsWorked with pea plants
4 Why Peas?Peas have many traits with 2 different forms that are easy to distinguish (ex: green or yellow seeds; tall or short plants)Could easily control mating of the pea plants through cross-pollinationPea plants are small, they grow quickly and easily, and they produce a lot of offspring.
5 Mendel’s CrossesIn one cross, Mendel crossed tall pea plants with short pea plantsAll of the offspring were tall!He then crossed two of the offspring tall plantsThe next offspring were ¾ tall and ¼ shortMendel said that 2 factors control each trait (these are genes found on chromosomes)Each form of a gene is called an allele.The two alleles are found on homologous chromosomes.
6 Mendel’s Crosses Parent x Parent = P1 generation Offspring x Offspring = F1 generationOffspring = F2 generation
7 Mendel’s Law of Dominance Mendel called the observable trait (all tall plants) dominant and the trait that disappeared (short plants) recessiveThe allele for tall plants is dominantThe allele for short plants is recessiveIf T = tall and t = shortTT = tall plant, Tt = tall plant, tt = short plant
8 Mendel’s Theory of Segregation Each parent passes on (at random) to offspring only one allele for each trait!A plant that is Tt can pass either T or t in a gamete.Ex: Humans have ____ chromosomes.When eggs and sperm are made, only half of these chromosomes are passed…one of each kind from mom and one of each kind from dadThat way a fertilized egg (and the baby) will have the normal # of chromosomes
9 Mendel’s Theory of Segregation Diploid cells have pairs of genes on pairs of homologous chromosomes.The 2 genes of each pair are separated during meiosis and end up in different gametes.
10 More vocabulary! Phenotype = individual’s observable traits Ex: (tall, short)Genotype = genes an individual carriesEx: TT, TtHomozygous = has 2 of the same allelesPurebred, true-breedingTT, ttHeterozygous = has 2 different allelesHybridTt
11 Monohybrid Cross Cross a single trait Cross 2 parents that are homozygous for different alleles of a single traitSaw purple allele is dominant to (masks) white allelePurple flower x White flowerAll purple flower plants705 purple224 whiteAbout a 3:1 ratio
12 Now lets investigate the heredity seen in Reebops!
13 Punnett Squares Can be used to show all possible offspring! Ex.: R = round seed, r = wrinkled seedHomozygous round x homozygous wrinkledWhat F1 offspring can be produced? What are the genotypes and phenotypes?
14 F2 GenerationNow let’s cross two of the heterozygous offspring from the F1 generation.
15 Dihybrid Cross Cross two traits Start with 2 parents that are homozygous for different alleles for 2 traitsRound Yellow Seed x Wrinkled Green SeedR= round Y = yellowr = wrinkled y = green
17 Mendel’s Theory of Independent Assortment Gene pairs for different traits are inherited independently of each otherEx: Genes for round seed shape are inherited independently of genes for yellow seed color!Note: We will see later that this does not always apply
18 Test Cross I have a guinea pig that is black. I know that the black allele (B) is dominant to the brown allele (b).What are the possible genotypes for my guinea pig?I want to breed guinea pigs, and I want to have pure-bred guinea pigs!How do I know if he is pure-bred?
19 Test CrossMy guinea pig may be BB or Bb. Both would show the black phenotype!To see if a dominant phenotype is due to a homozygous dominant or a heterozygous phenotype, I can…Cross it with one that is homozygous recessive! B B B bb b