Chapter 14 A How inheritance works a Blending hypothesis i Traits inherited from mother blend with those form the father child has a trait that is in between the two like water colors ii After many generations the population would become homogenous b Second hypothesis Particulate inheritance i Parents pass on discrete heritable units genes that retain their separate identities in offspring same nose etc The gene doesn t change ii Genes are not altered as they are passed one from generation to the next B Gregor Mendel a Entered an Augustinian monastery in 1843 University of Vienna background in mathematics experimentation and botany b Began breeding garden peas to study inheritance C Advantages of pea plants for the study of genetics a Many varieties with distinct heritable characters such as seed color with different variants green yellow of these characters b Each pea plant has male and female sexual organs c Will self fertilize but Mendel could cross pollinate them easily d Short generation time birth to birth a Each pea is fertilized separately so individual peas within a pod can have different traits D Variations within a pea pod such as smooth wrinkled or coloration E Typical Breeding experiment a True breeding produce the same trait generation after generation when you breed it over and over you get the same trait b Parental traits are crossed together to get the first filial generation or F1 i Monohybrid Cross hybrid of one character ii Does not support blending hypothesis of inheritance iii Purple and white flowers were crossed together and the white trait was absent in the first filial generation but reappeared again in the F2 F Mendel s discoveries a b Law of Segregation Law of independent assortment G The Law of segregation a Alternative version of genes different alleles account for variations in inherited characters b Alleles vary in the DNA sequence at the specific locus different genetic sequence in nucleotides For each character an organism inherits two alleles one from each parent c i A diploid organism inherits one set of chromosomes from each parent ii Two copies of each locus H Genotype is the underlying genes that determine the phenotype a A diploid organism has 2 copies of each gene 2 alleles I Phenotype is the physical function bodily characteristic appearance that is observed a genotype environment J White flowers were recessive a F1 first allele generation offspring of parents b F2 when you cross the F1 s K Variations in the genotype a Homozygous heterozygous i There may be several possible versions of a gene thus several possible alleles b Homozygous individual has two identical alleles for a specific gene i Example PP or pp c Heterozygous individual has two different alleles for a specific gene i Example Pp L One allele may dominate the other a Mendel s characters showed complete dominance b Heterozygote Pp i P dominant allele Purple ii p recessive white iii Dominant allele P determines the Phenotype of heterozygote iv Genotype Pp purple phenotype c Alleles segregate from one another during gamete formation meiosis i Diploid plant Pp ii 50 of the gametes will have allele P iii 50 of the gametes will have allele p M Apply this to Mendel s monohybrid cross monohybrid is for one trait a 3 1 phenotype ratio in F1 b 1 2 1 genotype ratio in the F2 N How did Mendel know the genotypes of the f2 progeny a Purple flower PP or Pp i He conducted a test cross O Law of independent assortment a Each pair of alleles segregates into gametes independently b Monohybrid cross used to follow a single character c Dihybrid cross used to follow the inheritance of 2 characters 2 genes i Example seed shape smooth or wrinkled seed color yellow or green d YYRR crossed with yyrr gametes are YR and yr when you cross them the F1 s and the P Y and R can sort together if they are close enough together on the chromosome OR Y and Y results are YyRr X YyRr and R sort independently Q The phenotypic ratio for dependent assortment of the alleles is the same ratio as mendel s ratio a The ratio for independent assortment is 9 3 3 1 b Follow just one character you will observe a 3 1 F2 ratio for each R Note Mendel s characters were on different chromosomes a Genes on the same chromosome may sort together i DISTANCE MATTERS S Probability Likelihood of Event Occurring a Probabilities i Zero an event with no chance of occurring to one an event that is certain to occur ii The probability of tossing heads with a normal coin is iii The probability of rolling a 3 with a six sided die is 1 6 iv The probability of rolling any other number is 1 1 6 5 6 T Rule of Multiplication a Probability of two events happening is the product of their respective probabilities i Flipping coins two possible outcomes heads and tails ii Likelihood of getting heads in one flip 1 2 iii Likelihood of getting two heads in a row 1 2 times 1 4 iv Use this to determine likelihood of getting both alleles rr 1 Same as getting two heads in a row times b What is the chance of getting a green offspring i The same as flipping heads on a coin ii If 20 offspring were produced times 20 U Allelic Interactions Incomplete dominance a Complete dominance heterozygote has phenotype of dominant allele b c Codominance Incomplete dominance V a Red pink white flowers b Heterozygote has phenotype in between the two alleles c d Allele remains intact as it is passed from one generation to the next e This is at the phenotype level It is not the same as blending inheritance W Codominance a Two alleles affect the phenotype in separate distinguishable ways such as blood types b M N and MN blood groups i Group M with genotype MM have one type of molecule on their red blood cells ii People of group N genotype NN have the other type iii Group MN have both molecules present c Details disease i Phenotypic levels ii Classification of the allelic interaction varies with level studied in Tay Sach s iii tt lack a functioning enzyme to breakdown gangliosides a lipid which accumulate in the brain harming brain cells and ultimately leading to death iv Tt organismal level complete dominance one functioning allele means an individual is normal v Molecular level codominance equal numbers of normal enzyme T enzyme a nonfunctional enzyme t are produced X How does a dominant allele dominate a Do not somehow subdue a recessive allele b Function as long as some of the enzyme is present c As in TaySachs presence of one normal allele provides enough functional enzyme to