PP x pp. Looking closer at Mendel s work. Gregor Mendel a monk named Gregor Mendel documented inheritance in peas in the mid-1800s

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1 Gregor Mendel a monk named Gregor Mendel documented inheritance in eas in the mid-1800s used eerimental method used quantitative analysis collected data & counted them ecellent eamle of scientific method Looking closer at Mendel s work self-ollinate urle-flower eas X urle-flower eas urle-flower eas white-flower eas white-flower eas What did Mendel s findings mean Traits come in alternative versions urle vs. white flower color alleles different alleles vary in the sequence of nucleotides at the secific locations of a gene urle-flower allele & white-flower allele are 2 DNA variations at flower-color locus different versions of gene on homologous chromosomes What did Mendel s findings mean Some traits mask others urle & white flower colors are searate traits that do not blend urle white light urle urle masked white dominant allele fully eressed recessive allele no noticeable effect the gene makes a non-functional rotein Genotye vs. henotye difference between how an organism looks & its genetics henotye descrition of an organism s trait genotye descrition of an organism s genetic makeu Elain Mendel s results using dominant & recessive henotye & gentotye Making crosses using reresentative letters flower color alleles or urle-flower eas white-flower eas 1

2 female / eggs Looking closer at Mendel s work self-ollinate urle-flower eas X urle-flower eas urle-flower eas white-flower eas white-flower eas henotye unnett squares male / serm % genotye 50% 1:2:1 % henotye Genotyes Homozygous = same alleles =, Heterozygous = different alleles = homozygous dominant henotye vs. genotye 2 organisms can have the same henotye but have different genotyes urle homozygous dominant urle heterozygous homozygous recessive Dominant henotyes It is not ossible to determine the genotye of an organism with a dominant henotye by looking at it. Test cross Cross-breed the dominant henotye unknown genotye with a homozygous recessive () to determine the identity of the unknown allele is it or 2

3 Test cross 50%:50% 1:1 Mendel s laws of heredity (#1) Law of segregation when gametes are roduced during meiosis, homologous chromosomes searate from each other each allele for a trait is ackaged into a searate gamete Law of Segregation What meiotic event creates the law of segregation Meiosis 1 Monohybrid cross Some of Mendel s eeriments followed the inheritance of single characters flower color seed color monohybrid crosses Dihybrid cross Other of Mendel s eeriments followed the inheritance of 2 different characters seed color and seed shae dihybrid crosses Dihybrid cross, eas YYRR yyrr self-ollinate Y = R = 9/16 eas, eas eas YyRr, wrinkled eas y = r = wrinkled 1/16 wrinkled wrinkled eas eas 9:3: 3

4 Dihybrid cross YyRr YyRr YR Yr yr yr YR Yr yr yr YYRR YYRr YyRR YyRr YYRr YYrr YyRr Yyrr YyRR YyRr yyrr yyrr YyRr Yyrr yyrr yyrr 9/16 wrinkled 1/16 wrinkled Mendel s laws of heredity (#2) Law of indeendent assortment each air of alleles segregates into gametes indeendently 4 classes of gametes are roduced in equal amounts YR, Yr, yr, yr only true for genes on searate chromosomes YyRr Yr Yr yr yr YR YR yr yr Law of Indeendent Assortment What meiotic event creates the law of indeendent assortment Meiosis 1 The chromosomal basis of Mendel s laws Trace the genetic events through meiosis, gamete formation & fertilization to offsring Review: Mendel s laws of heredity Law of segregation monohybrid cross single trait each allele segregates into searate gametes established by Meiosis 1 Law of indeendent assortment dihybrid (or more) cross 2 or more traits each air of alleles for genes on searate chromosomes segregates into gametes indeendently established by Meiosis 1 Genetics & robability Mendel s laws: segregation indeendent assortment reflect same laws of robability that aly to tossing coins or rolling dice 4

5 female / eggs robability & genetics robability & genetics Calculating robability of making a secific gamete is just like calculating the robability in fliing a coin robability of tossing heads 50% robability making a gamete 50% Outcome of 1 toss has no imact on the outcome of the net toss robability of tossing heads each time 50% robability making a gamete each time 50% Calculating robability male / serm serm egg offsring 1/2 Rule of multilication Chance that 2 or more indeendent events will occur together robability that 2 coins tossed at the same time will land heads u robability of Calculating dihybrid robability Rule of multilication also alies to dihybrid crosses heterozygous arents YyRr robability of roducing yyrr robability of roducing y gamete = 1/2 robability of roducing r gamete = 1/2 robability of roducing yr gamete = robability of roducing a yyrr offsring = 1/4 1/4 = 1/16 Rule of addition Chance that an event can occur 2 or more different ways sum of the searate robabilities robability of serm egg offsring 1/4 + 1/4 1/2 5