Revisiting Dihybrid Punnett Squares

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Revisiting Dihybrid Punnett Squares. What exactly is a dihybrid cross? Predicting the outcomes from crossing 2 traits. Why do we use them? Instead of doing to monohybrid crosses, you can combine them to see all the possible combinations from that particular mother and father. - PowerPoint PPT Presentation


  • Revisiting Dihybrid Punnett SquaresWhat exactly is a dihybrid cross?Predicting the outcomes from crossing 2 traits. Why do we use them?Instead of doing to monohybrid crosses, you can combine them to see all the possible combinations from that particular mother and father.

  • Dihybrid Crosses ContdWhat do the tops and sides of a Punnett Square represent?The gametes from the mother and father that are going to mix (fertilize) to make the possible offspring in the middle.Webbed feet (W) in ducks are dominant to un-webbed (w) feet. If a mother duck is heterozygous for webbed feet, and the father is homozygous for webbed feet, will any of their ducklings have un-webbed feet?Mother = Ww, Father = WWWWWwW WW WW wW wEach gamete is haploid. The mothers eggs can have either W or w; fathers sperm can have either W or W.

  • Dihybrid Crosses ContdWhy do we have a Punnett Square with 4 boxes on each side instead of 2?There will be 2 possible alleles that can be passed on for each trait. You will have 4 total options to include all the possibilities of combining the 2 traits.Short beaks (b) in ducks are recessive to long beaks (B) feet. If a father duck has a short beak, and the mother is a carrier for short beaks, will any of their ducklings have the same type of beak as their mother??Mother = bb, Father = BbThe mother can pass on a B or a b; the father can pass on a b or a b towards the beak trait.Remember, the mother can pass on a W or a w allele for webbed feet and the father can pass on a W or a WSO, all the possible gamete combinations are:Mother: WB,Wb, wB, wbFather: Wb, Wb, Wb, Wb

  • Putting it all togetherMothers gamete choices: WB, Wb, wB, wbFathers gamete choices: Wb, Wb, Wb, WbBy taking all the daughter cell possibilities, were covered no matter what gametes end up getting fertilized to restore diploidy.WBWbwBwbWbWbWbWbWWBbWWBbWWBbWWBbWWbbWWbbWWbbWWbbWwBbWwBbWwBbWwBbWwbbWwbbWwbbWwbb

  • Codominance, Polygenic Inheritance and Blood TypesContinuing our exploration of patterns of inheritance with

  • CodominanceHeterozygote expresses both alleles conditionsEx. A black rooster bred with a white hen produces a black and white checkered chicken.Usually uses both capital letters (black= B, white=W , checkered = BW)

  • Codominance practice: cross a black rooster with a white hen BBWWResults:100% checkered (BW)BWBWBWBWKey:B = blackW = whiteBW = checkered

  • Now lets cross a checkered hen with a checkered rooster.BWWBResults:25% Black50% Checkered25% White(1:2:1)BBBWBWWW

  • Polygenic InheritanceTrait controlled by 2 or more genesMay be on the same or different chromosomesShows a range, intermediate is most common phenotypeUpper and lower case letters used

  • Skin color: A polygenic traitDetermining # of Genes Involved in Skin ColorObserved distribution of skin colorExpected distribution- 1 geneExpected distribution- 4 genesExpected distribution- 3 genesRange of skin colorLightRightNumber of individuals

  • And the answer isSkin color is actually due to 5 genesGenotypes darkest to lightest:AABBCCDDEE would be darkest skinnedAaBbCcDdEe would be medium skinnedaabbccddee would be lightest skinned

  • Influence of External EnvironmentIn arctic foxes temperature has an effect on the expression of coat color. In winter, fur is white; in summer, fur is brown

  • Leaves can have different sizes, thicknesses, and shapes depending on the amount of light they receive.Influence of External Environment

  • Influence of Internal EnvironmentThe internal environments of males and females are different because of hormones and structural differences.An organisms age can also affect gene function.Ex. Adult male lions manes

  • Peacock (male) Peahen (female)Coloration may also be caused by differences in hormones between sexes

  • Blood type quick factsRed blood cells are called erythrocytesProteins on their surfaces are called antigens, controlled by genesAntigens make antibodies to foreign substances, which includes RBCs with different antigens on their surface4 phenotypes: A, B, AB, O3 alleles: IA, IB, i

  • The lA allele is dominant to i, so inheriting either the lAi alleles or the lA lA alleles from both parents will give you type A blood.Phenotype ASurface molecule A is produced.Surface molecule A

  • The lB allele is also dominant to i.Phenotype BTo have type B blood, you must inherit the lB allele from one parent and either another lB allele or the i allele from the other.Surface molecule B is produced.Surface molecule B

  • The lA and lB alleles are codominant. Phenotype ABIf you inherit the lA allele from one parent and the lB allele from the other, your red blood cells will produce both surface molecules and you will have type AB blood.Surface molecule BSurface molecule A

  • Phenotype ONo antigens produced

  • Check your chart!

  • Possible genotypes for each phenotype:A=IA IA or IAiB=IBIB or IBiAB =IAIBO=ii

  • Now lets put your skills to the testCan you save these patients?