Presentation on theme: "Incomplete dominance This is when neither allele is dominant."— Presentation transcript:
1 Incomplete Dominance, Codominance, Multiple Alleles, and Sex-Linked Genes
2 Incomplete dominance This is when neither allele is dominant. Both alleles are expressed and contribute equally to the phenotype.A heterozygous genotype has an intermediate phenotype as there is partial influence from both alleles.Example: Red + White = Pinkflower flower flower
3 Incomplete dominance Snapdragons can be red (alleles = RR)white (alleles = rr)pink (alleles = Rr)If you cross a two pink flowers, is it possible to produce a white flower?¼ Red¼ White½ PinkYes!
4 Codominance Both alleles are dominant. They are independent, so there is no 'blending' as in the snapdragons, instead the phenotype is a result of the full expression of both alleles.Example: black + White = B&W spotteddog dog dog
5 Codominance Dogs can be Black (alleles = BB) White (alleles = bb) Spotted (alleles = Bb)Is it possible for a black dog to have one parent that is white?No!
6 Multiple alleles (blood typing) In the case of the ABO blood grouping, there are 3 alleles for one geneThey are written a little differently:i : this allele is recessiveIA : this allele is co-dominantIB : this allele is co-dominant
7 Multiple alleles (blood typing) Blood group (phenotype):A ……………………………..B ……………………………..AB ……………………………O ……………………………..Possible genotype:IA IA or IAiIBIB or IBiIAIBii
8 Multiple alleles (blood typing) A father with homozygous type A blood has a child with a mother that has heterozygous type B blood.Is it possible for them to have a child with type O blood?
9 Sex determinationGender is determined by sex chromosomes in many animals.The XY System:Female are XX, males are XYY makes the guy!!!What are the odds that a couple have a boy?50/50
10 Sex-linked genesSome genes are linked to the sex chromosomes and are inherited with them.Hemophilia is carried on the X chromosome.The normal allele is dominant (H)The allele for hemophilia is recessive (h)
11 Sex-linked genes XHXH = normal female XHXh = carrier female XhXh = female w/hemophiliaXHY = normal maleXhY = male w/hemophiliaA carrier does not have the disease, but can pass it on to their offspring.
12 Sex-linked genesIf a female carrier has offspring with a normal male, what is the chances that their offspring will have hemophilia?25%
13 Sex-linked genesIn cats the allele for coat color is carried on the X chromosome.The alleles are black and orange but they are codominant.XBXB = black femaleXBY = black maleXbXb = orange femaleXbY = orange maleXBXb = tortoiseshell female
14 Sex-linked genesCan an orange male and a black female produce a tortoiseshell male?No!
15 Sex-linked genesWhat is the genotype of the father?
16 Sex-linked genes Mother can provide XB or XO Father can provide Y plus 1 other allele.Since 1 offspring is XO XO, the father must provide 1 of these allele.Therefore, the father's genotype is XOY