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Bookend 1. In a heterozygous tall plant, the ____________ trait shows. It is represented by a _________ letter. ( T ) 2. Tt is a tall or short plant. 3. The ___________ allele does not show in heterozygous individual ( t ). 4. It is ‘covered’ or ‘hidden’ by the _________ allele. 5. The genotype or phenotype is the letters that stand for the versions of the genes. Dominant/Recessive 1. In a heterozygous individual, the dominant trait shows 2. Represented by a capital letter T 3. Tt is a tall plant 4. The recessive allele does not show in heterozygous individual 5. It is ‘covered’ or ‘hidden’ by the dominant allele. 6. The genotype is the letters that stand for the versions of the genes. (Go to SASinschool) Genetics Review of Punnett Squares And Incomplete dominance Codominance Multiple Alleles Polygenic inheritance And Sex determination Punnett Squares • Are used to find the possible genotypes of the offspring (children) of a mating • Also to find the probability of each genotype occurring • Each child (mating) is a new occurrence… each child has the same chance as previous children. Probability Ratios Homozygous . Heterozygous. Homozygous Dominant . . Recessive 1TT 2Tt 1tt 25% 50% 25% Dominant Phenotype: Recessive Phenotype 3 Tall : 1 Short 75% 25% Generation 1. P = Parental = first parents observed (usually homozygous) 2. F1 = First filial = first children of P generation 3. F2 = Second filial = Children of F1, grandchildren of P Draw the Punnett square and answer the question 1. A student crosses two true (pure) breeding pea plants. One has yellow pods and the other has green pods. Yellow is dominant to green. Parent plant genotypes ____ X ____ Draw Punnett square. What phenotypic results will the student find in the F1 generation? Draw the Punnett square and answer the question 2. Guinea pig coat color is determined by a single gene. The allele for black coat color is dominant to brown. In a cross between two black-haired guinea pigs, 20 offspring are born. If both parents were heterozygous, probability would predict that approximately how many of the 20 offspring would have brown hair? Answer the Question 3. What term describes an allele whose characteristic phenotype is masked by the presence of a second, different allele? Draw the Punnett square and answer the question 4. Fifty percent of the offspring produced by a cross between pea plants have seeds with a wrinkled (r) appearance caused by the presence of a homozygous recessive gene. What were the genotypes of the parents? Incomplete Dominance • In the heterozygous individual the phenotype is roughly halfway between the homozygous phenotypes In Snapdragons Red X White -> Pink RR X R’R’ or CRCR X CWCW -> CRCW Codominance • • • • Both alleles are expressed (show) AB Blood groups Checkered chickens Roan Horses • Denoted with Capital letter with super script IAIB Blood Groups A = IA B = IB O = i Multiple Alleles • 3 or more possible alleles • Blood Type Alleles IA, IB, i • Each individual gets only 2 alleles, one on each homologous chromosome Polygenic Inheritance • 2 or more genes controlling the same trait • Traits vary continuously • Hair color • skin color • height Determining Sex • Females are XX, Males are XY • Females have two full sized X chromosomes • Males have one full sized X and one small Y chromosome. The father determines the sex of the child by supplying the X or Y Sex linked Genes • • • • Genes on the X chromosome Hemophilia Color Blindness Muscular Dystrophy Sex linked Continued • Seen most often in men because they carry only 1 X chromosome • The trait only shows in women if they are homozygous • Women are usually carriers • Boys inherit the X chromosome from their mother • Girls must inherit it from both parents Bookend 1. Rr is ____________ for red color. 2. R1R2 is a genotype for __________ dominance and would result in a pink flower 3. AB blood group is an example of ___- dominance. 4. A, B, O blood groups are an example of ___________ ___________ 5. Girls normally have 2 ___ chromosomes 6. Boys normally have 1 ___ and 1 ___ chromosome.