NAME ___ANSWER KEY________________ PUNNETT SQUARE PRACTICE #1 Use a Punnett Square to show the possible offspring from the crosses given and answer the questions: IN PEAS: R = round r = wrinkled t = short T = tall Y = yellow peas P = purple flowers y = green peas p = white flowers MAKING MONOHYBRID CROSSES: Use colors to circle the offspring with the same phenotype. Y Y Yy Yy What is the genotype of a HOMOZYGOUS YELLOW SEED plant? = __YY_____ What is the genotype of A HOMOZYGOUS GREEN SEED plant? = ___yy_____ y What is the genotype of a HETEROZYGOUS YELLOW plant? = ___Yy_____ y Yy Yy Make a cross between a PURE YELLOW SEED parent and a PURE GREEN SEED parent. POSSIBLE OFFSPRING GENOTYPE PHENOTYPE __Yy_______ __Yellow seeds_______________ What is the probability an offspring will show the DOMINANT TRAIT (YELLOW SEEDS)? __100% or 4/4_______ What is the probability an offspring will show the RECESSIVE TRAIT (GREEN SEEDS)? _0% or 0/4_______ * * * * * * * * * * * * * * * MAKING MONOHYBRID CROSSES: Use colors to circle the offspring with the same phenotype. P P What is the genotype of a PURE PURPLE FLOWERED plant ? = _PP_______ What is the genotype of a PURE WHITE FLOWERED plant? = __pp_______ p Pp Pp p Pp Pp What is the genotype of a HYBRID PURPLE FLOWERED plant? = _Pp_______ Make a cross between a HOMOZYGOUS PURPLE FLOWERED plant and a HOMOZYGOUS WHITE FLOWERED plant. POSSIBLE OFFSPRING GENOTYPE PHENOTYPE __Pp______ __purple flowers_______________ What is the probability an offspring will show the DOMINANT TRAIT (PURPLE FLOWERS)? _100% or 4/4__________ What is the probability an offspring will show the RECESSIVE TRAIT (WHITE FLOWERS)? _0% or 0/4____________ SEE A PATTERN FOR HOMOZYGOUS MONOHYBRID CROSSES: If you cross plants that are PURE DOMINANT for a trait with plants that are PURE RECESSIVE for that trait, _100___ % of the offspring will show the DOMINANT trait and the _recessive________ trait will not show at all. USE THE PATTERN ABOVE TO MAKE PREDICTION ABOUT A CROSS If you cross a HOMOZYGOUS ROUND SEED plant with a PURE WRINKLED SEED plant 100% will look __Round________________ 0% will look ___Wrinkled_________________ The offspring will have a 100% probability of having the _Rr_____ genotype. * * * * * * * * * * * * * * 3. MAKE SOME HETEROZYGOUS MONOHYBRID CROSSES B A black coat (B) is DOMINANT in guinea pigs. A brown coat (b) is RECESSIVE. b What is the genotype of a HOMOZYGOUS BLACK guinea pig? = __BB_____ B BB Bb What is the GENOTYPE of a HETEROZYGOUS BLACK guinea pig? =__Bb_______ What is the GENOTYPE of a brown guinea pig? =__bb________ b Bb bb Make a cross between TWO HETEROZYGOUS BLACK guinea pigs. POSSIBLE OFFSPRING GENOTYPE PHENOTYPE ___BB________ __black_______________ ___Bb________ __black________________ __bb_________ ___brown______________ What is the probability that a baby will be black? __3/4_______ What is the probability that a baby will be brown? __1/4_______ What is the probability the baby will be a HYBRID? __1/2______ What is the probability the baby will be HOMOZYGOUS DOMINANT ? _1/4________ What is the probability the baby will be HOMOZYGOUS RECESSIVE? ___1/4________ * * * * * * * * * 4. Purple fur (P) is DOMINANT in monsters. Yellow fur (p) is RECESSIVE. P p * * * * What is the genotype of a PURE PURPLE monster? = _PP_______ What is the GENOTYPE of a HETEROZYGOUS purple monster? __Pp_______ P PP Pp What is the GENOTYPE of a YELLOW monster? = ___pp_____ Make a cross between TWO HETEROZYGOUS PURPLE MONSTERS. p Pp pp GENOTYPES POSSIBLE OFFSPRING PHENOTYPES _PP__________ ___purple______________ _Pp__________ ___purple______________ __pp_________ ___yellow______________ * * What is the probability that a baby will be purple ? _3/4_________ What is the probability that a baby will be yellow? _1/4_________ What is the probability the baby will be a heterozygous? _1/2________ What is the probability the baby will be HOMOZYGOUS DOMINANT ? __1/4_______ What is the probability the baby will be HOMOZYGOUS RECESSIVE? ____1/4_______ * * * * * * * * * * SEE A PATTERN FOR HETEROZYGOUS MONOHYBRID CROSSES: * * * * If you cross 2 parent plants that are BOTH HETEROZYGOUS for a trait the offspring will show a _3 : 1____ phenotypic ratio. __75___ % of the offspring will show the DOMINANT trait and __25___ % of the offspring will show the RECESSIVE trait. USE DOMINANT OR RECESSIVE TO FILL IN THE BLANKS BELOW: ¼ of the offspring will have two __dominant_________ alleles, ½ will be hybrids with one __dominant_____ and one ___recessive__ allele, and ¼ will have two ___recessive______ alleles. USE THE PATTERN ABOVE TO MAKE PREDICTION ABOUT A CROSS If you cross two HETEROZYGOUS ROUND SEED plants 75% will look _____Round_____________ 25% will look ______Wrinkled____________ The probability is: ¼ will have the genotype _RR__ ½ will have the genotype _Rr__ ¼ will have the genotype _rr__ Scientists have been investigating the genetic make up of the residents in Bikini Bottom. Complete the following questions about these inhabitants. For each genotype below, indicate whether it is HETEROZYGOUS (HE) or HOMOZYGOUS (HO). TT __HO_____ Bb ___HE__ DD ___HO__ tt ___HO___ Ff ___HE__ Dd __HE_____ ff ___HO___ bb ___HO__ BB __HO___ FF __HO__ Determine the PHENOTYPE for each genotype given. IN SPONGE PEOPLE the allele for YELLOW BODY COLOR (Y) is DOMINANT to BLUE (y). YY = ___yellow________ Yy = __yellow__________ yy = __blue____________ IN SPONGEPEOPLE the allele for SQUARE SHAPE (S) is dominant to ROUND (s). SS = __square_________ * * * Ss = __square___________ * * * ss = ____round___________ * * * * * * * * 5. SpongeBob Squarepants recently met SpongeSuzie Roundpants at a dance. SpongeBob is HETEROZYGOUS for his square pants, but Suzie is ROUND. Use the gene code above to create a Punnett square to show the possibilities that could result if SpongeBob and SpongeSuzie had children. S What is Spongebob’s genotype? ____Ss_________ s What is Spongesuzie’s genotype? ____ss_______ * s Ss ss What are the chances a child will have a square shape? __2______ out of 4 OR _50______% s Ss ss What are the chances a child will have a round shape? __2______ out of 4 OR __50_____% * * * * * * * * * * * * * * In SQUID PEOPLE the allele for LIGHT BLUE SKIN (B) is DOMINANT over the GREEN (b) allele. Everyone in Squidward’s family has light blue skin. His family brags that they are a “purebred” line. He recently married a nice girl with light green skin, which is recessive. Create a Punnett square to show the possible offspring from this match. B List the possible genotypes and phenotypes for the kids B _Bb________ b Bb b What are the chances of a child with green skin? __0____% Bb Bb Bb __Light blue skin____________ Would Squidward’s children still be considered “purebreds”? EXPLAIN WHY or WHY NOT. YES NO All of Squidward’s children are hybrids and could potentially pass green skin on to their own children. H H d Hd Hd d Hd Hd H d d Hd dd d Hd dd T T t Tt Tt t Tt Tt T t t Tt tt t Tt tt PUNNETT SQUARES #3 IN PEAS: R = round r = wrinkled T = tall t = short Y = yellow peas P = purple flowers y = green peas p = white flowers 8. MAKING HOMOZYGOUS TWO GENE CROSSES: (X = crossed with) Use colors to circle the offspring with the same phenotype. HOMOZYGOUS TALL & ROUND Parent genotype __TTRR____________ Possible gametes _TR___ X PURE SHORT & WRINKLED ____ttrr_______________ _tr___ tr What percent will be? TR __100% TALL & ROUND __0___ SHORT & ROUND TtRr __0___ TALL & WRINKLED __0___ SHORT & WRINKLED SEE A PATTERN FOR HOMOZYGOUS TWO GENE CROSSES: If you cross plants that are PURE DOMINANT for TWO TRAITS with plants that are PURE RECESSIVE for TWO TRAITS, __100___ % of the offspring will look DOMINANT for BOTH traits and the __recessive_________ traits will not show at all. 9. MAKING HETEROZYGOUS DIHYBRID CROSSES: Use different colors to circle the offspring with the same PHENOTYPE HETEROZYGOUS TALL & ROUND Parent genotype __TtRr____________ Possible gametes _TR_ _Tr_ _tR_ _tr_ X HYBRID TALL & ROUND ___TtRr_______________ _TR___ _Tr___ _tR___ _tr___ TR Tr tR tr TR TTRR TTRr TtRR TtRr __3/16__ TALL WRINKLED Tr TTRr TTrr TtRr Ttrr __9/16_____ TALL ROUND tR TtRR TtRr ttRR ttRr __1/16_____ SHORT WRINKLED tr TtRr Ttrr ttRr ttrr __3/16_____ SHORT ROUND What is the probability the offspring will be 10. MAKING HETEROZYGOUS DIHYBRID CROSSES: Use different colors to circle the offspring with the same PHENOTYPE. HYBRID TALL with YELLOW PEAS X HETEROZYGOUS TALL with YELLOW PEAS Parent genotype __TtYy_____________ ___TtYy___________________ Possible gametes TY_ _Ty_ _tY_ _ty_ _TY_ _Ty__ tY_ ty_ TY Ty tY ty What is the probability the offspring will be TY TTYY TTYy TtYY TtYy __3/16_ SHORT w/ YELLOW PEAS Ty TTYy TTyy TtYy Ttyy tY TtYY TtYy ttYY ttYy ty TtYy Ttyy ttYy ttyy __3/16_ TALL w/ GREEN PEAS _1/16__ SHORT w/ GREEN PEAS _9/16__ TALL w/ YELLOW PEAS FIND THE PATTERN FOR HETEROZYGOUS DIHYBRID CROSSES : If you cross 2 parent plants that are BOTH HETEROZYGOUS for TWO TRAITS, the offspring will show a __9_ : _3_ : _3_ : _1_ phenotypic pattern. Fill in the blanks below with: DOMINANT or RECESSIVE 9/16 of the offspring will show both __dominant__________ traits. 3/16 will look _dominant________ for trait 1 and __recessive______ for trait 2. 3/16 will look __recessive________ for trait 1 and __dominant______ for trait 2. 1/16 will look __recessive_________ for both traits. USE THIS PATTERN TO TELL THE POSSIBLE OFFSPRING OF A HETEROZYGOUS DIHYBRID CROSS WITHOUT USING A PUNNETT SQUARE: R = round r = wrinkled T = tall t = short RrTt X RrTt 9/16 will look Round and Tall 3/16 will look Round and Short 3/16 will look Wrinkled and Tall 1/16 will look Wrinkled and Short P = purple p= white T= tall t = short PpTt X PpTt 9/16 will look Purple and Tall 3/16 will look Purple and Short 3/16 will look White and Tall 1/16 will look White and Short DIFFERENT PATTERNS FOR HOMOZYGOUS AND HETEROZYGOUS CROSSES: Rhett and Scarlett are expecting a baby. Rhett’s rich uncle has promised them $1 million if their baby has blue eyes and is a boy to carry on the family name. In humans males have Xy alleles and females have XX alleles. Brown eyes (B) are dominant over blue eyes (b). Rhett has brown eyes. Scarlett has blue eyes. Fill in the Punnett square with Rhett and Scarlett’s possible gametes. Rhett’s Genotype BbXy Possible gametes _BX__ _bX_ _By_ _by_ Scarlett’s Genotype bbXX _bX What genotype does a baby need to be a blue eyed boy? _bbXy___________ (and get the $1 million) Use a Punnett square to show the possible genotypes for their baby. bX BX bX By by __1/4_ Brown eyed boys BbXX bbXX BbXy bbXy __1/4_ Brown eyed girls __1/4_ Blue eyed girls __1/4_ Blue eyed boys What is the probability they will have a BLUE-EYED BOY and get the $1 million? __25% or 1/4______ Why does this cross not follow the 9:3:3:1 pattern for DIHYBRID (2 gene) crosses? Both parents have to be dihybrids for a dihybrid cross. Since Scarlett is homozygous for her b’s and X’s, she’s not a dihybrid. Punnett Square practice problems obtained from Cheryl Stover (Thanks, Cheryl!)
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