Monohybrid & Dihybrid Crosses Review Monohybrid & Dihybrid Crosses

DOMINANT/RECESSIVE T t capital Dominant Recessive lower-case _____________ allele is represented by a ____________ letter. (usually the first letter of the trait) ____________ allele is represented by the SAME _________________ letter. EX: Tall = ______ Short =______ capital Recessive lower-case T t NOT S for short

HOMOZYGOUS HETEROZYGOUS When both alleles in the pair are the _______, the organism is _______________ or __________ EX: ____ or ___ When both alleles in the pair are _____________, the organism is _________________ or _____________ Ex: ____ SAME HOMOZYGOUS PURE TT tt DIFFERENT HETEROZYGOUS HYBRID Tt

PHENOTYPE/GENOTYPE The ________________ of an organism is its _____________ The ____________of an organism is its _____________ genetic makeup GENOTYPE appearance PHENOTYPE

MAKING A CROSS for only a __________ trait = ____________________ ONE GENE MONOHYBRID CROSS A Punnett square for a MONOHYBRID CROSS looks like this:

PUNNETT SQUARES are used to show possible offspring from a cross between 2 parents _______________ go at top and on left side Boxes show ____________ ___________________ Parent alleles T T T t possible offspring combinations

STEPS FOR MAKING CROSSES Figure out parent alleles Choose Punnett size Put in parent gametes Fill in offspring combinations probabilities phenotypes genotypes 1. ___________ what _________________ are 2. ________correct__________ square __________ 3. ______ possible_______________________ 4. ______ boxes with _____________________ 5. Determine ____________of_____________& ____________

T t TALL = ____ SHORT = ____ IN PEA PLANTS Tall is dominant over short LET’S MAKE A CROSS! PURE TALL PURE SHORT X

PURE TALL parent What are the parent alleles? T T _________ HOMOZYGOUS   What gametes can it make? T T

PURE SHORT parent What are the parent alleles? t t _________ HOMOZYGOUS   What gametes can it make? t t

T t T t T t T t T t _____ of the offspring ____ % ___/4 will be ALL 100 4 T t T t Tt TALL GENOTYPE _____ PHENOTYPE _______

HYBRID TALL parent What are the parent alleles? T t _________ HETEROZYGOUS   What gametes can it make? T t

T t T t T t T T T t t t GENOTYPES ¼ = _____ ½ = _____ TT Tt tt 3/4 75 TALL PHENOTYPES ____ or ____% _________ ____ or ____% _________ 1/4 25 SHORT

PRACTICE MAKING GAMETES for a MONOHYBRID CROSS Tall = ____ Round seeds = ___ Short = ____ Wrinkled seeds = ___ T t r

What are the possible gametes? Homozygous Tall parent = What gametes can it produce? T T   T T

What are the possible gametes? PURE wrinkled parent = What gametes can it produce? rr   r r

What are the possible gametes? Heterozygous Round parent = What gametes can it produce? R r   R r

What are the possible gametes? Hybrid Tall parent = What gametes can it produce? Tt   T t

DIHYBRID CROSSES (2 traits) http://mac122.icu.ac.jp/BIOBK/BioBookgenintro.html

Mendel also asked the question? Does the gene that determines if a seed is round or wrinkled have anything to do with the gene for seed shape? Must a seed that is yellow also be round?

MAKING A CROSS with ___________________= ____________________ TWO gene traits DIHYBRID CROSS A Punnett square for a DIHYBRID CROSS looks like this:

Figure 11-10 Independent Assortment in Peas Section 11-3

LET’S MAKE A DIHYBRID CROSS HOMOZYGOUS YELLOW ROUND HOMOZYGOUS GREEN WRINKLED rryy RRYY 1. ___________ what _________________ are 2. ________correct__________ square __________ 3. ______ possible_______________________ 4. ______ boxes with _____________________ 5. Determine ____________of_____________& ____________ Figure out parent alleles Choose Punnett size Put in parent gametes Fill in offspring combinations probabilities phenotypes genotypes

LAW OF __________________________ the factors are distributed to gametes independently of other factors INDEPENDENT ASSORTMENT Image modified from: http://anthro.palomar.edu/mendel/mendel_1.htm

PRACTICE MAKING GAMETES WHAT ARE THE POSSIBLE GAMETES THIS PARENT CAN MAKE? HOMOZYGOUS ROUND YELLOW Each gamete should get one of each kind of gene R R Y Y R Y R Y R Y R Y ___________ ____________ _____________ _____________

PRACTICE MAKING GAMETES WHAT ARE THE POSSIBLE GAMETES THIS PARENT CAN MAKE? Each gamete should get one of each kind of gene HOMOZYGOUS WRINKLED GREEN r r y y r y r y r y r y ___________ ____________ _____________ _____________

PRACTICE MAKING GAMETES WHAT ARE THE POSSIBLE GAMETES THIS PARENT CAN MAKE? HETEROZYGOUS ROUND YELLOW Each gamete should get one of each kind of gene R r Y y R Y r y r Y R y ___________ ____________ _____________ _____________

RY RrYy ROUND YELLOW ry 100% of offspring = _______ genotype RrYy RrYy RrYy RrYy RrYy RrYy RrYy RrYy RrYy RrYy RrYy RrYy RrYy 100% of offspring = _______ genotype _______________________ phenotype ROUND YELLOW

X R r Y y R r Y y MAKE ANOTHER CROSS HETEROZYGOUS ROUND YELLOW

POSSIBLE PARENT GAMETES? RY ry Ry ry

heterozygous dihybrid 9:3:3:1 RY Ry rY ry ____ Round & Yellow ____ Round & green ____ Wrinkled & yellow ____ wrinkled & green 9 RY Ry rY ry RRYY RRYy RrYY RrYy RRYy RRyy RrYy Rryy RrYY RrYy rrYY rrYy RrYy Rryy rrYy rryy 3 3 1 heterozygous dihybrid Sign of a ______________________ cross is a _____________ ratio in offspring. 9:3:3:1

__________ratio is a clue that it’s a 9 ____ ____________ TRAIT 1 ; ____________ TRAIT 2 ____ ____________ TRAIT 1; _____________ TRAIT 2 ____ ____________ TRAIT 1; _____________ TRAIT 2 dominant dominant 3 dominant recessive 3 recessive dominant 1 recessive recessive __________ratio is a clue that it’s a ____________________________cross 9:3:3:1 HETEROZYGOUS TWO gene

PRACTICE MAKING GAMETES for DIHYBRID CROSSES http://www.emc.maricopa.edu/faculty/farabee/BIOBK/BioBookTOC.html

What are the possible gametes? R R T T pure round & pure tall = __________ ____ ____ _____ ______ What gametes can it produce?     R T R T R T R T

What are the possible gametes? T t R R Heterozygous Tall = __________ & pure round ____ ____ _____ ______ What gametes can it produce?     T R t R t R T R

What are the possible gametes? T t r r Hybrid tall = __________ & pure wrinkled ____ ____ _____ ______ What gametes can it produce?     T r t r t r T r

What are the possible gametes? T t R r Heterozygous tall = __________ & hybrid round ____ ____ _____ ______ What gametes can it produce?     T R t r t R T r

The Law of Dominance In a cross of parents that are pure for contrasting traits, only one form of the trait will appear in the next generation.  Offspring that are hybrid for a trait will have only the dominant trait in the phenotype. The Law of Segregation During the formation of gametes (eggs or sperm), the two alleles responsible for a trait separate from each other.  Alleles for a trait are then "recombined" at fertilization, producing the genotype for the traits of the offspring. The Law of Independent Assortment Alleles for different traits are distributed to sex cells (& offspring) independently of one another.

INDEPENDENT ASSORTMENT MENDEL'S GENETIC LAWS Summary: LAW PARENT CROSS OFFSPRING DOMINANCE TT x tt tall x short 100% Tt tall SEGREGATION Tt x Tt tall x tall 75% tall 25% short INDEPENDENT ASSORTMENT RrGg x RrGg round & green x round & green 9/16 round seeds & green pods 3/16 round seeds & yellow pods 3/16 wrinkled seeds & green pods 1/16 wrinkled seeds & yellow pods