1 Dihybrid Cross - Weebly · Dihybrid Cross n Hybrid is another way of saying heterozygous. A...
Transcript of 1 Dihybrid Cross - Weebly · Dihybrid Cross n Hybrid is another way of saying heterozygous. A...
Life Science: MolecularDihybrid Crosses
Second Law of Heredity
n By observing the inheritance patterns for two different traits Mendel proposed the second law of genetics the principle of independent assortment.
Independent Assortment
Genes for different traits can segregate independently during the formation of gametes.
n Each dominant trait is represented by a capital letter, ‘R’ for round, ‘Y’ for yellow.
n The recessive traits are represented by lower case letters, ‘r’ for wrinkled, ‘y’ for green, etc.
n When writing a genotype for two traits we use 4 letters, (e.g. RRYY)
RRYYRY
RY
Two-Factor Cross
RY
RY
Two-Factor Cross: F1
Punnett Square:n A double homozygous
dominant male produces one type of gamete (RY).
RRYY
RY RY RY RY
rryy
Two-Factor Cross: F1
Punnett Square:n A double homozygous
recessive female produces one type of gamete (ry).
RRYY rryy
ry ry ry ry
RY RY RY RY
Two-Factor Cross: F1
Punnett Square:n All of the F1 individuals are
heterozygous for both traits.
ry
ry
ry
ry
RRYY rryy
RrYy RrYy RrYy RrYy
RrYy RrYy RrYy RrYy
RrYy RrYy RrYy RrYy
RrYy RrYy RrYy RrYy
RY RY RY RY
Dihybrid Cross
n Hybrid is another way of saying heterozygous. A hybrid plant has one of each allele.
n A plant that is heterozygous for two different traits (e.g. RrYy) is called a double-heterozygote, or dihybrid.
Two-Factor Cross: F2
RrYy
RY Ry rY ry
RrYyPunnett Square:n A double heterozygous
male produces four types of gametes (RY, Ry, rY, ry).
Two-Factor Cross: F2
RY Ry rY ry
RY Ry rY ry
RrYy RrYyPunnett Square:n A double heterozygous
male produces four types of gametes (RY, Ry, rY, ry).
Two-Factor Cross: F2
Punnett Square:n The dominant and
recessive traits appear in different combinations in the F2 generation.
RY
Ry
rY
ry
RRYY RRYy rRYY rRyY
RRYy RRyy rRYy rRyy
RrYY RryY rrYY rryY
RrYy Rryy rrYy rryy
RY Ry rY ry
RrYy RrYy
Phenotypic Ratios
Pheno = Physical
n 9/16 Round & Yellow
RY
Ry
rY
ry
RRYY RRYy rRYY rRyY
RRYy RRyy rRYy rRyy
RrYY RryY rrYY rryY
RrYy Rryy rrYy rryy
RY Ry rY ry
RrYy RrYy
RY
Ry
rY
ry
RRYY RRYy rRYY rRyY
RRYy RRyy rRYy rRyy
RrYY RryY rrYY rryY
RrYy Rryy rrYy rryy
RY Ry rY ry
Phenotypic Ratios
Pheno = Physical
n 9/16 Round & Yellown 3/16 Round & Green
RY
Ry
rY
ry
RRYY RRYy rRYY rRyY
RRYy RRyy rRYy rRyy
RrYY RryY rrYY rryY
RrYy Rryy rrYy rryy
RY Ry rY ry
RrYy RrYy
Phenotypic Ratios
Pheno = Physical
n 9/16 Round & Yellown 3/16 Round & Greenn 3/16 Wrinkled & Yellow RY
Ry
rY
ry
RRYY RRYy rRYY rRyY
RRYy RRyy rRYy rRyy
RrYY RryY rrYY rryY
RrYy Rryy rrYy rryy
RY Ry rY ry
RrYy RrYy
Phenotypic Ratios
Pheno = Physical
n 9/16 Round & Yellown 3/16 Round & Greenn 3/16 Wrinkled & Yellown 1/16 Wrinkled & Green
RY
Ry
rY
ry
RRYY RRYy rRYY rRyY
RRYy RRyy rRYy rRyy
RrYY RryY rrYY rryY
RrYy Rryy rrYy rryy
RY Ry rY ry
RrYy RrYy
Phenotypic Ratios
n Mendel’s experimental results were very close to the 9:3:3:1 ratio that Punnett squares predict.
9 Round (dominant) and Yellow (dominant)
3 Round (dominant) and Green (recessive)
3 Wrinkled (recessive) and Yellow (dominant)
1 Wrinkled (recessive) and Green (recessive)