DIHYBRID INHERITANCE DIHYBRID INHERITANCE Only complete dominance is

DI-HYBRID INHERITANCE

DI-HYBRID INHERITANCE **Only complete dominance is assessed at this level**

DI-HYBRID INHERITANCE Di-hybrid inheritance is the inheritance of two genes controlling two different features.

DI-HYBRID INHERITANCE Di-hybrid inheritance is the inheritance of two genes controlling two different features. The genes may have two or more different alleles.

DI-HYBRID INHERITANCE Di-hybrid inheritance is the inheritance of two genes controlling two different features. The genes may have two or more different alleles. The alleles may be on the same (homologous) chromosome so are linked, or they may be on different chromosomes so are not linked. http: //biology. clc. uc. edu/courses/bio 105/sex-link. htm

NO LINKAGE This is the typical form of dihybrid inheritance. EG – in pea plants, tall stem (T) is dominant to short stem (t) and yellow seeds (Y) are dominant to green seeds (y).

NO LINKAGE This is the typical form of dihybrid inheritance. EG – in pea plants, tall stem (T) is dominant to short stem (t) and yellow seeds (Y) are dominant to green seeds (y). The two genes are on different homologous chromosomes. T t Homologous chromosomes with gene for stem length (Tt) Y y Homologous chromosomes with gene for seed colour (Yy)

NO LINKAGE Cross a tall, yellow seeded plant pure breeding for both traits (TTYY)

NO LINKAGE Cross a tall, yellow seeded plant pure breeding for both traits (TTYY) With a short, green-seeded plant pure breeding for both traits (ttyy)

NO LINKAGE Cross a tall, yellow seeded plant pure breeding for both traits (TTYY) With a short, green-seeded plant pure breeding for both traits (ttyy) Each gamete must inherit an allele for height as well as seed colour.

NO LINKAGE Cross a tall, yellow seeded plant pure breeding for both traits (TTYY) With a short, green-seeded plant pure breeding for both traits (ttyy) Each gamete must inherit an allele for height as well as seed colour. The combination of alleles is random because of independent assortment.

NO LINKAGE Cross a tall, yellow seeded plant pure breeding for both traits (TTYY) With a short, green-seeded plant pure breeding for both traits (ttyy) Each gamete must inherit an allele for height as well as seed colour. The combination of alleles is random because of independent assortment. The tall yellow plant can only produce gametes with T and Y alleles, and the short green plant t and y

NO LINKAGE Cross a tall, yellow seeded plant pure breeding for both traits (TTYY) With a short, green-seeded plant pure breeding for both traits (ttyy) Each gamete must inherit an allele for height as well as seed colour. The combination of alleles is random because of independent assortment. The tall yellow plant can only produce gametes with T and Y alleles, and the short green plant t and y Therefore – the cross would be TTYY x ttyy

SO FIRSTLY… We cross the tall yellow (TY) with the short green (ty) ty TY Tt. Yy The F 1 generation are all tall plants with yellow seeds.

NOW… We have to work out how to put Tt. Yy into a big punnett square.

NOW… We have to work out how to put Tt. Yy into a big punnett square. T & Y to get TY T & y to get Ty t & Y to get t. Y t & y to get ty

NOW, THE F 2 GENERATION Tt. Yy x Tt. Yy TY Ty t. Y ty Try complete it yourselves. t. Y ty

NOW, THE F 2 GENERATION Tt. Yy x Tt. Yy TY Ty t. Y ty TY TTYy Tt. YY Tt. Yy Ty TTYy TTyy Tt. Yy Ttyy t. Y Tt. Yy tt. YY tt. Yy ty Tt. Yy Ttyy tt. Yy ttyy

NOW, THE F 2 GENERATION Tt. Yy x Tt. Yy TY Ty t. Y ty TY TTYY Tall, yellow TTYy Tall, yellow Tt. YY Tall, yellow Tt. Yy Tall, yellow Ty TTYy Tall, yellow TTyy Tall, green Tt. Yy Tall, yellow Ttyy Tall, green t. Y Tt. YY Tall, yellow Tt. Yy Tall, yellow tt. YY tt. Yy Short, yellow ty Tt. Yy Tall, yellow Ttyy Tall, green tt. Yy ttyy Short, yellow Short, green

RATIOS The expected ratio is 9 tall, yellow seeded: 3 tall, green seeded : 3 short yellow seeded: 1 short, green seeded.

RATIOS The expected ratio is 9 tall, yellow seeded: 3 tall, green seeded : 3 short yellow seeded: 1 short, green seeded. The 9: 3: 3: 1 ratio is ALWAYS the probability of getting each phenotype when two heterozygote dihybrids with complete dominance and the alleles are not linked.

PURE-BREEDERS Same with monohybrids

PURE-BREEDERS Same with monohybrids EG – a pea plant is tall with yellow seeds. We need to find out whether it is homozygous or heterzygous for one or both features. (TTYY/TTYy/Tt. YY/Tt. Yy)

PURE-BREEDERS Same with monohybrids EG – a pea plant is tall with yellow seeds. We need to find out whether it is homozygous or heterzygous for one or both features. (TTYY/TTYy/Tt. YY/Tt. Yy) If the offspring are all tall with yellow seeds the parent was homozygous for both genes (TTYY)

PURE-BREEDERS Same with monohybrids EG – a pea plant is tall with yellow seeds. We need to find out whether it is homozygous or heterzygous for one or both features. (TTYY/TTYy/Tt. YY/Tt. Yy) If the offspring are all tall with yellow seeds the parent was homozygous for both genes (TTYY) Some tall and some short but all with yellow seeds – the parent is only homozygous for seed colour (Tt. YY)

PURE-BREEDERS Same with monohybrids EG – a pea plant is tall with yellow seeds. We need to find out whether it is homozygous or heterzygous for one or both features. (TTYY/TTYy/Tt. YY/Tt. Yy) If the offspring are all tall with yellow seeds the parent was homozygous for both genes (TTYY) Some tall and some short but all with yellow seeds – the parent is only homozygous for seed colour (Tt. YY) All tall but some with green seeds and some with yellow, the parent is only homozygous for height (TTYy)

PURE-BREEDERS Same with monohybrids EG – a pea plant is tall with yellow seeds. We need to find out whether it is homozygous or heterzygous for one or both features. (TTYY/TTYy/Tt. YY/Tt. Yy) If the offspring are all tall with yellow seeds the parent was homozygous for both genes (TTYY) Some tall and some short but all with yellow seeds – the parent is only homozygous for seed colour (Tt. YY) All tall but some with green seeds and some with yellow, the parent is only homozygous for height (TTYy) Some tall and some short, some green and some yellow, then the parent is heterozygous for both height and seeds (Tt. Yy)

QUESTION When sweetpea plants pure breeding for purple flowers and long pollen grains were crossed with sweetpeas that are pure breeding for red flowers and round pollen grains, all the F 1 offspring had purple flowers and long pollen grains. a) Give the genotype of the F 1 offspring b) Now cross the F 1 gens