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.  DI-HYBRID INHERITANCE

 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. Tt Yy  Homologous chromosomesHomologous chromosomes with gene for stem length (Tt) 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 NO LINKAGE

 We cross the tall yellow (TY) with the short green (ty)  The F1 generation are all tall plants with yellow seeds. SO FIRSTLY… ty TYTtYy

 We have to work out how to put TtYy into a big punnett square. NOW…

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

 TtYy x TtYy  Try complete it yourselves. NOW, THE F2 GENERATION TYTytYty TY Ty tY ty

 TtYy x TtYy NOW, THE F2 GENERATION TYTytYty TYTTYYTTYyTtYYTtYy TyTTYyTTyyTtYyTtyy tYTtYYTtYyttYYttYy tyTtYyTtyyttYyttyy

 TtYy x TtYy NOW, THE F2 GENERATION TYTytYty TYTTYY Tall, yellow TTYy Tall, yellow TtYY Tall, yellow TtYy Tall, yellow TyTTYy Tall, yellow TTyy Tall, green TtYy Tall, yellow Ttyy Tall, green tYTtYY Tall, yellow TtYy Tall, yellow ttYY Short, yellow ttYy Short, yellow tyTtYy Tall, yellow Ttyy Tall, green ttYy Short, yellow ttyy Short, green

 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. RATIOS

 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/TtYY/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/TtYY/TtYy)  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/TtYY/TtYy)  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 (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/TtYY/TtYy)  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 (TtYY)  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/TtYY/TtYy)  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 (TtYY)  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 (TtYy) PURE-BREEDERS

 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 F1 offspring had purple flowers and long pollen grains. a)Give the genotype of the F1 offspring b)Now cross the F1 gens QUESTION