In maize, liguleless (l) is recessive to having ligules (L), and dwarf (d) is recessive to tall (D). These two genes are linked on chromosome 3. A cross is made and the F2 consisted of the following progeny:

F2 phenotype Number of progeny
Ligules, tall 6156
Liguleless, tall 1344
Ligules, dwarf 1344
Liguleless, dwarf 1156

a. In this cross, are these genes in coupling or repulsion? Why?
b. What were the phenotype and the genotype of the P and F1 generations?
c. Calculate the percent recombination between these two genes.

given,

LL║ll  and DD║dd,

after crossing over,    Ld║Ld  ×   lD║lD

LLdd × llDD

in F1 generation, they will give, , , LLDD, lldd → LlDd

in eF2 generation, the offsprings will be,  ×  

LLDD ,LLdd, LLDd, llDD, lldd, llDd, LlDD, Lldd, LlDd

1. yes, these genes are coupling.

2. → phenotypes of parental genes = ligules, liguleless, tall and dwarf

    genotypes of parental genes= LLdd, llDD i.e; heterozygous

 →   phenotypes of F1 generation = 25% Ligules, 25% tall, 25% ligules-tall, 25% liguleless-dwarf

      genotypes of F1 generation = heterozygous ; LlDd that is ligules-tall

3. recombination frequency= no of recombinant / total progeny × 100%

                                              = (1344+1344) / 6156+1344+1344+1156  × 100%

                                              = 2688/ 10000 × 100%

                                              = 26.88 %

that means linkage happened

and the map distance is 26.88 map unit.

c. earths continental crust is thicker than its lithosphere.

because, the lithosphere is the outermost layer of the earth/ 100 km thick and is defined by its machanical properties.the lithosphere contains oceanic and continental crust that varies in age and thickness across locations and geologic time. the lithosphere is the coolest layer of the earth in terms of temperature. the term lithosphere should not be confused with the use of "geosphere" which is used to indicate all of earth systems, including the atmosphere, hydrosphere   and biosphere. the surface of the earth can be divided into the continental crust and the oceanic crust.   the continental crust is made mostly of granite while the oceanic crust is made of basalt. the average thickness of the continental crust is 25 miles and the average thickness of the oceanic crust is 5 miles.   three types of rock, igneous, sedimentary, and metamorphic, make up the surface of the earth. that's why 3 option is preferable.