If A/A ⋅ B/B is crossed with a/a ⋅ b/b and the F1 is testcrossed, what percentage of the testcross progeny will be a/a ⋅ b/b if the two genes are (a) unlinked; (b) completely linked (no crossing over at all); (c) 10 m. u. apart; (d) 24 m. u. apart?

a) 25%; b) 50%; c) 45%; d) 38%

Explanation:

A/A B/B X a/a b/b

F1: A/a B/b

Testcross A/a B/b X a/a b/b

The homozygous recessive individual only produces ab gametes.

The F1 produces four types of gametes (each of them with a frequency of 1/4):  AB, Ab, aB and ab.

25% of the progeny will be a/a b/b.

AB/AB X ab/ab

F1: AB/ab

Testcross AB/ab X ab/ab

The F1 produces only two types of gametes, the parentals (each of them with a frequency of 1/2):  AB and ab.

50% of the progeny will be ab/ab.

AB/AB X ab/ab

F1: AB/ab

Testcross AB/ab X ab/ab

The F1 produces four types of gametes, the parentals AB and ab and the recombinants Ab and aB.

Since the genes are 10mu apart, 10% of the produced gametes will be recombinant and 90% will be parentals. Since there are two types of parental gametes, each of them has a frequency of 45%.

45% of the progeny will be ab/ab.

This is very similar to c).

Since the genes are 24mu apart, 24% of the produced gametes will be recombinant and 76% will be parentals. Since there are two types of parental gametes, each of them has a frequency of 38%.

38% of the progeny will be ab/ab.

surface mining destroys mountain tops, landscapes, forests and wildlife habitats. on top of that, it leads to soil erosion and destruction of agricultural land. the landscape changes can also disrupt river channels and streams, which leads to flooding. which, can destroy plant life and other animals as well.

explanation:

succession returns a disturbed

ecosystem to a more stable state. this is also classified into two (2) types:

primary succession and secondary succession. the primary succession arises when

a new land is transformed and a bare rock has been exposed providing an environment

that can be occupied for the first time. while, secondary succession occurs

when a previously occupied environment was disturbed that kills much of all its

community

explanation: