Among cattle, having horns is a recessive trait. cattle without horns, which are called polled cattle, are common. suppose a horned male mated with a polled female. their offspring are all polled. on maturity, two cattle of the f1 generation mated. their offspring are a mix of polled and horned cattle. in the f2 generation, is homozygous hi dominant and is homozygous recessive. a.ppb. ppc. pp

Let say, polled (without horn) parent cattle is dominant (PP) and parent horned cattle is recessive (pp). They cross bred which produced all polled calf F1 generation. F1 will be hybrid for trait horn (Pp). On Selfing of F1 progeny ( Pp x Pp) will give  1 homozygous polled  (PP) cattle, 2 heterozygous polled (Pp) cattle and 1 cattle with horn recessive (pp) in F2 generation.

Homozygous dominant: PP recessive: pp

Explanation:

The easiest way to resolve this is by drawing Punnetts squares.

First, you know the F0 is composed of a horned male (to be horned it has to be recessive, so pp) and a polled female (this one could de PP or Pp).

All F1 results polled. If you draw Punnett's square, you'll discover to have all polled female has to be dominant PP.

pp x PP = Pp Pp pP pP = 100% Pp

The alleles of all F1 offspring will be Pp. If you cross two F1 your probabilities are:

Pp x Pp = PP Pp pP pp = 25% PP 50% Pp 25%pp

This means, 25% of the offspring have horns on F2.

relative dating involves things like higher layers are most recent than rocks lower in the sequence. this can be extended to the known sequence of fossils. rocks containing rabbit fossils are later than those containing dinosaur fossils.  

absolute dating methods mainly use radioactive elements that have known rates of decay and produce recognizable products. for example potassium 40 decays to produce argon. once a rock has solidified the argon is trapped. by measuring the argon and potassium0 you can get an accurate number for the age.  

some other methods are good for archaeological ages. dendrochronology involves recognizing the sequence of tree rings. the orientation of magnetized particles in baked clay can be used to date a fire.

hope this .. .