pairs of chromosomes inherited by offspring can be inherited from either
parent and in any random combination so each offspring has its own unique
identity (unless an identical twin from a single egg). As already mentioned
when genetic recombination takes place a special type of cell division takes
place during the formation of sperm and egg cells that gives them the
correct number of chromosomes. Each has only half the number of chromosomes
other body cells have. Inside the cells that produce sperm and egg cells,
chromosomes become paired and each may swap a portion of its genetic
material for the matching portion of its mate. After this crossover occurs
the chromosomes separate and are parceled out into individual sex cells.
Each of the chromosomes moves independently of the others. So what
chromosome of one pair is inherited doesnít influence what copy of the other
32 pairs is inherited.
egg or sperm, the gametes, receive one of 2 possible chromosomes 32 times
(the total number of possibilities is 2 raised to the 32nd power)
or more than 1,589 million possibilities.
recombination of genes makes it impossible to predict the outcome of any
given mating and until more genetic markers have been identified pedigree
charts using the rules of inheritance is the only way of planning matings.
is a misconception is that genes alter from one generation to the next. This
is simply not the case. The particular
characteristic is either expressed in the individual or recessive. Remember Mendel and his peas and Thomas and his fruit
What does alter though is the
overall genetic base as the 32 pairs of chromosomes could be inherited from
either parent in random combination. Each new individual is unique and
involves a random recombination of its parents. Hence two siblings can be
unlike e.g. Sadlerís Wells and Fairy King. It is important to recognize that
every individual is unique and represent a combination of genes that have
never been together before in that particular combination. With humans the
number of potential pedigrees before a repeat is necessary has been
estimated at 10^477. This is somewhere between a number I cannot imagine and
infinity. I have heard the figure 300 billion mentioned.