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BRIAN: In this lab,
your task is going to be

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to write a program in C that simulates
the inheritance of blood type genes

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within a family.

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To give a little bit
of science background,

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your blood type is
determined by alleles.

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Alleles are different
versions of a gene.

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And there are three different
alleles with regard to blood type,

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called A, B, and O.

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Each person has two of these alleles.

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Maybe you have two
A's, two B's, two O's.

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Or maybe you mix and match, have
an A and a B, or a B and an O,

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or an A or an O, for example.

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And when a parent has a child, each
parent passes on one of their alleles

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to their child.

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So for example, if we
imagine two parents,

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one that has a blood type of AB
and one who has a blood type of OO,

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tthen their child is going to
inherit one blood type of little

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from each of their parents.

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For example, we might randomly
choose A from one parent,

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and between the other parent O, and
ultimately get a blood type of AO.

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But we also could have gotten a
blood type of BO, for example.

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Which of the two alleles is passed
on is just chosen at random.

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In order to simulate this type of
inheritance inside of our program,

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we're going to need some
sort of data structure

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that lets us represent the connection
between people and their parents,

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as well as what alleles they
have for their blood type.

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And because there is no type
built into C to do just that,

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we can create a type of
our own using a typedef.

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So here, we have typedef struct
person, where every person is going

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to be represented by these two fields.

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Struct person star *parents[2] means
that every person is going to have

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an array of 2 parents, where each of
those parents is going to be a pointer

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to another person.

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Meanwhile, every person is also going to
have an array of two characters called

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alleles, representing which two alleles,
A, B, or O, this particular person has.

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And because each person has two alleles,
this is going to be an array of size 2

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to represent both of those alleles.

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So in the example we saw before, we
might, for this particular child,

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have the letter A stored at this child's
alleles 0 and 0 stored at alleles 1.

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And meanwhile, parents[0] would point to
one of the parents and parents[1] would

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point to the other parent.

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Let's see how these pieces
now would come together inside

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of the distribution code that
we give to you for the lab.

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There is a fair amount
of distribution code

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that we already give to
you inside of inheritance.c

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But let's try and distill it
to just what's most important.

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Here we'll notice that same
typedef, that we define a person

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as having pointers to two parents
in this array of 2 pointers

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and also having an
array of two characters,

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representing the two alleles that
this person has for their blood type.

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Next up is this relevant variable
called const int GENERATIONS,

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a constant integer, which is
set equal to the number of 3.

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And this is going to represent
the number of generations of data

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that we're going to simulate generating.

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In this case, we're simply
waiting three generations

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worth of data for blood types,
which means we're not just

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going to simulate the single
child, but also generation

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2, their parents, and also generation
3, that child's grandparents as well.

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We then have some
prototypes for functions,

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but let's skip down to the
main function to really see

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what it is that this program is doing.

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The main function is
already written for you.

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Nothing you need to do here.

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But we start by seeding the
random number generator,

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just so that we're able to generate
pseudo random numbers, which

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is going to be useful.

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Because when we decide
how genes are inherited,

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we want to be able to randomly
choose which gene is going

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to be passed on from parent to child.

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Next we call the create_family function
to create a family with a specified

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number of generations, returning a
pointer to the most recent generation

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of person in that family.

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So if we create a family
with three generations,

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we'll end up with a
pointer to one person.

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But using their parent
pointers, we could

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access that child's parents as
well as that child's grandparents,

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but no further if we're only looking
at a family with three generations.

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The create_family function
will be up to you to write.

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But the print family
function we will write.

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After you've already
created a family, we've

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already written for you a function
that will take that family

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and print them out as a
hierarchical family tree,

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printing out what blood type each
of the people in that family has.

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Finally, you'll write
the free_family function,

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which will free all of the memory
that you may have allocated

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in the process of creating this family.

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Because recall that
for each of the people

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that you want to represent
inside of your computer's memory,

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you'll likely need to
allocate memory for them

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by using the malloc function to
allocate some memory dynamically.

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But any time you allocate
memory with malloc,

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you'll also want to free that memory,
giving it back to the computer

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so that it can be used
for other purposes.

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Here then, in the
create_family function,

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is going to be what you'll implement,
allocating memory for a new person

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and then dealing with
two possible cases.

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One, if there are potential
parents that this child has

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that we need to recursively
generate, or else,

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if we're just generating
a single generation,

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generating just a single
person without any parent data.

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You'll also, then, write the
free_family function, which

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takes as input a pointer to a person p.

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And the task for this function is to
free p as well as any ancestors of p.

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So if person p has parents or
grandparents or other ancestors

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as well, you'll want to
make sure to free them, too.

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The print family function
we've written for you.

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No need to do anything here.

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It takes a person and goes ahead
and prints out their entire family

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tree, along with their blood types.

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And this random allele function that
we wrote might be helpful for you, too.

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It randomly chooses
an allele, A, B, or O,

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which can be useful
if you get to a point

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where you need to randomly
generate an allele

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to store inside of that allele's array.

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So with that distribution
code in mind, let's then

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walk through what it is that
your program is going to do.

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The first thing you should do is
complete the create_family function

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to create a family with a
specified number of generations.

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In order to do so, the
first thing you should do

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is allocate memory for a
new person, calling malloc,

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passing in size of
person to make sure you

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have enough memory for a new person.

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And then you'll use that person
to potentially generate ancestors

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if there are more generations
that you need to work with.

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So if generations is greater than 1,
meaning there are more generations

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that you need to generate,
then you'll recursively

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create those previous generations.

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What does it mean to recursively
create previous generations?

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Well, if you're trying to create a child
that has two generations of parents

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then you'll recursively call
the create_family function

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for each of those parents
where each one of those parents

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will have one generation of
parents, and so on and so forth.

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So if generations is
greater than 1, you'll

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want to recursively create
those previous generations.

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And using the return value you get
from those create_family functions,

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you'll update this new person's parents,
setting parents[0] equal to the result

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of one recursive call and setting
parents[1] equal to the result of some

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other recursive call.

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After you set that
person's parents, recall

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that every person not only
has two pointers to parents,

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but also has two alleles.

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So now you'll need to do the
actual inheritance step, inheriting

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one allele from each parent at random.

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So you want to inherit the alleles from
the parents by looking at one parents

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two alleles, randomly choosing one, and
setting that as the child's allele 0.

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And then doing the same with the other
parent, looking at their two alleles,

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randomly choosing one, and using one of
those as alleles[1] so that the child

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ends up with two alleles, one
inherited from either parent.

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Otherwise, if generations
is equal to 1, that

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means you're only generating one
generation worth of family, that is,

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an individual person with no parents.

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And if that's the case, then both of the
parent pointers should be set to null.

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And because there is nothing
to inherit, because we

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don't have any data
about the parents, you'll

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go ahead and randomly generate
alleles for each of the two

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alleles for this particular person.

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And recall that, in
the distribution code,

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we give to you a function that will
randomly generate those alleles.

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The final step for this lab is going
to be to write the free_family function

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to free all of that allocated memory.

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Recall that every time you called
the create_family function,

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you were calling malloc
at least once in order

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to generate data for a new
person, to allocate memory

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for that person dynamically
inside of the computer's heap.

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Now, after you've
malloced that memory, it's

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your task at the end of the
program to free all of that memory

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up and give it back to the computer.

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In order to do so, you'll want
to first handle the base case.

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If the input to free_family is null,
there is no action you should take.

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You should never be
freeing the null pointer.

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But after that, you'll want to
deal with the recursive case,

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recursively freeing the parents, and
then after that, freeing the child.

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How do you recursively free the parents?

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Well, you'll want to call
the free_family function

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on each of the child's two parents.

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Recursively then, that
will also call for a family

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on the child's grandparents
and higher generations,

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if there are other generations, as well.

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And after those parents have been
freed then you can use free in order

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to free the child as well,
ultimately freeing all of the memory

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that you've allocated
throughout the program.

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After you've written
these two functions,

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you should then be able to run
your inheritance program in order

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to simulate the inheritance of blood
types across multiple generations,

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seeing what blood types
the grandparents had,

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seeing how those blood types translated
into the blood types of a child's

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parent, and ultimately, what blood
type that child inherited as well.

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My name is Brian.

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And this was inheritance.

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