This content provides a comprehensive overview of Topic 6 for GCSE Biology: Inheritance, Variation, and Evolution, covering key concepts from DNA structure and reproduction to genetic variation, evolution theories, and biological classification.
Mind Map
คลิกเพื่อขยาย
คลิกเพื่อสำรวจ Mind Map แบบอินเตอร์แอคทีฟฉบับเต็ม
in this video we're going to be looking
at topic six of GCSE biology and that is
inheritance variation and evolution here
are some of the subtopics we're going to
be looking at in a bit more depth
throughout this video and as always all
of these pages are going to be available
on my Etsy page which is linked in the
description thank you very much for
watching and I hope you
enjoy first of all we have DNA now as
you can see the big diagram across from
the top to the bottom of the screen is
effectively what DNA looks like DNA has
a double helix structure which just
means it has two of these big spirals
going all the way through it and within
it which are the multicolored lines
going across are base pairs that make up
genetic code now in the top left you see
a photo of an animal cell inside that
animal cell we have a nucleus and inside
the nucleus as we zoom in are these
chromosomes which are those little x's
and then if we look at one of those
chromosomes a tiny section of a
chromosome is called a gene and those
genes are made up of these DNA
strands it is very important you
understand the diagram going on here as
it's something you will be asked about
in your
exam next we have the definition of a
genome The genome is just the entire set
of genetic material within an organism
now this could vary from person to
person everyone will have their
different DNA this will also be the same
for plants or any other multicellular
organism in the world
next we look at reproduction there are
two types of reproduction we have sexual
and asexual it is very important you
understand the differences between these
two things starting off with sexual
reproduction sexual reproduction
involves two parents it produces gametes by
by
meiosis and it is a mixture of genetics
from each parent so one from the mother
and one from the
father in asexual reproduction it
involves one parent produces identical
Offspring via mitosis which is cell
division we would have explored in a
previous Topic in paper one and The
Offspring are genetically identical
there is no variation whatsoever this is
something that plants use a lot so they
will have Merry stems in their roots and
shoots and that is how they grow upwards
soil next we look at
meiosis here is a diagram for meiosis
down the left hand side again very
important that you're able to understand
this if you have any questions please
ask me down in the comments I will get
back to you the bullet points on the
right just explain each stage that's
going on here so the cell duplicates its
DNA before the cell division as you can
see we have two of every chromosome
going down in a line in the top
cell next these chromosomes line up in
the center of the cell before they are
pulled apart to either side so in the
third stage of this diagram on the left
hand side you can see they're being
pulled apart to their separate sides and
then once they're at their either end
the cells will divide again into four
different gametes so gamt again are
those sex cells that have half the DNA
required and the point of this is that
when they then fuse together with
another gami they will produce a full
chromosomes next we have genetic
diagrams and
variation genetic diagrams there's not
really much to it to be honest this is
fairly straight forward the only thing
you do need to know is how a punet
square works so I've given us an example
and this is a punet square down here the
the 2x two table in the bottom left so
what I've shown here is The Offspring
between a male and a female now everyone
knows it is a 50% chance whether you get
a a male or a female Offspring so a boy
or a girl when they're born uh and this
is the reason for it so a male will have
XY chromosomes which is down the left
hand side and a female has XX
chromosomes you don't need to worry too
much about that just remember those two
things and you can see here if we purely
just combine the two things it shows us
four different options that we could get
and you can see there is two out of four
possibilities of getting an XX
chromosome which is 50% chance of a male
or 50% chance of getting an XY
chromosome which is female and that is
why we have 50% chance of either getting
a boy or a girl where they're born
this can also be used to determine
phenotypes or physical features in
Offspring so a good example is eye color
so let's say the XY it doesn't exactly
work the same way but let's say the XY
is for blue eyes and the XX is for brown
eyes so if two people were to have an
offspring then there would be a certain
chance of them having blue eyes or brown
eyes as a result of it something I
haven't actually included in this which
I would recommend you looking at is
dominant and essive Ali so please do
take the time especially triple students
combined students is good that you know
about it as well uh but that is
something that's very important the
dominant Ali will determine they they
effectively have more power than the recessive
recessive
alals next we look at variation so
genetic variation is just differences in
the genes and Ali between organisms so
this is a
genotype sometimes genetic variation can
be caused by mutations and sometimes
this can lead to disorders such as polya
or cystic fibrosis these are two common
genetic disorders that it is good you
know about because sometimes again they
do ask you about it in maybe a case
study or something equivalent to that
and sometimes genetic variation isn't
the only thing and environmental
variation can also cause changes so
physical differences or those phenotypes
again can be caused by factors other
than genes such as food or exercise so
if you put two identical twins if one of
them eats I don't know 4,000 calories a
day and the other one only eats 2,000
calories a day and goes to the gym or
you know sits in a chair all day with
bad posture they're going to grow apart
to be different and that's an example of environmental
