Genetics | NCEA Level 1 Science Strategy Video | StudyTime NZ


– Kia ora I’m Kiya – And I’m McKenzie – And this is StudyTime’s
Level 1 science video for genetics. Genetics is another meaty,
level 1 science standard with lots of definitions to learn and lots of concepts to memorize. – But luckily, like a lot
of other bio standards, we can break it down into
three rough sections, the first of which being DNA
and how exactly it works, inheritance and variation, and thirdly, reproduction, survival,
and good old evolution. – If you want to really
get into the content, check out our walk-through guides, but, follow this video
for strategies for success to come out on top for these exams. – For Bio in NCEA, it’s
critical that you know your definitions very strongly
and that you’re comfortable with using them in a range
of situations so you can use the context in your answers. So some of the key definitions
for this standard is gene, allele, chromosome,
mutation, genotype, phenotype, gamete, zygote, dominant,
recessive, homozygous, heterozygous, pure
breeding, punnett squares, and pedigree charts. Alongside all these definitions
is a really common question asking you to explain the
difference between DNA, genes, alleles, chromosomes,
and resulting genotypes and phenotypes. So, what is DNA? It’s a molecule that holds
all of our genetic information like a blueprint, and it stays
in the nucleus of the cell until it undergoes mitosis or meiosis. Now what DNA has is links
of base sequences that code for amino acids and proteins
that carry out functions in our body. Now a length of DNA is called a gene, and an allele is an alternate
version of a gene. So say for example the gene is eye color. An allele of it might be
blue eyes versus brown eyes. Now that’s a relationship
between genes and alleles. Now these result in
genotypes and phenotypes. So what your genotype is is
it’s the pair of chromosomes that you have for a gene,
and these can be dominant or recessive, and what the
phenotype is the physical expression of this gene. So if you’re having
trouble remembering it, remember that phenotype,
physical expression, you got that P-H, P-H there, so link those together in your mind. – This standard is all
about variation which is the differences that individuals
can have in their genetic makeup. One of the main ways of
gaining variation is through mutation, which is a change
in a DNA base sequence, meaning that a different
protein is made and a different phenotype is produced. This is important because
it results in the production of a new allele. Another way of gaining
variation is through meiosis. Remember meiosis creates
gametes or sex cells, whearas mitosis is the
production of non-sex cells or somatic cells. Each individual has 23
pairs of chromosomes, meaning two copies of a gene,
and therefore two alleles. For example, you can
have a big W and small w where big W is one allele
and small w is another. Each gamete made in
meiosis has only one set of our 23 chromosomes, so
only one copy of a gene. One set is from our mom,
and one for our dad. Chromosomes shuffled randomly
increases variation during meiosis, and this random
assortment ensures that a different gamete is produced each time. Another source of variation
is through fertilization. Sex reproduction combines
DNA from two parents using gametes. A gamete has one set of
chromosomes, and you can combine this with another
pair and set of chromosomes to make a unique individual. So random male and female
chromosomes will combine to make a unique zygote,
or fertilized egg. So this random reproduction
increases variation through individuals. – As you’ve been painfully aware of by now this standard also
requires that you interpret and sometimes draw punnett
square or pedigree charts. Now what punnett sqaures are
is it shows you the expected genetypic outcome of a
pairing of two organisms. Now within this, for merit and
excellence, what you really want to be doing is
discussing how it’s all a game of probability, and that
there will sometimes be a difference between your
expected phenotype outcome and what actually happens,
the practical outcome. And this is because, every
pairing, every fertilization is completely by chance,
and what this means that every time fertilization
occurs you have a one in four chance of getting any of
those genotypic outcomes. Now pedigree charts can
be kind of thought of as a genetic family tree,
where you’re shown all the phenotypes of individuals within a family. And for merit and excellence
in this section, what you really wanna be doing is
predicting the genotypes based off the phenotypes, and here’s a way that you can do it. If you have two parents
that both show the dominant gene, however they produce
an individual that is homozygous recessive and
showing the recessive gene, what this means is that
both parents have to be heterozygous to both
produce a recessive gene that fertilizes together. Using things like this, you
can predict the genotype of sometimes the entire
pedigree charts, and this is really really useful in
understanding exactly what is going on. – Another question that
is commonly asked is the difference between
inheritable and non-inheritable variation, or in basic
terms, when is a change in phenotype passed down to an offspring? Inheritable variation can be
passed down to an offspring and it involves a change
or mutation in the DNA, whereas non-inheritable
variation might be due to an environment or only
occurring in non-sex cells and only affects that
organism and won’t be passed down onto your offspring. For example, if you
get a scar on your arm. Based on that, a phenotype
is therefore determined by both genetics and the environment. Just because an individual
has a gene or allele that codes for a specific
trait, doesn’t necessarily mean that the phenotype will express it, as the environment may change
around that individual. – Our final tip comes in
the form of the differences between asexual and sexual reproduction. Where asexual reproduction
is fast and effective but it doesn’t have a lot
of opportunity to introduce genetic variation. Sexual reproduction is
time-effective and can be costly, but it does introduce more
variation which is obviously very beneficial. Now these benefits will come
in the form of resistance to new selection pressures. So if a new selection
pressure is introduced, whether this be due to a natural disaster or a new predator, what it
means is if the gene pool is more varying, it’s more likely
that within this gene pool there is an allele that
is resistant to this new selection pressure. It’s important to bear in mind
that you’re not discussing new mutations forming in
response to new selection pressures and that it
is all a 100% by chance. Now asexual reproduction,
because of this reduction in genetic variation, is
obviously far less resistant to new selection pressures. So this is the StudyTime’s level one strategy video for genetics. One final tip from us, if
you’re struggling to know where to get started,
highly recommend learning your definitions, these are
important to every question that you’re going have to
answer, so it’s a really good way to get a good idea of
the standard as a whole. – And if you want to get
more into the content of the standard, check out our StudyTime walk-through guides,
available for free online or if you want to buy them in
print with next day delivery. And check out past exams, practice writing out those answers. Cool. That’s been it from us guys. Good luck and thank you for watching. (upbeat music)

11 Comments

Add a Comment

Your email address will not be published. Required fields are marked *