Genes and Inheritance [5]: Inheritance – Part 2 (High band Biology)
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Genes and Inheritance [5]: Inheritance – Part 2 (High band Biology)

A Level Biology: Genes and Inheritance 5 Ð
Inheritance Part 2 Hi! Welcome to my fifth video in the series
and this one is looking at Genetic crosses. In this video, we are going to be looking
at the Genetic cross; looking at earlobe attachment which is leading on the previous video. In this case, we are looking at a mother with
this genotype and the genotype is the genetic make-up of an organism. The mother has one
dominant allele and one recessive. The father has one dominant and one recessive. Both of
them have this phenotype unattached. What this means is that the dominant allele must
be the unattached allele. The E represents unattached and e represents the attached ear
lobe. There is a specific name for this type of
genotype where the two alleles are different and thatÕs referred to as heterozygous. Hetero
means different. If the two alleles are the same, if they were ee, then that would be
referred to as homozygous; also the same if they were EE. Heterozygous means different.
Homozygous means the same. The fatherÕs genotype is Ee. That means that
in his sperm, he only carries one of these alleles. That is very important. Gametes or
sex cells only carry half the genetic information. They only carry one allele, in this case,
earlobe attachment. The fatherÕs sperm can either have the allele for unattached or it
can have the allele for attached. The same is true with the mother. You notice that this
has been represented on this diagram. These are the sperm, obviously, the detail and these
are the eggs. In this part of the diagram, this section
here, this is known as a Punnett square and what it shows is the different possibilities
of the genotype of the offspring. What you have are the two possibilities of the sperm.
The sperm can either have the unattached ear lobe or it can have the attached. Here you
have the eggs which can have the unattached ear lobe allele or the attached and what we
are going to do is we are going to put these together to form the genotype or the possible
genotype of the offspring. In this case, it would be EE, which would
be a homozygous individual. In this case, E from the mom and e from the father and that
makes this heterozygous. In this case eE, again this is the heterozygous genotype because
the e from the egg and the E from the sperm. In this case, ee is a homozygous individual
because it has two recessive alleles. This shows the different possibilities that are
available. Possibilities is a really key term here because
by chance, you would expect the offspring between these two individuals. You would expect
a 1/4 chance for them to have this genotype; a 1/2 chance to have these two genotypes;
and 1/4 to have these genotypes. On the face of it, you would say unlikely.
What is less likely is that these two individuals would have a child that has an attached ear
lobe, but there is a 1/4 chance of that. The overwhelming outcome should be the fact that
the child should have an unattached ear lobe because in the 3 of the 4 cases, thatÕs what
the genotype indicates. But this doesnÕt mean to say that if these
individuals have three kids, that they couldnÕt all have attached ear lobes. It would be unlikely.
The first kid having that genotype would be 1/4. The second would be 1/4 and the third
would be 1/4, so that would be 1/64 chance that it is possible, but it is unlikely. A carrier is whatÕs technically known as
an individual who carries the allele for a certain condition. In this case, if the condition
is having attached ear lobes, then these two individuals that are heterozygous with eE,
these two (Ee & eE) are whatÕs technically known as the carrier and if this was a genetic
disease, sometimes we refer to this (ee) being a sufferer. ThatÕs a 25% case you would expect
this outcome. In summary, a heterozygous individual or heterozygous
means a set of alleles which are different, in this case Ee. Homozygous is a set of alleles
which are the same; with this example, EE or ee. A carrier is an individual who carries
the allele for the condition but doesnÕt have it, so in this case, heterozygous Ee
and sufferer, someone who has a particular condition; in this case ee. [end of audio Ð 05:13]
A Level Biology: Genes and Inheritance 5 Ð Inheritance Part 2

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