Genes and Inheritance [4]: Inheritance (A Level Biology)


Uploaded by freeeschool on 02.09.2012

Transcript:
A Level Biology: Genes and Inheritance 4 - Inheritance
Hi! Welcome to my fourth video in the series and this one is looking at genetic inheritance.
In the last video, we were looking at how sex is inherited. In this video, we are going
to look at how different characteristics are inherited, particularly on this one, looking
at whether your ear lobes are attached or not.
On the diagram here, you have a picture of a pair of chromosomes. Located on each on
these arrows here, these indicate two alleles. An allele is a version of a gene. In this
case, you have an uppercase “E” and a lowercase “e”. An uppercase letter represents
an allele which is dominant and a lower case letter represents an allele which is recessive.
With the dominant allele, you only need one of those alleles for it to be expressed, whereas
with the recessive allele, you need two of them. Because alleles usually come in pairs,
you therefore, to have an attached ear, you need to have ee.
This diagram here shows us somebody with an unattached ear lobe and somebody with attached.
This individual A would have the following genotypes or could have the following genotypes.
Essentially, a genotype is the genetic make-up of an organism or an individual. For ear lobe
attachment gene, he could have the following alleles: Ee, eE, EE.
Like I said before, if it is dominant, it only needs one of those alleles for it to
be expressed, hence, in this case, Ee or ee. But in the case of B, their genotype must
be the only genotype they could possibly have is ee, because for a recessive allele or a
recessive gene to be expressed, then you need two within your genotype. That is the only
possible permutation.
A genotype is essentially the genetic make-up of an organism. There is another word called
phenotype and that is how it is expressed. In this case, all that mean are either you
have gotten an unattached or attached ear lobe and that’s your phenotype. Another
phenotype might be eye color or hair color. So phenotype is how it is expressed.
In summary, a gene is a code for a characteristic. An allele is a version of a gene and your
alleles can either be dominant, which they usually represent in letter form in uppercase
or they can be recessive, usually in lowercase.
The alleles can be found in pairs and so they’re usually found one on each chromosome. For
the dominant allele, you only need one of those for it to be expressed. In the case
of attached or unattached ear lobe, then you only need one of them to be present. In this
case, A whereas with the recessive allele, you need both, in order to be expressed, so
ee.
Your genotype is the genetic make-up of an organism, so these codes are Ee or ee and
the phenotype is how it is expressed. In this example, you have an attached ear lobes or
unattached.
[end of audio – 3:26] A Level Biology: Genes and Inheritance 4 - Inheritance
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