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TOPIC 3
Genetics
15 hours
http://bio.owu.edu/gen.htm
3.1 Genes
3.2 Chromosomes
http://www.goodismanlab.biology.gatech.edu/teaching.htm
January 29th/2015
Adapted from: Taylor, S. (2009). Chromosomes, Genes, alleles and
mutations (Presentation). Science Video Resources. [Online]
Wordpress. http://i-biology.net/ibdpbio/
Genetic information
The chromosome is composed of two main
molecules.
a) DNA
b) Proteins called histones.
This image was taken shortly after DNA a
replication but before the prophase. It is
composed of two daughter chromatids joined
at the centromere.
The chromosome is super coiled by a factor
around x16,000. The DNA molecule is about
1.8m long but is located in the nucleus which is
only 10um in diameter!
Eukaryote chromosomes are made of DNA and
proteins.
http://click4biology.info/c4b/4/gene4.1.ht
m#one
A gene occupies a specific
position on a chromosome
i
A heritable factor that
consists of a length of DNA
and influences a specific
characteristic
ALLELE are the various
specific forms of a gene
Alleles differ from each
other by one or only a
few bases
New alleles are formed
by mutation.
4.1.3 Define gene mutation.
4.1.4 Explain the consequence of a base substitution mutation in relation to the processes of
transcription and translation, using the example of sickle-cell anemia.
Homologous chromosomes have the same genes as each
other, in the same sequence, but not necessarily the same
alleles of those genes.
http://apbrwww5.apsu.edu/thompsonj/Anatomy%20&%20Physiology/2010/20
10%20Exam%20Reviews/Exam%201%20Review/Ch03%20Mitosis%20and%20T
he%20Cell%20Cycle.htm
4.2.2 Define homologous chromosomes.
The two DNA molecules formed by DNA
replication prior to cell division are
considered to be sister chromatids until the
splitting of the centromere at the
start of anaphase. After this, they are
individual chromosomes.
Karyogram
Pictures can be taken of the human chromosomes during the metaphase.
They can then be arranged into pairs on the basis of size and structure.
SHORT ANIMATION:
http://www.mwit.ac.
th/~bio/assets/karyot
ype_mutation.swf
The chromosomes appear as pairs of sister chromatids.
• There are 23 pairs (46 chromosomes) therefore this is human.
• In this case the 23rdpair in this case are one long pair of chromatids (Xchromosome) and one very short (Y chromosome).
• Females = XX
• Males = XY
HOMEWORK: in your notebook, for
Wednesday 11th of February.
1. Print an image of what you find and analyze the results.
2. Comparison of genome size in T2 phage,
Escherichia coli, Drosophila melanogaster, Homo
sapiens and Paris japonica.
• Remember that genome size refers to the total
amount of DNA of a species or organism.
• This comparison must be in your notebook.
3. Print an image of what you find and analyze the results.
http://www.ebi.
ac.uk/Tools/msa
/clustalo/
4. Prepare this question:
Explain the causes of sickle-cell anemia.
(8)
Markscheme:
caused by gene mutation;
(sickle-cell anemia) due to a base substitution (mutation);
changes the code on the DNA;
which leads to a change in transcription / change in mRNA;
which (in turn) leads to a change in translation / change in
polypeptide chain/protein;
(the tRNA) adds the wrong amino acid to the polypeptide chain;
glutamic acid replaced by valine;
produces abnormal hemoglobin;
causing abnormal red blood cell/erythrocyte shape / sickle shape;
which lowers the ability to transport oxygen;
sickle-cell allele is codominant;
homozygote/HbS HbS have sickle cell anemia/is lethal / heterozygote/
HbS HbA has the sickle trait/is carrier (and is more resistant to malaria);
8 max
Write it down in your notebook