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4.1 Chromosomes, Genes, Alleles
and Mutations
Topic 4 Genetics
Genetics
 4.1.1 State that eukaryote chromosomes are made of DNA
and proteins.
 The names of the proteins (histones) are...
Genetics
 4.1.2 Define gene, allele and genome.
 Gene: a heritable factor that controls a specific
characteristic. (The ...
Genetics
 4.1.3 Define gene mutation.
 The terms point mutation or frameshift mutation will not
be used
 4.1.4 Explain ...
Genetics
 Aim 8: There is a variety of social issues associated with
sickle-cell anemia, including the suffering due to a...
Genetics
 Genetics is the study of variation and inheritance.
 The basic unit of inheritance is the gene.
 A gene is a ...
Alleles
 The locus of a gene is its position on a chromosome. The
same gene will have the same locus on the same
chromoso...
Chromosomes
 Genes are made up of DNA (deoxy ribonucleic acid).
 Genes are part of a larger molecule called chromosome.
...
Human Chromosomes
 Chromosomes are visible when the cell starts to divide.
 Human body cells have 46 chromosomes;
 23 p...
Karyotyping
 A complete set of chromosomes is called a karyotype.
 Each chromosome has genes specific for that
chromosom...
Karyotyping
Male Karyotype Female Karyotype
Gene Mutations
 Genes are nearly always passed from parent to offspring
without mistakes.
 Occasionally a change will oc...
Sickle-cell anaemia
 Mutation in hemoglobin gene
 GAG has mutated to GTG (a base substitution)
 In translation, this ca...
Genetics
 4.1.1 State that eukaryote chromosomes are made of DNA
and proteins.
 The names of the proteins (histones) are...
Genetics
 4.1.2 Define gene, allele and genome.
 Gene: a heritable factor that controls a specific
characteristic. (The ...
Genetics
 4.1.3 Define gene mutation.
 The terms point mutation or frameshift mutation will not
be used
 4.1.4 Explain ...
Genetics
 Aim 8: There is a variety of social issues associated with
sickle-cell anemia, including the suffering due to a...
4.1 chromosomes, genes, alleles & mutations
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4.1 chromosomes, genes, alleles & mutations

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4.1 chromosomes, genes, alleles & mutations

  1. 1. 4.1 Chromosomes, Genes, Alleles and Mutations Topic 4 Genetics
  2. 2. Genetics  4.1.1 State that eukaryote chromosomes are made of DNA and proteins.  The names of the proteins (histones) are not required, nor is the structural relationship between DNA and the proteins.
  3. 3. Genetics  4.1.2 Define gene, allele and genome.  Gene: a heritable factor that controls a specific characteristic. (The differences between structural genes, regulator genes and genes coding for tRNA and rRNA are not expected at SL).  Allele: one specific form of a gene, differing from other alleles by one or a few bases only and occupying the same gene locus as other alleles of the gene.  Genome: the whole of the genetic information of an organism.
  4. 4. Genetics  4.1.3 Define gene mutation.  The terms point mutation or frameshift mutation will not be used  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.  GAG has mutated to GTG causing glutamic acid to be replaced by valine, and hence sickle-cell anemia.
  5. 5. Genetics  Aim 8: There is a variety of social issues associated with sickle-cell anemia, including the suffering due to anemia, personal feelings if one has either inherited or passed on the sickle-cell allele, questions relating to the desirability of genetic screening for the sickle-cell allele before having children, and the genetic counselling of carriers of the allele.  There are also ethical issues relating to screening of fetuses and abortion of those found to have a genetic disease.
  6. 6. Genetics  Genetics is the study of variation and inheritance.  The basic unit of inheritance is the gene.  A gene is a heritable factor that controls a specific characteristic.  A gene is a segment of chromosome that contain the code required to direct the manufacture of a polypeptide or RNA molecule.  All the genes of an organism are known collectively as the genome.
  7. 7. Alleles  The locus of a gene is its position on a chromosome. The same gene will have the same locus on the same chromosome.  Different forms of a gene are called alleles. An allele is a form of a gene differing from other alleles of the gene by a few bases at most and occupying the same locus as the other alleles of that gene.  One of the most studied sets of alleles are the alleles controlling blood type:  Controlled by 3 alleles A (IA ), B (IB ) O (i)
  8. 8. Chromosomes  Genes are made up of DNA (deoxy ribonucleic acid).  Genes are part of a larger molecule called chromosome.  Eukaryotic chromosomes are are made up of DNA and proteins.  When DNA coils up to form a chromosome, it wraps around special proteins called histones to form a nucleosome.  A nucleosome consists of DNA wrapped around 9 histone proteins.
  9. 9. Human Chromosomes  Chromosomes are visible when the cell starts to divide.  Human body cells have 46 chromosomes;  23 pairs of chromosomes  one set from the mother and one set from the father  22 pairs of autosomes (non sex chromosomes)  1 pair of sex chromosomes  XX –female  XY – male
  10. 10. Karyotyping  A complete set of chromosomes is called a karyotype.  Each chromosome has genes specific for that chromosome making it identifiable.  Karyotyping is arranging the chromosomes in pairs according to their structure.  The chromosomes are arranged depending upon:  Their length  The position of their centromere  Karyotyping can be used to detect chromosome aberrations in foetuses.  eg: An amniocentesis to check for Downs syndrome (47 Chromosomes)
  11. 11. Karyotyping Male Karyotype Female Karyotype
  12. 12. Gene Mutations  Genes are nearly always passed from parent to offspring without mistakes.  Occasionally a change will occur in a gene.  This is called a Gene Mutation.  Gene mutations can be:  Base substitution – one base is changed for another  Frameshift mutation:  Insertions - insertion of one or more bases  Deletions – deletion of one or more bases  An example of a base substitution is Sickle-cell anaemia.
  13. 13. Sickle-cell anaemia  Mutation in hemoglobin gene  GAG has mutated to GTG (a base substitution)  In translation, this causes causing glutamic acid to be replaced by valine  Hemoglobin has a different shape  RBC becomes sickle-shaped  Can block capillaries
  14. 14. Genetics  4.1.1 State that eukaryote chromosomes are made of DNA and proteins.  The names of the proteins (histones) are not required, nor is the structural relationship between DNA and the proteins.
  15. 15. Genetics  4.1.2 Define gene, allele and genome.  Gene: a heritable factor that controls a specific characteristic. (The differences between structural genes, regulator genes and genes coding for tRNA and rRNA are not expected at SL).  Allele: one specific form of a gene, differing from other alleles by one or a few bases only and occupying the same gene locus as other alleles of the gene.  Genome: the whole of the genetic information of an organism.
  16. 16. Genetics  4.1.3 Define gene mutation.  The terms point mutation or frameshift mutation will not be used  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.  GAG has mutated to GTG causing glutamic acid to be replaced by valine, and hence sickle-cell anemia.
  17. 17. Genetics  Aim 8: There is a variety of social issues associated with sickle-cell anemia, including the suffering due to anemia, personal feelings if one has either inherited or passed on the sickle-cell allele, questions relating to the desirability of genetic screening for the sickle-cell allele before having children, and the genetic counselling of carriers of the allele.  There are also ethical issues relating to screening of fetuses and abortion of those found to have a genetic disease.

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