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  1. 1. KARYOTYPE <ul><li>Refers to the chromosome complement of a cell or a whole organism </li></ul><ul><li>In particular , it shows the number, size, and shape of the chromosomes as seen during metaphase of mitosis </li></ul><ul><li>Chromosomes numbers vary considerably among organisms and may differ markedly between closely related species </li></ul><ul><li>Organism Chromosome number (2n) </li></ul><ul><li>Drosophila 8 </li></ul><ul><li>Honey bee 32 or 16 </li></ul><ul><li>Goldfish 94 </li></ul><ul><li>Rat 42 </li></ul><ul><li>Rabbit 44 </li></ul><ul><li>Cat 38 </li></ul><ul><li>Dog 78 </li></ul><ul><li>Gorilla 48 </li></ul><ul><li>Chimpanzee 48 </li></ul><ul><li>Human 46 </li></ul>
  2. 3. Chromosome structure <ul><li>This chromosome has two chrom a tids. </li></ul><ul><li>Each chromatid contains an identical copy of the DNA molecule </li></ul><ul><li>In non-dividing cells, chromosomes exist as single-armed structure with one chromatid </li></ul><ul><li>The chromosome consists of a protein coated strand which coils in three ways during the time when the cell prepares to divide </li></ul>Figure 1. Chromatin and condensed chromosome structure during metaphase of cell division
  3. 4. Human karyotype
  4. 5. Karyotyping <ul><li>Karyotyping is the process of finding the chromosomal characteristics of a cell </li></ul><ul><li>Chromosomes can be stained to show banding. Chromosome structure and banding can be used to arrange the chromosome in the i r pairs </li></ul><ul><li>Application of karyotyping can be found in an amniocentesis or chronic villus sampling </li></ul><ul><li>How to read karyotype? </li></ul><ul><li>Dark and light elements of the chromosome show which parts tak e part in cell division </li></ul><ul><li>You may check the number of chromosome and the gender </li></ul>
  5. 7. Sex inheritance <ul><li>In many animals sex is determined by a pair of sex chromosomes </li></ul><ul><li>All the rest of the chromosomes are called autosomes </li></ul><ul><li>In humans there are two types of sex chromosome, called X and Y chromosome </li></ul><ul><li>The X chromosome is much larger </li></ul><ul><li>than the Y, and carries many genes </li></ul><ul><li>which are not present on the </li></ul><ul><li>Y chromosome </li></ul>Figure 2. Sex chromosomes in human
  6. 9. Sex linkage <ul><li>A gene which is found on one of the sex chromosome and on the other is called a sex-linked gene </li></ul><ul><li>Chromosome X Chromosome Y </li></ul><ul><li>Duchenne muscular dystrophy sex determining factor </li></ul><ul><li>Retinis pigmentosa genes involved in growth </li></ul><ul><li>Kidney stones and spermatogenesis genes </li></ul><ul><li>Haemophilia </li></ul><ul><li>Red-green colour blindness </li></ul><ul><li>Spastic paraplegia </li></ul><ul><li>Adrenoleukodystrophy </li></ul>
  7. 10. Sex linkage in Drosophila melanogaster
  8. 11. Red-green colour blindness <ul><li>Sex linked conditions such a red-green colour blindness are therefore much commoner in men than in women </li></ul>A – the normal dominant allele allows full colour vision a – the less common recessive allele produces red-green colour blindness
  9. 12. Haemophilia <ul><li>The most well-known sex-linked disease </li></ul><ul><li>It is caused by a recessive allele of a gene which codes for the production of one of the proteins involved in blood clotting – Factor VIII </li></ul><ul><li>Females with haemophilia are almost unknown . If a male has one defective allele he will have the haemophilia condition . </li></ul>
  10. 14. <ul><li>Sex-linkage – revision </li></ul><ul><li>Sex-linkage occurs when t h e genes carried on the sex chromosomes </li></ul><ul><li>Conditions like colour blindness and haemophilia are much more common in men t ha n in woman and are said to be sex-linked </li></ul><ul><li>Sex-linked genes are found on the X chromosome </li></ul><ul><li>Since females have 2 X chromosomes, they can have 2 dominant alleles (homozygous dominant), 2 recessive alleles (homozygous recessive) or 1 dominant and 1 recessive allele (heterozygous). Males only have 1 X chromosome. This means that the terms homozygous or heterozygous do not apply </li></ul><ul><li>Mendel's first law </li></ul><ul><li>Law of segregation </li></ul><ul><li>‘ Parental factors (genes) are in pairs and split so that one factor is present in each gamete’ </li></ul><ul><li>Mendel's second law </li></ul><ul><li>Principle of independent assortment </li></ul><ul><li>‘ Any of one pair of characteristics may combine with either one of another pair’ </li></ul>
  11. 15. An example of a chromosome mutation – Down's syndrome <ul><li>Down's syndrome is caused by the possession of an extra chromosome 21 (an example of a trisomy ) </li></ul><ul><li>Chromosome 21 is one of the smaller chromosomes </li></ul><ul><li>People with Down's syndrome therefore usually have 47 chromosomes in their cells </li></ul><ul><li>The possession of extra chromosomes is known as polysomy </li></ul><ul><li>The extra chromosome 21 usually comes from the mother's egg. This happens because of an error during meiosis in her ovary in which the 2 chromosome 21s fail to separate, both of them going into one daughter cell and none into the other. This error is called non-disjunction </li></ul><ul><li>Children with Down's syndrome have characteristic facial features: slanting eyes, back of head flat, broad flat face, short nose, abnormal nose, small and arched palate, big wrinkled tongue, dental anomalies </li></ul>
  12. 18. Pre-natal testing <ul><li>There are two common pre-natal tests: </li></ul><ul><li>Chorionic villus sampling </li></ul><ul><li>Amniocentesis </li></ul><ul><li>Chorionic villus sampling: </li></ul><ul><li>It is a pre-natal test that can be done at 11-12 weeks of pregnancy </li></ul><ul><li>It involves taking a sample of the chronic villi in order to obtain cells from tissue that originally came from the zygote </li></ul><ul><li>The cells will therefore have the same genetic composition as the cells of the unborn baby so a karyotype can be made </li></ul><ul><li>Amniocentesis </li></ul><ul><li>Can be done around the 16th week of the pregnancy </li></ul><ul><li>A sample of the amniotic fluid (containing fetal cells) is taken and a culture is made </li></ul><ul><li>When sufficient cells have been obtained a karyotype can be done to detect chromosome abnormalities </li></ul>
  13. 19. Chorionic villus sampling
  14. 20. Amniocentesis
  15. 21. Multiple alleles