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    Karyotype Karyotype Presentation Transcript

      • Refers to the chromosome complement of a cell or a whole organism
      • In particular , it shows the number, size, and shape of the chromosomes as seen during metaphase of mitosis
      • Chromosomes numbers vary considerably among organisms and may differ markedly between closely related species
      • Organism Chromosome number (2n)
      • Drosophila 8
      • Honey bee 32 or 16
      • Goldfish 94
      • Rat 42
      • Rabbit 44
      • Cat 38
      • Dog 78
      • Gorilla 48
      • Chimpanzee 48
      • Human 46
    • Chromosome structure
      • This chromosome has two chrom a tids.
      • Each chromatid contains an identical copy of the DNA molecule
      • In non-dividing cells, chromosomes exist as single-armed structure with one chromatid
      • The chromosome consists of a protein coated strand which coils in three ways during the time when the cell prepares to divide
      Figure 1. Chromatin and condensed chromosome structure during metaphase of cell division
    • Human karyotype
    • Karyotyping
      • Karyotyping is the process of finding the chromosomal characteristics of a cell
      • Chromosomes can be stained to show banding. Chromosome structure and banding can be used to arrange the chromosome in the i r pairs
      • Application of karyotyping can be found in an amniocentesis or chronic villus sampling
      • How to read karyotype?
      • Dark and light elements of the chromosome show which parts tak e part in cell division
      • You may check the number of chromosome and the gender
    • Sex inheritance
      • In many animals sex is determined by a pair of sex chromosomes
      • All the rest of the chromosomes are called autosomes
      • In humans there are two types of sex chromosome, called X and Y chromosome
      • The X chromosome is much larger
      • than the Y, and carries many genes
      • which are not present on the
      • Y chromosome
      Figure 2. Sex chromosomes in human
    • Sex linkage
      • A gene which is found on one of the sex chromosome and on the other is called a sex-linked gene
      • Chromosome X Chromosome Y
      • Duchenne muscular dystrophy sex determining factor
      • Retinis pigmentosa genes involved in growth
      • Kidney stones and spermatogenesis genes
      • Haemophilia
      • Red-green colour blindness
      • Spastic paraplegia
      • Adrenoleukodystrophy
    • Sex linkage in Drosophila melanogaster
    • Red-green colour blindness
      • Sex linked conditions such a red-green colour blindness are therefore much commoner in men than in women
      A – the normal dominant allele allows full colour vision a – the less common recessive allele produces red-green colour blindness
    • Haemophilia
      • The most well-known sex-linked disease
      • 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
      • Females with haemophilia are almost unknown . If a male has one defective allele he will have the haemophilia condition .
      • Sex-linkage – revision
      • Sex-linkage occurs when t h e genes carried on the sex chromosomes
      • Conditions like colour blindness and haemophilia are much more common in men t ha n in woman and are said to be sex-linked
      • Sex-linked genes are found on the X chromosome
      • 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
      • Mendel's first law
      • Law of segregation
      • ‘ Parental factors (genes) are in pairs and split so that one factor is present in each gamete’
      • Mendel's second law
      • Principle of independent assortment
      • ‘ Any of one pair of characteristics may combine with either one of another pair’
    • An example of a chromosome mutation – Down's syndrome
      • Down's syndrome is caused by the possession of an extra chromosome 21 (an example of a trisomy )
      • Chromosome 21 is one of the smaller chromosomes
      • People with Down's syndrome therefore usually have 47 chromosomes in their cells
      • The possession of extra chromosomes is known as polysomy
      • 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
      • 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
    • Pre-natal testing
      • There are two common pre-natal tests:
      • Chorionic villus sampling
      • Amniocentesis
      • Chorionic villus sampling:
      • It is a pre-natal test that can be done at 11-12 weeks of pregnancy
      • It involves taking a sample of the chronic villi in order to obtain cells from tissue that originally came from the zygote
      • The cells will therefore have the same genetic composition as the cells of the unborn baby so a karyotype can be made
      • Amniocentesis
      • Can be done around the 16th week of the pregnancy
      • A sample of the amniotic fluid (containing fetal cells) is taken and a culture is made
      • When sufficient cells have been obtained a karyotype can be done to detect chromosome abnormalities
    • Chorionic villus sampling
    • Amniocentesis
    • Multiple alleles