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Genetic, Disorders, PRESENTED BY:, NGANGOM LUCKY DEVI, LECTURER, ZOOLOGY, JOHNSTONE HR. SEC. SCHOOL
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2, , Introduction, , , Organisms reproduce- formation of, offspring of the same kind., , The resulting offspring most often do not, totally resemble the parent., Branch of biology that deals with the, heredity and variation- Genetics., , , , , Heredity- the transmission of characters or traits, from parents to, their offsprings., , , , Inheritance- the process by which, characters pass on from one generation to the, next., , , , Variation-it is the degree by which, progeny differ from their parents., , Ngangom Lucky Devi, Lecturer Zoology, Johnstone Hr. Sec. School
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Some important terminologies for, genetics, , , Allele or allelomorph- two or more alternative or, constrasting forms of a gene. They occupy same locus, (position of gene) on two homologous chromosomes., , , , Phenotype: The external appearance of an organism due, to the influence of genes and environmental factors., , , , Genotype: The genetic constitution of an individual, responsible for the phenotype ., , , , Phenotypic ratio: The correct proportion of phenotype in, population., , , , Genotypic ratio: The correct proportion of genotype in, population., , Ngangom Lucky Devi, Lecturer Zoology, Johnstone Hr. Sec. School, , 3
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Some important terminologies for, genetics, , , Homozygous: The individual having identical genes in an, allelic pair for a character. Eg: TT, tt., , , , Heterozygous: The individual heving unidentical genes in, an allelic pair for a character. Eg: Tt., , , , Dominant gene: The gene that expresses its character in, heterozygous condition., , , , Recessive: The gene that fails to express its character in, heterozygous condition., , , , Hybrid: The progeny obtained by crossing two parents that, differ in characters., , , , Back cross: The cross between F1 hybrid and one of its, parents., , , , Test cross: The cross between hybrid and its homozygous, recessive parent. It is used to identify the genotype of the, hybrid., , Ngangom Lucky Devi, Lecturer Zoology, Johnstone Hr. Sec. School, , 4
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Gregor Johann Mendel (1822-1884):, Father of Genetics, , , Gregor Johann Mendel: Father of Genetics, , , , The termed “Genetics” was coined by Bateson in 1906. He is, considered as “Father of modern genetics”., , , , Gregor Mendel developed the principles of heredity while, studying seven pairs of inherited characteristics in pea plants, , , , Although the significance of his, work was not recognized during, his lifetime, it has become the, basis for the present-day field of, genetics., , Ngangom Lucky Devi, Lecturer Zoology, Johnstone Hr. Sec. School, , 5
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6, , Mendel’S Approach, Conducted hybridization (artificial pollination/ cross pollination), experiment for 7 years 1856-1863 & proposed law of, inheritance., Applied statistical analysis & mathematical logic for biology, problems., Large sampling size- greater credibility to data., Experiments- true breeding pea lines (continuous self, pollination)., Confirmation of inference from experiments on successive, generations of test plants, proved general rules of inheritance., Mendel investigated two opposing traits- tall & dwarf, yellow &, green seed., , Ngangom Lucky Devi, Lecturer Zoology, Johnstone Hr. Sec. School
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7, , Why Mendel selected pea plant????, , , , Pure variety are available., Pea plants are easy to cultivate., , , , Life cycle of plants are only few months. So that result, can be got early., , , , Contrasting trait are observed., , , , Flowers are bisexual and normally self pollinated., , , , Flowers can be cross pollinated only manually., , , , Hybrids are fertile., , Ngangom Lucky Devi, Lecturer Zoology, Johnstone Hr. Sec. School
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Seven pair of contrasting characters selected by, Mendel for his experiment., , Ngangom Lucky Devi, Lecturer Zoology, Johnstone Hr. Sec. School, , 8
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9, , GENETIC DISORDERS, , , A genetic disorder is caused by a mutation to a gene, group of, genes, or entire chromosome., , , , Remember, genes carry instructions to build proteins., , , , When these instructions are mutated, proteins can’t get build, correctly., , , , Genetic disorders generally occur in two different varieties., , a) Chromosomal defect (chromosomal mutations), b) Gene defect (gene mutations), , Ngangom Lucky Devi, Lecturer Zoology, Johnstone Hr. Sec. School
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10, , GENETIC DISORDERS, , , Genetic disorders grouped into two categories –, 1. Mendelian disorder, 2. Chromosomal disorder, , Mendelian Disorders, , , Mendelian disorders are mainly determined by alteration or, mutation in the single gene., , , , It obey the principle of Mendelian inheritance (principles of, inheritance) during transmission from one generation to other., , , , Mendelian disorder- traced in family by pedigree analysis, • E.g. Haemophilia, Colorblindness, Cystic fibrosis, Sickle cell, anemia, Phenylketonuria, Thalesemia etc., , Ngangom Lucky Devi, Lecturer Zoology, Johnstone Hr. Sec. School
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Haemophilia/Hemophilia, (John Otto,1803), , , It is a sex- linked recessive disease., , , , It is genetically transmitted disease which were common in, Europe (E.g., Queen Victoria and her descendents)., , , , Also known as “ Bleeder’s disease” due to continuous bleeding, even after minor cut due to the absence of antihaemophiliac, globulin or factor VIII (haemophilia A) and plasma thromboplastin, or factor IX (haemophilia B or Christmas disease)., , , , In Europe, it is commonly known as “Royal disease” because of, the close intermarriages amongst the royal families of Europe., , Ngangom Lucky Devi, Lecturer Zoology, Johnstone Hr. Sec. School, , 11
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12, , Haemophilia/ Hemophilia, , , Haemophilia is genetically due to the presence of a recessive sex linked, gene “h” carried by X chromosome (Xh), , , , A female becomes haemophiliac only when both its X chromosomes carry, the gene (XhXh)- homozygous condition., , , , However, such female generally die before birth because the combination, of these two recessive alleles is lethal., , , , A female having only one allele for haemophilia (XXh) appears normal, because the allele for normal blood clotting present on the X chromosome, is dominant. Such females are known as “Carrier”., , , , In males, it is expressed in XY having haemophilic X chromosome (XhY)., , Ngangom Lucky Devi, Lecturer Zoology, Johnstone Hr. Sec. School
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Cross between normal male and, carrier woman, , Ngangom Lucky Devi, Lecturer Zoology, Johnstone Hr. Sec. School, , 13
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Cross between hemophilic male and, carrier woman, , Ngangom Lucky Devi, Lecturer Zoology, Johnstone Hr. Sec. School, , 14
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COLOUR BLINDNESS (Red-green, blindness; Horner,1876), , , It is a recessive sex-linked trait in which the eye fails to distinguish red and, green colours., , , , The gene for the normal vision is dominant., , , , The normal gene and its recessive allele are carried by X chromosome., , , , In females, colour blindness appears only when both the sex chromosomes, carry the recessive (XcXc)., , , , The females have normal vision but function as carrier if a single recessive, gene for colour blindness is present (XXc)., , , , In males the defect appears in the presence of a single recessive gene (XcY), because Y chromosome of male does not carry any gene for colour vision., , Ngangom Lucky Devi, Lecturer Zoology, Johnstone Hr. Sec. School, , 15
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Cross between female carrier and, normal male, , Ngangom Lucky Devi, Lecturer Zoology, Johnstone Hr. Sec. School, , 16
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Cross between carrier mother and, colour blind father using Punnet’s, square, , Ngangom Lucky Devi, Lecturer Zoology, Johnstone Hr. Sec. School, , 17
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18, , Sickle cell anemia (Herrick,1904), , , It is an autosomal heredity disorder in which erythrocytes, become sickle shaped under oxygen deficiency., , , , It is caused by the formation of an abnormal, haemoglobin-S which differs from normal haemoglobin-A, in only one amino acid- 6th amino acid of β-chain., , , , Here, the 6th amino acid i.e., glutamic acid (GAG) is, replaced by valine (GUG) due to single base substitution, from GAG to GUG., , , , HbsHbs- Sickle cell anemia, , , , HbAHbs- Carrier, , , , HbAHbA- Normal, , Ngangom Lucky Devi, Lecturer Zoology, Johnstone Hr. Sec. School
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Figure showing a single nucleotide, change in DNA encoding β-globin, , Ngangom Lucky Devi, Lecturer Zoology, Johnstone Hr. Sec. School, , 19
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20, , Cross between two sickle cell carriers, , Ngangom Lucky Devi, Lecturer Zoology, Johnstone Hr. Sec. School
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21, , PHENYLKETONURIA (PKU), , , Inborn error of metabolism- inherited as autosomal, recessive trait., , , , It is due to the defect of the gene producing the enzyme, phenylalanine, hydroxylase. This enzyme responses for the conversion of phenylalanine, (amino acid) to tyrosine., , , , As a result, Phenylalanine is accumulated & converted into phenylpyruvic, acid & other derivatives., , , , Accumulation in brain result- mental retardation., , , , Excreted in urine- poor absorption by kidney, , Ngangom Lucky Devi, Lecturer Zoology, Johnstone Hr. Sec. School
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22, , THALASSEMIA (Cooley,1925), , , It is autosomal recessive blood disorder which appears in children of two, unaffected carriers (heterozygous parents)., , , , The defect can occur due to mutation or deletion of the genes controlling the, formation of globin chains( commonly alpha and beta) of Hb., , , , Imbalanced synthesis of globin chains of Hb causes anaemia., , , , Depending upon the globin chain affected, thalassemia is of three types:, , 1. Alpha thalassemia: caused by the defective formation alpha globin on, chromosome number 16., 2. Beta thalassemia: decreased synthesis of beta globin on chromosome, number 11., 3. Delta thalassemia: due to defective allele of HBD (haemoglobin subunit, delta)gene present on chromosome number 11 that forms delta chain of Hb., , Ngangom Lucky Devi, Lecturer Zoology, Johnstone Hr. Sec. School
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Chromosomal Disorders, , , Chromosomal disorders are caused due to absence or excess or abnormal, arrangement of one or more chromosome., , , , These are non- heritable and pedigree analysis of a family does not help in, tracing the pattern of inheritance of such chromosomal disorder., , , , These are of two types: abnormalities due to aneuploidy and aberrations, either in autosomes or in sex chromosomes., , 1., , AUTOSOMAL ABNORMALITIES: These are due to autosomal aneuploidy and, aberrations. Some of the disorders are as follows- Down’s syndrome,, Edward’s syndrome, Patau’s syndrome and Cri du chat syndrome., , 2., , SEX CHROMOSOMAL ABNORMALITIES: These are due to sex chromosomal, aneuploidy. Examples: Turner’s syndrome and Klinefelter’s syndrome., , Ngangom Lucky Devi, Lecturer Zoology, Johnstone Hr. Sec. School, , 23
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DOWN’S SYNDROME (Mongolian, Idiocy, Mongolism, 21- trisomy), , , It was first reported in 1866 by Langdon Down., , , , It is an autosomal aneuploidy, caused by the, presence of an extra chromosome number, 21., , , , Thus, the egg possesses 24 chromosomes, instead of 23 and offspring has 47, chromosomes (45+XY in male, 45+XX in, female) instead of 47., , Ngangom Lucky Devi, Lecturer Zoology, Johnstone Hr. Sec. School, , 24
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25, , Characteristics:, , , Rounded face, broad forehead, permanently open mouth,, protruding tongue, projecting lower lip, short neck, flat hands and, stubby (small) fingers, many loops on finger tips, furrowed tongue,, broad palm with characteristic palmer crease., , , , The victim has little intelligence (IQ below 40), , , , Heart and other organs may be defective., , , , Gonads and genitalia are undeveloped., , Ngangom Lucky Devi, Lecturer Zoology, Johnstone Hr. Sec. School
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26, , Edward’s syndrome (18-trisomy), , , It was described by Edward in 1960., , , , It is due to an extra chromosome number 18., , , , Thus total number of chromosome is 47., , , , It occurs more often in females than in males., , , , The affected person keeps the fingers tightly clenched, against the palm of the hand. Others symptoms are small, jaws, defomed ears, small mouth, nose and fingers, small, sternum and pelvis., , , , The patient is mentally retarded and dies within 6 months, after birth., , Ngangom Lucky Devi, Lecturer Zoology, Johnstone Hr. Sec. School
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27, , Patau’s syndrome (13- trisomy), , , It was described by Patau in 1960., , , , This syndrome is due to an extra, chromosome number 13., , , , The affected person has small head and, abnormalities of the face, eyes and, forebrain, cleft lip and cleft palate, low, set deformed ears, small chin and the, hands are often clenched., , , , The average life span is about 4 months., , Ngangom Lucky Devi, Lecturer Zoology, Johnstone Hr. Sec. School
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28, , Contd.., , Ngangom Lucky Devi, Lecturer Zoology, Johnstone Hr. Sec. School
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29, , Cri du chat (Cat cry) syndrome, , , It was first described by Lejeune in 1963 in, France., , , , The affected newborn cries like mewing of a, cat. Hence it is named “Cri du chat”., , , , This condition is due to a deletion of half part in, the short arm of the chromosome number 5., , , , It is very rare in occurrence., , , , The affected person has a small head, widely, spacid eyes, cry like kitten, receding chin and, congital heart defect., , Ngangom Lucky Devi, Lecturer Zoology, Johnstone Hr. Sec. School
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30, , Contd…, , Ngangom Lucky Devi, Lecturer Zoology, Johnstone Hr. Sec. School
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31, , TURNER’S SYNDROME (Turner, 1938), , , Turner syndrome (TS), sometimes referred to as, congenital ovarian hypoplasia syndrome., , , , It is the most common sex chromosomal, abnormality affecting girls and women., , , , It occurs when one of the X chromosomes is, missing, either partially or completely (44+X0)., , , , This phenomenon is included under monosomy, (2n-1)., , Ngangom Lucky Devi, Lecturer Zoology, Johnstone Hr. Sec. School
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32, , Symptoms:, , , Short statue (less than 5 feet), , , , Undeveloped breasts, small uterus, puffy fingers,, webbed neck and abnormal intelligence., , , , Cardiovascular abnormalities and hearing impairment., , , , They may not menstruate or ovulate resulting infertility., , , , Presence of rudimentary ovaries. Therfore they are, sterile., , Ngangom Lucky Devi, Lecturer Zoology, Johnstone Hr. Sec. School
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33, , Klinefelter’s syndrome (Klinefelter, 1942), , , Klinefelter syndrome is caused by an, additional X chromosome (44+XXY) which is, included under trisomy (2n+1)., , , , Klinefelter syndrome is not directly inherited, – the additional X chromosome occurs as a, result of either the mother's egg or the, father's sperm having the extra X, chromosome (an equal chance of this, happening in either), so after conception, the chromosome pattern is XXY rather than, XY., , Ngangom Lucky Devi, Lecturer Zoology, Johnstone Hr. Sec. School
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34, , Symptoms:, , , Such persons are sterile males (called, feminized male) with undeveloped testes., , , , Mental retardation, female like sparse, body hairs, and knock knees, long limbs, and with some female characteristics such, as feminine pitched voice., , , , Enlarged breasts- gynaecomastia., , , , 1 in every 500 male births is victim of this, syndrome., , Ngangom Lucky Devi, Lecturer Zoology, Johnstone Hr. Sec. School
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35, , Thank you
