Linked inheritance
- 1. LINKED INHERITANCE Name: Jeny Jose Subject: Cytogenetics Semester: 1 Course: Agricultural Biotechnology University: Szent Istvan University
- 2. Inheritance ïŽ Inheritance means the pattern in which the gene will be transferred from parents to off-springs, i.e. from one generation to the next. ïŽ The gene to be transferred if present on the 22 autosomal pair in case of humans or generally in autosomes are called Autosomal Linked Inheritance. ïŽ If the gene to be transferred is present on any of the sex chromosomes of our body is called Sex Linked Inheritance.
- 3. Autosomal Inheritance ïŽ All the genes produce proteins in our body e.g. Hepatocytes produces enzymes for digestion and metabolism, the genes responsible for which are present in the autosomes of our body. ïŽ The autosomal inheritance will look like ïŽ A- dominant allele, AA, aa homozygous pair of genes. ïŽ a- Recessive allele, Aa heterozygous pair of genes. ïŽ For instance When the dominant gene is responsible for eye colour blue recessive allele is responsible for an eye colour black and the inherited genes are âaaâ, only then will the off-spring show black eye colour. ïŽ It is not dependant on gender, both female and male have equal chance of inheriting the genes and exhibiting the characteristic property of the gene.
- 4. Mendelian Genetics ïŽ According to Mendelâs concept i.e. Mendelian Genetics, âą A fly having Wild Characteristics of Yellow colour and Normal wings will have the genes BBVV- BV (Gametes) Dominant âą A mutant having the colour black and Vestigial wings will have the genes bbvv- bv (Gametes) Recessive âą On Crossing the hybrid will be heterozygous with the genes BbVv, âą The daughter was wild type and so was the male because of Dominant wild type characteristics.
- 5. Crossing of Hybrid and Mutant ïŽ On crossing the hybrid(BbVv) with homozygous mutant (bbvv). The gametes of hybrid would be: ï§ BV, Bv, bV, bv ïŽ The gametes of mutant would be: ï§ bv The progeny will have the genes: ï§ BbVv (Yellow and normal wings) ï§ Bbvv (Yellow and vestigial wings) ï§ bbVv (Black and Normal wings) ï§ Bbvv ( Black and Vestigial wings) the ratio hypothetically was supposed to be 1:1:1:1
- 6. Gametes BV Bv bV bv bv BbVv Bbvv bbVv bvbv Hybrid Mutant Hypothetical result
- 7. Actual Results ïŽ The above should have been the result but it was observed by Morgan that ïŽ 83% were (Yellow with normal wings or Black with Vestigial wings) i.e. PARENTAL TYPE. ïŽ 17% were (Yellow with Vestigial wings or Black with normal wings) After repeating the experiments several time, Morgan found the same results, then a student under Thomas D. Morganâs tutelage, Alfred Sturtevant stated that the genes are linked i.e. they are on the same chromosome. Mendelian Genetics + Chromosome = Chromosomal Genetics.
- 9. Recombinant ïŽ The recombinants can be created only when it creates a copy of itself with the same gene and after crossing over, it is cut between the two genes and swapping of the chromosomal genes.
- 10. Inference ïŽ If the two genes are really far, then crossing over is random and cutting can be any place. ïŽ But if the two genes are closer, it is less likely to cut between the two genes in order to create recombinant chromosome. ïŽ To have recombinant chromosome the crossing over should be such that it cuts the chromosome into half. ïŽ Frequency of recombination depends on the relative position of genes. ïŽ If it is less than 50% then the genes are linked otherwise they are on different chromosomes.
- 11. Genetic Linkage ïŽ Genetic linkage is the tendency of DNA sequences that are close together on a chromosome to be inherited together during the meiosis phase of sexual reproduction. Two genetic markers that are physically near to each other are unlikely to be separated onto different chromatids during chromosomal crossover, and are therefore said to be more linked than markers that are far apart. ïŽ Genetic linkage is the most prominent exception to Gregor Mendel's Law of Independent Assortment. The first experiment to demonstrate linkage was carried out in 1905.
- 12. Sex-Linked inheritance ïŽ In mammals there are male and females alleles and several characteristics differentiate a man from woman for which a whole set of genes work together. ïŽ XY- Sex determining chromosome (MALE) ïŽ XX- Sex determining chromosome (FEMALE) They do not just have sext determining traits. They also: âą X- Codes for 1500 genes âą Y- codes for 78 genes (SRY gene that plays a role in development of testes)
- 13. X- linked inheritance ïŽ X-linked inheritance means that the gene causing the trait or the disorder is located on the X chromosome. ïŽ Females have two X chromosomes, while males have one X and one Y chromosome. ïŽ Carrier females who have only one copy of the mutation do not usually express the phenotype, although differences in X chromosome inactivation can lead to varying degrees of clinical expression in carrier females since some cells will express one X allele and some will express the other.
- 14. Examples of X-Linked Recessive disorder The most common X-linked recessive disorders are: ïŽ Red-green color blindness, a very common trait in humans and frequently used to explain X- linked disorders. Between seven and ten percent of men and 0.49% to 1% of women are affected. Its commonness may be explained by its relatively benign nature. It is also known as daltonism. ïŽ Hemophilia A, a blood clotting disorder caused by a mutation of the Factor VIII gene and leading to a deficiency of Factor VIII. It was once thought to be the "royal disease" found in the descendants of Queen Victoria. This is now known to have been Hemophilia B ïŽ Hemophilia B, also known as Christmas Disease, a blood clotting disorder caused by a mutation of the Factor IX gene and leading to a deficiency of Factor IX. It is rarer than hemophilia A. As noted above, it was common among the descendants of Queen Victoria. ïŽ Duchenne muscular dystrophy, which is associated with mutations in the dystrophin gene. It is characterized by rapid progression of muscle degeneration, eventually leading to loss of skeletal muscle control, respiratory failure, and death.
- 15. Continued.. ïŽ Becker's muscular dystrophy, a milder form of Duchenne, which causes slowly progressive muscle weakness of the legs and pelvis. ïŽ X-linked ichthyosis, a form of ichthyosis caused by a hereditary deficiency of the steroid sulfatase (STS) enzyme. It is fairly rare, affecting one in 2,000 to one in 6,000 males. ïŽ X-linked agammaglobulinemia (XLA), which affects the body's ability to fight infection. XLA patients do not generate mature B cells. B cells are part of the immune system and normally manufacture antibodies (also called immunoglobulins) which defends the body from infections (the humoral response). Patients with untreated XLA are prone to develop serious and even fatal infections. ïŽ Glucose-6-phosphate dehydrogenase deficiency, which causes nonimmune hemolytic anaemia in response to a number of causes, most commonly infection or exposure to certain medications, chemicals, or foods. Commonly known as "favism", as it can be triggered by chemicals existing naturally in broad (or fava) beans.
- 16. Explanation of X-linked chromosome with examples ïŽ Colour Blindness where Mutation is on X chromosome (recessive mutation) ïŽ Xn = Normal traits o X ïŽ Xc = Colour Blindness carried on X chromosome. Case 1: So if a cross between carrier woman and normal male will result in It results in 1 normal and 1 carrier daughter i.e. 0 colour blind Daughter but sons have a 50% Chance of being colour blind if They have a carrier mother gametes Xn Y Xn XnXn XnY Xc XcXn XcY
- 17. ïŽ Case 2: If a cross is made between a colour blind woman and a normal male ïŽ The results indicate that the daughters will be carriers and not clour blind where as both the sons will be colour blind. ïŽ Therefore it is clear that Sex linked inheritance, males are more prone to get the disease. gametes Xn y Xc XcXn XcY Xc XcXn XcY
- 18. Haemophilia ïŽ It is a disease which impairs the body's ability to make blood clots, a process needed to stop bleeding. This results in people bleeding longer after an injury, easy bruising, and an increased risk of bleeding inside joints or the brain. It is also an X linked inherited disease. ïŽ Females have three different types of genotypes: XX = normal ; XhX =Carrier ; XhXh= has Haemophilia ïŽ Males have two genotypes: XY= normal ; XhY= Haemophilic
- 19. ïŽ Case 1: haemophilic male Ï normal female ïŽ In such a case both the daughters would be carriers and the sons would be but no child would be haemophilic. The fathers transmits characters to daughter not son, whereas the mother does the same to sons. Gametes Xh Y X XXh XY X XXh XY Case 2: A carrier female Ï normal male Gametes X Y Xh XhX XhY X XX XY ÂŒ children haemophilic; 50% males haemophilic. 1/7000 males have haemophilia whereas the chances of a female being haemophilic is 1/49,000,000
- 20. References ïŽ https://www.youtube.com/watch?v=Wfxf9xmYI_M ïŽ https://www.youtube.com/watch?v=-ROhfKyxgCo ïŽ https://www.youtube.com/watch?v=KaxSDryqB6M ïŽ https://www.youtube.com/watch?v=KaxSDryqB6M ïŽ https://www.youtube.com/watch?v=3CtM4AaOxQ0
- 21. Thankyou