GENETICS - PART 1
Quick Fatcs:
• Study of heredity and variation is called genetics.
• Term genetics was given by - Bateson.
• Father of genetics - Gregor Johann Mendel.
• Father of experimental genetics - Thomas Hunt Morgan.
• Father of human genetics - Archibald Garrod.
Some Terms in Genetics
1. Gene: It is segment of DNA. It is basic unit of heredity
2. Back cross: It is cross which is performed between hybrid and one of its parents.
3. Test cross: Test cross is crossing of offspring with unknown dominant phenotype with the individual homozygous recessive for the trait.
4. Monohybrid cross: It is a cross between two organisms of a species which is made to study the inheritance of a single pair of alleles or factors of a character.
5. Monohybrid ratio: Monohybrid ratio is usually 3:1 (phenotypic ratio) or 1: 2:1 (genotype ratio) in which 25% of the individuals carry the recessive trait, 25% pure dominant and 50% have hybrid dominant trait.
6. Dihybrid cross: It is a cross between two organisms of a species which is made to study the inheritance of two pairs of factors or alleles of two genes.
7. Dihybrid ratio: Dihybrid ratio is 9: 3: 3: 1 (phenotypic ratio) where 9/16 first recessive and second dominant and 1/16 carry both the recessive traits.
8. Mendel conducted cross hybridization experiments on Garden Pea plant (Pisum sativum). The first was the Principle of segregation, which claimed that each trait was specified by paired hereditary determinants (alleles of genes) that separate from each other during gamete formation. This law is also called Law of purity of gametes or Law of splitting of hybrids.
9. Gregor Mendel was the first individual to apply a modem scientific approach to the study of heredity. Mendel proposed two basic principles of trasmission genetics.
10. Mendel's second basic conclusion was the Principle of independent assortment, which stated that the segregation of one pair of genes-controlling a given trait - was not influenced by the segregation of other gene pairs. The chormosome theory provided a physical basis for the principle of independent assortment. Genes located on different chromosomes move to gametes independently of each other during meiosis.
HUMAN BLOOD GROUPS AND MULTIPLE ALLELE
• The system of blood groups in humans was discovered by Karl Landsteiner in 1900s.
• There are four phenotypes of Blood namely A, B, AB and O produced by three different alleles.IA ,IB and i of a gene.
• The allele IA and IB are equally dominant and do not interfere with expression of each other hence the allele IAIB are said to be co-dominant because both are expressed in the phenotype AB.
• Linkage is the phenomenon of certain genes staying together during inheritance through generations without any change or separation due to their being present on the same chromosomes.
• Linkage in the genes can be identified by test cross.
• The rearrangements of linked genes due to crossing over is known as recombination. Recombination also occurs due to chance separation of chromosomes during gametogenesis and their random coming together during fertilization.
SEX DETERMINATION
• Henking discovered X body in spermatogenesis of few insects and it was given name of X chromosome. Due to involvment of X and Y chromosomes in determination of sex, they were called sex chromosomes.
• Rest of the chromosomes which determine other metabolic character of the body are called autosomes.
• Study of heredity and variation is called genetics.
• Term genetics was given by - Bateson.
• Father of genetics - Gregor Johann Mendel.
• Father of experimental genetics - Thomas Hunt Morgan.
• Father of human genetics - Archibald Garrod.
Some Terms in Genetics
1. Gene: It is segment of DNA. It is basic unit of heredity
2. Back cross: It is cross which is performed between hybrid and one of its parents.
3. Test cross: Test cross is crossing of offspring with unknown dominant phenotype with the individual homozygous recessive for the trait.
4. Monohybrid cross: It is a cross between two organisms of a species which is made to study the inheritance of a single pair of alleles or factors of a character.
5. Monohybrid ratio: Monohybrid ratio is usually 3:1 (phenotypic ratio) or 1: 2:1 (genotype ratio) in which 25% of the individuals carry the recessive trait, 25% pure dominant and 50% have hybrid dominant trait.
6. Dihybrid cross: It is a cross between two organisms of a species which is made to study the inheritance of two pairs of factors or alleles of two genes.
7. Dihybrid ratio: Dihybrid ratio is 9: 3: 3: 1 (phenotypic ratio) where 9/16 first recessive and second dominant and 1/16 carry both the recessive traits.
8. Mendel conducted cross hybridization experiments on Garden Pea plant (Pisum sativum). The first was the Principle of segregation, which claimed that each trait was specified by paired hereditary determinants (alleles of genes) that separate from each other during gamete formation. This law is also called Law of purity of gametes or Law of splitting of hybrids.
9. Gregor Mendel was the first individual to apply a modem scientific approach to the study of heredity. Mendel proposed two basic principles of trasmission genetics.
10. Mendel's second basic conclusion was the Principle of independent assortment, which stated that the segregation of one pair of genes-controlling a given trait - was not influenced by the segregation of other gene pairs. The chormosome theory provided a physical basis for the principle of independent assortment. Genes located on different chromosomes move to gametes independently of each other during meiosis.
HUMAN BLOOD GROUPS AND MULTIPLE ALLELE
• The system of blood groups in humans was discovered by Karl Landsteiner in 1900s.
• There are four phenotypes of Blood namely A, B, AB and O produced by three different alleles.IA ,IB and i of a gene.
• The allele IA and IB are equally dominant and do not interfere with expression of each other hence the allele IAIB are said to be co-dominant because both are expressed in the phenotype AB.
• Linkage is the phenomenon of certain genes staying together during inheritance through generations without any change or separation due to their being present on the same chromosomes.
• Linkage in the genes can be identified by test cross.
• The rearrangements of linked genes due to crossing over is known as recombination. Recombination also occurs due to chance separation of chromosomes during gametogenesis and their random coming together during fertilization.
SEX DETERMINATION
• Henking discovered X body in spermatogenesis of few insects and it was given name of X chromosome. Due to involvment of X and Y chromosomes in determination of sex, they were called sex chromosomes.
• Rest of the chromosomes which determine other metabolic character of the body are called autosomes.
MUTATION
• Phenomenon that results in alteration of DNA sequence and consequently results in change in genotype and phenotype of an organism is called mutation.
• Mutagens are various chemical and physical factors that induce mutations, e.g., UV radiations, carcinogenic chemicals like nicotine, nitric oxide (NO).
GENETIC DISORDER
• A genetic disorder is a disease that is caused by an abnormality in an individual's DNA.
HAEMOPHILIA
• A protein involved in clotting of blood is affected in an affected individual; if person gets a cut, will result in non-stop bleeding.
• Females are heterozygous and carriers of haemophilia.
SICKLE CELL ANAEMIA
• It is due to inheritance of defective allele coding for P-globin. It results in the transformation of HbA into HbS in which glutamic acid is replaced by valine at 6th position in each of two β-chains of haemoglobin.
• It is an excellent example of single mutation.
PHENYLKETONUNA
• Affected individual lacks enzyme phenylalanine hydroxylase that converts ammo acid phenylalanine to tyrosine.
• It is characterized by severe mental retardation, hypopigmentation of skin & hair, eczema, etc.
To be Continued in Part 2
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