Introduction to Genetics SS 2024 PDF

# Introduction to Genetics ## Introduction - All living organisms including human beings need to reproduce for continuation of their species - All the offsprings inherit a copy of all information from their parents - needed to develop into functioning member - This information is carried as DNA (D...

# Introduction to Genetics ## Introduction - All living organisms including human beings need to reproduce for continuation of their species - All the offsprings inherit a copy of all information from their parents - needed to develop into functioning member - This information is carried as DNA (Deoxyribonucleic acid) ## DNA - Double stranded molecule made up of two chains of nucleotides - Nucleotides consist of 3 subunits - Sugar - Deoxyribose - Phosphate group - Base - A, G, T, C - Each base along one strand of DNA pair with a base on the other strand with hydrogen bonds - Complementary base pairing - A with T - C with G - DNA carries a huge amount of information that determines all biological activities of an organism & also transmits them from one to the next generation - This information is kept as bases within DNA ## Genetic code - These bases are arranged in a precise order making a code - This code can be read during protein synthesis - This DNA molecule wrapped around histone protein forming chromatin - Chromatin is diffuse & hard to see under the light microscope - When cell prepares to divide, chromatin is supercoiled & packaged into highly visible, compact, sausage shaped chromosomes ## Chromosomes - In human each cell contains 46 chromosomes, arranged in 23 pairs - Of each pair, one chromosome comes from mother & the other from father - During cell division each chromosome is duplicated to form two identical sister chromatids joined by the centromere - Each chromatid is essentially a one DNA molecule - Homologous chromosomes - chromosomes belonging to same pair ## Diploid cells A cell with 23 pair of chromosomes (total 46 chromosomes) ## Haploid cells Cell with 23 chromosomes instead 46 ## Karyotype The complete set of chromosomes in a cell or An individual's complete set of chromosomes ## Numbering of chromosomes - Each pair of chromosome is numbered - First 22 pairs are collectively known as autosomes - chromosomes of each pair are identical - 23rd pair - sex chromosomes - Two chromosomes are not identical - Y chromosome is much shorter than X - Y is carried only by male - A child inheriting two X chromosomes (XX) from each parent is a female - XY - male ## Genes - Functional unit of DNA - gene - Genes are arranged along the length of chromosomes - Genes contain information in the form of codes - genetic codes - These codes involve in making a specific protein - Normally genes exist in pairs - The gene on one chromosome is matched with the other chromosome of the homologous pair at the equivalent site / locus ## Alleles - Different forms of gene - Eg: Gene for the eye colour - Brown colour allele (B) - Blue colour allele (b) - Each person inherit one allele for each gene from each parent - Trait - observed characteristic of that allele combination - Homozygous - An organism is homozygous for gene if it has two identical alleles for that gene - Eg: BB, bb for eye colour - Heterozygous - An organism is heterozygous for a gene if it has two different alleles - Eg: Bb for eye colour - Dominant allele - one that mask the presence of a recessive allele in a heterozygous individual. Only one copy of allele is needed to express the dominant trait - Recessive allele - one that is only expressed if an individual has two copies of it - Eg: For the eye color - BB-Brown eyes - Bb-brown eyes - bb - blue eyes ## Inheritance - Process by which genetic information is passed from parents to their offsprings - Parental genes mix up & displays a variety of genetic variations in a new born infant - Two types of inheritance - Autosomal inheritance - Sex-linked inheritance ## Autosomal inheritance - Transmission of genes located on autosomes - Eg: Tongue Rolling ability of a person - Dominant trait - Tongue rolling ability - Its gene - Tongue rolling (T) - dominant allele - Non rolling (t) - recessive allele ## Codominance - Both alleles in a heterozygous individual are expressed - There may be more than two alleles that code to determine a certain characteristic & more than one allele can be dominant - Eg: Determination of blood group - Three possible alleles - Allele code for A type antigen (A) - B type antigen (B) - no antigens at all (0) - Dominant alleles - Express themselves when present together - Recessive alleles - Present only in homozygous recessive - Possible allele combinations in an individual - AA - Blood group A - AB - Blood group AB - BB - Blood group B - AO - Blood group A - BO - Blood group B - OO - Blood group O ## Sex linked inheritance - Sex is determined by X and Y chromosomes - Y chromosome is shorter than X - Therefore Y chromosome carries less genes than X - Many genes in the X chromosome are not matched or paired with genes in Y - Traits coded for on the section of the X chromosome that has no corresponding material on the Y are sex-linked ## Example - Gene that code for normal colour vision is present only in the X chromosome & that gene is in dominant form (XH) - There is a rare recessive form of this gene (xh) due to a mutation which code for red-green colour blindness - A female who carries the faulty form of the gene (Xh) in one chromosome, most likely to have normal form of gene on the other chromosome - XH Xh - They are known as carriers for the colour blindness (They are not colour blind but carry the gene for their children) - If this faulty form of the gene (Xh) is got by a male child he will become colour blind because he has only one X chromosome