LIF 111 Lecture 1: Introduction to Biology and Genetics (PDF)

LIF 111: Lecture 1 25 September 2024 Why Biology? https://www.youtube.com/watch?v=7L7x0BAqWis Introduction to Biology https://www.youtube.com/watch?v=B_PQ8qYtUL0&ab_channel=Fran kGregorio Introduction to Genetics https://...

LIF 111: Lecture 1 25 September 2024 Why Biology? https://www.youtube.com/watch?v=7L7x0BAqWis Introduction to Biology https://www.youtube.com/watch?v=B_PQ8qYtUL0&ab_channel=Fran kGregorio Introduction to Genetics https://www.youtube.com/watch?v=M4zHVRLXkgw&ab_channel=Fra nkGregorio Introduction to DNA https://www.youtube.com/watch?v=1vm3od_UmFg&ab_channel=bio interactive  25 September, 2024 Life 111_Part II Principles of Inheritance: Information processing in living systems Introduction to heredity: inheritance of chromosomes; comparison of asexual and sexual reproduction; meiosis and sexual life cycles; origins of genetic variation Mendel's discoveries; extending Mendel Ian genetics; Mendel Ian inheritance in human Chromosomal basis of inheritance: Relating Mendel's principles to chromosomes; Sex chromosomes and sex linked inheritance; errors and exceptions in chromosomal inheritance DNA as the genetic material; DNA replication and repair Gene to protein: connection between genes and proteins; synthesis and processing of RNA; synthesis of protein Organization and control of prokaryotic genomes Organization and control of eukaryotic genomes: chromatin structure; control of gene expression DNA technology and genomics: DNA cloning; DNA analysis and genomics; practical applications of DNA technology Genetic basis of development: single cell to multi cellular organism.  Key announce for the course content, attendance, evaluation during end-sem examination LIF111  No question from the first part will be asked  Score from first and second part will be 50% of each to make the 100% of the score  There will be 10 marks, each for attendance mid-sem and end-sem  LIF 101 Topic (1) Laws of inheritance Learning goal: What is transmitted from parents to progeny? What determines our traits? Do transmissions of these traits follow a certain rule?  A short Background: Ideas about heredity/inheritance Blending inheritance Preformation 19th Century N. Hartsoecker in 1695 First scientific theory explaining heredity – Mendel’s laws  Gregor Johann Mendel (1822 – 1884) Priest in Augustinian Monastery in Brno, Czechoslovakia  His work with peas laid the foundation for genetics. He was a University educated priest He studied math and science. He returned to the monastery and taught high school. He took care of the monastery’s garden.  He was curious why some plants were like their parents & others were not. He cross pollinated the pea plants by brushing pollen from the stamens of one plant to the pistil of another.  Peas normally self pollinate so he had to take the stamens that make About Mendel pollen off the second plant. The Augustinian Abbey of St Thomas, Brno In the early 1800s About Mendel  Mendel’s experiment Flower: Plant organ for sexual reproduction, that produces gametes (sex cells) and are necessary for fertilization to occur Note that there are specialized organs for reproduction Mendel’s work represent one of the earliest example of experimental biology What is true breeding? Does this mean blending of inheritance? Step 1 : Carry out an experiment & examine the results Does this refute/discar d blending of What are inheritance? P, F1 and F2  Step 2 : Make assumptions based on the observations Heritable features are characters (coloration) and their variations are traits (purple or white). Traits are determined by factors. ‘P’ for purple, ‘p’ for white. Let’s assume Pp traits are always in pairs: PP, Pp or pp  When two factors are present in the same individual one is seen physically – this is thus dominant (purple) while the other one (white) is recessive  Characteristics “seen” in an individual pp constitutes its phenotype (appearance). Characteristic “present” in an individual constitutes its genotype. Note the terminologies introduced : character, t, trait, factors, dominan , recessive, phenotype genotype.  Let’s now see if these assumptions Can you define these help explain the results terms now? Step 3: Explain the results based on the observations & assumptions made Explanation based on first laws of probability: P p P p The first Law of probability states that the results of one chance event have no effect on the results of subsequent (or another) chance event. Thus, the probability of obtaining heads the second time you flip it remains at ½. The second law of probability states that the chances of two independent events happening together is the product of their individual probability Punnett square  Interpret results Interpretations are based on the assumptions made : factors represent traits, there are two factors for each trait in each plant – one maternally derived and the other paternally derived Starting with PP and pp plants in the second generation (F2) we will end up with 3: 1 phenotypic ratio when the factors (P, p) segregate from each other during gamete formation Note this term segregation: Questions: What segregates? When ? What is the evidence of their segregation? Genotypic and phenotypic ratios in F2 generations Homozygous Heterozygous Homozygous  End of essential concept of inheritance Rest of your learning is application of this concept  Solve problem: Application of Mendelian laws in understanding human inheritance & disease Background Information b-thalassemia is a form recessive genetic disorder that reduces the production of hemoglobin. In acute cases it is lethal. www.ygyh.org/thal/ inherited (your genes your health) Observation Baby with b-thalassemia is born to a couple who were otherwise normal Question How will you explain this observation? Unpack the problem first b-thalassemia is a recessive genetic disorder while the parents are normal: this means that both the parent are heterozygous and therefore carriers. T/t Progeny of (T/t X T/t) would thus be: (T/T, T/t and t/t) Since b-thalassemia is recessive genetic disorder the unfortunate baby was genotypically t/t t’s consider inheritance of two different pairs of fact What Which one does R Character : texture of the seeds is and r Traits smooth (R ) and rough dominant? mean? ( r) Character : color of the seeds Pp Traits yellow (Y) and green (y) Monohybrid If a plant is true breeding smooth and yellow – RrYy how can we represent its genotype? Di-hybrid RRYY If a plant is true breeding rough and green – how can we represent its genotype? rryy  What will be the consequence if a true breeding smooth and yellow plant is crossed with another true breeding plant which is rough and yellow? P1 RRYY X rryy 8/22  First, find the types of gamete s that are possibl e dihybrid Y=1/2 R=1/2 YR=1/4 Second, speculate the outcome if factors of original parent segregate together Notice, however, that These results demands explanation this inheritance follows based on an another law of the law of segregation inheritance: namely, the law of independent assortment  Law of Independent assortment (This law tells how different Mendelian factors are distributed following segregation) The Law of Independent Assortment states that alleles of different genes assort independently of one another during gamete formation. Alleles: each of two or more alternative forms of a gene(factor) that arise by mutation  Your homework: Explain the P1 applications of the first and second laws of probability F1 during the formation of the F2 gametes of the F1 parent The dihybrid ratio Let’s revise  RECAP Assumptio What is n: assumed here? For each trait there Law of segregation is one pair of alleles Alleles (factors) representing a given trait segregate (separate) during gamete formation, and randomly unite at fertilization. An interpretation based How this on first & second law of inference was probability: drawn? Each gamete receive only one of the two alleles (factors) How to read ? Example http://en.wikipedia.org/wiki/Mendelian_inheritance  RECAP First law of First law of probabilit probability y Second law Second law of of probability probability The First Law of Probability states that the results of one chance event have no effect on the results of subsequent chance events. Second Law of Probability, which states that the probability of independent chance events occurring together is the product of the probabilities of the separate events. This is also called a monohybrid cross. Why?? RECAP  Genetic vocabulary Alleles: the factors representing a trait. Since we now call these factor as genes, alleles essentially mean different version of the same gene Carrier: An individual which is heterozygous, meaning a given pair of allele are not identical. A carrier often carries a defective version of the gene along with its normal version Define the following: Homozygous: ?? Law of segregation: ?? Phenotype: ?? Trait : ??? Dominant: ??? Connect two terms Dominant and phenotype Connect three terms Dominant , phenotype and allele Construct a full sentence using all the above terms shown in genetic vocabulary  Let’s revise and solve problems All subsequent slides here are for you to revise and think about the concept A law can always be validated further Test cross Purple X White Pp pp Third Step : Validate the idea further ??  Explain why did Mendel took two contrasting factors to demonstrate this rule of inheritance, namely, the law of segregation?  What will be the consequence if these factors do not segregate over succeeding generations ?  What is the modern term for Mendelian factors?  Why should these factors be in pairs at all? What is the consequence of the operation of law of independent assortment in our own inheritance ?  Use the following words to complete the sentence below allele(s), diploid, gamete(s), gene, haploid A ______organism contains two _____ of each ______ in all cells except its _________which are _________ and contain only one.  Use the following words to complete the sentence below. dominant, homozygous, non-identical, heterozygous, identical All non-reproductive cells contain two alleles of each gene. When those alleles are ____________, the cell is said to be _____________. When those alleles are _____________, the cell is said to be _______________, in which case the cell’s (or organism’s) phenotype is dictated by the _____________ allele. For your further revision  Problem  The tyrosinase gene, TYR, is necessary for production of the skin pigment melanin in humans. A recessive allele, tyr, of this gene causes the most frequent form of albinism. Homozygotes (tyr / tyr) do not produce melanin, while heterozygotes (TYR / tyr) are unaffected. What is the probability that a child born to a couple, both heterozygous for (TYR/tyr) will be albino?  Your answer should be based on use of the correct symbols  Define the terms used in the above question  Problem 1. One gene has alleles A and a. another has allele B and b. For each genotype, what type(s) of gametes will form? Assume that independent assortment occurs. a. AABB Which one of the b. AaBB parental c. Aabb Which one of genotypes is a d. AaBb the parents is product of a not a hybrid? monohybrid Answers: cross? Parental Gamete types genotype formed Which set of AABB AB gametes display AaBB AB (1/2) & aB(1/2) evidence of Aabb Ab (1/2), ab(1/2) independent assortment? AaBb AB (1/4), Ab (1/4) Explain why aB (1/4), ab (1/4) there are four types of gametes  Home work 2. What will be the genotypes of offspring from the following matings? Indicate the frequencies of each genotype among a. AABB x aaBB b. AaBB X AABb c. AaBb X aabb d. AaBb X AaBb Step 1: In each case, first identify the types gametes formed by each parent Step 2: Place these gametes at the designated positions in a Punnett square Step 3. Display the genotypes of the products of fusion of these various gametes in the Punnett square Step 4. Describe the phenotypes of the genotype of the progeny and their ratios