LIF111 Lecture 2 - Mendelian Genetics (27 September 2024) PDF

LIF111/101 Lecture 2: 27 September 2024 (final part of Mendelian genetics) Introduction to Genetics https://www.youtube.com/watch?v=B_PQ8qYtUL0&t=12s&ab_channel=FrankGregorio An example of shortest animation for Mendelian genetics htt...

LIF111/101 Lecture 2: 27 September 2024 (final part of Mendelian genetics) Introduction to Genetics https://www.youtube.com/watch?v=B_PQ8qYtUL0&t=12s&ab_channel=FrankGregorio An example of shortest animation for Mendelian genetics https://www.youtube.com/watch?v=Mehz7tCxjSE&ab_channel=TED-Ed  RECAP Assumptio n: What is 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 This is also called a monohybrid cross. Why?? 4/21  RECAP Test cross Purple X White Pp pp Explain the design/purpos e of this ?? cross What does this cross reveal? 5/21 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) Two Thus, Y is version a Character : color of the seeds an allele trait are Traits yellow (Y) and green (y) of y & called vice versa alleles If a plant is true breeding smooth and yellow – how can we represent its genotype? 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 8/21  What happens in the F2 generation? First, find the types of gametes that are possible F1 YyRr X Second, Why this is speculate F2 called law of the independent outcome if assortment factors of original parent segregate together  Law of Independent assortment (This law tells how different Mendelian factors are distributed randomly/independent of each other following segregation) The Law of Independent Assortment states that segregating alleles of different genes assort independently of one another during gamete formation. P1 F1 F2 The dihybrid ratio  Explain why did Mendel took two contrasting factors to demonstrate this rule of inheritance, namely, the law of segregation?  What is the modern term for Mendelian factors?  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. 1. One gene has alleles A and a. another has allele B and b. For each of the four genotypes below, what type(s) of gametes will form? Assume independent assortment occurs. a. AABB b. AaBB c. Aabb Speculate d. AaBb the genotypes and Parental Gamete types phenotypes genotype formed of the AABB AB progeny in F2 AaBB AB (1/2) & aB(1/2) Aabb Ab (1/2), ab(1/2) 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 position 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  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.  Fruit fly, Drosophila X Wild type vestigial mutant What should be the mutant Allele symbol: Vg vg allele symbol? Information: mutant is recessive What should be the genotype of the mutant fly? vg/vg What could be the genotype of the wild type fly Vg/Vg Vg/vg Cross wild type & vg mutant X Wild type vestigial mutant Step 1 Write their Vg/Vg vg/vg genotype Step 2 Write genotypes of Vg vg their gametes Step 3 Write genotypes Vg/vg the F1 progeny Step 4 Mention the phenotype of F1 progeny  What was the genotype of this parent X Wild type vestigial mutant How would you explain this F1 progeny outcome? 50% 50%  Which one Earlobe Earlobe should attache free be Ff d and which one ff Add Father Mother symb ol Ff and ff Children 50% 50%  Does understanding Mendelian genetics make practical sense to our life? Why marriage b Thalassaemia amongst near relative is not a good idea? What is inbreeding? What is consanguineous marriage Can you inherit genes that may give rise to a disease later on? On average, a woman with a BRCA1 or BRCA2 gene mutation has up to a 7 in 10 chance of getting breast cancer by age 80. If you have inherited a mutated copy of either gene from a parent, you have a higher risk of breast cancer. Breast Cancer Gene Testing Kits The first FDA-approved breast cancer gene test kit supplied by 23andMe, a company that is popular for producing reports that identify a person’s ancestry 23andMe Holding Co. is a publicly held personal genomics and biotechnology company based in South San Francisco, California  Application of these understanding of Mendelian genetics in our own life Cancer prevention treatment On February 16, 2013, the 37-year-old Jolie underwent a preventive double mastectomy after learning she had an 87 percent risk of developing breast cancer due to a defective BRCA1 gene. Her maternal family history warranted genetic testing for BRCA mutations: her mother, actress Marcheline Bertrand, had breast cancer and died of ovarian cancer, while her grandmother died of ovarian cancer. Her aunt, who had the same BRCA1 defect, died of breast cancer three months after Jolie's operation. The mastectomy, which lowered her chances of developing breast cancer to under five percent. Two years later, in March 2015, after annual test results indicated possible signs of early ovarian cancer, she underwent a preventive removal of an ovary and its fallopian tube, as she had a fifty percent risk of developing ovarian cancer due to the same genetic anomaly.  New Topic for the next class Chromosomal basis of Mendelian inheritance Mendel explained inheritance in pea in 1865 – it was not called a law in those days – it was hardly noticed. The physical basis of Mendelian inheritance became evident when chromosomes were discovered and their transmission in somatic cells (by Mitosis) and Gametes (Meiosis) was understood in the early 1900s Summary of our current understanding  Some Gamete terminologi es Gamete Haploid Diploid Chromosome s Entire set of chromosomes in humans arranged in pairs Are these Are these How male Why are these cells cells and females chromosomes diploid or somatic or are in pairs haploid? germ cells different?  Which one of the two germ cells may carry Y chromosome? Sperm Egg 1. How many sets of chromosome do we carry? 2. How many versions (alleles) of a given gene can we carry if every chromosome is in pair? 3. What happens during the gamete (sperm or egg) formation (meiosis) ? Do the allele pairs stay together? Some sample questions Q. What do we mean when we use the terms monohybrid cross and dihybrid cross? (there is only one correct answer) A monohybrid cross involves a single parent, whereas a dihybrid cross involves two parents A dihybrid cross involves organisms that are distinct from each other with respect to alleles of two traits while a monohybrid cross involves only one A monohybrid cross is performed for one generation, whereas a dihybrid cross is performed for two generations Q. A = big apples; R = red apples; a = small apples; r = yellow apples. You have one tree that produces big yellow apples and another tree that produces small red apples. When the two are crossed, you find that half the offspring trees produce big red apples and half produce big yellow apples. a. AArr and aaRr b. Aarr and aaRr c. AARr and AArr d. AaRr and AaRr e. AaRr and aarr Which of the parents, (a) to ( e), likely gave rise to the offsprings mentioned?