7. Patterns of Inheritance

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Biology Lecture 7 DNMU


<ul><li>1.PATTERNSOFINHERITANCE</li></ul> <p>2. PLAN OF LECTURE1. GENETICS and HUMAN GENETICS2. MAIN CONCEPTS of GENETICS3. MENDELS LAWS of INHERITANCE4. MONOGENOUS DISEASES5. MENDELIAN TRAITS IN HUMANS 3. STUDENTS INDEPENDENT STUDY PROGRAMObjectives for Students Independent Studies1. General genetics and human genetics as sciences.2. The main terms of genetic.3. The classification of cross: monohybrid, dihybrid,polyhybrid and test cross.4. Patterns of inheritance.5. Mendels Laws of inheritance6. Mendelian Traits in humans.7. Monogenous diseases.Applicable literature materials:Medical biology / K. L. Lasarev Simferopol: IADCSMU, 2002. p. 114 - 123. 4. KEY WORDS AND PHRASES:GENETIC, ANTHROPOGENETIC, HEREDITY,INHERITANCE, GENE, GENOTYPE, PHENOTYPE,GENOME, ALLELE, LOCUS, HETEROZYGOUS,HOMOZYGOUS, GENETIC ANALYSIS, DOMINANTCHARACTER, RECESSIVE CHARACTER,MONOHYBRID CROSS, POLYHYBRID CROSS, TESTCROSS, MENDELIAN TRAITS, MONOGENOUSDISEASES. 5. Genetics is the science that learnsthe peculiarities of the hereditaryand variability, which are the maincharacteristics of living things. Human genetics (anthropogenetic)is the science that learns thepeculiarities of hereditary andvariability in human organism. 6. 2. MAIN CONCEPTS of GENETICS Heredity - is the transmission ofcharacteristics from parent tooffspring through the gametes. Gene - a unit of heredity, a segmentof a DNA that contains all theinformation required for synthesis ofpolypeptide chain. Each gene has aspecific position (locus) on achromosome. 7. Allele- an alternate form of a gene, thatcan occupy a particularchromosomal locus. In humans andother diploid organism there aretwo alleles, one on eachchromosome of a homologous pair. 8. An individual who has twoidentical alleles for a gene at aparticular locus on homologouschromosomes is homozygous for thatgene.An individual with two differentalleles at a particular locus onhomologous chromosomes isheterozygous. 9. INHERITANCE - is the way of passing ofhereditary information, which depends onthe forms of reproduction.During asexual reproduction the maintraits are inherited through spores orvegetative cells, thats why the maternaland daughter cells are very similar.During sexual reproduction the maintraits are inherited through gametes. 10. Genotype- is the genetic constitution of anorganism (a diploid set of genes). The genotype describes the organismsalleles, whole the phenotype describes theoutward expression (physical appearance ofan individual) of an allele combination. The phenotype of an individual is theobservable outward manifestation of thegenes that it carries. Genome - is a collection of genes of anorganism in cells (may be a haploid set ofgenes). 11. THE GENERAL GENETIC SYMBOLS OFSOLVING THE SITUATIONAL TASKS:1) By Latin letters (, )mark allelesgenes, which reply to alternative traits(signs).2) The parent generation is called as"P".3) Female genotype is written first andhas the symbol (the mirror ofVenus, the godess of beauty); 12. 4) the male genotype the symbol isused (the shield and the spear of Mars- god of war).5) The interbreeding is marked by thesign of multiplication (x).6)The offsprings are called as letter F(Lat. filii) with numeral index, whichbelongs to number of the generation( F1 - children, F2 -grandchildren, etc.) 13. MONOHYBRID CROSSESPF1F2parentsf i l i if i l i i 14. THE CROSSES THAT INVOLVE ONLY ONETRAIT (ONLY ONE PAIR ALLELES) ARECALLED MONOHYBRID CROSSES.THE CROSS BETWEEN INDIVIDUALS, WHICHDIFFER IN TWO VARIOUS TRAITS (TWO PAIRSALLELES) ARE CALLED DYHYBRID CROSSES (TWOPAIRS GENES IN TWO PAIRS OF CHROMOSOMES- NOT LINKED INHERITANCE). 15. 3. MENDELS LAWS of INHERITANCEI. The law of monotony of the firstfilial generation:DURING CROSSING TWO HOMOZYGOUSWHICH ARE DIFFER FROM EACH OTHER BY ONETRAIT ALL PROGENY IN THE FIRST FILIALGENERATION IS MONOTONY AS WELL ASPHENOTYPIC AND GENOTYPIC. 16. LAW OF MONOTONYP parentsF1AAaaAaG: Aa 17. II. THE LAW OF SEGREGATION:STATES THAT FROM A PAIR OF CONTRASTINGCHARACTERS (ALLELES) ONLY ONE IS PRESENTIN A SINGLE GAMETE AND IN F2 THESECHARACTERS ARE SEGREGATED IN THE RATIOOF THREE TO ONE (3:1) BY PHENOTYPEAND 1:2:1 BY GENOTYPE. 18. LAW OF SEGREGATIONPG:F23 : 1parentsAa AaA, aA, aAA Aa aaAa 19. III. LAW OF INDEPENDENT ASSORTMENTBased upon the results of the dihybridcross, Mendel proposed what is nowknow asTHE LAW OF INDEPENDENT ASSORTMENT,WHICH STATES THAT A GENE FOR ONE TRAITDOES NOT INFLUENCE THE TRANSMISSION OFA GENE FOR ANOTHER TRAIT. 20. This is the classic dihybrid ratio, which indicates thatboth parent are heterozygous at both loci. 21. This ratio is the result of the two genes behaving completelyindependently of each other in the cross (not-linked inheritance). 22. MENDELIAN TRAITS in HUMANSMENDELS LAWS APPLY TO ALL DIPLOIDSPECIES.THE NATURE OF THE PHENOTYPE ISIMPORTANT WHEN-EVALUATINGTRANSMISSION OF MENDELIAN TRAITS.IN HUMANS, DISORDERS OR TRAITS CAUSEDBY A SINGLE GENE ARE CALLED MENDELIANTRAITS. 23. MENDELIAN TRAITS in HUMANS 24. Brachydactyly - Short fingers. Polydactyly - Extra fingers andtoes. Huntingtons disease -Degradation of nervous system,starting in middle age.SOME DOMINANT TRAITS IN HUMANS: 25. BrachydactylyPolydactyly 26. Huntingtonsdisease 27. SOME RECESSIVE TRAITS IN HUMANS: Albinism - Lack of melaninpigmentation. Alkaptonuria - Inability tometabolize homogenic acid. Duchenne muscular dystrophy- Wasting away of muscles duringchildhood. 28. Albinism- Lack ofmelaninpigmen-tation. 29. Alkaptonuria- Inability tometabolizehomogenicacid 30. Duchennemusculardystrophy </p>