Mendelian inheritance

“Introduction Biology PART : Mendelian Inheritance Kittisak Buddhachat, Ph.D

Outline of Mendelian Inheritance1. To understand the Mendelian theory LAW I : Law of Segregation LAW II : Law of Independent Assortment2. Pedigree analysis

1 Mendel’s Genetics • Gregor Johann Mendel (Father of Genetics) in 1865 and 1866 • Model for study is “Peas” • many distinct varieties such as colour, shape and etc. • true-breeding—>self- fertilisation, test cross, back cross • short time for observation

1 Mendel’s Genetics Mendelian words ❖ Locus = a position of gene on the chromosome ❖ Allele = a form of gene

1 Mendel’s Genetics Mendelian words • Genotype = genetic information regulates the physical physical trait • Phenotype = physical appearance or quantitative trait • Dominant allele = one determine organism’s appearance • Recessive allele = no noticeable effect on organism’s appearance

1 Mendel’s Genetics Mendelian words ❖ Homozygous/Homozygote = two identical alleles ❖ Heterozygous/Homozygote = two different allelesPwPw PbPb PwPb

1 Mendel’s Genetics ❖ Character = flower colour ❖ Variant of character = trait/phenotype (i.e. white or purple flower) ❖ Quality character or discrete character ❖ Quantitative character or continuous character such as height, volume and color shading

1 Mendel’s Genetics First law: Law of Segregation “A pairs of gene variants are separated into gamete cells, referred to as allele” The cross of monohybrid results in the Ratio of Phenotype = 3:1 The German botanist Oscar Hertwig in 1876, and the Belgian zoologist Edouard Van Beneden in 1883 who proved this law by observation of meiosis division

1 Mendel’s GeneticsFirst law: Law of Segregation Example I: Example II: Bb   x    Bb BB x Bb F0 1/2 1/2 1/2 1/2Gamete B bB bF1 BB : Bb : bb = _______________ 1/__ 1/__ 1/__ 1/__ BB : Bb : bb = ___________________

1 Mendel’s Genetics Second law: Law of Independent Assortment “Genes for different traits can be segregated and the different genes can be assorted independently during the formation of gametes” Dihybrid cross = two heterozygous of two characters Ratio of Phenotype = 9:3:3:1 This law occurs in meiotic metaphase I

1 Mendel’s Genetics Meiosis and Mendelian Law A location of gene = locus Several locations = loci

1 Mendel’s GeneticsSecond law: Law of Independent Assortment F0 Example I:Gamete AaBb x         AaBb 1/4 1/4 1/4 1/4 1/4 1/4 1/4 1/4 1/4 1/4 1/4 1/4 AB Ab aB ab AB Ab aB ab AB Ab aB ab 1/4 ABF1 1/__ 1/4 Ab 1/__ 1/__ 1/__ 1/4 aB 1/4 ab AABB : AABb : AAbb: AaBB : AaBb: Aabb: aaBB: aaBb :aabb = __________________________________________________________

1 Mendel’s GeneticsSecond law: Law of Independent AssortmentExample I: 1/4AA 1/4BB =___________AaBb x  AaBb 1/2Bb =___________ 1/4bb =___________ Aa x Aa1/4AA : 2/4Aa : 1/4aa 1/2Aa 1/4BB =___________ 1/2Bb =___________ 1/4bb =___________ Bb x Bb 1/4aa 1/4BB =___________1/4BB : 1/2bb : 1/4bb 1/2Bb =___________ 1/4bb =___________

1 Mendel’s GeneticsSecond law: Law of Independent Assortment Example II: ___AA ___BB =___________ AABb x  AaBB ___Aa ___Bb =___________ ___aa ___bb =___________ AA x Aa ___BB =______________AA : ___Aa : ___aa ___Bb =___________ Bb x BB ___bb =______________BB : ___bb : ___bb ___BB =___________ ___Bb =___________ ___bb =___________

1 Mendel’s Genetics Relationship among alleles

1 Mendel’s Genetics Relationship among allelesCo-dominance and multiple allele Pleiotropy

2 Pedigree analysis Human and Mendelian’s Law

2 Pedigree analysis Human and Mendelian’s LawDominantly inherited Disorder Recessively inherited DisorderRatio of Dwarf : Normal = 1 :1 Ratio of Albino : Normal = 3 :1

Questions?The pedigree is the inheritance of alkaptonuriadisorder (highlighted).This allele of alkaptonuria is dominant orrecessive ? Interesting trait : curled-black ear How would you determine whether the curl allele is dominant or recessive? How would you obtain true-breeding curl cats?