Module II Mendelian Genetics & Probability Theory

SEXUAL REPRODUCTION involves Manufacture of gametes (gametogenesis) through the process of meiosis (consists of 2 specialized cell divisions in which the chromosome number of the resulting cells is reduced from diploid (2n) to a haploid (n) number) Gametogenesis occurs in specialized cells in the reproductive organs (gonads) In animals, testes are male gonads and ovaries are female gonads The union of male and female gametes (fertilization) produces a zygote In humans, male gametes are sperms and female gametes are ova

GENETICS Genetics is the study of heredity and variation in organisms Genes are the hereditary units transmitted from one generation to the next Genes reside in the long molecules of deoxyribonucleic acid (DNA) that exists within the cell DNA, in conjunction with a protein matrix forms nucleoprotein and becomes organized into structures called chromosomes that are found in the nucleus of the cell

ALLELES Mutation is a change in some part of the DNA The result of a mutation is a change of character or trait of the individual Through a mutation, a gene may be changed into two or more alternative forms called alleles Homologous chromosomes are genetically similar

MENDEL’S LAWS Law of segregation: If a parent contains 2 alleles of a trait, only 1 is transmitted through a gamete to the offspring Law of independent assortment: Segregation of one gene pair occurs independently of any other gene pair

MENDELIAN INHERITANCE (Assumes Mendel’s Laws and independence of environmental conditions) Phenotype – traits possessed by an organism ( may be visible, like color) Genotype – All alleles of a gene possessed by an individual. Classified as: A)Homozygous – union of gametes carrying identical alleles; produce homozygotes B)Heterozygous – union of gametes carrying different alleles; produce heterozygotes

DOMINANT & RECESSIVE ALLELES A Dominant allele of a gene dictates the phenotype of the organism. Indicated by a capital letter, a homozygous dominant individual could have a genotype shown as AA. A heterozygous genotype would be shown as Aa to indicate the presence of a recessive allele form of the gene. A Recessive allele does not determine phenotype in the presence of a dominant allele. Indicated by a lower case letter. A homozygous recessive individual could have a genotype shown as aa. A heterozygous individual who possesses a recessive allele is called a carrier

SIX MONOFACTORIAL CROSSES (summarized in table below) Cross No. Mating Expected ratios of first filial generation GenotypesPhenotypes 1BB X bb All BbAll black 2Bb X Bb 1 BB : 2 Bb : 1 bb3 black : 1 white 3BB X BB All BBAll black 4bb X bb All bbAll white 5Bb X BB 1 BB : 1 BbAll black 6Bb X bb 1 Bb : 1 bb1 black : 1 white