1. Module II
Mendelian Genetics &
Probability Theory

2. 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

3. 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

4. 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

5. 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

6. 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:
Homozygous – union of gametes carrying identical alleles; produce homozygotes
Heterozygous – union of gametes carrying different alleles; produce heterozygotes

7. 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

8. SIX MONOFACTORIAL CROSSES (summarized in table below)
Mating
Expected ratios of first filial generation
Genotypes
Phenotypes 1
BB X bb
All Bb
All black 2
Bb X Bb
1 BB : 2 Bb : 1 bb
3 black : 1 white 3
BB X BB
All BB 4
bb X bb
All bb
All white 5
Bb X BB
1 BB : 1 Bb 6
Bb X bb
1 Bb : 1 bb
1 black : 1 white