Understanding and Teaching Biological Sciences GENETICS

Outline I.Meiosis and Sexual Reproduction II.The Principles of Inheritance III.How DNA is a code for traits IV.Applications of DNA Technology

I.Meiosis and Sexual Reproduction A.Meiosis Forms gametes needed for sexual reproduction. Reduces the number of chromosomes by half. Genetic recombination occurs. Nondisjunction is an error that can occur during meiosis.

I. Meiosis and Sexual Reproduction B.Sexual Reproduction Gametes combine during the process of fertilization. Fertilization restores the diploid number of chromosomes within the zygote.

II. The Principles of Genetics A.Origin of Genetics B.Mendel’s Laws C.Predicting genotypes and phenotypes D.Patterns of inheritance

A.Origin of Genetics Mendel’s Experiments Phenotypic Ratios

B.Mendel’s Laws i)The Units of Heredity ii)Law of Segregation iii)Law of Independent Assortment

i)The Units of Heredity Genes, like chromosomes, are present in pairs. Different versions of genes are called alleles; they can be normal (wild-type) or mutant. Most mutant alleles are recessive. These alleles, like chromosomes, segregate during meiosis. There are more genes than chromosomes, so each chromosome must have many genes. Alleles of different genes can recombine during meiosis.

ii)Law of Segregation The two members of a gene pair segregate from each other into the gametes; so half the gametes carry one member of the pair and the other half of the gametes carry the other member of the pair.

Meiosis accounts for segregation of alleles Before meiosis I, each chromosome replicates After meiosis I, the homologues segregate After meiosis II, each gamete has one allele

iii)Law of Independent Assortment Different gene pairs assort independently in gamete formation if the gene pairs are on separate chromosomes

C.Predicting Genotypes and Phenotypes i)Punnet Squares ii)Pedigree Analysis iii)Hardy-Weinberg Equilibrium

i)Punnett Squares Reginald Punnett - English geneticist Worksheet - Reindeer Recessives Download and print worksheet. Fill out and bring to class

Punnett Square Example Parents

ii)Pedigree Analysis

Pedigree Charts Autosomal dominant - both sexes affected Autosomal recessive - both sexes affected but fewer in number Sex-linked recessive - only males affected

ii)Pedigree Analysis Worksheet: Cystic Fibrosis Pedigree Download and print worksheet Fill out and bring to class

iii)Hardy-Weinberg Analysis Godfrey Hardy - British mathematician Wilhelm Weinberg - German physician

Genetic Variation within Populations Here is one Locus with 3 alleles No individual can have more than 2 alleles The gene pool is the sum of all the alleles found in a population X 1 =.20 X 2 =.50 X 3 =.30 These are allele frequencies

Calculating Hardy–Weinberg Genotype Frequencies (Part 1)

Figure 23.7 Calculating Hardy–Weinberg Genotype Frequencies (Part 2)

Hardy-Weinberg Equation Hardy–Weinberg equation: p 2 + 2pq + q 2 = 1

D.Patterns of Inheritance Dominance Incomplete Dominance Codominance - blood types Sex-linked traits - Males have only one allele for most X- linked genes, so rare alleles appear phenotypically more often in males.