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, eachchromosome replicates

After meiosis I, thehomologues segregate

After meiosis II, eachgamete has one allele

iii) Law of Independent Assortment

Different gene pairs assort independentlyin gamete formation if the gene pairs areon 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 oneLocus with3 alleles

No individualcan have morethan 2 alleles

The gene pool isthe sum of all thealleles found ina population

X1 = .20X2 = .50X3 = .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:

p2 + 2pq + q2 = 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.