Biology 102Biology 102

Patterns of InheritancePatterns of Inheritance

Lecture outlineLecture outlineDown Syndrome: ClarificationDown Syndrome: ClarificationPatterns of Inheritance: IntroductionPatterns of Inheritance: Introduction

Why study genetics?Why study genetics?Useful vocabularyUseful vocabularyHistorical perspective: Gregor Mendel’s Historical perspective: Gregor Mendel’s

studiesstudiesPatterns of Inheritance: ConceptsPatterns of Inheritance: Concepts

Inheritance of single traitsInheritance of single traits Inheritance of multiple traitsInheritance of multiple traits

Same chromosomeSame chromosomeDifferent chromosomeDifferent chromosome

Down SyndromeDown Syndrome Occurs due to non-Occurs due to non-

disjunction during disjunction during anaphase of meiosis 1 anaphase of meiosis 1 (sketch)(sketch)

Results in 3 copies of Results in 3 copies of chromosome 21chromosome 21

25% of cases are 25% of cases are caused by abnormal caused by abnormal spermsperm

Note size of Note size of chromosomechromosome Why important?Why important?

Why study patterns of inheritance?Why study patterns of inheritance?

Understand genetic disease Understand genetic disease What does the diagnosis mean?What does the diagnosis mean?How do they get the “odds” that a child will How do they get the “odds” that a child will

have a disease?have a disease?What is gene therapy?What is gene therapy?

Make informed decisions about Make informed decisions about genetically-modified organismsgenetically-modified organismsWhat a GMO is, and what it is not…What a GMO is, and what it is not…

Patterns of InheritancePatterns of Inheritance VocabularyVocabulary

GeneGene LocusLocus TraitTrait AlleleAllele Homologous chromosomesHomologous chromosomes HomozygousHomozygous HeterozygousHeterozygous genotypegenotype phenotypephenotype DominantDominant recessiverecessive

11 22 33 44 55 66 77 88 99 1010 1111 1212 1313 1414 1515 1616 1717 1818 1919 2020 2121 2222 2323 2424 2525 2626Loci:Loci:

Chromosome from One ParentChromosome from One Parent

Homologous Chromosome from Other ParentHomologous Chromosome from Other Parent

11 22 33 44 55 66 77 88 99 1010 1111 1212 1313 1414 1515 1616 1717 1818 1919 2020 2121 2222 2323 2424 2525 2626Loci:Loci:

M locus has gene that

controls leaf color. Plant

homozygous for this gene

D locus has gene that

controls plant height. Plant homozygous for this gene

Bk locus has gene that

controls fruit shape. Plant

heterozygous for this gene

Gregor MendelGregor Mendel

His BackgroundHis Background

Experimental designExperimental design1.1. Chose pea plants with Chose pea plants with

distinct “either/or” distinct “either/or” characterisitcscharacterisitcs

2.2. Could control fertilization of Could control fertilization of plantsplants

• Performed “crosses” of Performed “crosses” of specific combinationsspecific combinations

3.3. Used statistics to analyze his Used statistics to analyze his datadata

His work revealed His work revealed patterns of inheritancepatterns of inheritance

Crosses with single traits: Crosses with single traits: First generation (F1)First generation (F1)

Which trait is dominant?Which trait is dominant?

Principles of inheritance that Principles of inheritance that cause this resultcause this result

True-breeding” plants are homozygous True-breeding” plants are homozygous for the particular trait in questionfor the particular trait in questionEach parent contributes only one allele typeEach parent contributes only one allele type

Crosses with single traits:Crosses with single traits:Second generation (F2)Second generation (F2)

F1 Offspring are heterozygotesF1 Offspring are heterozygotes

Each parent contributes one of two Each parent contributes one of two allele typesallele types

Punnett Square MethodPunnett Square Method

Chalk talk!Chalk talk!

Crosses with two traitsCrosses with two traits If genes are on different chromosomes, they If genes are on different chromosomes, they

sort independentlysort independently

Punnett squares: 2 traitsPunnett squares: 2 traits

Chalk talk!Chalk talk!

Genes on the same chromosome Genes on the same chromosome tend to be inherited togethertend to be inherited together

They are on the same chromosome. They are on the same chromosome. Considered to be “linked”.Considered to be “linked”.

Recombination creates new Recombination creates new combination of “linked” allelescombination of “linked” alleles

The farther away two genes are on a The farther away two genes are on a chromosome from each other, the more chromosome from each other, the more likely they will be exchanged during likely they will be exchanged during crossing over crossing over