Biology 102 Patterns of Inheritance

Lecture outline Down Syndrome: Clarification Down Syndrome: Clarification Patterns of Inheritance: Introduction Patterns of Inheritance: Introduction Why study genetics? Why study genetics? Useful vocabulary Useful vocabulary Historical perspective: Gregor Mendel’s studies Historical perspective: Gregor Mendel’s studies Patterns of Inheritance: Concepts Patterns of Inheritance: Concepts Inheritance of single traits Inheritance of single traits Inheritance of multiple traits Inheritance of multiple traits Same chromosome Same chromosome Different chromosome Different chromosome

Down Syndrome Occurs due to non- disjunction during anaphase of meiosis 1 (sketch) Occurs due to non- disjunction during anaphase of meiosis 1 (sketch) Results in 3 copies of chromosome 21 Results in 3 copies of chromosome 21 25% of cases are caused by abnormal sperm 25% of cases are caused by abnormal sperm Note size of chromosome Note size of chromosome Why important? Why important?

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 have a disease? How do they get the “odds” that a child will have a disease? What is gene therapy? What is gene therapy? Make informed decisions about genetically-modified organisms Make informed decisions about genetically-modified organisms What a GMO is, and what it is not… What a GMO is, and what it is not…

Patterns of Inheritance Vocabulary Vocabulary Gene Gene Locus Locus Trait Trait Allele Allele Homologous chromosomes Homologous chromosomes Homozygous Homozygous Heterozygous Heterozygous genotype genotype phenotype phenotype Dominant Dominant recessive recessive

Loci: Chromosome from One Parent Homologous Chromosome from Other Parent 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 Mendel His Background His Background Experimental design Experimental design 1.Chose pea plants with distinct “either/or” characterisitcs 2.Could control fertilization of plants Performed “crosses” of specific combinationsPerformed “crosses” of specific combinations 3.Used statistics to analyze his data His work revealed patterns of inheritance His work revealed patterns of inheritance

Crosses with single traits: First generation (F1) Which trait is dominant? Which trait is dominant?

Principles of inheritance that cause this result True-breeding” plants are homozygous for the particular trait in question True-breeding” plants are homozygous for the particular trait in question Each parent contributes only one allele type Each parent contributes only one allele type

Crosses with single traits: Second generation (F2)

F1 Offspring are heterozygotes Each parent contributes one of two allele types Each parent contributes one of two allele types

Punnett Square Method Chalk talk! Chalk talk!

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

Punnett squares: 2 traits Chalk talk! Chalk talk!

Genes on the same chromosome tend to be inherited together They are on the same chromosome. Considered to be “linked”. They are on the same chromosome. Considered to be “linked”.

Recombination creates new combination of “linked” alleles The farther away two genes are on a chromosome from each other, the more likely they will be exchanged during crossing over The farther away two genes are on a chromosome from each other, the more likely they will be exchanged during crossing over