Chapter 2: Single Gene Inheritance Jan 10 th 2014 Office Hours: Thurs & Fri 9:00 – 10:00 am

Gene Discovery: Genetic approach to understanding any biological property is to find subset of genes in the genome that influence the property and understand their function at the molecular level One approach to gene discovery is to isolate mutants and check each one for single-gene inheritance patterns

Mutants: individual organisms having altered form of a normal property or character Wild type: normal (or most prominent) form of that property in an organism Gene Discovery begins with search for mutants in a specific biological process Most direct method of gene discovery: visually screen a collection of a large number of individuals looking for chance occurrence of a mutant(s) within the population Terms used in the detection of inheritance patterns

WT Flower Arabidopsis thaliana The most prominent genetic model in plant biology Produces pollen Holds ovule

Genetic analysis begins with mutants Apetala (no petals) Ap1 ap2 and ap3 have separate genes that are defective in the formation of petals

2.1 Single Gene Inheritance Patterns First example of an analysis of single gene inheritance: Gregor Mendel, 1860s Genetic analysis predates Gregor Mendel, but Mendel's laws form the theoretical basis of our understanding of the genetics of inheritance. two innovations to the science of genetics: developed pure lines counted his results, statistics Pure Lines: for phenotype in question, all offspring produced by matings within members of the pure line were identical for the phenotype Property = character or trait Phenotype: form taken by a character Mendel always started with pure lines (pure breeding lines)

Mendel’s Pea Plan: What makes a good model genetic organism? Garden Pea

Mendel studied 7 different contrasting phenotypes Pea = seed (containing embryo … it’s a zygote)

Cross-pollination and selfing are two types of crosses Two different individuals (Out Cross)

Represents the first generation of two pure bred parents Plants produced from the previous generation are yellow AND green. This occurs due to dominance and recessance The reciprocal cross refers to switching the genders (aka female yellow, male green). The results would be the same for future generations

What is the result of the reciprocal cross? What happened when individual F2 seeds were grown and the resulting plant selfed? 1.Green pea ? 2.Yellow pea? With respect to previous slide: Same results Green pea

Mendel’s crosses resulted in specific phenotypic ratios

Table 2-1 Results of All Mendel's Crosses in Which Parents Differed in One Character

Gene = hereditary factor responsible for pea color Each plant has a pair of this type of gene Gene comes in 2 forms called alleles - Y (yellow) and y (green) Plant can be Y/Y, y/y, or Y/y In Y/y plant Y dominates so phenotype = yellow Phenotype of Y/y plant defines Y allele =dominant and y allele = recessive During meiosis, members of gene pair segregate equally into gametes (eggs or sperm) = Mendel’s 1 st law / law of equal segregation Single gamete contains only one member of the gene pair At fertilization gametes fuse randomly to create zygote Mendel’s Law of Equal Segregation

Notation: YY= 2 alleles in 1 individual Uppercase= DOMINANT lowercase= recessive Mendel’s Law of Equal Segregation

Punnets’s square

Homozygote: has identical pair of alleles Heterozygote: allele of the pair differ Monohybrid: heterozygote for one gene Monohybrid cross: cross of 2 heterozygotes Individual can be: Homozygous dominant (Y/Y) Heterozygous (Y/y) Homozygous recessive (y/y) Genotype: the allelic combinations that underlie phenotype More Genetic Terminology

A single-gene model explains Mendel’s ratios

Genotypic Ratio: 1 : 2 : 1 Y/Y Y/y y/y Yellow: Yellow : green Phenotypic Ratio: 3 : 1 Y/__ : y/y Yellow : Green 1:1 The underscore denotes either Y or y

Backcross - the cross of an F 1 hybrid to one of the two pure breeding (homozygous) parents Testcross - the cross of any individual to a homozygous recessive parent; used to determine if the individual is homozygous dominant or heterozygous Reciprocal Cross – a cross, with the phenotype of each sex reversed as compared with the original cross Allows a test the role of parental sex on inheritance pattern. Ex] genotype A(female) X genotype B(male) is the reciprocal cross of genotype B(female) X genotype A(male).

Review: 2.1 Mendel’s law of equal segregation In meiosis, members of a gene pair separate equally into gametes Message: All 1:1, 3:1 and 1:2:1 ratios diagnostic of single gene inheritance and are based on equal segregation in a heterozygote