Genetics

Which one of these is not like the other???

Mutants

Contrasting Traits

Relationship of Phenotype to Genotype The phenotype is the outward expression of all alleles governing a given trait The genotype is the alleles present in the genome The gene products encoded by the gene (alleles) give rise to the phenotype

A Controlled Cross between Two Plants

Mendel’s Experiment 1 (Part 1)

Mendel’s Experiment 1 (Part 2)

Mendel’s Explanation of Experiment 1

Phenotype Dominant trait  One that appears exclusively in F 1 generation Recessive trait  One masked in the F 1 but reappearing in some of F 2 offspring

Mendel’s Monohybrid Cross Results

Mendel’s Law of Segretation Each parent contains two factors governing a particular trait  2 dominants  1 dominant + 1 recessive  2 recessives The factors are separated during reproduction and only 1 from each parent is passed to offspring Alleles of a gene segregate during meiosis Each somatic cell contains 2 alleles of each gene, while gametes contain only 1.

Meiosis Accounts for the Segregation of Alleles

Homozygosity vs Heterozygosity Homozygosity –  alleles are same Heterozygosity  alleles are different Homozygous dominant and heterozygous individuals have same phenotype (dominant) Homozygous recessive individuals have recessive phenotype

Homozygous or Heterozygous?

Dihybrid Crosses and Independent Assortment What is result of crosses between individuals differing in two traits? Do alleles of for different traits segregate together or separately?

Meiosis Accounts for Independent Assortment of Alleles

Relationships between Alleles In diploid organisms there are 2 alleles for every gene (locus) in the genome One allele was inherited from father and the other from mother Multiple alleles may exist in a population of organisms although only 2 are present at any one time in an individual Each gene encodes a gene product (protein or RNA) Alleles interact in following ways  Complete dominance/recessiveness  Co-dominance  Incomplete dominance

Phenotype vs Genotype Phenotype – appearance/function Genotype – set of alleles present in genome

ABO Blood Types: Multiple Alleles Showing Complete Dominance or Co-dominance A dominant to O B dominant to O A co-dominant to B Co-dominance results when alleles each encode a functional enzyme, however, the encoded enzymes differ in their specificities Phenotype

Incomplete Dominance r encodes a non-functional protein R encodes a functional protein Rr makes ½ the amount of R-protein as an RR flower Rr flowers are less intensely colored

Pedigree Analysis

Crossing Over Results in Genetic Recombination

Linkage: When Alleles Do Not Sort Independently

Recombinant Frequencies

Steps toward a Genetic Map

Map These Genes (Part 1)

Map These Genes (Part 2)

Figure Map These Genes (Part 3)

Figure Map These Genes (Part 4)

Figure Map These Genes (Part 5)

Eye Color Is a Sex-Linked Trait in Drosophila

Figure Red-Green Color Blindness is a Sex-Linked Trait in Humans

Epistasis Epistasis occurs when the alleles of one gene cover up or alter the expression of alleles of another gene. Coat color in mice:  B allele produces a banded pigment pattern, called agouti, while the b allele results in unbanded hairs.  genotypes BB or Bb produce agouti. genotype bb is black.  Alleles at the A locus determine if any pigment is made. The genotypes AA and Aa have color and aa are albino.

Epistatic Gene Interaction B is an enzyme that actively interupts deposition Aa Non-functional pigment producing enzyme Functional pigment producing enzyme A is an enzyme that actively synthesizes pigment bB Sequential pigment deposition Constant pigment deposition

Epistasis Pigment producing enzyme pigment precursor molecule pigment molecule Deposition of pigment in hair pigmented hair aa pigment precursor molecule pigment molecule BB or Bb pigmented hair AA or Aa pigment precursor molecule pigment molecule bb Solid color hair aa pigment precursor molecule pigment molecule bb pigmented hair AA or Aa pigment precursor molecule pigment molecule BB or Bb Striped hair genotype

Quantitative Traits Traits exhibiting a range of phenotypic variance that can be quantified (measured)  Height, weight, seed yield, life span etc… Traits are simultaneously controlled by many alleles  Additive alleles  Proteins encoded by various alleles function in tandem to influence trait Genes functioning in this manner are referred to as quantitative trait loci (QTLs)

Quantitative Trait Loci 2 genes control seed color for a given plant and each gene has 2 alleles Genes: A/a, B/b, Any given plant can be of one of the following genotypes  AABB, AaBB, aaBB, AABb, AAbb, AaBb, Aabb, aaBb, aabb  Each allele of each gene can “add” a given amount of activity to generating a color phenotype.  A and B add the most color, a and b add less color  Therefore a range of colors can exist (5 categories)  AABB – darkest  AABb, AaBB – next darkest  AaBb, aaBB, AAbb – mid range color  Aabb, aaBb – very little color  aabb – least color