Genetics

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

Mutants

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 F1 generation

• Recessive trait One masked in the F1 but reappearing in some of F2

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

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

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 10.22 Map These Genes (Part 3)

Figure 10.22 Map These Genes (Part 4)

Figure 10.22 Map These Genes (Part 5)

Eye Color Is a Sex-Linked Trait in Drosophila

Figure 10.24 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 pigmentis made. The genotypes AA and Aa have color andaa are albino.

Epistatic Gene Interaction

B is an enzyme that actively interupts deposition

AaNon-functional pigment producing enzyme

Functional pigment producing enzyme

A is an enzyme that actively synthesizes pigment

bBSequential pigment deposition

Constant pigment deposition

EpistasisPigment producing

enzymepigment precursor molecule

pigment molecule

Deposition of pigment in hair pigmented

hair

aapigment precursor molecule

pigment molecule

BB or Bbpigmented

hair

AA or Aapigment precursor molecule

pigment molecule

bb Solid color hair

aapigment precursor molecule

pigment molecule

bbpigmented

hair

AA or Aapigment precursor molecule

pigment molecule

BB or BbStriped hair

genotype 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