Review Mendel’s “rules of the game” 1) Genes occur in pairs - Genetic characteristics are controlled by genes that exist in pairs called alleles. 2) Dominance/Recessiveness- When two unlike alleles responsible for a single character are present in a single individual, one is dominant (expressed) to the other which is said to be recessive (silent). 3) Segregation- during formation of the gametes, the paired alleles separate or segregate randomly.

Question Yellow seeded plants in the F2 are predicted to have either GG or Gg genotypes. Is there a way to distinguish the genotype? Test Cross The organism of dominant phenotype but unknown genotype is crossed to a homozygous recessive individual.

Test Cross X + g G gg Gg Gg gg ? GG Possible sperm cells Possible egg cells gg Gg o Gg gg ? GG If the offspring show 1:1 ratio of dominant:recessive phenotypes, the parent in question must have been heterozygous (Gg).

Test Cross + X g G Gg Gg gg ? GG Possible sperm cells Possible egg cells Gg o Gg gg ? GG If the offspring show only the dominant phenotype, the parent in question must have been a homozygous dominant (GG) individual.

Discovering genes via Mutant analysis Generating mutants Chemical mutagenesis (EMS) base transition, point mutation Radiation deletions Transposons/ T-DNA tags insertion/deletions (indels)

Forward Genetics - from phenotype to gene ID the phenotype ID the physiological, developmental, molecular differences ID the gene (DNA sequence)

And observing segregation ratios Planned crosses and Punnett squares, Pedigree analysis Mutant or polymorphism analysis Autosomal dominant/recessive Sex-linked genes

If A represents a gene that displays autosomal dominant/recessive inheritance. The genotype of I-1 must be: AA Aa Insufficient data to tell The genotype of I-1 must be: AA Aa Insufficient data to tell

Homozygous for the “R” allele Homozygous for the “r” allele 1 2 3 R r   If the DNA seen on gel 1 is from a pea plant heterozygous for “R” and “r” at the SBE1 locus, the DNA in lane 2 is most likely from a pea plant Homozygous for the “R” allele Homozygous for the “r” allele Unable to make functional starch branching enzyme 1 That is making twice the normal amount of starch branching enzyme 1   If the DNA seen on gel 1 is from a pea plant heterozygous for “R” and “r” at the SBE1 locus, the DNA in gel 2 is most likely from a pea plant Homozygous for the “R” allele Homozygous for the “r” allele Unable to make functional starch branching enzyme 1 That is making twice the normal amount of starch branching enzyme 1

Reverse Genetics - from gene to phenotype Mutate, knockout, over-express the gene ID a gene Analyze the morphological, physiology, developmental effects (the phenotype).

Independent Assortment Chapter 3

Dihybrid cross - crosses between individuals that differ in two traits.

Mendel’s dihybrid crosses P1 cross P1 cross X X yellow, round green, wrinkled green, round yellow, wrinkled F1 yellow, round

Self-pollination of the F1 X F1 yellow, round yellow, round 9/16 yellow, round 3/16 yellow, wrinkled F2 3/16 green, round 1/16 green, wrinkled

X GW Gw gW gw + F2 GGWW GGWw GgWW GW GgWw Generation Gw GGWw GGww GgWw yellow (Gg), round (Ww) yellow (Gg), round (Ww) GW Gw gW gw o + o F2 GGWW GGWw GgWW GW GgWw Generation Gw GGWw GGww GgWw Ggww GgWW GgWw gW ggWW ggWw GgWw gw Ggww ggWw ggww

Mendel’s dihybrid ratio 9:3:3:1 Mendel’s Second Principle of Inheritance Independent Assortment - during gamete formation, segregating pairs of unit factors assort independently of each other.

But, what if X yellow (Gg), round (Ww) yellow (Gg), round (Ww)

X GW GW gw gw + F2 GW GGWW GGWW GgWw GgWw Generation GW GGWW GGWW GgWw yellow (Gg), round (Ww) yellow (Gg), round (Ww) GW GW gw gw o + o F2 GW GGWW GGWW GgWw GgWw Generation GW GGWW GGWW GgWw GgWw gw GgWw GgWw ggww ggww gw GgWw GgWw ggww ggww

Phenotypic Ratio X Expected F2 9 Yellow, round 3 Yellow, wrinkle 3 yellow (Gg), round (Ww) yellow (Gg), round (Ww) Expected F2 9 Yellow, round 3 Yellow, wrinkle 3 green, round 1 green, wrinkle Resulting F2 12 Yellow, round Yellow, wrinkle green, round 4 green, wrinkle

Chromosomal Basis of Inheritance

Meiosis (the prelude to sexual reproduction) For sexual reproduction to occur, chromosomes must be duplicated and divided between the gametes.

Meiosis I

Meiosis II

Independent Assortment - during gamete formation, segregating pairs of chromosomes (not genes) assort independently of each other.

Mitosis takes place in Haploid cells only Diploid cells only Haploid or diploid cells Bacterial cells None of the above Mitosis takes place in Haploid cells only Diploid cells only Haploid or diploid cells Bacterial cells None of the above

Meiosis takes place in Haploid cells only Diploid cells only Haploid or diploid cells Somatic cells None of the above Meiosis takes place in Haploid cells only Diploid cells only Haploid or diploid cells Somatic cells None of the above

Polygenic Traits (Quantitative trait loci, QTLs) Observation: Wheat kernel color is a continuum from white dark red

Experiment 1 P1 X + o o F1 - all light red

Experiment 2 X F1 + o o F2 1 6 15 20 15 6 1

Frequency Diagram

Wheat Kernel Color 3 loci (polygenic), 6 different alleles Dark white red F2 seed color # of dominant alleles 6 5 4 3 2 1 0

Continuous variation is determined by two or more genes. These are polygenic or quantitative traits.

Cytoplasmic Segregation (Non-Mendelian Genetics) Chloroplast DNA (cpDNA) Mitochondrial DNA (mt DNA)

Cytoplasmic Segregation

Test Cross ? Reciprocal crosses Who’s the pollen donor?

A human disease associated with dysfunction of mitochondria, which results from a mutation in a single autosomal gene locus in nuclear DNA, is most likely to: Be inherited from the mother, because mitochondria are not inherited from the father Show heteroplasmy in the progeny of affected individuals, depending on chance events during meiosis Show a non-Mendelian inheritance pattern, because the number of mitochondria varies from cell to cell Show a Mendelian inheritance pattern None of the above A human disease associated with dysfunction of mitochondria, which results from a mutation in a single autosomal gene locus in nuclear DNA, is most likely to: Be inherited from the mother, because mitochondria are not inherited from the father Show heteroplasmy (a mix of WT and mutant mitochondria) in the progeny of affected individuals, depending on chance events during meiosis Show a non-Mendelian inheritance pattern, because the number of mitochondria varies from cell to cell Show a Mendelian inheritance pattern None of the above