1. 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.

2. 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.

3. 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).

4. 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.

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

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

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

8. 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

9. Homozygous for the “R” allele Homozygous for the “r” allele 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

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

11. Independent Assortment
Chapter 3

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

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

14. Self-pollination of the F1X F1
yellow, round
yellow, round
9/16 yellow, round
3/16 yellow, wrinkled F2
3/16 green, round
1/16 green, wrinkled

15. 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

16. 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.

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

18. 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

19. 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

20. Chromosomal Basis of Inheritance

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

22. Meiosis I

23. Meiosis II

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

25. 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

26. 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

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

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

29. Experiment 2 X F1 + o o F2

30. Frequency Diagram

31. Wheat Kernel Color 3 loci (polygenic), 6 different alleles Dark white
red F2
seed color
# of dominant
alleles

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

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

34. Cytoplasmic Segregation

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

38. 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