1 / 38

Understanding Mendel's Rules of Genetic Inheritance

This review summarizes Mendel's rules of genetic inheritance, including genes occurring in pairs, dominance/recessiveness, segregation, dihybrid crosses, and the chromosomal basis of inheritance. It also covers techniques for discovering and analyzing genes.

ealdrich
Download Presentation

Understanding Mendel's Rules of Genetic Inheritance

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

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

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

  4. Possible sperm cells g g o o + G Possible egg cells Gg Gg Gg Gg G Test Cross X 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 • Aa • Insufficient data to tell • The genotype of I-1 must be: • AA • Aa • Aa • Insufficient data to tell

  9. 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

  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, wrinkled green, round green, wrinkled yellow, round F1 yellow, round

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

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

  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. o o + X yellow (Gg), round (Ww) yellow (Gg), round (Ww) GW GW gw gw 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 yellow (Gg), round (Ww) yellow (Gg), round (Ww) Expected F2 1 green, wrinkle 3 green, round 9 Yellow, round 3 Yellow, wrinkle Resulting F2 4 green, wrinkle 0 green, round 12 Yellow, round 0 Yellow, 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. o o + Experiment 1 P1 X F1 - all light red

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

  30. Frequency Diagram

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

  36. 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

More Related