Table of contents

1. Introduction to Genetics51m
2. Mendel's Laws of Inheritance3h 37m
3. Extensions to Mendelian Inheritance2h 41m
4. Genetic Mapping and Linkage2h 28m
5. Genetics of Bacteria and Viruses1h 21m
6. Chromosomal Variation1h 48m
7. DNA and Chromosome Structure56m
8. DNA Replication1h 10m
9. Mitosis and Meiosis1h 34m
10. Transcription1h 0m
11. Translation58m
12. Gene Regulation in Prokaryotes1h 19m
13. Gene Regulation in Eukaryotes44m
14. Genetic Control of Development44m
15. Genomes and Genomics1h 50m
16. Transposable Elements47m
17. Mutation, Repair, and Recombination1h 6m
18. Molecular Genetic Tools19m
- Genetic Cloning
  9m
- Methods for Analyzing DNA
  9m
19. Cancer Genetics29m
- Overview of Cancer
  21m
- Cancer Mutations
  7m
20. Quantitative Genetics1h 26m
21. Population Genetics50m
- Hardy Weinberg
  19m
- Allelic Frequency Changes
  31m
22. Evolutionary Genetics29m

4. Genetic Mapping and Linkage

Mapping Genes

Genetics

4. Genetic Mapping and Linkage

Mapping Genes

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In Drosophila, Dichaete (D) is a mutation on chromosome III with a dominant effect on wing shape. It is lethal when homozygous. The genes ebony body (e) and pink eye (p) are recessive mutations on chromosome III. Flies from a Dichaete stock were crossed to homozygous ebony, pink flies, and the F₁ progeny, with a Dichaete phenotype, were backcrossed to the ebony, pink homozygotes. Using the results of this backcross shown in the table,Phenotype NumberDichaete 401ebony, pink 389Dichaete, ebony 84pink 96Dichaete, pink 2ebony 3Dichaete, ebony, pink 12wild type 13What is the sequence and interlocus distance between these three genes?

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In Drosophila, a cross was made between females—all expressing the three X-linked recessive traits scute bristles (sc), sable body (s), and vermilion eyes (v)—and wild-type males. In the F₁, all females were wild type, while all males expressed all three mutant traits. The cross was carried to the F₂ generation, and 1000 offspring were counted, with the results shown in the following table.Phenotype Offspringsc s v 314+ + + 280+ s v 150sc + + 156sc + v 46+ s + 30sc s + 10+ + v 14No determination of sex was made in the data.Using proper nomenclature, determine the genotypes of the P₁ and F₁ parents.

Open Question

Another cross in Drosophila involved the recessive, X-linked genes yellow (y), white (w), and cut (ct). A yellow-bodied, white-eyed female with normal wings was crossed to a male whose eyes and body were normal but whose wings were cut. The F₁ females were wild type for all three traits, while the F₁ males expressed the yellow-body and white-eye traits. The cross was carried to an F₂ progeny, and only male offspring were tallied. On the basis of the data shown here, a genetic map was constructed.Phenotype Male Offspringy + ct 9+ w + 6y w ct 90+ + + 95+ + ct 424y w + 376y + + 0+ w ct 0Could the F₂ female offspring be used to construct the map? Why or why not?

Open Question

Another cross in Drosophila involved the recessive, X-linked genes yellow (y), white (w), and cut (ct). A yellow-bodied, white-eyed female with normal wings was crossed to a male whose eyes and body were normal but whose wings were cut. The F₁ females were wild type for all three traits, while the F₁ males expressed the yellow-body and white-eye traits. The cross was carried to an F₂ progeny, and only male offspring were tallied. On the basis of the data shown here, a genetic map was constructed.Phenotype Male Offspringy + ct 9+ w + 6y w ct 90+ + + 95+ + ct 424y w + 376y + + 0+ w ct 0Construct a map, assuming that white is at locus 1.5 on the X chromosome.

Open Question

The table given here lists the arrangement of alleles of linked genes in dihybrid organisms, the recombination frequency between the genes, and specific gamete genotypes. Using the information provided, determine the expected frequency of the listed gametes. Assume one map unit equals 1% recombination and, when three genes are involved, interference is zero.

Dihybrid Recombination Gamete
Genotype Frequency Genotype
A. DE/de 8% De
B. AD/ad 28% ad
C. DEF/def E–F 24% dEf
D–E 8%
D. BdE/bDe B–D 18% Bde
D–E 8%

Open Question

Drosophila females homozygous for the third chromosomal genes pink and ebony (the same genes from Problem 16) were crossed with males homozygous for the second chromosomal gene dumpy. Because these genes are recessive, all offspring were wild type (normal). F₁ females were testcrossed to triply recessive males. If we assume that the two linked genes, pink and ebony, are 20 mu apart, predict the results of this cross. If the reciprocal cross were made (F₁ males—where no crossing over occurs—with triply recessive females), how would the results vary, if at all?

Open Question

The Rh blood group in humans is determined by a gene on chromosome 1. A dominant allele produces Rh+ blood type, and a recessive allele generates Rh-. Elliptocytosis is an autosomal dominant disorder that produces abnormally shaped red blood cells that have a short life span resulting in hereditary anemia. A large family with elliptocytosis is tested for genetic linkage of Rh blood group and the disease. The lod score data below are obtained for the family.

Over what range of θ do lod scores indicate significant evidence in favor of genetic linkage? <>

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