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Questions and Answers
What does the non-equiprobability of parental and recombinant phenotypes suggest about the F1 female's gametes?
What does the non-equiprobability of parental and recombinant phenotypes suggest about the F1 female's gametes?
What does it indicate when the traits studied did not undergo independent assortment?
What does it indicate when the traits studied did not undergo independent assortment?
In genetic mapping, how are distances expressed in genetic maps?
In genetic mapping, how are distances expressed in genetic maps?
Which of the following statements is true regarding allelic associations during meiosis?
Which of the following statements is true regarding allelic associations during meiosis?
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How many different types of gametes does the double recessive male produce in this scenario?
How many different types of gametes does the double recessive male produce in this scenario?
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What did Morgan use to induce mutations in Drosophila?
What did Morgan use to induce mutations in Drosophila?
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Which phenotype represents the most prevalent characteristics in a population according to Morgan's study?
Which phenotype represents the most prevalent characteristics in a population according to Morgan's study?
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What type of genes does intra-chromosomal recombination primarily involve?
What type of genes does intra-chromosomal recombination primarily involve?
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What was one of the dominant characteristics in Morgan's Drosophila?
What was one of the dominant characteristics in Morgan's Drosophila?
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What does the term 'test cross' refer to in Morgan's experiments?
What does the term 'test cross' refer to in Morgan's experiments?
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What was the outcome of Cross A in Morgan's dihybrid cross with pure strains?
What was the outcome of Cross A in Morgan's dihybrid cross with pure strains?
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What type of offspring does interchromosomal mixing lead to in a test cross?
What type of offspring does interchromosomal mixing lead to in a test cross?
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Which of these statements best describes the F1 generation produced in Cross A?
Which of these statements best describes the F1 generation produced in Cross A?
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What does Mendel's first law of inheritance pertain to?
What does Mendel's first law of inheritance pertain to?
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What does dihybridism study in genetics?
What does dihybridism study in genetics?
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During which stage of meiosis does interchromosomal mixing take place?
During which stage of meiosis does interchromosomal mixing take place?
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In a dihybrid cross, what is produced in the F1 generation?
In a dihybrid cross, what is produced in the F1 generation?
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What generates recombined phenotypes in a dihybrid cross?
What generates recombined phenotypes in a dihybrid cross?
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What is the main principle established by Mendel through dihybrid crosses?
What is the main principle established by Mendel through dihybrid crosses?
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Which statement best describes the law of independent assortment?
Which statement best describes the law of independent assortment?
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In a dihybrid cross, which trait combination results from a double homozygous recessive test cross?
In a dihybrid cross, which trait combination results from a double homozygous recessive test cross?
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Which condition must be true for the law of independent assortment to apply?
Which condition must be true for the law of independent assortment to apply?
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How many types of gametes does a double recessive male produce in a dihybrid cross?
How many types of gametes does a double recessive male produce in a dihybrid cross?
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What does the presence of four types of offspring in equiprobable proportions indicate about gene behavior during meiosis?
What does the presence of four types of offspring in equiprobable proportions indicate about gene behavior during meiosis?
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What does it mean for alleles to be transmitted independently?
What does it mean for alleles to be transmitted independently?
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What aspect of alleles is determined through a test cross?
What aspect of alleles is determined through a test cross?
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Study Notes
Introduction to Genetics
- Course number 2: Dihybridism
- Course number 3: Linked genes
- Module: Genetics
- Second Level LMD
- Academic year 2024-2025
Dihybrid Cross (Unrelated Genes)
- Dihybrid cross: Study of two traits
- Case of unrelated genes
- Mendel's law of segregation (first law): Followed a single trait (single character)
- Two alleles of a single gene at a segregated locus when gametes are formed
- F1 progeny from monohybrid cross are heterozygous for the trait
- Mendel's second law of inheritance (Dihybridism) observed two traits simultaneously
- Mendel's investigation focused on whether the alleles from different genes segregate dependently or independently
- Hybrids produced in F1 generation by crossing pure parents with different traits; heterozygous for both traits
Dihybridism and Interchromosomal Mixing
- Dihybridism: Examining transmission of two allele pairs (two characters)
- Interchromosomal mixing (recombination): Independent disjunction of allele pairs located on different homologous chromosomes
- Interchromosomal mixing occurs during metaphase 1 and anaphase 1 of meiosis
- Recombined phenotypes appear in quantities equal to parental phenotypes
Law of Character Matching
- Transmission of seed shape has no influence on seed color transmission
- Two characters are passed down independently
- Allele pairs controlling the traits appear independently
Law of Independent Assortment
- Based on dihybrid cross
- Each allele pair separates independently from the other during gamete formation
- Strictly applicable to genes located on different, non-homologous chromosomes
- Genes close together on a chromosome tend to be passed together
Segregation and Independent Assortment
- During meiosis I, tetrads can arrange themselves in 2^n different ways.
- Example illustrating the concept of segregation and independent assortment including gene for eye color and hair color (with example of meiosis stages)
Dihybrid Cross Experiment
- Two pea plants (one with yellow-round seeds, the other with green-wrinkled seeds) cross
- F1 plants heterozygous for both traits
- Self-fertilized F1 plants produce F2 generation
- Predictions of phenotypic ratios based on independent assortment hypothesis differ from non-independent assortment
Test-Cross Dihybrid
- Determining if a dominant trait is homozygous or heterozygous
- Test-cross involves crossing with a recessive homozygous individual
- Same procedure applies for dihybrid cross with recessive homozygous individual
Crossover Interpretation
- Four offspring types in equal proportions with parental and recombinant phenotypes
- Double recessive male produces only one type of gamete
- Female F1 produces four types of gametes, each trait encoded by different gene
- Genes in question behave independently during meiosis; no allelic associations
- Interchromosomal mixing leads to varying phenotypes in the test-cross progeny
Case of Linked Genes (Intra-chromosomal Recombination)
Discovery of Gene Linkage
Morgan's Material variations
Crossover for Two Characters
- Example of experiment with Drosophila with body color (gray/black) and wing type (normal/vestigial)
- Observed crossbreed results illustrate presence of mixing
- Example of different result of a cross (phenotypic ratio) in a F1 generation of Drosophila
Interpretation of Crossing
- The parents are homozygous, resulting in F1 generation that is heterozygous for the characteristics being studied
- Only one dominant trait is expressed (wings and body color example)
- Two trait crossing did not follow independent assortment as expected
- Four phenotypic offspring types with parental types in larger ratio
- Female F1 produces four gamete types and each trait encoded by different gene
Genetic Mapping
- Genetic maps: Distances in centimorgans (CM)
- Physical maps: Distances in base pairs (bp), kilobases (kb), megabases (Mb)
Genetic Maps and Recombination Frequency
- Genetic distances reflect recombination frequency (RF)
- During meiosis, crossing-over exchanges chromosome segments
- Genes close together have lower recombinations
- Centimorgans (CM) measure genetic distances
- Recombination frequency used to create genetic maps (illustrative example with Morgan Experiment)
Construction of a Genetic Map
- Constructing a map based on recombination frequencies (example of calculation)
- Illustrating calculation of genetic distance between genes using recombinants
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Description
This quiz explores key concepts in genetics related to Drosophila research by Morgan. Questions cover gamete types, independent assortment, and genetic mapping. Test your understanding of alleles, phenotypes, and the principles of inheritance.
