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Gene linkage may or may not be linked to one another.
Gene linkage may or may not be linked to one another.
True
Most of the progenies resemble the parentals.
Most of the progenies resemble the parentals.
True
A strong tendency for the parental combinations to be inherited results in high recombination rate.
A strong tendency for the parental combinations to be inherited results in high recombination rate.
False
Gene linkage causes low recombination rate.
Gene linkage causes low recombination rate.
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Gene linkage is when only few recombinants are produced.
Gene linkage is when only few recombinants are produced.
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Some genes are partially linked.
Some genes are partially linked.
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Linkage can be either complete or incomplete.
Linkage can be either complete or incomplete.
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Complete linkage means that genes are always inherited together.
Complete linkage means that genes are always inherited together.
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Recombinants are the result of non-sister chromatid crossing-over.
Recombinants are the result of non-sister chromatid crossing-over.
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Crossing-over involves sister chromatids, and recombinant types are produced.
Crossing-over involves sister chromatids, and recombinant types are produced.
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Linkage of the segregating genes of a dihybrid leads to deviations from the 9:3:1:1 F2 phenotypic ratio.
Linkage of the segregating genes of a dihybrid leads to deviations from the 9:3:1:1 F2 phenotypic ratio.
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The frequency of recombination dictates the deviation from the 9:3:1:1 ratio.
The frequency of recombination dictates the deviation from the 9:3:1:1 ratio.
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The strength of linkage is expressed as linkage value.
The strength of linkage is expressed as linkage value.
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Linkage value = (Total no. of crossover types / total no. of population) x 100.
Linkage value = (Total no. of crossover types / total no. of population) x 100.
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Valuable information on linkage relations can be obtained when the cross involves 3 genes in the same chromosome.
Valuable information on linkage relations can be obtained when the cross involves 3 genes in the same chromosome.
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The heterogametic sex of a species has higher crossover frequencies.
The heterogametic sex of a species has higher crossover frequencies.
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As maternal age increases, crossing-over tends to decrease.
As maternal age increases, crossing-over tends to decrease.
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In Drosophila, temperatures cooler or warmer than 22°C tend to increase the rate of crossing over.
In Drosophila, temperatures cooler or warmer than 22°C tend to increase the rate of crossing over.
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In Drosophila, females selected for reduced recombination frequencies pass this trait through their daughters. This means that the cross-over factors are carried in the cytoplasm.
In Drosophila, females selected for reduced recombination frequencies pass this trait through their daughters. This means that the cross-over factors are carried in the cytoplasm.
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Young Drosophila females on high Ca showed decreased crossing over.
Young Drosophila females on high Ca showed decreased crossing over.
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Larval starvation at certain ages generally increased crossing-over.
Larval starvation at certain ages generally increased crossing-over.
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Certain genes affect chromosome pairing, while others can alter the process once pairing has been completed.
Certain genes affect chromosome pairing, while others can alter the process once pairing has been completed.
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Genes located close to the centromere show reduced crossing-over, indicating physical distance does not play a role.
Genes located close to the centromere show reduced crossing-over, indicating physical distance does not play a role.
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Crossing-over increased upon injection of antibiotics.
Crossing-over increased upon injection of antibiotics.
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Increases in crossing-over were observed when Drosophila were exposed to X-ray irradiation.
Increases in crossing-over were observed when Drosophila were exposed to X-ray irradiation.
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Every sexually reproducing cell is bisexual.
Every sexually reproducing cell is bisexual.
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A cell's sex is determined by the potential for either a male or female gamete to develop.
A cell's sex is determined by the potential for either a male or female gamete to develop.
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Genetic determination of sex is a genetically regulated process.
Genetic determination of sex is a genetically regulated process.
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Sex determination can be determined by factors in addition to the genotype, such as environmental cues and the cell's potential for either a male or female gamete to develop.
Sex determination can be determined by factors in addition to the genotype, such as environmental cues and the cell's potential for either a male or female gamete to develop.
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In molluscs, both Crepidula and Patella, sexuality is typically determined by a specific sex-determining gene.
In molluscs, both Crepidula and Patella, sexuality is typically determined by a specific sex-determining gene.
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With haplo-diploidy, unfertilized eggs develop into males and are haploid.
With haplo-diploidy, unfertilized eggs develop into males and are haploid.
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Study Notes
Linkage and Recombination
- Genes may or may not be linked.
- Most offspring resemble parental combinations.
- Gene linkage results in a lower recombination rate.
- Recombinants are produced in smaller numbers following linkage.
- Some genes are partially linked.
- Linkage can be complete or incomplete.
Complete Linkage
- Genes are tightly linked; they are always inherited together.
- An example of complete linkage is demonstrated by the inheritance of purple eye and vestigial wing genes in Drosophila.
Incomplete Linkage
- Recombination results from non-sister chromatid crossing-over during meiosis.
- Crossing-over is the process of homologous chromosomes exchanging parts.
- If sister chromatids cross over, recombinant types are not produced.
Determination of Linkage
- The strength of linkage is measured by the linkage value.
- Linkage value is (total number of crossover types/total number of population) * 100.
- Linkage values can be determined for crosses involving three genes.
- Linkage values vary depending on the frequency of recombination.
Factors Affecting Recombination Frequencies
- Sex: The heterogametic sex (e.g., male in Drosophila) often has lower crossover frequencies.
- Maternal Age: Crossing over tends to decrease with increasing maternal age.
- Temperature: Temperature (cooler/warmer than 22°C) tends to increase crossing over in Drosophila.
- Cytoplasmic Effects: Recombination frequencies can change when certain traits are selected.
- Nutrition: High levels of Calcium may decrease crossing over while larval starvation may increase crossing over.
- Genotype: Certain genes can impact conditions for exchange
- Centromere: Proximity to the centromere often results in decreased crossing over.
- Chemical Effects: Certain chemicals can increase crossing over.
- Radiation: Radiation exposure can increase crossing over.
Sex Determination
- Genetic Sex Determination: Sex is determined by the direct consequences of the genotype as well as other factors affecting the genotype.
- Multiple Genes: Multiple genes, especially in molluscs like Crepidula and Patella, show continuous variation in sexuality.
- Haplo-Diploidy: In insects like bees and ants, unfertilized eggs develop into males and fertilized eggs into females.
- Environmental Sex Determination: Sex is influenced by environmental factors including temperature during development, presence of certain hormones, and other factors.
Chromosomal Sex Determination
- XX-XO mechanism (e.g., Protenor): Males have one X chromosome and females have two.
- XX-XY mechanism (e.g., mammals): Males have one X and one Y chromosome and females have two X chromosomes.
Sex Linkage
- X-linked inheritance involves genes located on the X chromosome.
- Several characteristics are dependent on the sex chromosome.
- Y-linked inheritance involves genes located on the Y chromosome.
- X-linked genes, such as hemophilia, are shown through inheritance.
- Y-linked inheritance shows characteristics passed from father to son.
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