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What is the easiest explanation for a black mouse (BB) crossed with a white mouse (bb) resulting in gray offspring?
What is the easiest explanation for a black mouse (BB) crossed with a white mouse (bb) resulting in gray offspring?
What is the best explanation for cattle having red (RR), white (WW), or roan (RW) hair?
What is the best explanation for cattle having red (RR), white (WW), or roan (RW) hair?
Codominance
If a red cow (RR) is crossed with a roan cow (RW), what would be the phenotypic ratio of the offspring?
If a red cow (RR) is crossed with a roan cow (RW), what would be the phenotypic ratio of the offspring?
Match the following genetic concepts with their descriptions.
Match the following genetic concepts with their descriptions.
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Which of the following is an example of a trait influenced by multiple genes?
Which of the following is an example of a trait influenced by multiple genes?
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In the case of coat color in labs and some mice, one gene determines the ______ and another gene determines whether that pigment is deposited in the hair.
In the case of coat color in labs and some mice, one gene determines the ______ and another gene determines whether that pigment is deposited in the hair.
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What is the concept called where two or more genes affect a single phenotype?
What is the concept called where two or more genes affect a single phenotype?
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The Y chromosome is responsible for determining sex in humans.
The Y chromosome is responsible for determining sex in humans.
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What is the term for a gene located on either the X or Y chromosome?
What is the term for a gene located on either the X or Y chromosome?
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Which disorder is an example of an X-linked disorder?
Which disorder is an example of an X-linked disorder?
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Females inherit two X chromosomes, which is double what males inherit.
Females inherit two X chromosomes, which is double what males inherit.
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Barr bodies are inactive X chromosomes found in the cells of female mammals.
Barr bodies are inactive X chromosomes found in the cells of female mammals.
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What is the term for genes located near each other on the same chromosome that tend to be inherited together?
What is the term for genes located near each other on the same chromosome that tend to be inherited together?
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What is the process of producing offspring with a new combination of genes from their parents called?
What is the process of producing offspring with a new combination of genes from their parents called?
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Offspring with phenotypes that are different from their parents are called ______.
Offspring with phenotypes that are different from their parents are called ______.
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What is the phenomenon that explains why some linked genes become separated during meiosis?
What is the phenomenon that explains why some linked genes become separated during meiosis?
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The further apart two genes are on a chromosome, the [blank] the probability of a crossing over event occurring between them and the [blank] the recombination frequency.
The further apart two genes are on a chromosome, the [blank] the probability of a crossing over event occurring between them and the [blank] the recombination frequency.
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What is the name of a genetic map based on recombination frequencies?
What is the name of a genetic map based on recombination frequencies?
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What is the name of the unit used to measure the distance between genes?
What is the name of the unit used to measure the distance between genes?
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What does 50% recombination indicate?
What does 50% recombination indicate?
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Some traits are located on DNA found in mitochondria or chloroplasts.
Some traits are located on DNA found in mitochondria or chloroplasts.
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Mitochondrial DNA is maternally inherited.
Mitochondrial DNA is maternally inherited.
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In plants, mitochondrial and chloroplast traits are paternally inherited.
In plants, mitochondrial and chloroplast traits are paternally inherited.
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What is the name of the statistical analysis used to compare observed results to expected results?
What is the name of the statistical analysis used to compare observed results to expected results?
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What is the purpose of the chi-square test?
What is the purpose of the chi-square test?
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The null hypothesis in a chi-square test assumes that any difference between observed and expected data is due to chance.
The null hypothesis in a chi-square test assumes that any difference between observed and expected data is due to chance.
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The degrees of freedom in a chi-square test are determined by subtracting 1 from the number of categories being analyzed.
The degrees of freedom in a chi-square test are determined by subtracting 1 from the number of categories being analyzed.
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The chi-square critical value for a p-value of 0.05 indicates a 95% confidence level that the observed data fits the expected data.
The chi-square critical value for a p-value of 0.05 indicates a 95% confidence level that the observed data fits the expected data.
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If the calculated chi-square value is greater than the critical value, what should be concluded?
If the calculated chi-square value is greater than the critical value, what should be concluded?
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If the calculated chi-square value is less than the critical value, it means that the null hypothesis is not rejected.
If the calculated chi-square value is less than the critical value, it means that the null hypothesis is not rejected.
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Environmental factors can influence gene expression, leading to what phenomenon?
Environmental factors can influence gene expression, leading to what phenomenon?
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Nondisjunction occurs when chromosomes fail to separate properly during meiosis.
Nondisjunction occurs when chromosomes fail to separate properly during meiosis.
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What is the name for the process of examining chromosomes to detect any abnormalities?
What is the name for the process of examining chromosomes to detect any abnormalities?
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Down Syndrome is caused by nondisjunction of chromosome 21.
Down Syndrome is caused by nondisjunction of chromosome 21.
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Genetic disorders can be linked to mutated alleles or chromosomal changes.
Genetic disorders can be linked to mutated alleles or chromosomal changes.
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Study Notes
Non-Mendelian Genetics
- Many traits don't follow ratios predicted by Mendel's laws due to varying degrees of dominance, multiple genes acting together, genes on sex chromosomes, adjacent genes on same chromosome segregating as a unit, and non-nuclear inheritance (chloroplast and mitochondrial DNA).
Degrees of Dominance
- Alleles show varying degrees of dominance.
- In Mendel's experiments, complete dominance was observed (homozygous dominant and heterozygous individuals are phenotypically the same).
- Incomplete dominance: neither allele is fully dominant; F1 generation's phenotype is a mix of parental phenotypes (e.g., red flowers crossed with white flowers produce pink offspring).
- Codominance: two alleles affect phenotype; both alleles are expressed (e.g., human blood type AB; alleles A and B are both expressed).
- Multiple alleles: genes existing in more than two alleles (e.g., human blood type; alleles are IA, IB, i).
Multiple Genes
- In many cases, two or more genes are responsible for determining phenotypes.
- Epistasis: the phenotypic expression of a gene at one locus affects a gene at another locus (e.g., coat color in labs and mice). One gene codes for pigment, while a second gene determines whether or not pigment is deposited in the hair.
- Polygenic inheritance: the effect of two or more genes acting on a single phenotype (e.g., height, human skin color).
Sex Chromosomes
- Specific genes can be carried on sex chromosomes (X or Y).
- Y-linked genes: genes specifically found on the Y chromosome (very few, so few disorders).
- X-linked genes: genes found on the X chromosome.
- Fathers can pass X-linked alleles to all their daughters but none of their sons.
- Mothers can pass X-linked alleles to both daughters and sons.
- If an X-linked trait is due to a recessive allele, females express the trait only if homozygous; males express the trait if they inherit it from their mother (they are hemizygous).
- X-linked disorders include Duchenne muscular dystrophy (progressive weakening of muscles), hemophilia (inability to properly clot blood), and color blindness (inability to correctly see colors).
- X-inactivation: during development, most of one X chromosome in each cell of a female becomes inactive and condenses into a Barr body. This helps regulate gene dosage in females.
Linked Genes
- Linked genes: genes located near each other on the same chromosome that tend to be inherited together.
- Recombination: production of offspring with a new combination of genes from parents.
- Parental types: offspring with the parental phenotype.
- Recombinants: offspring with phenotypes different from the parents.
- Crossing over: chromosomes from one paternal chromatid and one maternal chromatid exchange corresponding segments during meiosis I.
- The further apart two genes are on the same chromosome, the higher the probability that a crossing over event will occur between them, and the higher the recombination frequency.
- Linkage maps: genetic maps based on recombination frequencies expressing the relative distances along chromosomes.
- 50% recombination means genes are far apart on the same chromosome or on two different chromosomes.
- Examples, including genetic mapping data, in this section.
- Recombination: production of offspring with a new combination of genes from parents.
Non-Nuclear DNA
- Some traits are located on DNA found in mitochondria or chloroplasts.
- In animals, mitochondria inherited maternally.
- In plants, both mitochondria and chloroplasts are maternally inherited.
Statistical Analysis: Chi-Square
- Chi-square: a form of statistical analysis comparing actual (observed) results to expected results.
- Helps determine if deviations from the expected results are due to chance or other factors (e.g., linked genes, data collection error).
- Designed to analyze categorical data.
- Formula: X² = ∑[(observed results – expected results)² / expected results].
- Example using data for the tongue rolling trait.
- Interpreting results using a chi-square table.
Environmental Effects on Phenotype
- Various environmental factors influence gene expression and lead to phenotypic plasticity.
- Individuals with the same genotype can exhibit different phenotypes in different environments.
- Examples include temperature affecting coat color in rabbits and Siamese cats, soil pH affecting flower color, and UV exposure increasing melanin production in the skin.
Chromosomal Inheritance and Disorders
- Some genetic disorders linked to affected or mutated alleles or chromosomal changes.
- Examples include Tay-Sachs disease (autosomal recessive, mutated HEXA gene, affects central nervous system, leading to blindness) and sickle cell anemia (autosomal recessive, mutated HBB gene, sickled cells contain abnormal hemoglobin).
Chromosomal Changes
- Nondisjunction: chromosomes fail to separate properly during meiosis.
- Karyotyping can detect nondisjunction.
- Example: Down syndrome (three copies of chromosome 21).
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Description
Test your understanding of non-Mendelian genetics, including degrees of dominance and the impact of multiple genes on inheritance. This quiz will cover concepts such as incomplete dominance, codominance, and the role of multiple alleles. Challenge yourself to grasp the complexities beyond Mendel's laws.
