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What is a characteristic feature of polygenic traits compared to single-gene traits?
Which factor complicates the analysis of polygenic traits due to the interaction of multiple genes?
What major challenge arises from each gene involved in polygenic traits having a small effect size?
What role do environmental factors play in the study of polygenic traits?
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What is a significant challenge in interpreting results from studies of polygenic traits?
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What term describes the phenomenon when individuals with a specific genotype do not express the expected phenotype?
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Which of the following can influence whether a dominant allele is expressed?
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Which chromosomal system is present in mammals?
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In the ZW system, which chromosomes are associated with male individuals?
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How many alleles for a specific gene can a diploid individual have?
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What type of sex determination system allows males to develop from unfertilized eggs?
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What is a key characteristic of polygenic traits?
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How can temperature influence sex determination in certain reptiles?
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Which process involves one gene masking the expression of another gene?
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Which of the following factors can affect sex determination?
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What potential effect do epigenetic modifications have on gene expression?
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What happens when there is a mutation in the SRY gene on the Y chromosome?
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Which of these is an example of multiple alleles for a single gene?
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Why can studying polygenic traits be challenging?
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In the XO system, what is the chromosome configuration for males?
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Which group of organisms demonstrates haplodiploidy?
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What is the chromosomal configuration for females in the XY system?
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Which type of sex determination can result from both genetic and hormonal influences?
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What is required for females to express an X-linked recessive trait?
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In X-linked dominant inheritance, how does severity of the trait's expression compare between males and females?
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How do males inherit their X chromosomes?
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What differentiates X-linked recessive traits from autosomal recessive traits in terms of expression in males?
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Which statement is true regarding carrier status in X-linked recessive inheritance?
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What characterizes X-linked genes compared to autosomal genes?
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What is true for organisms regarding haploid and diploid cells?
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Which of the following correctly describes the inheritance pattern for autosomal genes?
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Why can females with X-linked dominant alleles experience variable severity in trait expression?
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Which of the following is NOT a characteristic of X-linked inheritance?
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How many chromosomes do haploid cells contain in humans?
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What is the primary function of meiosis?
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Which type of cells predominantly make up the human body?
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In which organisms are haploid cells typically limited to gametes?
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Which statement about diploid cells is correct?
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What condition is an example of incomplete penetrance?
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Which process produces genetically identical diploid daughter cells?
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What characterizes the life cycle of certain fungi and algae regarding cell types?
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Which of the following does not typically have both haploid and diploid cells?
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What is the chromosome composition of a diploid cell?
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Study Notes
Incomplete Penetrance
- Not all individuals with a dominant allele express the associated phenotype.
- Even if an individual carries the dominant allele, they might not show the trait.
- Example: Polydactyly - a condition with extra fingers or toes.
Reasons for Incomplete Penetrance
-
Genetic background:
- Modifier genes: other genes can influence whether the dominant allele is expressed.
- Epistasis: one gene can mask or modify the expression of another gene.
-
Epigenetic modifications:
- DNA methylation and histone modification: These changes do not alter the DNA sequence but can affect gene expression.
- Epigenetic modification can turn genes on or off, influencing whether a trait is expressed.
Allele Number
- Population: Multiple alleles can exist for a single gene in a population.
- Individual: A diploid individual has two alleles for each gene, one from each parent.
- Example: ABO blood group system - three alleles (IA), (IB), and (i).
Polygenic Traits
- Characteristics influenced by multiple genes, often located on different chromosomes.
- Example: human height.
- Exhibit continuous variation rather than discrete categories.
Challenges Studying Polygenic Traits
- Small Effect Size: Each gene has a small effect, requiring large studies.
- Gene-Gene Interactions: The interaction between many genes can be complex.
- Environmental Influences: Environmental factors can significantly impact polygenic traits.
- Complex Genetic Architecture: Many loci spread across the genome.
- Data Interpretation: It is challenging to pinpoint specific genetic variants solely responsible for the trait.
Sex Determination Systems
- XY system:
- Males: XY chromosomes.
- Females: XX chromosomes.
- ZW system:
- Females: ZW chromosomes.
- Males: ZZ chromosomes.
- XO system:
- Females: XX chromosomes.
- Males: XO chromosomes.
- Haplodiploidy:
- Males develop from unfertilized eggs and are haploid.
- Females develop from fertilized eggs and are diploid.
Factors Determining Sex
- Hormonal influences: Hormones can play a big role in sex determination.
- Genetic mutations: Mutations in specific genes can lead to variations in sex determination.
- Temperature: In some reptiles, temperature can determine sex. Warmer temps may lead to females, cooler temps to males.
X-linked Inheritance
- Refers to inheritance patterns for genes located on the X chromosome.
X-linked Recessive Inheritance
- Males:
- Only have one X chromosome - a single recessive allele will result in the expression of the trait.
- Females:
- Have two X chromosomes - need two copies of the recessive allele for the trait to be expressed.
- If they carry one copy, they are carriers.
X-linked Dominant Inheritance
- Males:
- A single dominant allele on the X chromosome will cause the trait to be expressed.
- This can be more severe due to the lack of a second X chromosome.
- Females:
- With one dominant allele will express the trait.
- Severity can vary depending on whether the allele is on one or both X chromosomes.
Differences from Autosomal Inheritance
-
Chromosome location:
- X-linked genes: on the X chromosome, which is one of the sex chromosomes.
- Autosomal genes: on autosomes, which are the non-sex chromosomes.
-
Inheritance patterns:
- X-linked traits: Males inherit X from their mother and pass it to all their daughters. Females inherit one X from each parent.
- Autosomal traits: Both males and females inherit autosomal genes equally from both parents.
-
Expression in males and females:
- X-linked recessive: more commonly expressed in males.
- Autosomal recessive: requires two copies of the recessive allele for the trait to be expressed - sex doesn't matter.
-
Carrier status:
- X-linked recessive: Females can be carriers. Males either have it or they don't.
- Autosomal recessive: Both males and females can be carriers.
Haploid and Diploid Cells
- Haploid cells (n): Contain a single set of chromosomes. Involved in sexual reproduction.
- Diploid cells (2n): Contain two sets of chromosomes, one from each parent, totaling 46 chromosomes in humans. Most body cells (somatic cells) are diploid.
Production of Haploid and Diploid Cells
- Mitosis: Diploid cells divide to produce two genetically identical diploid cells. Used for growth and repair.
- Meiosis: Haploid cells are produced by meiosis, a process that reduces the chromosome number by half, producing four genetically diverse cells. Crucial for producing gametes.
Do All Organisms Have Both Haploid and Diploid Cells?
- Most animals: Have both haploid and diploid stages. Diploid cells make up the majority of the organism.
- Plants: Exhibit an alternation of generation: Both haploid and diploid stages are prominent in their life cycle.
- Fungi and Algae: Some species spend most of their cycle in a haploid state, and only become diploid briefly during sexual reproduction.
- Certain insects: Like male bees, ants, and wasps are haploid throughout their lives while females are diploid.
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Description
Explore the concept of incomplete penetrance in genetics, where not all individuals with a dominant allele show the associated phenotype. This quiz covers reasons such as genetic background and epigenetic modifications, as well as the implications of allele number in a population.