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Questions and Answers
What are Mendel's "hereditary factors" called?
What are Mendel's "hereditary factors" called?
genes
How can the location of a particular gene be seen?
How can the location of a particular gene be seen?
by tagging isolated chromosomes with a fluorescent dye that highlights the gene
The chromosome theory of inheritance states that Mendelian genes have specific loci on chromosomes.
The chromosome theory of inheritance states that Mendelian genes have specific loci on chromosomes.
True
Chromosomes undergo segregation and independent assortment, as described by the chromosome theory of inheritance.
Chromosomes undergo segregation and independent assortment, as described by the chromosome theory of inheritance.
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The behavior of chromosomes during meiosis cannot explain Mendel's laws of segregation and independent assortment.
The behavior of chromosomes during meiosis cannot explain Mendel's laws of segregation and independent assortment.
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What type of offspring have a phenotype that matches one of the parental phenotypes?
What type of offspring have a phenotype that matches one of the parental phenotypes?
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What type of offspring have nonparental phenotypes, meaning new combinations of traits?
What type of offspring have nonparental phenotypes, meaning new combinations of traits?
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A 50% frequency of recombination is observed for any two genes located on the same chromosome.
A 50% frequency of recombination is observed for any two genes located on the same chromosome.
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What mechanism breaks the physical connection between genes on the same chromosome?
What mechanism breaks the physical connection between genes on the same chromosome?
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Recombinant chromosomes bring alleles together in different combinations within gametes?
Recombinant chromosomes bring alleles together in different combinations within gametes?
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Which of these are true regarding the effects of nondisjunction?
Which of these are true regarding the effects of nondisjunction?
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What type of offspring results from a zygote with one copy of a particular chromosome?
What type of offspring results from a zygote with one copy of a particular chromosome?
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What type of offspring results from a zygote with three copies of a particular chromosome?
What type of offspring results from a zygote with three copies of a particular chromosome?
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Polyploidy is common in plants but not animals.
Polyploidy is common in plants but not animals.
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Deletions in chromosomes can lead to four types of changes in chromosome structure.
Deletions in chromosomes can lead to four types of changes in chromosome structure.
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Duplications in chromosomes are generally lethal.
Duplications in chromosomes are generally lethal.
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In inversions of chromosomes, the balance of genes is normal.
In inversions of chromosomes, the balance of genes is normal.
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Alterations in chromosome number and structure can occur in humans and other mammals, but are not associated with any serious disorders.
Alterations in chromosome number and structure can occur in humans and other mammals, but are not associated with any serious disorders.
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Some types of aneuploidy disrupt the genetic balance to a greater extent than others.
Some types of aneuploidy disrupt the genetic balance to a greater extent than others.
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What condition is characterized by having three copies of chromosome 21?
What condition is characterized by having three copies of chromosome 21?
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Down Syndrome affects approximately one out of every 600 children born in the United States.
Down Syndrome affects approximately one out of every 600 children born in the United States.
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The frequency of Down Syndrome decreases with the age of the mother.
The frequency of Down Syndrome decreases with the age of the mother.
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Aneuploid conditions involving sex chromosomes tend to disrupt the genetic balance more than those involving autosomes.
Aneuploid conditions involving sex chromosomes tend to disrupt the genetic balance more than those involving autosomes.
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What syndrome results from an extra chromosome in a male, producing XXY individuals?
What syndrome results from an extra chromosome in a male, producing XXY individuals?
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A male with an extra Y chromosome (XYY) always exhibits a defined syndrome.
A male with an extra Y chromosome (XYY) always exhibits a defined syndrome.
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Females with trisomy X (XXX) often display noticeable physical differences from other females.
Females with trisomy X (XXX) often display noticeable physical differences from other females.
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What is the only known viable monosomy in humans?
What is the only known viable monosomy in humans?
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Chronic Myelogenous Leukemia (CML) is associated with duplication in a chromosome.
Chronic Myelogenous Leukemia (CML) is associated with duplication in a chromosome.
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Study Notes
Chapter 12: The Chromosomal Basis of Inheritance
- Mendel's "hereditary factors" are genes, segments of DNA located along chromosomes
- Gene location can be visualized by tagging isolated chromosomes with a fluorescent dye highlighting the gene
- Mitosis and meiosis were first described in the late 1800s
- The chromosome theory of inheritance states that Mendelian genes have specific loci (positions) on chromosomes
- Chromosomes undergo segregation and independent assortment during meiosis
- Chromosome behavior during meiosis accounts for Mendel's laws of segregation and independent assortment
Morgan's Choice of Experimental Organism
- Morgan used Drosophila melanogaster (fruit flies) for research
- Fruit flies are convenient for genetic studies due to:
- High offspring production
- Short generation time (every two weeks)
- Only four pairs of chromosomes
Morgan's First Mutant Phenotype
- Wild-type phenotypes are common in fly populations
- Mutant phenotypes are traits alternative to the wild type
- The first mutant phenotype Morgan discovered was white eyes instead of red (the wild type)
Correlating Behavior of a Gene's Alleles with Behavior of a Chromosome Pair
- Morgan mated male flies with white eyes and female flies with red eyes
- All F₁ offspring had red eyes
- F₂ offspring showed a 3:1 red:white ratio, but only males had white eyes
- Morgan concluded eye color was related to sex
Correlating Behavior of a Gene's Alleles with Behavior of a Chromosome Pair (Continued)
- Morgan determined that the white-eyed mutant allele is located on the X chromosome
- His findings supported the chromosome theory of inheritance
Concept 12.2: Sex-Linked Genes Exhibit Unique Patterns of Inheritance
- Sex chromosome behavior correlates with eye-color gene white allele behavior
The Chromosomal Basis of Sex
- Humans and other mammals have an X and a Y chromosome
- Two X chromosomes develop female anatomy, one X and one Y develop male anatomy
The Chromosomal Basis of Sex (Continued)
- The ends of the Y chromosome are homologous to regions of the X chromosome
- These homologous regions allow X and Y chromosomes to pair during meiosis in males
- Each ovum contains an X chromosome
- A sperm may contain either an X or a Y chromosome
- Other animals have different sex determination methods
The Chromosomal Basis of Sex (Continued)
- A gene on a sex chromosome is called a sex-linked gene
- Genes on the X chromosome are X-linked genes and there are many
- Genes on the Y chromosome are Y-linked genes; there are few
Inheritance of X-Linked Genes
- X-linked genes follow specific inheritance patterns
- A female expressing a recessive X-linked trait needs two copies of the allele (homozygous)
- A male expressing a recessive X-linked trait needs only one copy (hemizygous)
- X-linked recessive disorders are more common in males
X Inactivation in Female Mammals
- In mammalian females, one X chromosome in each cell is randomly inactivated during embryonic development
- The inactive X condenses into a Barr body
- If a female is heterozygous for a gene on the X chromosome, she will be a mosaic for that trait
Concept 12.3: Linked Genes Tend to Be Inherited Together
- Each chromosome (except the Y) contains hundreds or thousands of genes
- Genes located near each other on the same chromosome tend to be inherited together (linked genes)
Recombination of Unlinked Genes: Independent Assortment of Chromosomes
- Mendel observed trait combinations in offspring that differ from either parent
- Offspring with phenotypes matching parental phenotypes are called parental types
- Offspring with nonparental phenotypes (new trait combinations) are called recombinants
- A 50% recombination frequency is observed for any two genes on different chromosomes
Recombination of Linked Genes: Crossing Over
- Morgan observed recombinant phenotypes even when genes were on the same chromosome
- He proposed that crossing over (the physical exchange between homologous chromosomes) breaks the connection between genes on the same chromosome
New Combinations of Alleles: Variation for Natural Selection
- Recombinant chromosomes create new allele combinations in gametes
- Random fertilization further increases the number of variant allele combinations
- The abundance of genetic variation is the raw material for natural selection
Concept 12.4: Alterations of Chromosome Number or Structure Cause Some Genetic Disorders
- Large-scale chromosome alterations in mammals often lead to spontaneous abortions or developmental disorders
- Plants are better able to tolerate such genetic changes
Abnormal Chromosome Number
- Nondisjunction occurs when homologous chromosomes or sister chromatids fail to separate during meiosis I or II
- One gamete receives two copies of a chromosome, the other receives no copy
- This results in aneuploidy (an abnormal number of chromosomes)
- A monosomic zygote has one copy of a particular chromosome, a trisomic zygote has three copies
- Polyploidy is a condition where an organism has three or more sets of chromosomes (e.g., triploidy, tetraploidy)
- Polyploidy is common in plants but rare in animals
Alterations of Chromosome Structure
- Chromosome breakage can result in four types of structural changes:
- Deletion (removes a segment)
- Duplication (repeats a segment)
- Inversion (reverses segment orientation)
- Translocation (moves segment to another chromosome)
Human Disorders Due to Chromosomal Alterations
- Chromosome number and structure alterations cause several serious disorders
- Some aneuploidy types affect the genetic balance less severely, allowing survival
- Individuals with these disorders exhibit characteristic symptoms (syndromes)
Down Syndrome (Trisomy 21)
- Down syndrome is a trisomy (three copies) of chromosome 21
- Individuals with Down syndrome have an increased risk associated with the mother's age during meiosis
Aneuploidy of Sex Chromosomes
- Aneuploid conditions involving sex chromosomes (e.g., Klinefelter syndrome (XXY), trisomy X (XXX), Turner syndrome (XO)) tend to be less severe than autosomal aneuploid conditions
- Klinefelter syndrome results from an extra X chromosome in males
- Trisomy X females typically have no unusual physical features except being slightly taller than average
- Turner syndrome results from a missing X chromosome in females
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Description
Explore the chromosomal basis of inheritance in this quiz, which covers key concepts such as Mendel's hereditary factors, the chromosome theory of inheritance, and the role of Drosophila melanogaster in genetic studies. Test your understanding of the mechanisms like segregation and independent assortment that underpin these foundational theories in genetics.
