44 Questions
What is the most likely explanation for all the white-eyed flies in the F2 generation being male?
The gene involved is located on the X chromosome.
What does the chromosome theory of inheritance from the early 20th century state?
Mendelian genes are at specific loci on the chromosome and, in turn, segregate during meiosis.
Why are males more often affected by sex-linked traits than females?
Males are hemizygous for the X chromosome.
How is the SRY gene best described?
A gene located on the Y chromosome that determines maleness.
What determines sex in birds?
ZW chromosome scheme
What causes black fur color in cats?
X-linked allele
What triggers male development in fruit flies?
Gene on the Y chromosome
What causes red-green color blindness in humans?
Sex-linked recessive trait
What leads to tortoiseshell fur color in cats?
X-linked gene inheritance
What determines gender differentiation in mammals?
SRY gene on the Y chromosome
When does clear gender differentiation in humans occur?
After the second month of gestation
What causes Duchenne muscular dystrophy in humans?
Recessive allele on the X chromosome
What leads to cinnabar eye color in fruit flies?
Sex-linked, recessive characteristic
What causes the requirement for expression of genes on the Y chromosome in humans?
Autosomal gene
How many active X chromosomes do female mammals have per cell?
One
What determines sex in humans?
SRY gene on the Y chromosome
What is the inheritance pattern of Glucose-6-phosphate dehydrogenase deficiency (G6PD) in humans?
X-linked recessive
In a Drosophila experiment, how is the mutant allele for yellow body inherited?
As a recessive allele
What does a recombination frequency of 50% indicate about the location of two genes?
They are likely located on different chromosomes
What is the relationship between gene linkage and probability of crossover?
Closer genes have lower probability of crossover
What is the proportion of sons expected to have G6PD if a woman with an affected father marries a man with the disease?
1/2
What does a testcross involving F1 dihybrid flies producing more parental-type offspring than recombinant-type offspring indicate?
The two genes are closely linked on the same chromosome
What is the adaptive advantage of recombination between linked genes?
Creation of new allele combinations acted upon by natural selection
What is the significance of one map unit in linkage mapping?
It represents a 1% frequency of recombination between two genes
Why can map units on a linkage map not be relied upon to calculate physical distances on a chromosome?
Due to the varying frequency of crossing over along the chromosome
What is the order of the genes on a chromosome map in a series of mapping experiments for Drosophila?
b-rb-cn-vg
What is the expected phenotype of a woman with 47 chromosomes, including three X chromosomes?
Healthy female of slightly above-average height
What process is primarily affected by mutations in mitochondrial genes?
Generation of ATP in muscle cells
What phenomenon explains the pattern of inheritance where the inheritance of variegated color on the leaves of certain plants is determined only by the maternal parent?
Inheritance of plastid genes
What is the most likely result of a defect in meiosis that results in the failure of spindle microtubules binding at the kinetochores?
The resulting cells will not receive the correct number of chromosomes in the gametes, a condition known as aneuploidy
If a pair of homologous chromosomes fails to separate during meiosis I, what is the chromosome number of the four resulting gametes with respect to the normal haploid number (n)?
n + 1; n + 1; n - 1; n - 1
What is the most likely mode of inheritance in the transmission of a trait in a particular family shown in the pedigree?
Mitochondrial
What genotype(s) and phenotype(s) will offspring have if a Dd egg-producing snail and a dd sperm-producing snail reproduce?
1/2 Dd:1/2 dd; all right-coiling
What is the approximate distance between genes A and B based on the recombination frequency?
3 map units
What is the term for a fragment joining a nonhomologous chromosome, which can lead to expression of inappropriate gene products in cancer cells?
Translocation
What is the most probable cause of a child with Down syndrome, born to a 39-year-old mother?
Nondisjunction in somatic cell production
What is the impact of trisomy 21 (47, trisomy 21) among the given aneuploidies?
Generally has the most severe impact on the health of an individual
What is the inheritance pattern of Glucose-6-phosphate dehydrogenase deficiency (G6PD) in humans?
X-linked recessive
What would result from a balanced translocation in the father's chromosome 4 and 12?
All of the above
What would result from nondisjunction of one chromosome during meiosis II in cell X?
All of the above
What does a testcross involving F1 dihybrid flies producing more parental-type offspring than recombinant-type offspring indicate?
The genes are closely linked
What is the term for the expression of inappropriate gene products in malignant tumors, such as translocations?
Oncogene activation
What would be the result of a recombination frequency of 50% between two genes?
The genes are unlinked
What would a testcross progeny of gray-bodied, normal-winged flies plus black-bodied, vestigial-winged flies equalling 17% of the total indicate?
Recombination between genes A and B was required for these phenotypes
Study Notes
Genetics and Inheritance Summary
- Glucose-6-phosphate dehydrogenase deficiency (G6PD) is inherited as an X-linked recessive allele in humans.
- A woman with a G6PD affected father marries a man with the disease; proportion of their sons expected to have the disease is 1/2.
- In a Drosophila experiment, a mutant allele for yellow body is inherited as recessive.
- Mutant allele for yellow body in Drosophila is X-linked.
- Gene linkage: closer genes on a chromosome have lower probability of crossover.
- In a testcross involving F1 dihybrid flies, more parental-type offspring than recombinant-type offspring are produced; the two genes are closely linked on the same chromosome.
- Recombination frequency of 50% indicates that the two genes are likely located on different chromosomes.
- One map unit is a 1% frequency of recombination between two genes.
- Recombination between linked genes comes about through crossovers resulting in chromosomal exchange.
- Adaptive advantage of recombination between linked genes: new allele combinations are acted upon by natural selection.
- Map units on a linkage map cannot be relied upon to calculate physical distances on a chromosome due to the varying frequency of crossing over along the chromosome.
- In a series of mapping experiments for Drosophila, the order of the genes on a chromosome map is b-rb-cn-vg.
Genetic Cross and Linkage Summary
- A geneticist performed a testcross with an organism heterozygous for three recessive traits and identified progeny with specific phenotypic distributions.
- Recombination between genes A and B was required for progeny phenotypes 1, 2, 5, and 6.
- The approximate distance between genes A and B was 3 map units based on recombination frequency.
- Closely linked genes are typically inherited together because they are located close together on the same chromosome.
- In a testcross, the distance between genes was found to be 15 map units.
- In Drosophila melanogaster, testcross progeny showed that gray-bodied, normal-winged flies plus black-bodied, vestigial-winged flies equaled 17% of the total.
- Nondisjunction of one chromosome during meiosis II in cell X would result in one-quarter of the gametes being n + 1, one-quarter being n - 1, and half being n.
- A fragment joining a nonhomologous chromosome is called translocation, which can lead to expression of inappropriate gene products in cancer cells.
- Trisomy 21 (47, trisomy 21) generally has the most severe impact on the health of an individual among the given aneuploidies.
- A balanced translocation in the father's chromosome 4 and 12 will result in one-quarter of sperm carrying the normal chromosomes, one-quarter carrying only the translocation chromosomes, and half carrying one normal and one translocated chromosome.
- Abnormal chromosomes in malignant tumors, such as translocations, may lead to the expression of inappropriate gene products, making the cancer worse.
- The most probable cause of a child with Down syndrome, born to a 39-year-old mother, is one member of the couple undergoing nondisjunction in somatic cell production.
Test your knowledge of genetics and inheritance with this quiz. Explore concepts such as X-linked inheritance, gene linkage, recombination, genetic crosses, aneuploidies, and chromosomal aberrations. Sharpen your understanding of genetic principles and their applications through a series of challenging questions.
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