38 Questions
In the XX-XY sex determination system, which of the following statements is true?
Males inherit their X chromosome from their father and their Y chromosome from their mother.
How many genes are there on the Y chromosome compared to the X chromosome in humans?
900–1400 genes on the Y chromosome and ~75 genes on the X chromosome
What determines maleness in the XX-XY sex determination system?
Sperm cells that carry the Y chromosome
During early development, every human embryo is potentially hermaphroditic until around which week of gestation?
Fifth week
At what stage does the gonadal tissue of a human embryo become sexually indifferent or neutral?
Fifth week of gestation
Which part of the neutral gonadal tissue may develop into a testis in a human embryo?
Medulla
In humans, how many X chromosomes do males inherit from each parent?
No X chromosomes from their father and one X chromosome from their mother
Which type of sex cells do females produce in the XX-XY sex determination system?
X gametes
What can be distinguished at the stage where the gonadal phenotype is sexually indifferent?
Neither male nor female reproductive structures
What determines maleness in humans according to the XX-XY sex determination system?
Sperm cells that carry the Y chromosome
In the XX-XO system, which of the following accurately describes the determination of maleness?
Males carry only one X chromosome (XO)
What is the role of the Wolffian ducts and Müllerian ducts in each embryo?
Differentiate into structures of the male reproductive tract
What is the function of the testis determining factor?
Cause undifferentiated gonadal tissue to form testes
What are the pseudoautosomal regions (PARs) critical for?
Segregation of the X and Y chromosomes during male gametogenesis
What genetic consequences result from having more than two copies of pseudoautosomal regions (PARs)?
Klinefelter’s Syndrome (XXY)
What is the function of Barr bodies in somatic cells of females?
Compensate for X chromosome dosage disparities
According to the Lyon hypothesis, when does X chromosome inactivation occur?
At the blastocyst 4- to 8-cell stage of development
What is the basis for sex determination in organisms with Haplodiploidy?
Number of chromosomes found per cell
What is the mechanism of sex determination in organisms with XX-XY system?
Females have XX chromosomes and males have XY chromosomes
In Drosophila melanogaster, which one of the following accurately describes the sex-linkage pattern for the gene controlling eye color?
F1 : Red eyed female : Red eyed male : white eyed male :: 2:1:1
What did Calvin Bridges' observation of flies with unusual phenotypes cytogenetically confirm?
Non-disjunction of chromosomes during gamete formation
Which statement accurately represents Morgan’s Hypothesis on X-linkage in Drosophila melanogaster?
Males have only one available gene site on their single X chromosome, whereas females have two available gene sites, one on each X chromosome.
What was the significance of conducting reciprocal crosses in the study of sex-linkage in Drosophila?
It allowed researchers to test if a gene or trait is autosomal or sex-linked.
What did the observation of unexpected phenotypes at a frequency more than the expected mutation rate in Morgan’s crosses indicate?
Non-disjunction of chromosomes during gamete formation
What was one result of X-linkage according to Morgan’s hypothesis?
Phenotypic traits controlled by recessive X-linked genes are passed from homozygous mothers to all sons.
Which of the following accurately describes the F1 offspring obtained in a reciprocal cross for an autosomal gene or trait?
All offspring will show the dominant phenotype for F1 for any monohybrid cross.
In Morgan’s studies, what did the observation of a white eyed male fly as opposed to red eyed flies lead to?
Curiosity that led to documenting one of the first cases of sex-linkage in Drosophila.
What genetic phenomenon did Calvin Bridges' observation confirm about the flies with unusual phenotypes?
Non-disjunction of chromosomes during gamete formation.
What did Bridges' observation confirm about the flies' rare phenotypes?
They were associated with particular chromosomes due to non-disjunction during gamete formation.
What is the sex determination system present in butterflies, birds, some reptiles, and amphibians?
ZZ-ZW system
According to Bridges, what plays a critical role in sex determination in Drosophila melanogaster?
X chromosomes and autosomes
What did Thomas H. Morgan observe in his Drosophila lab cultures, leading to his studies of sex-linkage?
A white eyed male fly
What was Morgan's hypothesis regarding the allele for white eyes in Drosophila?
It is found on the X chromosome but absent from the Y chromosome
What is the definitive method to test for sex-linkage?
Reciprocal crosses
In a reciprocal cross, if the gene or trait is autosomal, what will be observed in the offspring?
All of the offspring will show the dominant phenotype for F1 for any monohybrid cross
What is observed in the offspring of a reciprocal cross if the gene or trait is sex-linked?
The offspring in F1 or F2 obtained in a reciprocal cross will be different
What did Calvin Bridges observe under the microscope to confirm his hypothesis regarding unusual phenotypes?
Chromosomes associated with particular phenotypes
What did unexpected phenotypes appearing at a frequency more than the expected mutation rate provide definite proof for?
Chromosomal theory of inheritance
Test your knowledge of sex determination and sex-linked inheritance in genetics with this quiz based on topics covered in BIO207H5S Introductory Genetics Winter 2024 Lecture 5 by Preeti Karwal, Ph.D.
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