BIO207H5S Introductory Genetics Winter 2024 Lecture 5: Sex Determination and Sex-linked Inheritance

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 Signup and view all the answers

At what stage does the gonadal tissue of a human embryo become sexually indifferent or neutral?

Fifth week of gestation Signup and view all the answers

Which part of the neutral gonadal tissue may develop into a testis in a human embryo?

Medulla Signup and view all the answers

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 Signup and view all the answers

Which type of sex cells do females produce in the XX-XY sex determination system?

X gametes Signup and view all the answers

What can be distinguished at the stage where the gonadal phenotype is sexually indifferent?

Neither male nor female reproductive structures Signup and view all the answers

What determines maleness in humans according to the XX-XY sex determination system?

Sperm cells that carry the Y chromosome Signup and view all the answers

In the XX-XO system, which of the following accurately describes the determination of maleness?

Males carry only one X chromosome (XO) Signup and view all the answers

What is the role of the Wolffian ducts and Müllerian ducts in each embryo?

Differentiate into structures of the male reproductive tract Signup and view all the answers

What is the function of the testis determining factor?

Cause undifferentiated gonadal tissue to form testes Signup and view all the answers

What are the pseudoautosomal regions (PARs) critical for?

Segregation of the X and Y chromosomes during male gametogenesis Signup and view all the answers

What genetic consequences result from having more than two copies of pseudoautosomal regions (PARs)?

Klinefelter’s Syndrome (XXY) Signup and view all the answers

What is the function of Barr bodies in somatic cells of females?

Compensate for X chromosome dosage disparities Signup and view all the answers

According to the Lyon hypothesis, when does X chromosome inactivation occur?

At the blastocyst 4- to 8-cell stage of development Signup and view all the answers

What is the basis for sex determination in organisms with Haplodiploidy?

Number of chromosomes found per cell Signup and view all the answers

What is the mechanism of sex determination in organisms with XX-XY system?

Females have XX chromosomes and males have XY chromosomes Signup and view all the answers

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 Signup and view all the answers

What did Calvin Bridges' observation of flies with unusual phenotypes cytogenetically confirm?

Non-disjunction of chromosomes during gamete formation Signup and view all the answers

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. Signup and view all the answers

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. Signup and view all the answers

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 Signup and view all the answers

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. Signup and view all the answers

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. Signup and view all the answers

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. Signup and view all the answers

What genetic phenomenon did Calvin Bridges' observation confirm about the flies with unusual phenotypes?

Non-disjunction of chromosomes during gamete formation. Signup and view all the answers

What did Bridges' observation confirm about the flies' rare phenotypes?

They were associated with particular chromosomes due to non-disjunction during gamete formation. Signup and view all the answers

What is the sex determination system present in butterflies, birds, some reptiles, and amphibians?

ZZ-ZW system Signup and view all the answers

According to Bridges, what plays a critical role in sex determination in Drosophila melanogaster?

X chromosomes and autosomes Signup and view all the answers

What did Thomas H. Morgan observe in his Drosophila lab cultures, leading to his studies of sex-linkage?

A white eyed male fly Signup and view all the answers

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 Signup and view all the answers

What is the definitive method to test for sex-linkage?

Reciprocal crosses Signup and view all the answers

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 Signup and view all the answers

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 Signup and view all the answers

What did Calvin Bridges observe under the microscope to confirm his hypothesis regarding unusual phenotypes?

Chromosomes associated with particular phenotypes Signup and view all the answers

What did unexpected phenotypes appearing at a frequency more than the expected mutation rate provide definite proof for?

Chromosomal theory of inheritance Signup and view all the answers