Biology: Sex Ratios and Population Statistics

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What is the primary sex ratio?

The proportion of each sex born
The ratio of males to females in the population
The actual proportion of male to female offspring
The proportion of males to females conceived in the population (correct)

What is the assumed basis for the theoretical sex ratio of 1:1?

Segregation of X and Y chromosomes during meiosis
Equal viability and motility of X- and Y-bearing sperm
Equal receptivity of the egg surface to X- and Y-bearing sperm
All of the above (correct)

What is the purpose of dosage compensation in humans and other mammals?

To maintain a 1:1 sex ratio
To balance the dose of X chromosome gene expression between males and females
To prevent excessive expression of X-linked genes
Both a and b (correct)

Based on the 1969 worldwide census data, which population had the highest secondary sex ratio?

Korean population (D) Signup and view all the answers

What does a secondary sex ratio of 1.06 for the Caucasian population in the United States indicate?

There were more males than females born (D) Signup and view all the answers

What is the difference between primary and secondary sex ratio?

Primary sex ratio reflects the proportion of males to females conceived, while secondary sex ratio reflects the proportion of each sex born (D) Signup and view all the answers

What determines the sex of an individual in Drosophila?

The ratio of X chromosomes to the number of haploid sets of autosomes (C) Signup and view all the answers

What is the normal ratio of X chromosomes to haploid sets of autosomes in female Drosophila?

2X:2A (D) Signup and view all the answers

What happens when the ratio of X chromosomes to haploid sets of autosomes exceeds unity in Drosophila?

An inviable female (metafemale) is produced (A) Signup and view all the answers

How does Drosophila achieve dosage compensation for X-linked genes in females?

Increased transcription rate of X-linked genes in males (D) Signup and view all the answers

What is the role of the Sxl (Sex-lethal) gene in Drosophila?

It induces female differentiation during sex determination (A) Signup and view all the answers

Which of the following statements about Caenorhabditis elegans is true?

Hermaphrodites have both testes and ovaries, while males have only testes (B) Signup and view all the answers

What is the primary reason for the deviation of the sex ratio from 1.0 in humans?

Differential survival rates of male and female embryos (A) Signup and view all the answers

Which of the following statements about dosage compensation is correct?

It ensures equal expression of X-linked genes in males and females (C) Signup and view all the answers

What is the primary determinant of sex in humans?

The presence or absence of the Y chromosome (C) Signup and view all the answers

Which of the following statements about sex chromosomes is correct?

The X and Y chromosomes are heteromorphic (dissimilar) (D) Signup and view all the answers

Which of the following factors can influence the secondary sex ratio (at birth) in humans?

All of the above (D) Signup and view all the answers

In which group of organisms is sex determination primarily influenced by temperature variation?

Many reptiles (C) Signup and view all the answers