Question

1. during double fertilization in flowering plants

a. one sperm fertilizes the egg and another fertilizes the central cell
b. both sperm fertilize the same egg
c. one sperm fuses with antipodal cells
d. all sperm fuse to form endosperm

1. the endosperm of a flowering plant is typically:

a. triploid
b. haploid
c. diploid
d. tetraploid

1. in mammals, males are:

a. heterogametic (xy)
b. homogametic (xx)
c. triploid
d. diplogametic (yy)

1. in birds, females are:

a. heterogametic (zw)
b. homogametic (zz)
c. diploid males
d. haploid females

1. in some insects, males have only one sex chromosome (xo), which means:

a. they lack a homologous x chromosome
b. they possess an extra y
c. they are triploid
d. they have no autosomes

1. in honeybees, males develop from:

a. unfertilized haploid eggs
b. fertilized diploid eggs
c. polyploid cells
d. degenerated oocytes

1. in certain reptiles and fish, sex is determined by:

a. environmental temperature or behavior
b. the ratio of x to autosomes
c. the presence of the y chromosome
d. mutations in mitochondrial dna

Explanation:

• 44: Double fertilization in flowering plants involves one sperm fusing with the egg (to form the zygote) and another sperm fusing with the central cell (to form the endosperm).
• 45: The endosperm is formed by the fusion of two polar nuclei (each \(n\)) and one sperm (\(n\)), so its ploidy is \(3n\) (triploid).
• 46: In mammals, males have \(XY\) sex - chromosomes (heterogametic as they produce two types of gametes with respect to sex - chromosomes: \(X\) and \(Y\)), while females are \(XX\) (homogametic, producing only \(X\) - bearing gametes).
• 47: In birds, the female has \(ZW\) sex - chromosomes (heterogametic, producing \(Z\) and \(W\) gametes) and the male has \(ZZ\) (homogametic).
• 48: In the \(XO\) system (e.g., some insects), males have only one \(X\) chromosome and lack a homologous partner (there is no \(Y\) chromosome in this system).
• 49: In honeybees, males (drones) develop from unfertilized eggs (haploid), while females (queen and workers) develop from fertilized eggs (diploid).
• 50: In certain reptiles (e.g., some turtles) and fish, sex is determined by environmental factors such as temperature (temperature - dependent sex determination) or social behavior (e.g., in some fish species, a change in social hierarchy can lead to sex change).

Answer:

1. A. One sperm fertilizes the egg and another fertilizes the central cell
2. A. Triploid
3. A. Heterogametic (XY)
4. A. Heterogametic (ZW)
5. A. They lack a homologous X chromosome
6. A. Unfertilized haploid eggs
7. A. Environmental temperature or behavior