Sexual reproduction

Question 1

How are gametes formed?

Answer 1

By meiosis in specialised reproductive organs called gonads. The cells that produce gametes are called germ cells.

Question 2

What are gametes?

Answer 2

A haploid cell, containing half the number of chromosomes than the parent cell, produced by meiosis. Mammal gametes are called egg or sperm.1

Question 3

What is a homologous pair of chromosomes?

Answer 3

Chromosome pairs of approximately the same length, centromere position, and staining pattern.

Question 4

Why do gametes need to contain the haploid number of chromosomes?

Answer 4

If gametes contained the same number of chromosomes as somatic cells then the combining of 2 gamete cells from the parents would cause a double in each successive generation.

Question 5

How is the diploid number restored after meiosis?

Answer 5

Fertilization of an egg and sperm both containing the haploid number restores the diploid number.

Question 6

What is a hermaphrodite?

Answer 6

An organism that contains both egg and sperm reproductive organs. The reproduce by internal sexual reproduction.

Question 7

True or false?

Meiosis is a non conservative process.

Answer 7

True. Meiosis does not maintain the number of chromosomes. It produces haploid cells. Mitosis is a conservative process because the number chromosomes is maintained.

Question 8

What 2 events create genetic diversity in gametes?

Answer 8

1. crossing over: homologous chromosomes exchange chromosomal segments
2. independent assortment: homologous pairs line up on equator and with random orientation.

Question 9

What is the importance of meiosis?

Answer 9

The production of gametes that allows species to reproduce. It also allows for genetic variation so in certain situations some species will have a higher chance of survival.

Question 10

What is recombination?

Answer 10

Process of generating new combinations of alleles of various genes both by crossing over and by independent assortment

Question 11

What is nondisjunction?

Answer 11

When a pair of chromosomes fail to disjoin during anaphase, meaning 2 copies of a chromosome are present in a gamete or one is missing.

Question 12

What is internal fertilisation?

Answer 12

When a male organism’s sperm fertilises a female organism’s egg inside the boy part of the female.

Question 13

What is external fertilisation?

Answer 13

Refers to when gametes are released into external environment. When a male organism’s sperm fertilises a female organism’s egg outside of the body.

Question 14

What are the disadvantages of external fertilisation?

Answer 14

• large energy cost due to large production of gametes
• low success rate
• requires appropriate environment

Question 15

What are the advantages of external fertilisation?

Answer 15

• can result in large number of offspring

Question 16

What are the disadvantages of internal fertilisation?

Answer 16

• harder to bring male and female into intimate contact
• risk of sexually transmitted disease
• limited amount of offspring produced

Question 17

What are the advantages of internal fertilisation?

Answer 17

• increased chance of sperm and egg meeting
• increased chance of successful fertilisation
• less energy required to produce gametes
• less gamete wastage

Question 18

What are the advantages of sexual reproduction?

Answer 18

Variation which results in some organisms having more suited characteristics to their environment and therefore and increased chance of survival.

Question 19

What are the disadvantages of sexual reproduction?

Answer 19

• energy cost of producing gametes
• energy cost of finding and securing a mate
• success rate of fertilisation

Question 20

What is the definition of meiosis?

Answer 20

A type of cell division that results in four daughter cells each with half the number of chromosomes of the parent cell, as in the production of gametes and plant spores.

Question 21

Why is meiosis necessary in organisms that reproduce sexually?

Answer 21

By undergoing meiosis the number of chromosomes is divided so that the gamete only receives one of each kind of chromosome. When fertilization occurs, the newly forming generation will have received one of each kind of chromosome from each parent, thus marinating the diploid number.

Question 22

Define the terms zygote, fertilization, and homologous chromosomes.

Answer 22

Zygote: fertilized egg.
Fertilization: the uniting of a sperm and egg to form a zygote.
Homologous chromosomes: a pair of chromosomes, one donated by each parent and both having the same length, basic gene sequence, centromeres at the same point.

Question 23

List three differences between mitosis and meiosis.

Answer 23

• Mitosis results in two cells; meiosis results in 4 cells.
• Mitosis results in cell genetically identical to the parent; meiosis results in cells that are different from the parent.
• Mitosis can be carried out in both haploid and diploid cells; meiosis can only occur in diploid cells.

Question 24

Define crossing over.

Answer 24

Exchange of genes between homologous chromosomes resulting in mixture of parental characteristics in offspring.