ScienceFreePrintable

Meiosis and Fertilisation Processes

A free science worksheet ready for your classroom. Open in Kuraplan to grab the print-ready PDF, customize it for your students, or generate a fresh version in seconds.

Download now

Name:Date:

Meiosis and Fertilisation Processes

Follow the chromosome trail from parent cells to offspring. Use the model and scenarios to explain how meiosis and fertilisation maintain chromosome number and create genetic variation.

A chromosome model

For this model organism, body cells have 2n = 4 chromosomes: one long and one short homologous pair. Each parent has one chromosome of each pair from each of their own parents. This simplified model shows chromosome behaviour, not every detail of real cells.

1.What does 2n = 4 mean? Choose the best explanation.

The cell has four pairs of chromosomes.
The diploid cell has four chromosomes in total, arranged as two homologous pairs.
The cell has four chromatids and no homologous chromosomes.
The haploid cell has four chromosomes.

2.At the end of meiosis, how many chromosomes are in each model gamete? State whether each gamete is haploid or diploid.

3.Match each process or structure to its role in the chromosome trail.

Meiosis
Crossing-over
Fertilisation
Zygote

Joins two haploid gametes to form a diploid cell
Reduces chromosome number to make haploid cells
Exchanges DNA between non-sister chromatids of homologous chromosomes
The first diploid cell formed after fertilisation

4.During which stage does crossing-over usually occur, and what is exchanged?

Solve the gamete mix-up

A lab technician checks the model organism’s reproductive cells. A normal gamete carries one chromosome from each homologous pair. In an unusual sample, both members of one homologous pair have moved into the same gamete.

5.The technician’s unusual gamete has both long homologues and one short chromosome. How many chromosomes does it contain? Is it a normal haploid gamete for this organism?

6.A normal gamete (n = 2) fuses with this unusual 3-chromosome gamete. How many chromosomes will the resulting cell have? Explain why its chromosome number differs from the usual zygote.

7.Which events can create genetic variation in offspring? Select all that apply.

Crossing-over between homologous chromosomes
Independent assortment of homologous pairs during meiosis
Random joining of an egg and sperm at fertilisation
Mitosis producing genetically identical body cells

8.A student says, “Fertilisation halves the chromosome number.” Is the student correct? Explain what fertilisation does to chromosome number instead.

9.In a species with 2n = 12, state the chromosome number in a gamete and in a typical zygote. Show how fertilisation relates the two numbers.

10.Compare meiosis and mitosis by giving one difference in their products and one difference in their role in an organism.

11.Explain one way genetic variation can help a population persist when its environment changes. Link your explanation to differences among offspring.