Meiosis 2021

Why do we need meiosis?

• To double the number of chromosomes going into sex cells

• To halve the number of chromosomes going into sex cells

• To triple the number of chromosomes going into sex cells

• To not change the number of chromosomes going into sex cells

Answer explanation

Remember, a new individual gets half its genetic information from its mom and half from its dad. So sex cells have half the number of chromosomes so the resulting individual has a full set of genetic info.

In MITOSIS cells are genetically _______, but in MEIOSIS cells are genetically ______.

• diferent, identical

• identical, different

• different, different

• identical, identical

Answer explanation

Mitosis makes 2 clones if you like, to grow, or replace worn out or damaged cells. Meiosis makes sex cells which have to be different to help the species have a better chance of survival.

When an area of a chromatid is exchanged with the matching area on a chromatid of its homologous chromosome, _________________ occurs.

• crossing over

• mutagenesis

• hybridization

• fertilization

Answer explanation

Crossing over is the swapping of genetic information to create more variety in the resulting sex cells.

Meiosis makes sperm and egg cells. In humans, sperm and egg cells each have _____ chromosomes. Therefore a fertilized human egg cell (sperm and egg cell combined) would create a cell with _____ chromosomes.

• 23, 46

• 46, 23

• 2, 4

• 50, 100

Answer explanation

So, human body cells have 46 chromosomes, so sex cells have half that number - 23.

During Metaphase I, how do the chromosomes line up on spindle?

• One homologous chromosome per spindle fiber

• Two homologous chromosomes per spindle fiber

• One random chromosome per spindle fiber

• Two random chromosomes per spindle fiber

Answer explanation

They line up side by side in homologous (similar) pairs so the number of chromosomes can be reduced.

Which phase is shown in the picture?

• Metaphase I

• Metaphase II

• Prophase I

• Anaphase II

Answer explanation

There are two cells present so it must be part of Meiosis II. Plus, the sister chromatids are being pulled apart, so it must be Anaphase. Put it together and it is Anaphase II.

Which phase is shown in the picture?

• metaphase I

• metaphase II

• anaphase I

• anaphase II

Answer explanation

The key is to recognize that the homologous chromosomes are in the Middle (metaphase) in pairs, which only happens in Meiosis I.

Which phase is shown in the micrograph?

• Anaphase I

• Anaphase II

• Telophase I

• Telophase II

Answer explanation

Four daughter cells means Telophase II.

Which of the following statements about Mitosis and Meiosis is TRUE?

• Both mitosis and meiosis result in identical cells

• In mitosis chromosomes line up one per spindle fiber, in meiosis they line up in homologous chromosomes per spindle fiber

• During prophase crossing over occurs in both mitosis and meiosis

• DNA is only replicated before mitosis as each resulting cell needs a complete set, whereas in meiosis the original DNA is just halved.

Answer explanation

Remember, in Metaphase II in meiosis, the homologous chromosomes line up in pairs so their number can be reduced.

Structure (b) is pointing to a

• chromatid

• chromosome

• centromere

• DNA

Answer explanation

The centromere is what holds the sister chromatids together after replication.