Question Video: Understanding the Role of Crossing Over in Meiosis Science

The diagram shows two chromosomes undergoing crossing-over. What is the advantage of this? [A] It creates completely new genes. [B] It reduces the risk of mutation. [C] It increases genetic variation. [D] It increases the likelihood of fertilization.

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Video Transcript

The diagram shows two chromosomes undergoing crossing-over. What is the advantage of this? (A) It creates completely new genes. (B) It reduces the risk of mutation. (C) It increases genetic variation. Or (D) it increases the likelihood of fertilization.

The question is asking us to work out what the advantage of a process called crossing-over is, which is shown to us in a diagram. In order to answer this question, we’re going to need to understand a little bit more about how genetic information is organized in animal cells into structures called chromosomes. The nucleus of animal cells, like this one, contains the genetic information as DNA. In animals like humans, DNA is organized into chromosomes, some of which we can see in the nucleus here.

In most human body cells, there are 46 chromosomes in total or two sets of 23. One set of these 23 comes from the mother, and the other set comes from the father. The chromosomes from the mother can be said to be homologous to the chromosomes from the father because they’re nearly identical. As there are two sets of chromosomes in most body cells, they’re called diploid cells. In gametes, like sperm cells from the father and egg cells from the mother, there is only one set of chromosomes. So, gametes can be described as haploid cells. Gametes are made through a process called meiosis.

Meiosis is a type of cell division where one parent cell can make four genetically different haploid daughter cells. The genetic variation in the gametes produced through meiosis is partly as a result of a process called crossing-over. This occurs during one of the stages of meiosis. As shown in this diagram, it includes swapping of some genetic information from each of the two homologous chromosomes in a pair.

There are four chromatids in each homologous pair of chromosomes and two chromatids in each single replicated chromosome from each parent. As each of these four chromatids will end up in different daughter cells by the end of meiosis, the swapping of sections of DNA between homologous chromosomes can increase the genetic variation of the gametes produced. This does not create new genes as sections of DNA are simply swapped between homologous chromosomes.

Crossing-over does not affect the risk of mutation of DNA, nor does it either increase or decrease the likelihood of fertilization. It simply trades a section of DNA between homologous chromosomes that may have slight differences. This can happen to many of the 23 chromosome pairs during meiosis and can increase genetic variation in the gametes. Therefore, we’ve worked out that crossing-over increases genetic variation.

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