Understanding the number of genes and the relative amount of DNA during meiosis

Understanding gene count and DNA relative amount during genetic meiosis

 

 

 

My son in high school says that the most difficult part in life science textbook is genetic part.
So, I looked at the genetics section, wondering if I could help him.
And I understood why my son said that the part, especially meiosis was difficult even in the genetic part.

But once you do it step by step, the prejudice that it is difficult will disappear.

Looking at the types of life science questions in the Korea University scholastic ability test (K-SAT), there are many test questions with 3 points out of 1 point, 2 points, and 3 points in the area of calculating the number of genes for each stage of meiosis.
It is fortunate that most of the questions give the premise that there is no mutation or crossover.

I'm guessing that perhaps in high school advanced life science courses, questions that consider intersections will come up...

There are 23 pairs of chromosomes in one human cell, for a total of 46 chromosomes, and the nuclear phase is expressed as "2n=46".
It's amazing that one cell has about 20,000 to 25,000 genetic traits!

Among them, it is fortunate that most of the CSAT questions are questions with a combination of two or three genetic traits.
Actually, if you understand the basic principle, it doesn't matter if it's 4 or 5.

First of all, I will summarize what I have understood and explained to my son as follows.

 

 

What is meiosis

 

1) Meiosis, also called germ cell division, is a cell division that occurs in the process of forming reproductive cells such as egg and sperm of animals.

Four daughter cells with n chromosomes are produced from one parent cell with 2n chromosomes through two successive cell divisions (meiosis 1 and meiosis 2).

Gametes of two gametes having n chromosomes produced through meiosis form a fertilized egg with 2n chromosomes again through fertilization.

 

2) Bivalent chromosome refers to the state in which homologous chromosomes are joined, and since a bivalent chromosome is composed of 4 chromatids, it is called a quaternary chromosome. Because of this, it is called meiosis

=> When you hear the word 2-valent chromosome, you understand that it is meiosis.

 

 

Understanding stages of 1st meiosis and 2nd meiosis

 

1st meiosis

① Interphase: DNA in the nucleus is replicated and doubled. ② Electromechanism: Chromosomes change into chromosomes and homologous chromosomes join together to form bivalent chromosomes, resulting in spindle threads. ③ Metaphase: The nuclear membrane disappears and spindle fibers attach to the centromere. Bivalent chromosomes are arranged in the equatorial plate ④Later: The centromere of homologous chromosomes is separated, and the chromosomes are separated into both poles by the spindle thread ⑤ Late stage: Nuclear membrane appears and cytoplasmic division occurs to form two daughter cells

 

2nd meiosis

① No interphase, no DNA replication ② Electrolysis: The chromatids separate and enter each daughter cell. spindle formation ③Metaphase: In , the chromosomes are arranged in the equatorial plate ④ Late stage: Centromere is separated and chromatids are separated into bipolar ⑤ Late Stage: Nuclear membrane appears, chromosomes are released into chromatin, and cytoplasmic division occurs to form four final daughter cells.

 

Determining gene combinations and relative amounts of DNA during meiosis

 

 

< The process by which sperm are produced from human G1-phase cell 1 >

<example question > A person's genetic trait (a) is determined by A, a (b) by B, b (c) by E, e The genes of (a) and (b) are on different autosomes, The gene in (c) is on the X chromosome. A person's (a), (b), (c) genotype is AaBBXeY. Find the relative amount of DNA in A,a,B,b,E,e in cells 1 to 6 in the following figure. In the cell on the left, the relative amount of DNA in cell No. 3 A and cell e in No. 4 is 2 and 0, respectively, and the relative amount of DNA in cells A, a, B, b, E, and e in cells 1 to 6 is calculated and the following table Please fill in

Everyone, try solving it too!  ^_^

Now, I will explain the process I understood and solved.

Hints from the passage above.

1) "The genes of (a) and (b) are on different autosomes,"

     => There are two pairs of autosomes.

2) "The gene in (c) is on the X chromosome. A person's (a), (b), (c) genotype is AaBBXeY"

    => C is a sex chromosome, but there is an e in X and no E in Y!

 

First, let's understand the changes in chromosome composition at each stage of meiosis by drawing a picture.

 

< Answer >

 

While preparing for the CSAT, the problem of asking the relative amount of DNA in meiosis is almost solved if you understand this.

Because the type of problem differs in the combination of chromosomes or the presence or absence of XY chromosomes, pay attention only to that....

 

Hope this helps..

 

 - I wrote the English version of what I understood in the hope that it would be helpful to many students who are struggling with the University scholastic ability test (SAT) especially those who have difficulty understanding meiosis. -