"Micro Topic Seven: Calculation Methods of Gene Frequency and Genotype Frequency" Biological Evolution PPT Courseware

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"Micro Topic Seven: Calculation Methods of Gene Frequency and Genotype Frequency" Biological Evolution PPT Courseware

Calculation of gene frequencies and genotype frequencies

(1) Calculate gene frequency based on the number of genotype individuals

law:

①Autosomal inheritance: Set A% and a% to represent the frequency of genes A and a respectively, AA, Aa, and aa to represent the number of individuals with three genotypes AA, Aa, and aa respectively, then:

A%＝2×AA＋Aa/2×（AA＋Aa＋aa）×100%

a%＝2×aa＋Aa/2×（AA＋Aa＋aa）×100%

②X-linked chromosome inheritance: XB% and Xb% are set to represent the frequency of genes XB and Xb respectively, XBXB, XBXb, XbXb, :

XB%＝2×XBXB＋XBXb＋XBY/2×（XBXB＋XBXb＋XbXb）＋XBY＋XbY×100%

Xb%＝2×XbXb+XBXb+XbY/2×(XBXB+XBXb+XbXb)+XBY+XbY×100%

[Typical Example 1] In the human MN blood group system, individuals with the LMLM genotype show the M blood type; individuals with the LMLN genotype show the MN blood type, and individuals with the LNLN genotype show the N blood type. In 1977, the Shanghai Central Blood Station surveyed 1,788 people and found that 397 had M blood type, 861 had MN blood type, and 530 had N blood type. Then the gene frequencies of LM and LN are approximately ________.

Analysis: For genes on autosomal chromosomes, the number of individuals of each genotype is known. When finding the gene frequency, the calculation is based on "gene frequency = total number of this gene in the population/total number of this allele in the population". There are 1788 individuals in this population, containing a total of 3576 genes. The total number of LM is 397×2+861×1=1655, and the frequency of LM is 1655/3576≈0.4628. Since the gene frequency in a population is LM+LN=100%, LN≈1-0.462 8≈0.537 2.

Answer: 46.28%, 53.72%

[Practice 1] A biology interest group in a certain school carried out a color blindness census in a research study activity. They first randomly selected 200 students (male and female students) from the 1,800 students in the school. Half and half) as the first batch of survey subjects, it was found that there were 3 female color blindness patients, 6 male color blindness patients, and 15 female color blindness gene carriers. So what is the approximate frequency of the color blindness gene among all students in this school?

Analysis: This question tests the concept of life and scientific thinking. According to sex-linked inheritance, females have two X chromosomes, while males have only one X chromosome. Since the color blindness gene and its alleles are only located on the The total number of genes is Xb + Since these 200 students were randomly sampled, the gene frequency of the color blindness gene among the students in the school is also 9%.

Answer 9%

(2) Calculate gene frequency based on genotype frequency

law:

① Autosomal inheritance: The frequency of a gene among alleles is equal to the sum of its homozygous frequency and 1/2 the heterozygous frequency.

②X-linked chromosome inheritance: Remove the percent sign in the genotype frequency, convert it into the number of genotypes, and then calculate the gene frequency according to the number of genotype individuals. When the number of female and male individuals is equal, it can also be calculated according to the following formula: the gene frequency of a certain gene = 2/3 (2 × the frequency of female homozygotes of a certain gene + the frequency of female heterozygotes + the frequency of male genotypes).

[Typical Example 2] When adjusting a certain wheat population, it was found that T (rust resistance) is dominant to t (susceptible to infection). Under natural circumstances, the wheat population can be pollinated freely. According to statistics, TT is 20% , Tt is 60%, tt is 20%, the wheat population is suddenly infected with rust in a large area, causing all susceptible wheat to die before flowering. Calculate the frequency of gene T in this wheat before it is infected with rust and after it is infected with rust, respectively ()

A.50% and 50% B.50% and 62.5%

C.62.5% and 50% D.50% and 100%

[Practice 2] According to a survey, among the students in a certain primary school, the proportion of genotypes is XBXB is 42.5%, XBXb is 7%, XbXb is 0.5%, XBY is 46%, and XbY is 4 %, then the gene frequencies of XB and Xb in this region are ()

A.6%, 8% B.8%, 92%

C.78%, 92% D.92%, 8%

(3) Calculate genotype frequency based on gene frequency

law:

① Autosomal inheritance: Set p and q to represent the frequencies of genes A and a respectively. According to the law of genetic balance, the frequency of genotype AA is p2, the frequency of genotype Aa is 2pq, and the frequency of genotype aa is q2.

②X-linked chromosome inheritance: Let the frequency of XB be p and the frequency of Xb be q. In the male population, the female population and the entire population, the gene frequencies of XB and Xb are p and q, and p+q=1. In the male population, the frequency of XBY = the frequency of XB = p, the frequency of XbY = the frequency of Xb = q; in the female population, the frequency of XBXB = p2, XbXb = q2, XBXb = 2pq. Since the number of males and females is equal, the frequency of a certain genotype in the entire population is 1/2 of the frequency of the genotype in the female (male) sex.

Keywords: Free download of the PPT courseware for high school biology compulsory course 2 of the People's Education Press, PPT download of calculation methods of gene frequency and genotype frequency, PPT download of the evolution of organisms, .PPT format;

For more information about the PPT courseware "Calculation Methods of Gene Frequency and Genotype Frequency in the Evolution of Biology", please click the Calculation Method of Gene Frequency and Genotype Frequency in the Evolution of Biology PPT tab.

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Update Time: 2024-10-03

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