"Microtopic 4: Problem-solving methods of sex-linked inheritance" PPT courseware on the relationship between genes and chromosomes

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"Microtopic 4: Problem-solving methods of sex-linked inheritance" PPT courseware on the relationship between genes and chromosomes

Part One: 1. "Sick Boys" and "Boys Are Sick" Issues

[Typical Example 1] The picture shows the family pedigree of two genetic diseases A and B (II-1 does not carry the disease-causing gene). The following statements about genetic diseases A and B and human inheritance are incorrect ()

A. It can be seen from the pedigree that the inheritance mode of disease A is dominant inheritance on the autosomal chromosome, and the inheritance mode of disease B is recessive inheritance on the X chromosome.

B. If III-1 and III-5 marry, the probability of giving birth to a sick boy is 1/4

C. If III-1 and III-4 marry, the probability of having a child with both diseases is 1/12

D. If III-1 and III-4 marry, the probability that the offspring will only suffer from nail disease is 7/12

[Practice 1] According to the following genetic pedigree of human red-green color blindness (red-green color blindness gene is represented by b), analyze and answer the following questions:

(1) The gene that controls red-green color blindness in humans is located on the ________ chromosome, and the patient’s genotype can be expressed as ________. The genetic characteristics of this type of genetic disease are _______________________________.

(2) Write the genotypes of the following members of the family: 4: ________, 10: ________, 11: ________.

(3) Member No. 14 is a color blind patient, and the disease-causing gene was passed on from an individual in the first generation. Write the transmission pathway of the color blindness gene using the member number and "→" ____________________________.

(4) If members 7 and 8 have a child, the probability of it being a color-blind boy is ________, and the probability of being a color-blind girl is ________.

[Method summary] "Sick boys" and "Sick boys" problems

(1) Autosomal inheritance

If the gene controlling a certain genetic disease is located on an autosomal chromosome, since the autosomal chromosomes and sex chromosomes are freely combined, then:

①The probability of a sick boy = the probability of a sick child × 12;

②The probability of a boy getting sick = the probability of having a sick child.

(2) Sex-linked inheritance

If the gene controlling a genetic disease is located on a sex chromosome, since the trait is linked to gender, then:

①The probability of an affected boy = the probability of an affected boy among all children in the offspring;

②The probability of the disease in boys = the probability of the disease in offspring boys.

Problem-solving methods for sex-linked inheritance PPT, part 2 content: 2. Scientific inquiry - determine whether the gene is located on an autosome or on the X chromosome

[Typical Example 2] The sex determination of a certain sheep is XY type. It is known that its black and white hairs are controlled by alleles (M/m), and the black hair is dominant to the white hair. In order to determine whether M/m is located on the X chromosome or an autosomal chromosome, a student mated multiple pairs of homozygous black-haired ewes with homozygous white-haired rams. In the second generation, black hair: white hair = 3:1 , we believe that based on this experimental data, it cannot be determined whether M/m is located on the M/m is located on the X chromosome; if ____________________________, it means M/m is located on the autosome.

[Practice 2] It is known that the gray body and luteal body of Drosophila are controlled by a pair of alleles, but the dominant-recessive relationship of this pair of relative traits and the chromosome where the allele is located are unknown. Classmate A crosses a gray-bodied female fly with a luteal male fly. In the offspring, ♀ gray body: ♀ luteal body: ♂ gray body: ♂ luteal body is 1:1:1:1. Classmate B used two different hybridization experiments to confirm that the gene controlling the corpus luteum is located on the X chromosome and is recessive. Please answer the following questions based on the above results:

(1) Based on classmate A’s experiments alone, can it be proven that the gene controlling the corpus luteum is located on the X chromosome and is recessive?

(2) Please use the offspring fruit flies obtained by classmate A as materials to design two different experiments. Both experiments can independently prove the conclusion of classmate B. (Requirement: Use only one hybridization combination in each experiment, and indicate the expected experimental results that support student B’s conclusion.)

Problem-solving methods for sex-linked inheritance PPT, part 3 content: 3. Scientific inquiry - determine whether the gene is located on the homologous segment of the X and Y chromosomes or only on the X chromosome

(1) Understanding of homologous and non-homologous segments of the X and Y chromosomes: In the homologous segments of the There are no mutual alleles, as shown below.

For homologous segments of X and Y (related genes are represented by B and b), the female genotypes are XBXB, XBXb, and XbXb, and the male genotypes are XBYB, XBYb, XbYB, and XbYb.

(2) Inheritance of homologous segment genes of X and Y chromosomes:

① In the homologous segments of X and Y, genes are paired and alleles exist, while in non-homologous segments, there are no alleles for each other.

②The inheritance of genes in homologous segments of X and Y chromosomes is similar to the inheritance of genes on autosomal chromosomes, but there are also differences, such as:

[Typical Example 3] It is known that eyes (B) and eyelessness (b) in fruit flies are controlled by a pair of alleles. There are currently several homozygous male flies with eyes and several female flies without eyes. It is assumed that chromosomal mutations and chromosomal exchanges do not occur. Please use the above strains as materials to design experiments to explore whether B/b is located on the X chromosome or on the homologous segments of X and Y. (Requirements: write down experimental ideas, expected experimental results, and draw conclusions)

Analysis: The dominant and recessive properties are known, the female has recessive traits, and the male has dominant traits, and both are homozygous. One-time cross method can be used.

[One question has many variables] It is known that the eyes and eyelessness of fruit flies are controlled by a pair of alleles B and b, and the dominance and recessiveness are unknown. There are currently two homozygous strains of Drosophila, eyed and eyeless, with half male and female individuals in each strain. It is assumed that chromosomal mutations and chromosomal exchanges do not occur. Please use the above strains as materials to design experiments to explore whether B/b is located on the X chromosome or on the homologous segments of X and Y. (Requirements: write down experimental ideas, expected experimental results, and draw conclusions)

Analysis: Use the orthogonal and inverse intersection methods when explicit and implicit are unknown.

Answer: Experimental idea: Let homozygous parents with a pair of opposite traits conduct reciprocal crosses to obtain F1 respectively. Observe and count the phenotypes and proportions of the reciprocal F1s.

Expect the results and draw the conclusion: If the phenotype and proportion of the reciprocal F1 are consistent, the alleles are located on the homologous segments of X and Y; if the phenotypes and proportions of the reciprocal F1 are inconsistent, the alleles Located on a non-homologous segment of the X chromosome.

Keywords: Free download of the PPT courseware for high school biology compulsory course 2 from the People's Education Edition, PPT download of the problem-solving method of sex-linked inheritance, PPT download of the relationship between genes and chromosomes, .PPT format;

For more information about the PPT courseware "The Relationship between Genes and Chromosomes, Problem-Solving Methods of Sex-Linked Inheritance", please click on the PPT tag of "The Relationship between Genes and Chromosomes, PPT Problem-Solving Methods of Sex-Linked Inheritance".

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Update Time: 2024-10-01

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