Biology 9 Lesson 28: Methods of studying human genetics
1. Theoretical Summary
1.1. Difficulties in studying human genetics
– Genetic phenomena in humans are similar to those in animals, such that offspring are similar to their parents, but also have different details from their parents. However, studying genetics in humans is more difficult, for two main reasons:
- People who reproduce late and have few children.
- For social reasons it is not possible to apply hybrid and mutagenic methods.
Therefore, in human genetic research, the commonly used methods are:
- Genealogical research.
- Study of twins.
1.2. Methods of studying human genetics
a. Genealogical research
A pedigree is a record of inheritance through the generations.
– Genealogical research method is a method of tracking the inheritance of a certain trait on people of the same family line through many generations to determine the genetic characteristics of that trait (that trait is dominant or not). recessive, determined by several pairs of genes, located on the same chromosome or on different chromosomes, genes located on autosomes or sex chromosomes…).
- Black skin, curly hair, thick lips are dominant traits
- White skin, straight hair, thin lips are recessive traits.
- Albinism, congenital deafness due to recessive gene mutations.
- Hemophilia, color blindness, and muscle atrophy are caused by recessive genes located on the X chromosome.
- In genealogical research, a number of symbols are often assigned to describe them.
b. Research on twins
– Twins are babies born at the same time.
– The most common twins are twins, which can be identical twins or fraternal twins.
- Identical twins are children of the same genotype and of the same sex.
- Fraternal twins are children of different genotypes, which may be of the same sex or sex.
– The meaning of studying twins:
- Helps determine the influence of the environment on traits, which traits are determined by genotype, which traits are most influenced by the environment. From there, appropriate nutrition and care regimens are proposed.
2. Illustrated exercise
Give the following pedigree:
+ Please determine the rate so that the children of husband and wife 2, 3 in the third generation are born without disease. Knowing that the gene for the trait is located on autosomes, the fourth person in the second generation is homozygous.
– Call the gene that determines the trait A, a (A>a).
+ Couples 1 and 2 in the 1st generation do not have the disease but have a child born with the disease, so this couple has a heterozygous genotype and the dominant gene is the normal gene (A), the recessive gene is the disease gene (a) .
+ The third person in the second generation is normal, so if there is genotype Aa, the ratio will be 2/3. The 4th person in the 2nd generation has genotype AA, so the 2nd person in the 3rd generation has the heterozygous genotype with the ratio of 2/3 x 1/2 = 1/3.
+ The children of the 5th, 6th generation in the second generation have people with the disease, so they have the heterozygous genotype, so the third person in the third generation has the heterozygous genotype with a ratio of 2/3.
- Thus, the ratio of children of husband and wife 2, 3 in the third generation born with the disease is 2/3 x 1/3 x 1/4 = 1/18.
- Thus, the ratio of children of husband and wife 2, 3 in the third generation born without disease is 1 – 1/18 = 17/18.
3.1. Essay exercises
Question 1: What is genealogical research? Why is that method used to study the inheritance of certain traits in humans?
Verse 2: What is the difference between identical and fraternal twins? What role does the method of studying twins play in the study of human genetics?
3.2. Multiple choice exercises
Question 1: Which of the following methods is not used to study human genetics:
A. Genealogical Research Methods
B. Cytological method
C. Analytical hybrid method
D. Methods of studying twins
Verse 2: Which of the following statements is true about identical twins?
A. Always the same gender
B. Always different in gender
C. Gender can be the same or different
D. Looks are always the same
Question 3: Given the pedigree of blood group traits in a family as follows:
Know that the blood group due to 3 alleles located on the chromosome is usually regulated as IA , IB , IO in which alleles IA and IB have equal degree of dominance and are completely dominant with allele IO. The percentage of people in the 3rd generation of the family with blood type O is:
Question 4: Co-birth is a phenomenon:
A. Two children are born in one birth of the mother
B. Many children are born in many births of the mother
C. Three children born in a single birth
D. Only one child is born in a mother’s birth
After completing this lesson, you should:
- Understand and apply genealogical research methods to analyze some traits or mutations in humans.
- Distinguish two cases: identical twins and fraternal twins.
- Understand the method and significance of the method of co-birth in genetic research, thereby explaining some common cases.