Teaching objectives
1. Let students know the basic knowledge of structure and substance related to heredity, that is, the relationship between chromosome, gene, genetic material (nucleic acid) and trait inheritance, and help students understand the material basis of genetic phenomena.
2. By analyzing the genetic phenomenon of a specific trait, help students understand the basic law of trait inheritance and guide students to analyze other genetic phenomena by using what they have learned.
3. In the process of distinguishing genetic diseases from other diseases, let students know the basic characteristics of genetic diseases and the biological reasons for prohibiting consanguineous marriage, and educate students about relevant legal knowledge.
Analysis of key points and difficulties
The concept of 1. gene and the concepts of dominant gene and recessive gene are the focus of this teaching, the difficulty of this section and the center of class discussion. Students have learned the name gene from various media and some popular science books, but they may not be able to clearly understand the nature of gene and the relationship between gene and traits. Therefore, in the teaching of this section, we can take the transmission of traits from the previous generation to the next generation as a clue to help students understand the basic knowledge about genes: the relationship between genes and chromosomes; The relationship between genes and biological traits, the transmission law of genes in organisms and the next generation, the relationship between dominant genes and recessive genes, and so on.
2. The relationship between the transmission law of the next generation chromosomes and gene transmission is also the focus and difficulty of this section. Understanding the activity of genes is helpful to understand the changes of chromosomes in somatic cells and germ cells, as well as in organisms and the next generation. In teaching, we can use charts and even make corresponding teaching AIDS to help students understand the law of chromosome activity.
The national marriage law stipulates that consanguineous marriage is prohibited. Why does the country pass legislation to prohibit consanguineous marriage? The focus of biology teaching should be to help students understand the genetic causes of the harm caused by consanguineous marriage-the cytological basis of genetic diseases and the reasons for the high probability of genetic diseases. We can use specific examples to understand the harm of consanguineous marriage.
Teaching process design
First, this topic suggests that the teaching hours should be 2 hours.
Second, the first class:
Preparation before class
At the end of the last class, a questionnaire was sent to the students to investigate some characteristics of their family members. The results of the survey are the materials discussed and analyzed by students in class. The questionnaire is as follows:
Before the investigation, teachers should pay attention to:
1. Students are required to fill in the form truthfully, and can't fill in it casually to complete their homework. Cultivate students' serious scientific attitude through this activity.
2. Explain to students how to identify these traits, especially the double eyelids and single eyelids in the upper eyelid features, and explain that they are not the characteristics after plastic surgery.
teaching process
Introduction After understanding the richness and diversity of the biological world, some students will ask some new questions: Will all kinds of creatures have the same laws in the process of survival and development? For example, how does each creature pass on its own characteristics to future generations? How did the first creatures occur and evolve? Can organisms live in isolation? What is the relationship between biology and environment? Wait a minute. We will discuss these questions in the future biology class and seek the answers to these questions.
The fifth part of the new lesson is the inheritance, evolution and ecology of biology.
Chapter I Inheritance and Variation of Organisms
Section 1 biological inheritance
1. Genetic phenomena:
The word "heredity" is no stranger to us. Students can find many genetic phenomena in daily observation, for example, as you sow, you reap; The son looks like his father, and so on. We know that different kinds of organisms have different morphological and physiological characteristics, and even different individuals of the same organism will be different in these aspects. These characteristics, that is, the morphological characteristics or physiological characteristics of organisms, are called traits.
After class, the students investigated some people's personalities. Through investigation, we have seen the continuation of these traits in the next generation. Is this continuity also a genetic phenomenon? Are these traits regular in the process of being passed down from generation to generation? Let's analyze these characteristics first.
Student activities
(1) Group discussion. Each group chooses a feature, and there are several ways to analyze the transmission of this feature from generation to generation. For example, a classmate's upper eyelids are double eyelids, and his parents are also double eyelids. This is a way of transmission. Is there any other way? You can analyze them according to the survey results of our group.
(2) class discussion. Each group introduces the results of group discussion, and there are several ways to convey the analyzed characteristics; Whether there are * * * similarities in various traits passed down from generation to generation; Summarize the results of discussion in the form of a list.
Trait characteristics
upper eyelid
Tongue (both sides rolled to the middle)
ear lobe
The thumb bends backwards.
Comparison between index finger and ring finger
I have the same characteristics as my parents.
I'm just like my father, not like my mother.
I am different from my father, just like my mother.
My personality is different from my parents'.
The same traits as parents, or one of them, is a phenomenon called heredity. Describe the concept of heredity in biological terms, which refers to the phenomenon that biological characters are passed on to future generations.
If the personality is different from that of parents, what is it called? Why do children have different characteristics from their parents? These issues will be discussed in the next section.
Heredity is a common phenomenon in biology. Students can meet anywhere around them. But how should we explain these phenomena? For example, why "as you sow, you reap"? How do organisms pass on traits to the next generation? Or how do organisms pass on traits to the next generation?
Question and discussion: Can parents directly pass on specific traits to their children? What did parents pass on to their children?
When we understand the process of human reproductive development, we already know that everyone is developed from a fertilized egg, and each fertilized egg is formed by the fusion of egg cells and sperm.
Judging from the process of reproductive development, the structure connecting parents and children is germ cells. Therefore, we can say that parents' traits are passed on to their offspring through germ cells-eggs and sperm. Similarly, various organisms pass on traits to their offspring through germ cells.
Question: Why can a small germ cell determine the traits of offspring?
We must study the internal structure of cells and the substances contained in them.
2. Chromosomes and genes:
(1) chromosome:
When scientists study cells, they find that there is a substance in the nucleus, which is easily dyed dark by alkaline dyes. Therefore, this substance is called chromosome. Scientists also found that the morphological structure and number of chromosomes in cells of various organisms are different. Each organism's chromosome has its own unique characteristics.
Show human chromosome and Drosophila (female) chromosome map: different organisms have different chromosome shapes.
Show the chromosome number of several organisms: different organisms have different chromosome numbers.
biology
chromosome number
body cell
germ cell
mankind
Article 46 (23 pairs)
Article 23
cattle
30 pieces (15 pairs)
Article 15
paddy field
Article 24 (12 pairs)
Article 12
corn
20 (10 pair)
Article 10
Question: What can be seen from the chromosome morphology and quantity of the above four organisms?
The morphological structure and number of chromosomes in cells of different species are different. The same species is relatively stable.
—— The chromosome number of somatic cells is twice that of germ cells, or the chromosome number of germ cells is 1/2 of somatic cells.
Further research on chromosomes in cells shows that every two chromosomes in somatic cells are always the same size and can be paired, so human somatic cells have 46 chromosomes, which are paired into 23 pairs, and maize somatic cells have 10 pairs.
Question and discussion: How do the chromosome numbers in somatic cells and germ cells change during reproductive development?
In this way, the number of chromosomes in children's somatic cells is the same as that of parents. For each pair of chromosomes in our somatic cells, one is from the father and the other is from the mother.
Question: Why do people pay so much attention to chromosome changes?
This is because the change of chromosome number law is closely related to the inheritance of organisms.
We know that biological genetic material exists in the nucleus, and in the nucleus, genetic material mainly exists in chromosomes. Each pair of chromosomes in a fertilized egg, one from the father and the other from the mother, has parents' chromosomes or parents' genetic material in the cells of the child developed from the fertilized egg. This is how the genetic material of parents is passed on to their children.
The genetic material in chromosomes is called nucleic acid. The DNA that students hear and see in radio, TV and newspapers is a kind of nucleic acid.
Question: Every living thing has many characteristics. How do genetic materials on chromosomes control these different traits?
(2) Gene:
The term "gene" is no stranger to students. But what is this? What does it have to do with biological characteristics?
Scientific research has found that different traits of organisms are determined by different genes. The gene we often say refers to the genetic material located on the chromosome and divided into several small units. These small units of genetic material that determine biological characteristics are called genes. For example, peas have red and white flowers, tall and short stems, and people's upper eyelids have double eyelids and single eyelids. Are determined by different genes.
Genes are small fragments of genetic material on chromosomes, so genes, like chromosomes, exist in pairs in somatic cells, with only one in germ cells.
Can we understand it as two genes in each pair of genes in our somatic cells, one from the father and the other from the mother?
In this lesson, we discussed and analyzed what is heredity, and learned that the inheritance of biological traits is passed on to future generations through germ cells, and the genetic material located on chromosomes ultimately determines the inheritance of traits. Specific to a certain trait, heredity is determined by genes. Different genes have different characteristics. After understanding this knowledge, some students will ask new questions. How do these genes determine traits? They are also a pair of genes. Why do some people have double eyelids and some people have single eyelids?
Why do children have different characteristics from their parents? We will discuss these problems in the next class.
Brief design of blackboard writing
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Third, the second category:
check against the authoritative text
(1) What is a trait? What is heredity? Please give an example. What is a chromosome? What is a gene?
(2) What is the genetic mode of biological traits? How does the number of chromosomes change in this process? How do genes change?
(3) Why do we say that half of the genetic material in our somatic cells comes from our father and half from our mother?
After introducing the last lesson, we studied chromosomes and genes, and we also raised several similar questions.
(1) How do a pair of genes determine traits?
(2) They are the same gene. Why do some people have double eyelids and some people have single eyelids?
(3) Why do children have different characteristics from their parents?
New lesson] Take the upper eyelid as an example to study the above problems.
Some biological traits are controlled by a pair of genes, such as human eyelids and earlobes.
Question discussion: A or A is the gene that controls the characteristics of the upper eyelid. How many ways will these two genes combine in the human body to determine what characteristics respectively? Students can discuss and put forward their own assumptions.
There may be three ways to combine A and A: aa, Aa, AA.
Question and discussion: If the trait aa decides is double eyelids, what trait AA decides? So what qualities will Aa determine?
Some students will ask why aa doesn't decide on double eyelids. In the process of studying this problem, it is found that the paired base countries in cells are obviously recessive, that is, dominant genes and recessive genes
3. Dominant and recessive genes:
Double eyelids are determined by dominant genes, expressed in capital letters, and the gene in cells is AA;
Single eyelid is determined by recessive gene, expressed in lowercase letters, and the intracellular gene is aa.
So if the gene is Aa, there are both dominant and recessive genes, what characteristics will it show?
When the gene is Aa, it cannot express recessive gene A, but only the traits determined by dominant gene A, so Aa is also a double eyelid.
Question discussion: Last class, when we analyzed the genetic patterns of several human traits, we took the characteristics of the eyelids as an example and summarized the following situations:
Slide show: (1) double eyelids for mom and dad, double eyelids for children;
(2) Mom and Dad have single eyelids, and children have single eyelids;
(3) Mom and Dad have double eyelids, and children have single eyelids;
(4) father's double eyelids, mother's single eyelids and children's double eyelids;
(5) Dad's double eyelids. Mother has a single eyelid, and the child has a single eyelid;
(6) father's single eyelid, mother's double eyelid and children's double eyelid;
(7) father's single eyelid, mother's double eyelid, and child's single eyelid.
Please use the knowledge of dominant and recessive genes to explain the above reasons.
Students can easily understand (1) and (2). Children inherit the characteristics of their parents, which is heredity. (4), (5), (6), (7) In some cases, it is acceptable for students that children inherit the characteristics of one parent. So, why is there a third situation? Did you make a mistake in the investigation? Is it possible that children and parents have different upper eyelids?
Question: Parents are two-faced. What happens to pairs of genes in somatic cells?
(1) Will the father's gene AA and the mother's gene AA give birth to offspring with single eyelids?
(2) Will the father's gene Aa, the mother's gene Aa, or the father's gene AA and the mother's gene AA give birth to offspring with single eyelids?
(3) If the father's gene Aa and the mother's gene Aa give birth to offspring with single eyelids? How did this offspring come into being?
Slide: textbook p. 133 Figure V-3.
Ask a question: Ask the students to think, will there be such a situation that both parents have single eyelids and give birth to a child with double eyelids? Explain the possible or impossible reasons.
Leave a small assignment for students to analyze the situations shown in slides (1), (2), (4) and (5) according to the above knowledge.
4. Genetic diseases and prohibition of consanguineous marriage:
It is a stipulation in China's marriage law to prohibit consanguineous marriage. Why are genetic diseases related to the provisions of the marriage law? We must first understand what genetic diseases are.
Please look at the picture below the textbook p. 1 133. This is a congenital idiot. The main characteristics of this kind of patients are congenital mental retardation, developmental retardation, sitting, lying and walking late, only monosyllabic words such as "father" and "mother", and some patients lack abstract thinking ability. This disease is congenital, but the parents of children with this disease may be normal. So, what is the cause of the patient's illness? Through research, it is found that the genetic material in the germ cells produced by the parents of patients has changed, so that patients are born with this disease, which is what we call genetic disease.
(1) Hereditary diseases: diseases caused by changes in genetic material belong to hereditary diseases.
Genetic diseases are caused by changes in genetic material and are not contagious. At present, there are more than 4,000 known human genetic diseases, such as albinism, color blindness and hemophilia. Some of these genetic diseases directly affect the normal life of patients and even lead to death.
In the past, hereditary diseases were generally incurable. With the development of science and technology, scientists try to restore the changed genetic material to normal activities to treat some genetic diseases. But at present, most genetic diseases are still incurable.
Ask a question: Genetic diseases are neither contagious nor curable. Can we ignore them and let them happen?
We can't treat it, but we can take some measures to reduce the occurrence of genetic diseases. Patients with these diseases bring mental and economic burdens to their families and have a certain impact on society. In order to improve the quality of the whole nation, we should try our best to reduce the occurrence of genetic diseases. How to reduce the occurrence of genetic diseases?
(2) Prohibition of consanguineous marriage:
According to statistics, the probability of children born after marriage suffering from genetic diseases is higher than that of children who are not closely related, such as cousins and cousins. For example, albinism, the possibility of children born by close relatives is 13.5 times that of children born by non-close relatives; In color blindness, the likelihood of children who are married by close relatives is 17.9 times that of children who are not married by close relatives. There is a mountain village somewhere in our country. Because there are many close relatives who get married and there are many fools, it is called "Fool Village".
Some students will ask, why do close relatives get married, and the chances of offspring suffering from genetic diseases will increase? We know that people who carry pathogenic genes may not necessarily show genetic diseases, such as diseases caused by recessive genes, but this gene may be passed on to the next generation. The blood relationship is far away, and the possibility of having the same pathogenic gene is relatively small. When close relatives get married, their genes are similar, and children born after marriage are more likely to get genetic diseases.
In order to improve the quality of the whole nation and reduce the harm of genetic diseases to families. Personal pain, China's marriage law clearly stipulates that consanguineous marriage is prohibited. It is illegal and not allowed for cousins to marry.
Summing up this lesson, we have a preliminary understanding of how genes determine specific biological traits, which can help us explain some genetic phenomena. We also have a preliminary understanding of the reasons and significance of why the state prohibits consanguineous marriage.
The inheritance of biological characters is very complicated and interesting. We have just learned the most basic knowledge here. We will continue to learn this knowledge in high school. If students are interested, they can read some related books or ask teachers or related personnel for advice.
Brief design of blackboard writing
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Small data
1. Determination of human chromosome number;
Humans have known chromosomes for more than 100 years. 1882, when the German cytologist W. Fleming was studying cell division, he found that there was a substance in the nucleus that was easily stained by alkaline dyes, and called it chromatin. 1888, German anatomist w. Waldeyer called it chromatin chromosome. Since then, people's research reports on chromosomes have been put forward, and people know the number of chromosomes in many biological cells. So, what is the number of human chromosomes? More than 30 years ago, geneticists have been unclear. Some geneticists believe that, like gorillas and chimpanzees, the number of human chromosomes is 48. 1952, Dr. Tao Chiuh Hsu, a Chinese American working in the University of Texas, stumbled upon the number of human chromosomes. One day, he observed cells in routine tissue culture and unexpectedly found well-distributed chromosomes under the microscope. The number of chromosomes is 46, not 48. Later, it took Dr. Tao Chiuh Hsu three months to find the reason for this "miracle". I don't know which experimenter in the laboratory mistook the equilibrium solution of cleaning cultured cells for hypotonic solution, and the cell membrane is easy to break in hypotonic solution, so the chromosome escapes and spreads well, which is clearly identifiable. Unfortunately, although Dr. Tao Chiuh Hsu discovered 46 human chromosomes instead of 48, he didn't stick to his discovery for various reasons. 1956, a famous China scholar and his colleagues proved that human beings have 46 chromosomes through experiments, and published the experimental results. For this reason, he won the Kennedy International Award in Friendship Star.
2. Chromosome number of common organisms:
biology
chromosome number
biology
chromosome number
biology
chromosome number
mankind
Article 46
donkey
Article 62
paddy field
Article 24
Ascaris equina
the second
mule
Article 63
Common wheat
Article 42
fruit fly
Eight articles
sheep
Article 54
barley
Article 14
domestic chicken
Article 78
goat
Article 60
pea
Article 14
dog
Article 78
pig
Article 38
corn
Article 20
cattle
Article 30
macaque
Article 42
Chinese cabbage
Article 18
horse
Article 64
gorilla
Article 48
gingkgo
Article 24
3. Genetic modes of common genetic diseases:
Monogenic inheritance: autosomal dominant inheritance: syndactyly and polydactyly;
Autosomal recessive inheritance: albinism, acquired deafness
X-linked recessive inheritance: hemophilia, red-green color blindness;
X-linked dominant inheritance: anti-vitamin D rickets;
Y-linked inheritance: hirsutism of external auditory canal;
Polygenic inheritance: cleft lip, congenital pyloric stenosis, congenital deformed foot, spina bifida, anencephaly;
Chromosome disease: abnormal chromosome number: congenital stupid disease;
Chromosome structural aberration: meow syndrome.
4. Incidence of consanguineous marriage and non-consanguineous marriage of recessive genetic diseases:
Disease name
Incidence of recessive genetic diseases
The incidence of consanguineous marriage is several times that of non-consanguineous marriage.
Among patients with this disease, 90% will get married by close relatives.
Non-blood marriage
Cousin marriage
Phenylacetonuria
1: 14 500
1: 1 700
8.5
35
Pigmented dry skin
1:23 000
1:2 200
10.5
40
albinism
1:40 000
1:3 000
13.5
46
achromatopsia
1:73 000
1:4 100
17.5
53
microcephaly
1:77 000
1:4 200
18.5
54
amaurotic idiocy
1:3 10 000
1:8 600
35.5
70
Congenital tinea scale
1: 1 000 000
1: 16 000
63.5
80