Chromosomes are located in the nucleus of the cell and are the main components of the nucleus.
The chemical composition of chromosomes is 50% DNA and 50% protein.
The function of chromosomes is to store hereditary information.
The chromosome can be single (from one chromatids) and double (of two chromatids). Centromere(primary constriction) is the junction of two chromatids.
- A single chromosome turns into a double chromosome during the process of DNA doubling (replication, reduplication) in interphase.
- A double chromosome turns into two single chromosomes (chromatids become daughter chromosomes) after the division of the centromere connecting them (in anaphase of mitosis and anaphase II of meiosis).
Sets of chromosomes
The set of chromosomes can be:
- single (haploid, n), in humans 23
- double (diploid, 2n), in humans 46
- triple (triploid, 3n)
- quadruple (tetraploid, 4n), etc.
The haploid set is characteristic of gametes (sex cells, sperm and eggs), as well as spores. The diploid set is characteristic of somatic cells (body cells).
- The haploid set turns into diploid during fertilization (two haploid gametes merge, resulting in a diploid zygote).
- The diploid set turns into haploid in the first division (independent divergence of homologous chromosomes occurs, the number of chromosomes is halved).
A triploid set of chromosomes is characteristic of the endosperm of seeds of flowering plants. During double fertilization the following merge:
- haploid sperm and egg; a diploid zygote is obtained, from which an embryo is formed;
- haploid sperm and diploid central cell of the embryo sac; a triploid endosperm is obtained.
Solving problems on the number of chromosomes:
1) You need to understand where given number of chromosomes:
- if in a gamete, then the number given in the problem is n
- if in a somatic cell, then 2n
- if in endosperm, then 3n
2) Math once, calculate n
- if 2n=24 then n=24/2=12
- if 3n=24 then n=24/3=8
3) Mathematics two: if n=24, then
- the gamete will have n=24
- in a somatic cell there will be 2n=2x24=48
- in the endosperm there will be 3n=3x24=72
You can also try to understand
37 tests on the topic
Choose one, the most correct option. Daughter chromatids become chromosomes after
1) separation of the centromere connecting them
2) alignment of chromosomes in the equatorial plane of the cell
3) exchange of sections between homologous chromosomes
4) pairing of homologous chromatids
Answer
Choose one, the most correct option. What set of chromosomes will the cells have after the first meiotic division if the mother cell contained 12 chromosomes?
1) 6
2) 12
3) 3
4) 24
Answer
Choose one, the most correct option. Tetraploid organism produces gametes
1) haploid
2) diploid
3) triploid
4) tetraploid
Answer
Choose one, the most correct option. Consists of one nucleic acid molecule combined with proteins
1) chloroplast
2) chromosome
3) gene
4) mitochondria
Answer
Choose one, the most correct option. Storage tissue (endosperm) in flowering plants has a set of chromosomes
1)n
2) 2n
3) Zn
4) 4n
Answer
Choose one, the most correct option. Restoration of the diploid set of chromosomes in the zygote occurs as a result
1) meiosis
2) mitosis
3) fertilization
4) conjugation
Answer
All but two of the features listed below are used to describe the cellular structure shown in the figure. Identify two characteristics that “drop out” from the general list and write down the numbers under which they are indicated.
1) always have the shape of the letter “X”
2) consist of DNA and proteins
3) when divided, they are compact and clearly visible under a microscope
4) duplication occurs in interphase
5) during division they are in the nucleus
Answer
1. Establish a correspondence between eukaryotic cells and the sets of chromosomes in them: 1) haploid, 2) diploid. Write numbers 1 and 2 in the order corresponding to the letters.
A) moss spore
B) pine sperm
B) frog leukocyte
D) human neuron
D) horsetail zygote
E) bee egg
Answer
2. Establish a correspondence between examples of cells and their sets of chromosomes: 1) haploid, 2) diploid. Write numbers 1 and 2 in the order corresponding to the letters.
A) horsetail spores
B) fern prothallus cells
B) sperm of angiosperms
D) lancelet blastomeres
D) moss sporophyte cells
E) endoderm cells of the gastrula hydra
Answer
SOMATIC - ENDOSPERM
1. There are 34 chromosomes in the karyotype of an apple tree. How many chromosomes will be contained in the endosperm cells of her seed? In your answer, write down only the corresponding number.
Answer
2. The diploid set of corn is 20 chromosomes. What set of chromosomes do corn endosperm cells have? Write down only the number of chromosomes in your answer.
Answer
3. There are 14 chromosomes in the cells of a rye leaf. What set of chromosomes does a rye endosperm cell have? Write down only the number of chromosomes in your answer.
Answer
4. There are 16 chromosomes in an onion leaf cell. What set of chromosomes do onion seed endosperm cells have? Write down only the number of chromosomes in your answer.
Answer
ENDOSPERM - SOMATIC
1. The endosperm cell of a cherry contains 24 chromosomes. What set of chromosomes does a cell of its leaf have? Write down only the number of chromosomes in your answer.
Answer
2. There are 36 chromosomes in the endosperm cells of a lily seed. What set of chromosomes does a lily leaf cell have? Write down only the number of chromosomes in your answer.
Answer
GAMETE - ENDOSPERM
1. The sperm of a flowering plant contains 10 chromosomes. How many chromosomes do the endosperm cells of this plant contain? Write down only the number of chromosomes in your answer.
Answer
2. How many chromosomes does the endosperm cell of a flowering plant seed contain, if the sperm of this plant has 7 chromosomes? Write down only the corresponding number in your answer.
Answer
ENDOSPERM - GAMETE
There are 30 chromosomes in the endosperm cell of a corn seed. What set of chromosomes does a corn egg have? In your answer, write down only the number of chromosomes.
Answer
GAMETE - SOMATIC (PLANTS)
1. The set of chromosomes of corn sperm is 10. What set of chromosomes do the somatic cells of this organism have? Write down only the number of chromosomes in your answer.
Answer
2. How many chromosomes are there in the cells of a cucumber leaf if there are 7 chromosomes in the cucumber sperm? In your answer, write down only the corresponding number.
Answer
GAMETE - SOMATIC (ANIMALS)
1. There are 19 chromosomes in the egg of a domestic cat, how many chromosomes are there in its brain cell? In your answer, write down only the number of chromosomes.
Answer
2. A fish sperm contains 28 chromosomes. What set of chromosomes does a fish somatic cell have? Write down only the number of chromosomes in your answer.
Answer
3. The set of chromosomes of the pea egg is 7. What set of chromosomes do the somatic cells of this organism have? Write down only the number of chromosomes in your answer.
Answer
4. The set of chromosomes of potato germ cells is 24. What set of chromosomes do the somatic cells of this organism have? Write down only the number of chromosomes in your answer.
Answer
5. There are 48 chromosomes in a hedgehog egg. What set of chromosomes does a hedgehog skin cell have? Write down only the number of chromosomes in your answer.
Answer
6. How many chromosomes does a somatic animal cell have if the gametes contain 38 chromosomes? Write down only the corresponding number in your answer.
Answer
SOMATIC - GAMETE (PLANTS)
1. The somatic cell of wheat contains 28 chromosomes. What set of chromosomes does her sperm have? Write down only the number of chromosomes in your answer.
Answer
2. There are 14 chromosomes in the somatic cells of barley. How many chromosomes are there in barley sperm? In your answer, write down only the number of chromosomes.
Answer
3. How many chromosomes does the gooseberry sperm nucleus have if the leaf cell nucleus contains 16 chromosomes. In your answer, write down only the corresponding number.
Answer
SOMATIC - GAMETE (ANIMALS)
1. There are 38 chromosomes in a cat’s somatic cell. What set of chromosomes does the egg of this organism have? Write down only the number of chromosomes in your answer.
Answer
2. There are 34 chromosomes in a fox somatic cell. What set of chromosomes does the sperm of this organism have? Write down only the number of chromosomes in your answer.
Answer
3. There are 56 chromosomes in a somatic cell of a fish’s body. What set of chromosomes does a fish sperm have? Write down only the number of chromosomes in your answer.
Answer
4. There are 78 chromosomes in a wolf somatic cell. What set of chromosomes do the sex cells of this organism have? Write down only the number of chromosomes in your answer.
Answer
5. The number of chromosomes in the somatic cells of a pigeon is 80. How many chromosomes are in the reproductive cells of a female pigeon? Write your answer as a number.
Answer
SOMATIC - SOMATIC
There are 14 chromosomes in the strawberry stem cells. What set of chromosomes does a strawberry embryo cell have? Write down only the number of chromosomes in your answer.
Answer
SOMATIC - ZYGOTE
1. The diploid set of cockroaches is 48 chromosomes. What set of chromosomes does a cockroach zygote have? Write down only the number of chromosomes in your answer.
Answer
2. There are 20 chromosomes in the nuclei of cells in the intestinal mucosa of a vertebrate animal. What number of chromosomes will the zygote nucleus of this animal have? In your answer, write down only the corresponding number.
Answer
3. The nucleus of a somatic cell of the human body normally contains 46 chromosomes. How many chromosomes are there in a fertilized egg? In your answer, write down only the corresponding number.
Answer
ZYGOTE - SOMATIC
1. How many chromosomes are contained in the nucleus of a skin cell if the nucleus of a fertilized human egg contains 46 chromosomes? In your answer, write down only the corresponding number.
Answer
The mass of all DNA molecules in the 46 chromosomes of one human somatic cell is about 6x10 -9 mg. What is the mass of all DNA molecules in a sperm? In your answer, write down only the corresponding number without x10 -9.
2. How many polynucleotide chains will each chromosome contain at the end of interphase? Write down only the number in your answer.
Answer
© D.V. Pozdnyakov, 2009-2019
An increase in the number of stressful situations and the presence of various additives, including genetically modified ones, in food lead to an increase in hereditary diseases. However, before studying what causes and what a violation of an individual’s genome leads to, it is necessary to know how many chromosomes a “normal” person has, that is, a person who has a full set of chromosomes.
The basis of any chromosomal structure is made up of deoxyribonucleic acid (DNA) and proteins, the latter accounting for up to 65% of the mass of the chromosome itself. The DNA double helix is “wound” around a protein base and is the main carrier of hereditary information. The deoxyribonucleic acid molecule consists of separate sections - genes that are responsible for certain characteristics of the body. It is thanks to her that the characteristics of the parents are transmitted to the offspring. However, a child almost equally inherits from his parents traits determined by genes: eye and hair color, hereditary diseases, the number of fingers and toes, and other characteristic features. Which genes the embryo will take from the mother and which from the father is determined when the fetus is conceived.
How many chromosomes does a healthy person have?
Chromosomes were discovered by the German cytogeneticist Walther Flemming in 1882, and they received their name, meaning “colored” body, from the German anatomist and histologist Heinrich Waldeyer six years later. Today it has been established that the karyotype (chromosomal set) of a healthy person consists of 46 chromosomes. If we translate this total number into pairs (as is customary in cytology), then the characteristic of the human genome, determined by the sign - how many chromosomes a healthy person has, the following - 22 pairs are called autosomes and are present in the body of healthy men and women, and another pair determines gender human and is characteristic of only one sex.
There are other characteristics of the human karyotype. If the chromosomes in a pair have the same characteristics and are separated, they belong to the diploid chromosome set. The sex chromosomes make up a haploid set, which unites (merges) when the sperm penetrates the egg and subsequent conception of the fetus.
Any violation of the karyotype leads to the occurrence of genetic diseases, many of which are transmitted hereditarily. The most well-known genetic diseases are Down syndrome and Patau syndrome.
How many chromosomes does a person with Down syndrome have?
Down syndrome was first identified as an independent disease of unknown etiology in 1966 by the English physician John Down, who called this disease “Mongolism.” The genetic cause of this disease was determined by the French geneticist, pediatrician Jérôme Lejeune in 1959, and he also determined how many chromosomes a person with Down syndrome has.
The genetic essence of the disease is as follows. When a fetus is conceived, a third, unpaired chromosome is added to one of the chromosome pairs (usually the twenty-first). As a result, the karyotype of a person with Down syndrome contains 47 chromosomes.
The main symptom of Down syndrome is the mental retardation of the individual. In this case, patients have pronounced external symptoms:
- increased tongue size;
- irregularly shaped, enlarged ears;
- the presence of skin folds on the eyelids;
- widened bridge of the nose;
- the presence of whitish spots on the eyeball.
Men experience reproductive dysfunction of varying severity; women are able to become pregnant.
Most people suffering from this disease do not live past the age of forty. They have problems with the gastrointestinal tract and are prone to dysfunction of the cardiovascular system.
Chromosome is a thread-like structure containing DNA in the cell nucleus, which carries genes, units of heredity, arranged in a linear order. Humans have 22 pairs of regular chromosomes and one pair of sex chromosomes. In addition to genes, chromosomes also contain regulatory elements and nucleotide sequences. They house DNA-binding proteins that control DNA functions. Interestingly, the word chromosome comes from the Greek word chrome, meaning color. Chromosomes received this name due to the fact that they have the peculiarity of being colored in different tones. The structure and nature of chromosomes vary from organism to organism. Human chromosomes have always been a subject of constant interest to researchers working in the field of genetics. The wide range of factors that are determined by human chromosomes, the abnormalities for which they are responsible, and their complex nature have always attracted the attention of many scientists.
Interesting facts about human chromosomes
Human cells contain 23 pairs of nuclear chromosomes. Chromosomes are made up of DNA molecules that contain genes. The chromosomal DNA molecule contains three nucleotide sequences required for replication. When chromosomes are stained, the banded structure of mitotic chromosomes becomes apparent. Each strip contains numerous DNA nucleotide pairs.
Humans are a sexually reproducing species with diploid somatic cells containing two sets of chromosomes. One set is inherited from the mother, while the other is inherited from the father. Reproductive cells, unlike body cells, have one set of chromosomes. Crossing over between chromosomes leads to the creation of new chromosomes. New chromosomes are not inherited from either parent. This accounts for the fact that not all of us exhibit traits that we receive directly from one of our parents.
Autosomal chromosomes are assigned numbers from 1 to 22 in descending order as their size decreases. Each person has two sets of 22 chromosomes, an X chromosome from the mother and an X or Y chromosome from the father.
An abnormality in the contents of a cell's chromosomes can cause certain genetic disorders in people. Chromosomal abnormalities in people are often responsible for the development of genetic diseases in their children. Those who have chromosomal abnormalities are often only carriers of the disease, while their children develop the disease.
Chromosomal aberrations (structural changes in chromosomes) are caused by various factors, namely deletion or duplication of part of a chromosome, inversion, which is a change in the direction of a chromosome to the opposite, or translocation, in which part of a chromosome is torn off and attached to another chromosome.
An extra copy of chromosome 21 is responsible for a very well known genetic disorder called Down syndrome.
Trisomy 18 results in Edwards syndrome, which can cause death in infancy.
Deletion of part of chromosome five results in a genetic disorder known as Cri-Cat Syndrome. People affected by this disease often have mental retardation and their crying in childhood resembles that of a cat.
Disorders caused by sex chromosome abnormalities include Turner syndrome, in which female sexual characteristics are present but characterized by underdevelopment, as well as XXX syndrome in girls and XXY syndrome in boys, which cause dyslexia in affected individuals.
Chromosomes were first discovered in plant cells. Van Beneden's monograph on fertilized roundworm eggs led to further research. August Weissman later showed that the germ line was distinct from the soma and discovered that cell nuclei contained hereditary material. He also suggested that fertilization leads to the formation of a new combination of chromosomes.
These discoveries became cornerstones in the field of genetics. Researchers have already accumulated a significant amount of knowledge about human chromosomes and genes, but much remains to be discovered.
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Chromosomes are intensely colored bodies consisting of a DNA molecule bound to histone proteins. Chromosomes are formed from chromatin at the beginning of cell division (in the prophase of mitosis), but they are best studied in the metaphase of mitosis. When chromosomes are located in the equatorial plane and are clearly visible under a light microscope, the DNA in them reaches maximum spiralization.
Chromosomes consist of 2 sister chromatids (duplicated DNA molecules) connected to each other in the region of the primary constriction - the centromere. The centromere divides the chromosome into 2 arms. Depending on the location of the centromere, chromosomes are divided into:
metacentric centromere is located in the middle of the chromosome and its arms are equal;
submetacentric centromere is displaced from the middle of the chromosomes and one arm is shorter than the other;
acrocentric - the centromere is located close to the end of the chromosome and one arm is much shorter than the other.
Some chromosomes have secondary constrictions that separate a region called a satellite from the chromosome arm, from which the nucleolus is formed in the interphase nucleus.
Chromosome rules
1. Constancy of number. Somatic cells of the body of each species have a strictly defined number of chromosomes (in humans - 46, in cats - 38, in Drosophila flies - 8, in dogs - 78, in chickens - 78).
2. Pairing. Each chromosome in somatic cells with a diploid set has the same homologous (identical) chromosome, identical in size and shape, but different in origin: one from the father, the other from the mother.
3. Individuality. Each pair of chromosomes differs from the other pair in size, shape, alternating light and dark stripes.
4. Continuity. Before cell division, the DNA doubles, resulting in 2 sister chromatids. After division, one chromatid at a time enters the daughter cells and, thus, the chromosomes are continuous - a chromosome is formed from a chromosome.
All chromosomes are divided into autosomes and sex chromosomes. Autosomes are all chromosomes in cells, with the exception of sex chromosomes, there are 22 pairs of them. Sexual chromosomes are the 23rd pair of chromosomes, which determine the formation of male and female organisms.
Somatic cells have a double (diploid) set of chromosomes, while sex cells have a haploid (single) set.
A certain set of cell chromosomes, characterized by the constancy of their number, size and shape, is called karyotype.
In order to understand the complex set of chromosomes, they are arranged in pairs as their size decreases, taking into account the position of the centromere and the presence of secondary constrictions. Such a systematic karyotype is called an idiogram.
For the first time, such a systematization of chromosomes was proposed at the Congress of Genetics in Denver (USA, 1960)
In 1971, in Paris, chromosomes were classified according to color and alternation of dark and light stripes of hetero- and euchromatin.
To study the karyotype, geneticists use the method of cytogenetic analysis, which can diagnose a number of hereditary diseases associated with disturbances in the number and shape of chromosomes.
1.2. Life cycle of a cell.
The life of a cell from the moment it arises as a result of division until its own division or death is called the life cycle of the cell. Throughout life, cells grow, differentiate and perform specific functions.
The life of a cell between divisions is called interphase. Interphase consists of 3 periods: presynthetic, synthetic and postsynthetic.
The presynthesis period immediately follows division. At this time, the cell grows intensively, increasing the number of mitochondria and ribosomes.
During the synthetic period, replication (doubling) of the amount of DNA occurs, as well as the synthesis of RNA and proteins.
During the post-synthesis period, the cell stores energy, spindle achromatin proteins are synthesized, and preparations for mitosis are underway.
There are different types of cell division: amitosis, mitosis, meiosis.
Amitosis is the direct division of prokaryotic cells and some cells in humans.
Mitosis is an indirect cell division during which chromosomes are formed from chromatin. Somatic cells of eukaryotic organisms divide through mitosis, as a result of which the daughter cells receive exactly the same set of chromosomes as the daughter cell had.
Mitosis
Mitosis consists of 4 phases:
Prophase is the initial phase of mitosis. At this time, DNA spiralization begins and chromosomes shorten, which from thin, invisible chromatin strands become short, thick, visible in a light microscope, and are arranged in the form of a ball. The nucleolus and nuclear membrane disappear, and the nucleus disintegrates, the centrioles of the cell center diverge to the poles of the cell, and the filaments of the spindle stretch between them.
Metaphase - chromosomes move towards the center, spindle threads are attached to them. Chromosomes are located in the equatorial plane. They are clearly visible under a microscope and each chromosome consists of 2 chromatids. During this phase, the number of chromosomes in the cell can be counted.
Anaphase - sister chromatids (appearing in the synthetic period during DNA doubling) move towards the poles.
Telophase (telos in Greek - end) is the opposite of prophase: chromosomes change from short thick visible to thin to long invisible in a light microscope, the nuclear membrane and nucleolus are formed. Telophase ends with the division of the cytoplasm to form two daughter cells.
The biological significance of mitosis is as follows:
daughter cells receive exactly the same set of chromosomes that the mother cell had, therefore a constant number of chromosomes is maintained in all cells of the body (somatic).
All cells, except sex cells, divide:
the body grows in the embryonic and postembryonic periods;
all functionally obsolete cells of the body (epithelial cells of the skin, blood cells, cells of the mucous membranes, etc.) are replaced by new ones;
processes of regeneration (restoration) of lost tissues occur.
Mitosis diagram
When a dividing cell is exposed to unfavorable conditions, the spindle of division can unevenly stretch the chromosomes to the poles, and then new cells with a different set of chromosomes are formed, and pathology of somatic cells occurs (heteroploidy of autosomes), which leads to disease of tissues, organs, and the body.
