Organisms in cells that do not have a nucleus are called. Prokaryotes - organisms whose cells do not have a nucleus

Eukaryotes are the most advanced organisms. In our article we will consider which of the representatives of living nature belongs to this group and what features of the organization allowed them to take a dominant position in the organic world.

Who are eukaryotes

According to the definition of the concept, eukaryotes are organisms whose cells contain a formed nucleus. These include the following kingdoms: Plants, Animals, Mushrooms. And it doesn't matter how complex their body is. Microscopic amoeba, volvox colonies, they are all eukaryotes.

Although the cells of real tissues can sometimes be devoid of a nucleus. For example, it is not found in erythrocytes. Instead, this blood cell contains hemoglobin, which carries oxygen and carbon dioxide. Such cells contain a nucleus only in the first stages of their development. Then this organelle is destroyed, and with this the ability of the entire structure to divide is lost. Therefore, having fulfilled their functions, these cells die.

The structure of eukaryotes

All eukaryotes have a nucleus in their cells. And sometimes not even one. This two-membrane organelle contains genetic information encoded in the form of DNA molecules in its matrix. The core consists of the surface apparatus, which provides the transport of substances, and the matrix, its internal environment. The main function of this structure is the storage of hereditary information and its transfer to daughter cells formed as a result of division.

The internal environment of the kernel is represented by several components. First of all, this is karyoplasm. It contains nucleoli and chromatin filaments. The latter are composed of proteins and nucleic acids... It is during their spiralization that chromosomes are formed. They are directly carriers genetic information... Eukaryotes are organisms in which, in some cases, nuclei of two types can form: vegetative and generative. A striking example this is an infusorium. Its generative nuclei carry out the preservation and transmission of the genotype, and the vegetative ones regulate

The main differences between pro and eukaryotes

Prokaryotes do not have a formed nucleus. This group of organisms includes the only one - Bacteria. But such a structural feature does not mean at all that there are no carriers of genetic information in the cells of these organisms. Bacteria contain circular DNA molecules - plasmids. However, they are located in the form of clusters in a certain place of the cytoplasm and do not have a common membrane. This structure is called a nucleoid. There is one more difference. DNA in prokaryotic cells is not bound to nuclear proteins. Scientists have established the existence of plasmids in eukaryotic cells. They are found in some semi-autonomous organelles, for example, in plastids and mitochondria.

Progressive features of the structure

Eukaryotes include organisms that are distinguished by more complex structural features at all levels of organization. First of all, this concerns the breeding method. provides the simplest of them - in two. Eukaryotes are organisms that are capable of all types of reproduction of their own kind: sexual and asexual, parthenogenesis, conjugation. This ensures the exchange of genetic information, the emergence and consolidation of a number of useful traits in the genotype, and hence the better adaptation of organisms to constantly changing conditions. environment... This feature allowed eukaryotes to occupy a dominant position in

So, eukaryotes are organisms in whose cells there is a formed nucleus. These include plants, animals, and fungi. The presence of a nucleus is a progressive structural feature that provides high level development and adaptation.

2731. Indicate one of the provisions of the cell theory
A) The unit of structure, life and development of organisms is the cell
B) The reproductive cell contains one allele of each gene
C) A multicellular embryo is formed from the zygote
D) In \u200b\u200bthe nuclei of eukaryotic cells, genes are linearly located in chromosomes

Abstract

2732. How many autosomes are contained in a human sperm?
A) 22
B) 2
B) 23
D) 4

Abstract

2733. Organisms, whose cells have a separate nucleus, are
A) eukaryotes
B) bacteria
C) prokaryotes
D) viruses

Abstract

2734. Parthenogenesis is a kind of sexual reproduction, in which a new organism develops from
A) diploid zygote
B) the first blastomeres
C) haploid spores
D) an unfertilized egg

Abstract

2735. The skin of tomato fruit may be smooth and pubescent (a). Please select
genotypes of parent plants with dominant phenotypes.
A) Aa, aa
B) Aa, Aa
B) A, a
D) AA, aa

Abstract

2736. Inheritance of the hemophilia gene located on the X chromosome in humans is an example
A) manifestation of the result of crossing over
B) sex-linked inheritance
C) independent inheritance of traits
D) intermediate inheritance of traits

2737. The appearance of different alleles of one gene occurs as a result
A) indirect cell division
B) modification variability
C) mutation process
D) combinative variability

2738. Why are bacteria isolated into an independent kingdom of the organic world?
A) under unfavorable conditions they multiply by mitosis
B) the absence of a nucleus in the cell
C) reproduce by spores
D) mostly heterotrophic organisms

Abstract

2739. Growth of a woody plant stem in thickness occurs due to cell division and growth
A) cambium
B) wood
B) plugs
D) bast

2740. Angiosperms are more highly organized plants than gymnosperms, as they form
A) zygote when gametes merge
B) seeds from ovules
C) fruits with seeds
D) an embryo protected by a seed coat

Adblock detector

Organelles special purpose contained in many plant and animal cells. These include organelles of movement (myofibrils, cilia, flagella, stinging capsules, etc.), supporting structures (tonofibrils), organelles that perceive external stimuli (for example, photoreceptors, statoreceptors, and phonoreceptors), neurofibrils, as well as cell surface structures associated with absorption and digestion of food (microvilli, cuticle, etc.)

Cilia and flagella - these are organelles protruding from the cell, having a diameter of about 0.25 microns and containing a bundle of parallel microtubules in the middle. The main function of these organelles is to move the cells themselves or move along the cells of the surrounding fluid and particles. Cilia and flagella are found on the surface of many types of cells and are found in most animals and some plants. In humans, bronchial epithelial cells have many cilia (up to 10 # 9 per 1 cm2). They make a layer of mucus with dust particles and remnants of dead cells constantly move upward. With the help of the cilia of the cells of the oviduct, the ovum moves along it. Flagella differ from cilia only in length. Thus, mammalian spermatozoa have one flagellum up to 100 microns long.

Organisms whose cells do not have nuclei bounded by a membrane.

Usually cilia are more than 10 times shorter than flagella. Thousands of cilia of one cell move in a coordinated manner, forming traveling waves on the surface of the plasma membrane.Each cilium works like a whip: a shock forward, in which the cilium fully straightens and transfers maximum force to the surrounding fluid, pushing it, and then, bending to reduce the resistance of the environment, it returns to its original position). The entire length of the cilium or flagellum is extended by microtubules - hollow protein cylinders with an outer diameter of 25 nm. Microtubules, like microfilaments, are polar; they elongate at one end due to polymerization of a globular protein. In cilia and flagella, they are arranged according to the 9 + 2 system; nine double microtubules (doublets) form the wall of a cylinder, in the center of which there are two single microtubules. The doublets are able to slide relative to each other, which causes the cilium or flagellum to bend.

Microtubules

Microtubules - protein intracellular structures that make up the cytoskeleton. Microtubules are hollow cylinders with a diameter of 25 nm. Their length can be from a few micrometers to, probably, several millimeters in the axons of nerve cells. Their wall is formed by tubulin dimers. Microtubules, like actin microfilaments, are polar: self-assembly of the microtubule occurs at one end, and disassembly at the other. In cells, microtubules play the role of structural components and are involved in many cellular processes, including mitosis, cytokinesis, and vesicular transport.

Microtubule structure are structures in which 13 tubulin α- / β-heterodimers are stacked around the circumference of a hollow cylinder. The outer diameter of the cylinder is about 25 nm, the inner diameter is about 15. One of the ends of the microtubule, called the plus-end, constantly attaches a free tubulin to itself. From the opposite end - the minus end - the tubulin units are split off.

Function Microtubules in the cell are used as "rails" for transporting particles. Membrane vesicles and mitochondria can move along their surface. Proteins called motor proteins are transported through the microtubules. These are high molecular weight compounds consisting of two heavy (about 300 kDa) and several light chains. In heavy chains, head and tail domains are distinguished. Two head domains bind to microtubules and are actually engines, while the tail domains bind to organelles and other intracellular formations to be transported.

In addition to the transport function, microtubules form the central structure of cilia and flagella - the axoneme. A typical axoneme contains 9 pairs of combined microtubules at the periphery and two complete microtubules at the center. Microtubules also consist of the centrioles and the spindle of division, which ensures the divergence of chromosomes to the poles of the cell during mitosis and meiosis. Microtubules are involved in maintaining the shape of the cell and the location of organelles (in particular, the Golgi apparatus) in the cytoplasm of cells.

ORGANOIDS FOR SPECIAL PURPOSE

Microtubules -long thin hollow cylinders 25 nm in diameter. microtubule walls are made of proteins	1.supporting function form an internal framework that helps cells to maintain their shape 2.motor function - are part of cilia and flagella
Mwyrosikroniti -fine structures made up of thousands of protein molecules linked to each other	They form a musculoskeletal system called the cytoskeleton. promotes the flow of cytoplasm in cells
Cilia -numerous cytoplasmic outgrowths on the membrane surface are formed by membrane-covered microtubules	Provide the movement of some unicellular organisms and the flow of fluids in organisms, removing dust particles
Flagella –– the surface structure present in many prokaryotic and eukaryotic cells and serving for their movement in a liquid medium or on the surface of solid media. The flagella of prokaryotes and eukaryotes differ sharply: the bacterial flagellum is 10–20 nm thick and 3–15 μm long; it is passively rotated by a motor located in the membrane; eukaryotic flagella up to 200 nm thick and up to 200 microns long, they can bend independently along their entire length. Eukaryotes often also have cilia, which are identical in structure to the flagellum, but shorter (up to 10 μm).	Serve for movement of unicellular organisms sperm and zoospores

Q.17.

Inclusions - optional components of the cell that arise and disappear depending on the metabolic state of the cell.

This is the accumulation of substances in the cell.

Classification:

Trophic (neutral lipids, polysaccharides, proteins)

Secretory (vacuoles, removing substances from the cell)

Excretory (metabolic products)

Pigmented - exogenous (carotene, dust, dyes)

- endogenous (hemoglobin, melanin)

Eukaryotes are organisms whose cells have a nucleus surrounded by a membrane envelope.

Features of the structure:

The shape of the cells is diverse, the sizes range from 5 to 100 microns.
Cells have similar chemical composition and metabolism.
The cells are divided by a membrane system into compartments.
Genetic material is concentrated mainly in chromosomes that have complex structure and are formed by DNA strands and histone protein molecules.
The cytoplasm contains membrane organelles, centrioles.
Cell division is mitotic.

Core- an obligatory structural component of every eukaryotic cell, containing genetic material. In animal cells, hereditary information is stored in nucleus and mitochondria... In plant cells - in the core, mitochondria and plastids. The core consists of:

1. Nuclear shell;

2. Karyoplasm;

3. Chromatin;

4. Nucleolus.

The shape of the nucleus depends on the shape of the cell itself and on the functions that it performs.

The size of the nucleus also mainly depends on the size of the cell.

Nuclear cytoplasmic index -the ratio of the volumes of the nucleus and the cytoplasm. A change in this ratio is one of the causes of cell division or metabolic disorders.

Nuclear shell the interphase nucleus consists of two elementary membranes (outer and inner); between them is the perinuclear space, which through the channels of the endoplasmic reticulum is connected with different parts of the cytoplasm. Both nuclear membranes are permeated poresthrough which the selective exchange of substances between the nucleus and the cytoplasm takes place. From the inside, the nuclear envelope is covered with a protein mesh - nuclear lamina which determines the shape and volume of the nucleus. To the nuclear lamina telomeric regions join chromatin strands. Microfilamentsform the inner core of the nucleus.

Collection of Ideal Social Studies Essays

The internal "skeleton" of the nucleus is of great importance for ensuring the orderly flow of the main processes transcription, replication, processing.Outside, the core is also covered microfilamentswhich are elements cytoskeleton cells... The outer nuclear membrane has on its surface ribosomes and is associated with membranes endoplasmic reticulum... The nuclear envelope has selective permeability... The flows of substances are regulated by the specific features of membrane proteins and nuclear pores (from 1000 to 10000).

The main functions of the nuclear envelope.

1. Formation of a cell compartment where genetically material is concentrated and conditions are created for its preservation and duplication.

2. Separation of the contents of the nucleus from the cytoplasm.

3. Maintaining the shape and volume of the nucleus.

4. Regulation of substance fluxes (various types of RNA and ribosome subunits enter the cytoplasm from the nucleus through the pores, and the necessary proteins, water, ions are transferred to the middle of the nucleus).

Karyoplasm - a homogeneous structureless mass filling the space between chromatin and nucleoli. It contains water / 75-80% /, proteins, nucleotides, amino acids, ATP, various types of RNA, ribosome subunits, metabolic intermediates and interconnects the structures of the nucleus and cytoplasm.

Chromatin

The genetic material in the interphase nucleus is in the form

intertwining chromatin filaments. It is a complex of DNA and proteins (deoxyribonucleoprotein- DNP)... In the process of mitosis, while spiraling, chromatin forms well-visible, intensely colored structures - CHROMOSOMES.

Nucleoli(one or more) -granular, rounded, highly colored structures without a membrane. The nucleoli are composed of proteins, RNA, lipids, and enzymes. The DNA content is not more than 15% and is located mainly in its center.

The nucleoli are fragmented at the beginning of cell division and are restored after its completion. In the nucleoli, 3 sites:

1. Fibrillary;

2. Granular;

3. Slightly colored.

- Fibrillar part of the nucleolus consists of RNA strands. This is the site of active synthesis of ribosomal RNA on rRNA - genes along the DNA molecule of decondensed chromatin.

- Granular site consists of RNA particles similar to cytoplasmic ribosomes. This is the place where RNA and ribosomal proteins unite and form mature small and large ribosome subunits.

— Lightly colored area the nucleolus contains DNA (inactive) that is not transcribed.

The formation of nucleoli is associated with secondary constrictions of metaphase chromosomes (nucleolar organizers), in the region of which genes encoding r-RNA synthesis are localized. In human cells, these functions are performed by chromosomes No. 13, 14, 15, 21, 22, which have satellites or satellites.

The main functions of the nucleoli:

Synthesis of ribosomal RNA.
Formation of ribosome subunits.

CORE FUNCTIONS:

1. Storage and transmission of hereditary information;

2. Regulation of all vital processes of the cell;

3. DNA repair;

4. Synthesis of all types of RNA;

5. Formation of ribosomes;

6. Realization of hereditary information by regulation of protein synthesis.

CHROMOSOMES.

Chromosomes -filamentous structures, clearly visible under a light microscope only during cell division, are formed from chromatin during its condensation. Depending on the degree condensation chromatin is subdivided into:

1. Heterochromatin - strong spiralized and genetically inactive, appears in the form of highly stained dark areas of the nucleus.

2. Euchromatin - low condensed, genetically active, is detected in the form of light areas of the nucleus.

Chemical composition of chromosomes :

1.DNA - 40%

2. Basic or histone proteins - 40%

3. Non-histone (acidic or neutral) - 20%

4. Traces of RNA, lipids, polysaccharides, metal ions.

Only eukaryotic cells have a nucleus. Moreover, some of them lose it in the process of differentiation (mature segments of the sieve tubes, erythrocytes). Ciliates have two nuclei: macronucleus and micronucleus. There are multinucleated cells that are formed by combining several cells. However, in most cases, there is only one nucleus in each cell.

The cell nucleus is its largest organelle (except for the central vacuoles of plant cells). It is the very first cell structure that was described by scientists. Cell nuclei are usually spherical or ovoid.

The nucleus regulates all cell activity. It contains chromatids - thread-like complexes of DNA molecules with proteins-histones (a feature of which is the content of a large number of amino acids lysine and arginine in them). The DNA of the nucleus stores information about almost all hereditary traits and properties of the cell and organism. During the period of cell division, chromatids spiralize, in this state they are visible under a light microscope and are called chromosomes.

Chromatides in a non-dividing cell (during interphase) are not completely despiralized. The tightly coiled parts of chromosomes are called heterochromatin... It is located closer to the shell of the kernel. To the center of the core is located euchromatin - a more despiralized part of chromosomes. RNA is synthesized on it, i.e. there is a reading of genetic information, gene expression.

DNA replication precedes nuclear division, which in turn precedes cell division. Thus, daughter nuclei receive ready-made DNA, and daughter cells receive ready-made nuclei.

The inner contents of the nucleus are separated from the cytoplasm nuclear envelopeconsisting of two membranes (external and internal). Thus, the cell nucleus belongs to two membrane organelles. The space between the membranes is called perinuclear.

The outer membrane in certain places passes into the endoplasmic reticulum (EPS). If ribosomes are located on the EPS, then it is called rough. Ribosomes can also mix on the outer nuclear membrane.

In many places, the outer and inner membranes merge with each other to form nuclear pores... Their number is not constant (on average they are in the thousands) and depends on the activity of biosynthesis in the cell. Through the pores, the nucleus and cytoplasm exchange various molecules and structures. Pores are not just holes, they are complex for electoral transport. Their structure is determined by various proteins, nucleoporins.

Molecules of mRNA, tRNA, ribosome subunits emerge from the nucleus.

Various proteins, nucleotides, ions, etc. enter the nucleus through the pores.

Ribosomal subunits are assembled from rRNA and ribosomal proteins into nucleolus(there may be several)... The central part of the nucleolus is formed by special sections of chromosomes ( nucleolar organizers), which are located next to each other. The nucleolar organizers contain a large number of copies of the genes encoding rRNA. Before cell division, the nucleolus disappears and is formed again already during the telophase.

The liquid (gel-like) content of the cell nucleus is called nuclear juice (karyoplasm, nucleoplasm)... Its viscosity is almost the same as that of the hyaloplasm (the liquid content of the cytoplasm), but the acidity is higher (after all, DNA and RNA, which are large in the nucleus, are acids). Proteins, various RNAs, ribosomes float in the nuclear juice.

What organisms are we talking about? These organisms are made up of one cell; The cage has a wall; Cells do not have nuclei; Hereditary information is concentrated in a single chromosome; Metabolism is carried out in the process of CHEMOSYNTHESIS or PHOTOSYNTHESIS; They appeared 3.8 - 3.1 billion years ago.

PROKARYOTES (BACTERIA) 1. The cell contains: Capsule Cell wall Plasma membrane Fixed cytoplasm Ribosomes Nucleoid 2. The cell does not contain: Nuclei Many organelles EUKARYOTES (plants, fungi, animals) 1. The cell contains: NUCLEUS Cell wall (R and D) Plasma membrane Mobile cytoplasm Organoids - endoplasmic reticulum - mitochondria - vacuoles - plastids - ribosomes, etc.

Basic terms and concepts EURARIOTA are organisms whose cells have a formed nucleus. Prokaryotes are organisms whose cells DO NOT have a formed nucleus. BACTERIA is a very small, unicellular, nuclear-free organism. CAPSULE - an extra layer of mucus on the surface of a bacterial cell.

Control: 1. Bacteria - unicellular and multicellular plants. 2. Some bacterial cells have a nucleus. 3. Bacteria, unlike plants, do not have a cellular structure. 4. Vibrios are referred to as rod-shaped bacteria. 5. The bacterial cell contains cytoplasm, ribosomes.

7. Aerobic 8. Anaerobic 9. Fermentation is an organism that requires oxygen to function. - an organism, for the life of which oxygen is NOT needed. - the process of extracting energy from nutrients in an oxygen-free environment (energetically of little benefit).

The importance of bacteria in NATURE: Take an active part in the cycle of substances, changing organic and inorganic compounds; Oxygen enrichment of the atmosphere (cyanobacteria); Food object for other organisms; Soil formation (formation of humus and humus) - soil bacteria; Improving soil fertility (nitrogen fixing bacteria); Cause diseases of plants and animals

The importance of bacteria in human life: ECOLOGICAL 1 (+). Wastewater treatment at treatment facilities, waste processing; 2 (+). Purification of the waters of the World Ocean from oil spills (in case of oil spills); 3 (+). Formation of mineral deposits (gas, oil, sulfur, iron). 4(-). Spoilage of food. Control measures: a) boiling; b) drying; c) sterilization; d) pasteurization; e) freezing.

What are the measures to prevent bacterial diseases? 1. Airing and wet cleaning of premises; 2. Observe the rules of personal hygiene; 3. Do not use unwashed or expired products; 4. Properly prepare food; 5. Avoid promiscuous relationships; 6. Boil tap water, as well as from unknown sources; 7. Conduct timely vaccination; 8. Destroy and decontaminate sick and dead animals. The bacterium is the object of research; The activity of bacteria is used in the production of: 1. Medicines - antibiotics; 2. Hormones - insulin; 3. Food products: -dairy products, cheeses; - winemaking, brewing; - pickling vegetables; -cooking vinegar; -silication.

Control: 1. Diphtheria, tetanus, tuberculosis, cholera, typhoid fever - bacterial diseases. 2. E. coli lives in the human digestive system. 3. Bacteria are actively involved in the cycle of substances in nature. 4. Nodule bacteria, being in symbiosis with legumes, are able to assimilate phosphorus. 5. Influenza and sore throat are diseases caused by bacteria. 6. What bacteria play the role of orderlies in nature? 7. What bacteria cause the fermentation process?

Question 1. What are the functions of the cell nucleus?
The nucleus in the cell performs the main functions:
1.storing and reproducing hereditary information that is stored in the nucleus in the form of DNA molecules that make up chromosomes;
2. regulation of metabolism in a cell is carried out due to the fact that the nucleus contains hereditary information about the structure of cellular proteins in the composition of nuclear chromosomes.

Question 2. What organisms are prokaryotes?
Prokaryotes - these are organisms whose cells do not have a formed nucleus. These include bacteria, blue-green algae (cyanobacteria), and archaea.

Question 3. How is the nuclear shell arranged?
Nuclear membrane - separates the contents of the nucleus from the cytoplasm. The nuclear envelope consists of two membranes, an outer and an inner membrane, which join together in the pore area. With an increase in the rate of metabolic processes between the nucleus and the cytoplasm, the number of pores increases; one can judge the activity of the nucleus by the number of pores. From the nucleus through the nuclear pores exit: mRNA, tRNA, ribosome subunits. Nuclear and ribosomal proteins, nucleotides, fats, carbohydrates, ATP, water and ions enter the nucleus from the cytoplasm. The outer nuclear envelope is connected to the granular endoplasmic reticulum. The inner nuclear envelope is in contact with the karyoplasm (nuclear juice), is devoid of ribosomes, and in some places is connected to chromatin.

Question 4. What is chromatin?
Chromatin Is a complex of DNA and proteins, mainly histone ones. Histone molecules with DNA form groups - nucleosomes. A DNA molecule connected to a nucleosome forms DNP (deoxyribonucleoprotein) - this is the smallest unit of a chromosome. Chromatin contains RNA, Ca2 + and Mg2 + ions, and the enzyme DNA polymerase, which is necessary for DNA replication. During the division of the nucleus, chromatin spirals and becomes visible under a light microscope, i.e. chromosomes begin to form (Greek chromo - color, soma - body.).

Question 5. What are the functions of the nucleoli?
Nucleoli - These are round, strongly compacted, not limited by the membrane areas of the nucleus. Their shape, size and number depend on the functional state of the nucleus. In a cell that performs the function of synthesizing a large amount of protein, there will be several nucleoli in the nucleus, or they will be large and loose, i.e. the function of the nucleolus is the synthesis of rRNA and the assembly of the small and large ribosome subunits. The nucleolus contains: 80% protein, 10-15% RNA, a small amount of DNA and other chemical components. In the prophase of cell division, ribosome subunits enter the cytoplasm through nuclear pores, the nucleolus DNA is packed into chromosomes with a secondary constriction or nucleolar organizer, and, accordingly, the nucleolus as a structure disintegrates and becomes an invisible structure, therefore it is sometimes said that it "dissolves".

Question 6. What does a chromosome consist of?
A chromosome is a DNA molecule attached to a special protein that makes it compact.

Question 7. Where are the chromosomes in bacteria?
Bacterial cells do not have a formed nucleus. The genetic apparatus of bacteria is represented by one circular DNA molecule (bacterial chromosome), which is attached at a certain place to the cell membrane and occupies a space in the cytoplasm called the nucleoid.

Question 8. What is a karyotype?
A karyotype is a specific set of chromosomes characteristic of a given type of organism. The karyotype is characterized not only by the number of chromosomes, but also by their size, shape, and location of the centromere.

Question 9. What is the name of the set of chromosomes in somatic cells?
As a rule, somatic cells contain a double set of chromosomes, which is called diploid.

Question 10. What is the set of chromosomes in gametes?
Gametes contain only one chromosome of each species, that is, they have a single set of chromosomes, which is called haploid.

Question 11. What is the haploid set of chromosomes in cancer cells, if the diploid is 118?
If the diploid set of chromosomes in cells is 118, then the haploid set will be half as much - 59 (118/2 \u003d 59).

Question 12. Can a diploid set contain an odd number of chromosomes?
A diploid set of chromosomes can contain an odd number of chromosomes. There are organisms that have only one sex chromosome in their somatic cells. For example, in some insects (bugs, grasshoppers), females are homogametic (XX), and males have only one sex chromosome (XO).