cage layer fatigue syndrome in birds is characterized by an inability to stand on their feet and fragile bones. It is mainly observed in young layer hens reared in batteries in the period of maximum egg-laying. Affected birds lie down and stopped eating. Egg shells become thin.
Written by: Dr. Jacquie Jacob, University of Kentucky
Cage layer fatigue is the equivalent of osteoporosis in chickens. It is a condition that primarily affects caged chickens that are at a high level of egg production (hence the name), and its cause is believed to be at least partially nutritional. Many layers are able to recover quickly from cage layer fatigue when they are removed from the cages and allowed to walk normally on the floor. Because exercise seems to alleviate the condition, lack of exercise in caged hens may be a partial cause.
Young layers at peak production require a large amount of calcium. If there is not sufficient calcium in the feed, the hen makes use of calcium stored in a special type of bone (referred to as medullary bone). As more and more calcium is withdrawn from the bones, they become weak and fragile.
Topdressing feed with oyster shell or limestone will usually reduce the incidence of cage layer fatigue in young hens. In older hens the problem is most likely a deficiency of phosphorus and/or vitamin D3. Therefore, for older hens, topdressing the feed with dicalcium phosphate and adding a vitamin and electrolyte supplement to the hens' drinking water may help reduce incidence of the condition.
If affected hens do not respond to treatment, they should be submitted to a poultry disease diagnostic laboratory to determine the cause of the symptoms. There are diseases that can cause conditions or symptoms similar to cage layer fatigue.

cage layer fatigue syndrome in birds is characterized by an inability to stand on their feet and fragile bones. It is mainly observed in young layer hens reared in batteries in the period of maximum egg-laying. Affected birds lie down and stopped eating. Egg shells become thin.
The calcium deficiency is layer hens results in initial removal of calcium from bones, to complete depletion of the medullary bone and thereafter, of the bone wall. The bones are strongly thinned and spontaneous fractures, especially of the tibia and the femur could occur. Although the severe calcium deficiency is often a triggering factor, the aetiology of the syndrome seems to involve other, yet unknown factors. The supplementation of calcium, phosphate and multivitamin preparations in the diet and rinking water, the regulation of avian population density into cages and ensuring adequate nutritional and drinking fronts are also contributing for the favourable outcome of the condition.

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The cervical vertebrae of the spine consist of seven bony rings that reside in the neck between the base of the skull and the thoracic vertebrae in the trunk. Among the vertebrae of the spinal column, the cervical vertebrae are the thinnest and most delicate bones. Yet, in spite of their size, the cervical vertebrae have the huge jobs of supporting the head, protecting the spinal cord, and providing mobility to the head and neck.
The cervical vertebrae are stacked along the length of the neck to form a continuous column between the skull and the chest Each cervical vertebra is named by its position in order from superior (C1 or first cervical vertebra) to inferior (C7 or seventh cervical vertebra). The C1 vertebra, which holds up the skull, is named the atlas after the mythological titan Atlas who similarly held the Earth on his shoulders. Similar to the C1 vertebra, the C2 vertebra is named the axis as it provides the axis upon which the skull and atlas rotate when the head is moved side to side.
Each cervical vertebra consists of a thin ring of bone, or vertebral arch, surrounding the vertebral and transverse foramina. The vertebral foramen is a large opening in the center of the vertebra that provides space for the spinal cord and its meninges as they pass through the neck. Flanking the vertebral foramen on each side are the much smallertransverse foramina. The transverse foramina surround the vertebral arteries and veins, which, along with the carotid arteries and jugular veins, have the vital job of carrying blood to and from the brain.
Extending from the vertebral arch are several bony processes that are involved in muscle attachment and movement of the neck. The spinous process extends from the posterior end of the arch and serves as a connection point for the muscles that extend the neck, such as the trapezius and spinalis muscles. On the left and right lateral sides of each vertebra is a transverse process that forms the insertion point for the muscles of the erector spinae group that extend and flex the neck.
A thickened region of bone known as the body lies anterior to the vertebral foramen and forms the main bone mass in all vertebrae except for the atlas. The bodies strengthen the vertebrae and support most of the weight of the tissues of the head and neck.Intervertebral disks made of rubbery fibrocartilage lie between the vertebral bodies to provide slight flexibility to the neck. Lateral to the vertebral bodies are flattened facets that form joints with the neighboring vertebrae and skull, allowing movement among the vertebrae. The axis has a very distinct shape due to the presence of the odontoid process, a tooth-like prominence that extends from its body superiorly toward the axis. The odontoid process serves as the axis upon which the atlas rotates at the atlantoaxial joint.
Despite being some of the smallest and lightest bones in the axial skeleton, the cervical vertebrae perform many important functions that are critical to the survival of the body. Vital nerves and blood vessels passing through the neck are protected from mechanical damage by the bony arches of the cervical vertebrae. The cervical vertebrae also provide support to the head and neck, including supporting the muscles that move this region of the body. The muscles that attach to the vertebral processes provide posture to the head and neck throughout the day and have the greatest endurance of all of the body’s muscles. Finally, the many joints formed between the skull and cervical vertebrae provide incredible flexibility that allows the head and neck to rotate, flex, and extend.

A Double-Helix Structure

DNA has a double-helix structure, with sugar and phosphate on the outside of the helix, forming the sugar-phosphate backbone of the DNA. The nitrogenous bases are stacked in the interior in pairs, like the steps of a staircase; the pairs are bound to each other by hydrogen bonds. The two strands of the helix run in opposite directions, so that the 5′ carbon end of one strand faces the 3′ carbon end of its matching strand. This antiparallel orientation is important to DNA replication and in many nucleic acid interactions.

DNA is a Double Helix

Native DNA is an antiparallel double helix. The phosphate backbone (indicated by the curvy lines) is on the outside, and the bases are on the inside. Each base from one strand interacts via hydrogen bonding with a base from the opposing strand.

Base Pairs

Only certain types of base pairing are allowed. For example, a certain purine can only pair with a certain pyrimidine. This means Adenine pair with Thymine, and Guanine pairs with Cytosine. This is known as the base complementary rule because the DNA strands are complementary to each other. If the sequence of one strand is AATTGGCC, the complementary strand would have the sequence TTAACCGG.

Antiparallel Strands

In a double stranded DNA molecule, the two strands run antiparallel to one another so that one strand runs 5′ to 3′ and the other 3′ to 5′. The phosphate backbone is located on the outside, and the bases are in the middle. Adenine forms hydrogen bonds (or base pairs) with thymine, and guanine base pairs with cytosine.

Source: Boundless. “Amino Acids.” Boundless Chemistry. Boundless, 08 Aug. 2016. Retrieved 15 Aug. 2016 from

Source: Boundless. “The DNA Double Helix.” Boundless Chemistry. Boundless, 26 May. 2016. Retrieved 15 Aug. 2016 from

Structure of an Amino Acid

Amino acids are the monomers that make up proteins. Each amino acid has the same fundamental structure , which consists of a central carbon atom, also known as the alpha (α) carbon, bonded to an amino group (NH2), a carboxyl group (COOH), and to a hydrogen atom. In the aqueous environment of the cell, the both the amino group and the carboxyl group are ionized under physiological conditions, and so have the structures -NH3+ and -COO-, respectively. Every amino acid also has another atom or group of atoms bonded to the central atom known as the R group. This R group, or side chain, gives each amino acid proteins specific characteristics, including size, polarity, and pH.

Amino acid structure

Amino acids have a central asymmetric carbon to which an amino group, a carboxyl group, a hydrogen atom, and a side chain (R group) are attached. This amino acid is unionized, but if it were placed in water at pH 7, its amino group would pick up another hydrogen and a positive charge, and the hydroxyl in its carboxyl group would lose and a hydrogen and gain a negative charge.

Types of Amino Acids

The name "amino acid" is derived from the amino group and carboxyl-acid-group in their basic structure. There are 21 amino acids present in proteins, each with a specific R group or side chain. Ten of these are considered essential amino acids in humans because the human body cannot produce them and they must be obtained from the diet. All organisms have different essential amino acids based on their physiology.

Types of amino acids

There are 21 common amino acids commonly found in proteins, each with a different R group (variant group) that determines its chemical nature. The 21st amino acid, not shown here, is selenocysteine, with an R group of -CH2-SeH.

Characteristics of Amino Acids

Which categories of amino acid would you expect to find on the surface of a soluble protein, and which would you expect to find in the interior? What distribution of amino acids would you expect to find in a protein embedded in a lipid bilayer?
The chemical composition of the side chain determines the characteristics of the amino acid. Amino acids such as valine, methionine, and alanine are nonpolar (hydrophobic), while amino acids such as serine, threonine, and cysteine are polar (hydrophilic). The side chains of lysine and arginine are positively charged so these amino acids are also known as basic (high pH) amino acids. Proline is an exception to the standard structure of an animo acid because its R group is linked to the amino group, forming a ring-like structure.
Amino acids are represented by a single upper case letter or a three-letter abbreviation. For example, valine is known by the letter V or the three-letter symbol val.

Peptide Bonds

The sequence and the number of amino acids ultimately determine the protein's shape, size, and function. Each amino acid is attached to another amino acid by a covalent bond, known as a peptide bond. When two amino acids are covalently attached by a peptide bond, the carboxyl group of one amino acid and the amino group of the incoming amino acid combine and release a molecule of water. Any reaction that combines two monomers in a reaction that generates H2O as one of the products is known as a dehydration reaction, so peptide bond formation is an example of a dehydration reaction.

Peptide bond formation

Peptide bond formation is a dehydration synthesis reaction. The carboxyl group of one amino acid is linked to the amino group of the incoming amino acid. In the process, a molecule of water is released.

When fertilization occurs between two true-breeding parents that differ in only one characteristic, the process is called a monohybrid cross, and the resulting offspring are monohybrids. Mendel performed seven monohybrid crosses involving contrasting traits for each characteristic. On the basis of his results in F1 and F2 generations, Mendel postulated that each parent in the monohybrid cross contributed one of two paired unit factors to each offspring and that every possible combination of unit factors was equally likely.
To demonstrate a monohybrid cross, consider the case of true-breeding pea plants with yellow versus green pea seeds. The dominant seed color is yellow; therefore, the parental genotypes were YY (homozygous dominant) for the plants with yellow seeds and yy (homozygous recessive) for the plants with green seeds, respectively. A Punnett square, devised by the British geneticist Reginald Punnett, can be drawn that applies the rules of probability to predict the possible outcomes of a genetic cross or mating and their expected frequencies.To prepare a Punnett square, all possible combinations of the parental alleles are listed along the top (for one parent) and side (for the other parent) of a grid, representing their meiotic segregation into haploid gametes . Then the combinations of egg and sperm are made in the boxes in the table to show which alleles are combining. Each box then represents the diploid genotype of a zygote, or fertilized egg, that could result from this mating. Because each possibility is equally likely, genotypic ratios can be determined from a Punnett square. If the pattern of inheritance (dominant or recessive) is known, the phenotypic ratios can be inferred as well. For a monohybrid cross of two true-breeding parents, each parent contributes one type of allele. In this case, only one genotype is possible. All offspring are Yy and have yellow seeds.

Punnett square analysis of a monohytbrid cross

In the P generation, pea plants that are true-breeding for the dominant yellow phenotype are crossed with plants with the recessive green phenotype. This cross produces F1 heterozygotes with a yellow phenotype. Punnett square analysis can be used to predict the genotypes of the F2 generation.
A self-cross of one of the Yy heterozygous offspring can be represented in a 2 × 2 Punnett square because each parent can donate one of two different alleles. Therefore, the offspring can potentially have one of four allele combinations: YY, Yy, yY, or yy. Notice that there are two ways to obtain the Yy genotype: a Y from the egg and a y from the sperm, or a y from the egg and a Y from the sperm. Both of these possibilities must be counted. Recall that Mendel's pea-plant characteristics behaved in the same way in reciprocal crosses. Therefore, the two possible heterozygous combinations produce offspring that are genotypically and phenotypically identical despite their dominant and recessive alleles deriving from different parents. They are grouped together. Because fertilization is a random event, we expect each combination to be equally likely and for the offspring to exhibit a ratio of YY:Yy:yy genotypes of 1:2:1. Furthermore, because the YY and Yy offspring have yellow seeds and are phenotypically identical, applying the sum rule of probability, we expect the offspring to exhibit a phenotypic ratio of 3 yellow:1 green. Indeed, working with large sample sizes, Mendel observed approximately this ratio in every F2 generation resulting from crosses for individual traits.
Beyond predicting the offspring of a cross between known homozygous or heterozygous parents, Mendel also developed a way to determine whether an organism that expressed a dominant trait was a heterozygote or a homozygote. Called the test cross , this technique is still used by plant and animal breeders. In a test cross, the dominant-expressing organism is crossed with an organism that is homozygous recessive for the same characteristic. If the dominant-expressing organism is a homozygote, then all F1 offspring will be heterozygotes expressing the dominant trait. Alternatively, if the dominant expressing organism is a heterozygote, the F1 offspring will exhibit a 1:1 ratio of heterozygotes and recessive homozygotes. The test cross further validates Mendel's postulate that pairs of unit factors segregate equally.

To fully examine each of the seven traits in garden peas, Mendel generated large numbers of Fand F2 plants, reporting results from 19,959 F2 plants alone. His findings were consistent.

What results did Mendel find in his crosses for flower color? First, Mendel confirmed that he had plants that bred true for white or violet flower color. Regardless of how many generations Mendel examined, all self-crossed offspring of parents with white flowers had white flowers, and all self-crossed offspring of parents with violet flowers had violet flowers. In addition, Mendel confirmed that, other than flower color, the pea plants were physically identical.
Once these validations were complete, Mendel applied the pollen from a plant with violet flowers to the stigma of a plant with white flowers. After gathering and sowing the seeds that resulted from this cross, Mendel found that 100 percent of the F1 hybrid generation had violet flowers. Conventional wisdom at that time would have predicted the hybrid flowers to be pale violet or for hybrid plants to have equal numbers of white and violet flowers. In other words, the contrasting parental traits were expected to blend in the offspring. Instead, Mendel's results demonstrated that the white flower trait in the F1 generation had completely disappeared.
Importantly, Mendel did not stop his experimentation there. He allowed the F1 plants to self-fertilize and found that, of F2-generation plants, 705 had violet flowers and 224 had white flowers. This was a ratio of 3.15 violet flowers per one white flower, or approximately 3:1. When Mendel transferred pollen from a plant with violet flowers to the stigma of a plant with white flowers and vice versa, he obtained about the same ratio regardless of which parent, male or female, contributed which trait. This is called a reciprocal cross: a paired cross in which the respective traits of the male and female in one cross become the respective traits of the female and male in the other cross. For the other six characteristics Mendel examined, the F1 and F2 generations behaved in the same way as they had for flower color. One of the two traits would disappear completely from the F1 generation only to reappear in the F2 generation at a ratio of approximately 3:1 .
Upon compiling his results for many thousands of plants, Mendel concluded that the characteristics could be divided into expressed and latent traits. He called these, respectively, dominant and recessive traits. Dominant traits are those that are inherited unchanged in a hybridization. Recessive traits become latent, or disappear, in the offspring of a hybridization. The recessive trait does, however, reappear in the progeny of the hybrid offspring. An example of a dominant trait is the violet-flower trait. For this same characteristic (flower color), white-colored flowers are a recessive trait. The fact that the recessive trait reappeared in the F2 generation meant that the traits remained separate (not blended) in the plants of the F1 generation. Mendel also proposed that plants possessed two copies of the trait for the flower-color characteristic and that each parent transmitted one of its two copies to its offspring, where they came together. Moreover, the physical observation of a dominant trait could mean that the genetic composition of the organism included two dominant versions of the characteristic or that it included one dominant and one recessive version. Conversely, the observation of a recessive trait meant that the organism lacked any dominant versions of this characteristic .

Results of Mendel's Garden Pea Hybridizations

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