Biology Notes Form 4

Biology Notes Form 4 – Form Four Biology

Define the term genetics
Differentiate between heredity and variation
Distinguish between continuous and discontinuous variations
Describe continuous and discontinuous variations
Observe variations in plants and animals
Describe the structure, nature and properties of chromosomes
Describe the structure, nature and properties of DNA molecule
Differentiate between DNA and RNA
Distinguish between F1 and F2 generation
Determine Mendel’s first law of inheritance
Define other terms used in inheritance such as phenotype, genotype, dominant gene, recessive gene, haploid and diploid
Demonstrate monohybrid inheritance in plants and animals
Predict outcomes of various genetic crosses
Construct and make use of pannet squares
Work out genotypic and phenotypic ratios
Predict outcomes of various crosses
Determine the unknown genotypes in a cross using a test cross
Describe albinism as an example of monohybrid inheritance in human beings
Explain the inheritance of ABO blood groups in human beings
Explain the inheritance of rhesus factor as an example of monohybrid inheritance in human beings
Predict the inheritance of blood groups human beings
Describe incomplete dominance
Describe inheritance of colour in flowers of mirabilis jalapa
Describe Inheritance of sickle cell anemia in human beings
Explain how sex is determined in human beings
Describe sex linkages in human beings
Define linkage and sex-linkage
Describe linkage in human beings e.g.colour blindness and hemophilia
Describe colour blindness as an example of sex-linked trait in human beings
Interpret pedigree of inheritance
Describe the Inheritance of hemophilia as an example of sex-linked traits in human beings
Define mutation
Differentiate between mutations and mutagens
List down causes of mutations
State the types of mutations
List down the various chromosal mutations
Describe chromosal mutations
Explain the Effects of chromosal mutations
Describe gene mutations and their effects on organisms
Describe areas in which the knowledge of genetics has been applied
Explain the practical applications of genetics
Define evolution
Explain the current concepts of the origin of life
Explain the current concepts on origin of life
Describe the study of fossils as evidence of organic evolution theory
Describe comparative anatomy as evidence of organic evolution
Describe occurrence of vestigial structures and geographical distribution of organisms as evidence of organic evolution
Describe comparative embryology, cell biology and biochemistry as evidence of organic evolution
Describe evolution of hominids
Describe Lamarck’s theory
Describe and discuss the struggle for existence and survival for the fittest
Describe and discuss new concepts of Darwin’s theory
Describe natural selection in action
Describe natural selection in nature
Describe the isolation mechanism in speciation
Describe Artificial selection in plants and animals and how it leads to speciation
Explain the importance of sexual reproduction in evolution
Define stimulus
Define irritability
Define response
Define tactic and tropic responses
List down tactic responses in plants
List down tropic responses in plants
Differentiate between tactic and tropic responses
Define geotropism
Describe geotropism in roots and shoots of plants
Differentiate between Phototropism and geotropism
Carry out experiments demonstrating both Phototropism and geotropism in a plant seedling
Carry out experiments to demonstrate tactic responses to light and water
Carry out experiments to show chemotactic response using fruit juice
Define Hydrotropism and thigmotropism
State the importance of Tactic and tropic responses
Explain the production of Plant hormones and their effects on plants
Carry out experiment to investigate hydrotropism
Carry out experiment to investigate etiolation
Demonstrate the knee jerk in a reflex action
Defined Conditioned reflex actions
Describe Conditioned reflex action using parlous dog
Compare simple and conditioned reflex actions
Explain the role of endocrine system in a human being
Explain the effect over secretion and under secretion of thyroxin and adrenaline
Isolate and list the similarities and differences between the endocrine and the nervous system
State the effects of drug abuse on human health
Draw and label the mammalian eye
State the functions of the mammalian eye
Describe how the structure of the mammalian eye is adapted to its functions
Dissect and display parts of the mammalian eye
Describe how an image is formed and interpreted in the mammalian eye
Describe Accommodation in the mammalian eye
Name and explain the Common eye defects
Describe Common eye defects and their corrections
Investigate the blind spot In the eye
Investigate which eye is used more during vision
Name and describe Common eye diseases
Draw and label the mammalian ear
Describe the mammalian ear and how it is adapted to its functions
Describe the mechanism of hearing
Discuss thick ear drum, damaged cochlea, raptured eardrum, fussed ossicles, otitis media, ostosceleross and tinnitus
Define support and movement
Describe the necessity of movement in plants and animals
Review the tissue distribution in monocotyledonous an dicotyledonous plants
Describe support in woody and non-woody stems
Describe the role of tendrils and tender stems in support
Observe prepared sections of woody and herbaceous stems
Observe a wilting plant
List the types of skeletons
Describe the role of exoskeleton in insects
Describe the role and components of endoskeleton
Describe the role of skeleton in vertebrates
Draw the structure of a finned fish (tilapia)
Calculate the tail power
Explain how locomotion occurs in fish
Name and draw the different fins and state their functions
Draw the human skeleton and identify the component parts
Identify and draw the skull
Identify bones of Axial skeleton in the vertebral column
Identify the cervical vertebrae
Identify the structures of the thoracic vertebrae
Relate the structure of the thoracic vertebrae to their functions
Identify the structures of lumbar, sacral and candal vertebrae
Show how ribs articulate with thoracic vertebrae
Draw and label Ribs and sternum
Relate the structure to their functions
Identify components of Appendicular skeleton
Draw the scapula bone and relate it to its functions
Identify the bones of the fore limbs
Draw the structure of the humerus, radius and ulna
Draw and label bones of the hand
Draw the pelvic girdle
Name the bones of The pelvic girdle
Relate the structure to their functions
Identify, draw and label the femur, tibia and tibula bones
Relate their structure to their functions
Draw and label the bones of the foot
Relate the structure of bones of the foot to their functions
Define a joint
List the three types of joints
Describe the types of joints
List examples of movable joints, hinge joints and bell and socket joints
Define Immovable joints
Name Immovable joints
Define muscles
Explain the differences between the three types of muscles
Identifying biceps and triceps in the arm movementGenetics
Introduction
Genetics is the study of inheritance.
The fact that the offspring of any species resemble the parents indicates that the characters in the parents are passed on to the offspring.
Factors that determine characters (genes) are passed on from parent to offspring through gametes or sex cells.
In fertilisation the nucleus of the male gamete fuses with the nucleus of the female gamete.
The offspring show the characteristics of both the male and the female.
Genetics is the study of how this heritable material operates in individuals and their offspring.Variations within Plant and Animal Species
Variation
The term variation means to differ from a standard.
Genetics also deals with the study of differences between organisms belonging to one species.
Organisms belonging to higher taxonomic groups e.g. phyla or classes are clearly different.
Although organisms belonging to the same species are similar, they show a number of differences or variations such that no two organisms are exactly the same in every respect.
Even identical twins, though similar in many aspects, are seen to differ if they grow in different environments.
Their differences are as a result of the environment which modifies the expression of their genetic make-up or genotype.
The two causes of variations are the genes and the environment.
Genes determine the character while the environment modifies the expression of that character.Continuous and Discontinuous Variation
Continuous Variations
The differences between the individual are not clear-cut.
There are intermediates or gradations between any two extremes.
Continuous variations are due to action of many genes e.g. skin complexion in humans.
In continuous variation, the environment has a modifying effect in that it may enhance or suppress the expressions of the genes.
Continuous variation can be represented in form of a histogram.
Example of continuous variation in humans is weight, height and skin complexion.
Linear measurements:
In humans, height shows gradation from tall, to tallest.
So does the length of mature leaves of a plant.
In most cases, continuous variation is as a result of the environment.Discontinuous Variations
These are distinct and clear cut differences within a species.Examples include:
Ability to roll the tongue.
An individual can either roll the tongue or not.
Ability to taste phenylthiourea (PTC); some individuals can taste this chemical others cannot.
Blood groups – and individual has one of the four blood groups A, B AB or O.
There are no intermediates.
Albinism – one is either an albino or not.
Discontinuous variations is determined by the action of a single gene present in an individual.Structure and Properties of Chromosomes
These are threadlike structures found in the nucleus.
They are normally very thin and coiled and are not easily visible unless the cell is dividing.
When a cell is about to divide, the chromosomes uncoil and thicken.
Their structure, number and behaviour is clearly observed during the process of cell division.
The number of chromosomes is the same in all the body cells of an organism.
In the body cells, the chromosomes are found in pairs.
Each pair is made up of two identical chromosomes that make up a homologous pair.
However sex chromosomes in human male are an exception in that the Y-chromosome is smaller.Number of Chromosomes
Diploid Number (2n)
This is the number of chromosomes found in somatic cells.
For example, in human 2n = 46 or 22 pairs (44 chromosomes) are known as autosomes (body chromosomes”)
while 1 pair is known as the sex chromosomes.
In Drosophila melanogaster, 2n = 8.Chromosome Structure
All chromosomes are not of the same size or shape.
In human beings; each of the twenty¬ three pairs have unique size and structure .
On this basis they have been numbered 1 to 23.
The sex chromosomes formthe 23rd pair.Properties of Chromosomes
Chromosomes are very long and thin.
They are greatly and loosely coiled and fit within the nucleus.
During cell division they shorten, become thicker and are easily observable.
Each consists of two chromatids.
The two chromatids are held at same position along the length, at the centromere.
Chromatids separate during cell division in mitosis and in the second stage of meiosis.
Chromosomes take most dyes and stain darker than any other part of the cell.
This property has earned them the name “chromatin material”
Each chromosome is made up of the following components:
Deoxyribonucleic acid (DNA) – this carries the genes.
It is the major component of the genetic material.
Protein e.g. histones.
Ribonucleic acid (RNA) is present in very small amounts.
Enzymes concerned with DNA and RNA replication – these are DNA and RNA polymerases and ligases.Structure of DNA
The structure of DNA was first explained in 1953 by Watson and Crick.
DNA was shown to be a double helix that coils around itself.
The two strands are parallel and the distance between the two is constant.Components of DNA
DNA is made up of repeating units called nucleotides.
Each nucleotide is composed of:
A five-carbon sugar (deoxyribose).
Phosphate molecule.
Nitrogenous base, four types are available i.e,
Adenine – (A)
Guanine – (G)
Cytosine – (C)
Thymine – (T)
The bases are represented by their initials as A, G, C and T respectively.
The sugar alternates with the phosphate, and the two form the backbone of the strands.
The bases combine in a specific manner, such that Adenine pairs with Thymine and Guanine pairs with Cytosine.
The bases are held together by hydrogen bonds. A gene is the basic unit of inheritance consisting of a number of bases in linear sequence on the DNA.
Genes exert their effect through protein synthesis.
The sequence of bases that make up a gene determine the arrangement of amino acids to make a particular protein.
The proteins manufactured are used to make cellular structures as well as hormones and enzymes.
The types of proteins an organism manufactures determines its characteristics.
For example, albinism is due to failure of the cells of an organism to synthesise the enzyme tyrosine required for the formation of the pigment melanin.
First Law of Heredity
It is also known as Law of Segregation (Mendel’s First Law).
The characters of an organism are controlled by genes occurring in pairs known as Alleles.
By definition, an allele is an alternative form of a gene controlling a particular characteristic.
Of a pair of such alleles, only one is carried in each gamete.
This is explained by first meiotic anaphase stage, when the homologous chromosomes are separated so that each carries one of the allelic genes.Monohybrid Inheritance
This is the study of the inheritance of one character trait that is represented by a pair of genes on homologous chromosomes.
Gregor Mendel (an Austrian monk) was the first person to show the nature of inheritance.
He did this through a series of experiments using the garden pea, Pisum sativum.
As opposed to others before him, the success in his work lay in the fact that:
He chose to study first a single character at a time (monohybrid inheritance).
He then proceeded to study two characters at time (dihybrid inheritance) .
He quantified his results by counting the number of offspring bearing each trait.
Each character he chose was expressed in two clearly contrasting forms.Examples
Stem length: some plants were tall while others were short.
Colour of unripe pods: some were green, others yellow.
There were no intermediates.Mendel’s Procedure
For each character, Mendel chose a plant that bred true.
A true or pure breed continues to show a particular trait in all the offspring in several successive generations of self-fertilisation.
He made one plant to act as the female by removing the stamens before the ovary was mature and protecting (e.g. by wrapping with paper).
The female plant from contact with any stray pollen.
When the ovary was mature, he carefully dusted pollen from the anthers of the selected male plant and transferred it to the stigma of the female plant.
Observations were then made on the resulting seeds or on the plants obtained when those seeds were planted.Results
For each pair of contrasting characters he studied, Mendel obtained the same results.
For example, when he crossed pure breeding tall plants with pure breeding short plants, the first offspring, known as the first filial generation (FI) were all tall.
When these were selfed i.e. self-fertilisation allowed to take place, the second generation offspring also know as the second filial generation or F2 occurred in the ratio of 3 tall: 1 short.
The same ratio was obtained for each of the other characters studied.
From this it is clear that one character i.e. tall is dominant over the short character.
A dominant character is that which is expressed alone in the offspring even when the opposite character is represented in the genotype.
The unexpressed character is said to be recessive.
From these results and others obtained when he studied two characters at the same time, Mendel concluded that gametes carry factors that are expressed in the offspring.
These factors are what we know today as genes.
Mendel put forward the following laws of inheritance:
Of a pair of contrasting characters, only one can be represented in a gamete.
For two or more pairs of such contrasting characters, each factor (gene) in the gamete acts independently of the others and may combine randomly with either of the factors of another pair during fertilisation.
Genetic experiments carried out to date confirm Mendel’s Laws of inheritance e.g. T.H. Morgan’s work on inheritance in the fruit fly Drosophila melanogaster.Terms used in Genetics Genotype:
The genes present in an individual. The genetic constitution of an individual. It is expressed in alphabetical notation.e.g TT,TtPhenotype:
The observed character or appearance i.e. the expression of the genes in the structure and physiology of the organism.
In some cases the phenotype is the product of the genotype and the environment. Phenotype is expressed in words.eg TALL,SHORT,RED WHITE .etc.Alleles:
These are alternative forms of the same gene that control a pair of contrasting characters e.g. tall and short.
They are found at the same position or gene-locus on each chromosome in a homologous pair.Homozygous:
This is a state where the alleles in an individual are similar e.g. TT (for tall)Heterozygous:
This is a state where the alleles are dissimilar i.e. each of the two genes responsible for a pair of contrasting characters are present
e.g. Tt. (T for tall; t for short)Hybrid:
This is the offspring resulting from crossing of two individuals with contrasting characters.Hybrid vigour or Heterosis:
The hybrid develops the best characteristics from both parents
i.e. it is stronger or healthier, or yields more than either parent.

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