Genetic is the study of heredity and variation in living things
HEREDITY OR INHERITANCE is defined as the transmission and expression of characteristics or traits in an organism from parents to offspring.
VARIATION is defined as the differences which exists between parents and offspring as well as a many the offsprings.
CHARACTERS OR TRAIT THAT CAN BE TRANSMITTED IN MAN
It is only those traits that constitute the genetic makeup of the parents that can be transmitted and expressed in the offspring.
These traits include colour of the skin, colour of eyes this colour of the hairs and hair texture, size of body stature, shape of the head , shape of the ears, shape of the month, lips, shape of the nose, length of the hands and legs,length of neck , Blood grouping, baldness, tongue rolling, hemophilia , voice, intelligences composure, aptitude , sickle cell anaemia are transmissible in animals while is transmissible include colour and shape of the leaves shoot , seed size and shape, colour of the flowers, size of the fruit and pigmentation
HOW CHARACTERS OR TRAITS GET TRANSMITTED FROM GENERATION TO GENERATION
Only characters controlled by genes can be transmitted A diploid organisms has two sets of chromosome referred to as homologues. Such an organism has two copies of each gene, with each copy occupying identical locations or loci on the homologous chromosomes.
Diploid organisms produce gametes by meiosis in their reproductive organs . A male individual produces egg cells or ova.. During meiosis the number of chromosome in a cell is halved , the gametes are therefore haploid containing one set of chromosome and gene only one copy of each gene.
During sexual reproduction, the gamete of a male and female individual fuse to form zygote. Each zygote is diploid as it gets one set of chromosomes, and hence one copy of each gene from the gametes of each parent. The gene an organism inherits during fertilization is called genotype remain constant throughout life span. The phenotype which is the physical appearance or features of an organism is determined by its genotypes and the environment in which it lives.
Basic Genetic concepts
GENE: This is defined as the physical unit of inheritance transmitted from due generation another and responsible for controlling the development of characters in the new organisms.
CHROMOSOMES: these are strands of genetic materials which are obvious during cell division. They are found in the nucleus where they carry the genes. They contain of DNA (deoxyribonucleic acid) and protein.
CHARACTER OR TRAIT; These are inheritable attributes or features possessed by an organism’s height or size.
ALLELOMORPHS these are pairs of genes or locus that controls contrasting character. Pair of allomorphs are called allelic pair while each member of the pair is the allele of the other.
PHENOTYPE: Is the sum total of all observable features of an organism s that is the physical, physical, physiological and behavioral traits e.g. height, weight, skin colour.
GENOTYPE; The term in used to describe those traits or sum total of the genes inherited from both parent or in order word, it is the genetic makeup or constitution of an individual. Genotype includes both the dominant and the recessive traits that form the genetic makeup of an individual.
DOMINANT charater;This is a trait that is expressed in an offspring when two individual with contrasting characters are crossed.
RECESSIVE: Character this is the trait from one parent which is masked or does not produce its effect in the presence of dominant gene or character. Shortnees is recessive character while fellness is dominant character. Recessive genes are gene which control recessive character,
HOMOZYGOUS: Is an individual with identical alleles in respect of a particular trait or character (TT or tt).
HETEROZYGOUS: An individual having two member of a pair of genes controlling a pair of contrasting alleles located on different on the same position on a pair of chromosome e.g. (Tt for tallness or a plant with Rr.
GAMETE – Is a single cell formed as a result of the union of a ale gamete with a female gamete
FILIAL -Generation – the offspring of parent make up the filial generation the first, second and third generations of offspring are known as first, second and third filial generations of offspring are known as first, second and third filial generation are denoted by the symbols F1, F2 and F3.
HYBRID: Is an offspring from a cross between parents that are generically different parents that are generically different but of the same species.
HYBRIDIZATION – is the crossing of a plant with contrasting character.
MONOHYBRIDIZATION: Involves the crossing of two organisms with two organisms with two pairs of contrasting character.
LOCUS- is the site for location of gene in a chromosome.
HAPLOLD- Is when an organism has one set of chromosomes in the same genete it is represented by (n).
DIPLOID– Is when an organism has two sets of chromosomes in the body cell. The bodies of animals and plants are diploid. Diploid number is represented by (2n).
MUTATION – Is a change in the genetic makeup of an organism that resulting in a new characteristic that is inheritable
BACKCROSS – This is the mating of an f1 individual with an individual which has the parental genotype.
PURE BREED – This simply means an individual that is homozygous.
CO-DOMINANCE – Is a situation where the phenotype of the heterozygote exhibits properties of both parents . Example of co-dominance is seen in ABO BLOOD GROUP SYSTEM IN HUMAN BLOOD GROUP a IS DOMINANT AS BLOOD GROUP b. If a child is product by two parents, one with blood group B and the other blood group A. The child will belong to blood group AB.
SEX – LINKED CHARACTER – These are characters that are carried by genes located on the sexchromosome . These genes or characters are said to be sex- linked and usually found in the X- chromosome they expressed in male children even when the gene is recessive . Such phenotype are expressed in female only when the two X – chromosomes are recessive or two x – chromosomes are recessive or carry the recessive gene. Example of characteristics expressed by genes that are located on sex chromosome include colour blindness, hemophilia , baldness.
MENDEL’S WORKS IN GENETICS
Gregor Mendel (1822 – 1884) was a Monk in Austtria. He is referred to as father of Genetics because of his work which formed the foundation for scientific study of heredity and variation Mendels Experiment .
Gregor Mendel carried out several experiment on how hereditary characters were being transmitted from generation to generation . He worked with garden pea called possum sativum.
Reasons for using the pea are follows.
_ Peas are usually self pollinating and he could pollinated them by himself.
_ They have a very short life span than animals and some other plants.
(1) He planted tall plants for several generation and discovered the plant produced were all plants in the same way he planted short pea plants for several generation. He also discovered that the plants produced were all short.
(2) He proceeded to plant tall plants and short pea plants . By the time the flowers were produced of the collected pollen grains of the tall pea plants tagged of male and pollinated the stigma of the shrt plant which is labeled as female.
He collected the pollen grain of the short plant and placed them on the stigma of the tall plant.
(3)Mendel area again picked the seed and he discovered that the plant were all tall. This he referred to it as first filial generation (fi)
(4) Mendel them crossed the f1 plants, collected their got from this were tall and short in the ratio 3 : 1 . He then called this stage second filial generation.
Mendelian Traits:
Mendel discovered trait or characters that be transmitted from parents to offspring. He studied various inherited characteristics in pea plant. The traits or character are: height/length, colour of seeds, surface of seed coat. Other examples of traits that can be transmitted from parents to offspring include: the blood group, the Rhesus factor, skin colour eye colour shape and body weight.
Mendelian Laws of inheritance
Mendel’s Laws of heredity explains the principals of Mendelian inheritance.mendel produced offspring of pea plant by self-polling on and cross –pollination and as a result of his experiments,he came out with his certain deductions termed mendel’s law.The two laws are
1. First law
Law of segregation states that genes are responsible for the development of individual and that they are independently transmitted from one generation to another without undergoing any alteration.
ii. Second Law
Law of independence assortment of genes
This law states that each character behaves as a separate unit and pair of alleles for a given character distributes itself in the gemetes during formation does not affect the way other allelic pair for other character distribute themselves. OR the Law State that when more than one factors are considered, each character behaves as a separate unit and is inherited independently of any other character.
How characters Manifest from Generation to Generation
a. Sex Determination-In human being,sex is determined by sex chromosome (23rd pairs).In female,the sex chromosomes are similar in size and shape,,they are referred to as “X” chromosome hence female have XX in (23rd) pairs. .Male on the other hand have contrasting (different) size and shape. One is an “X” chromosome while other is a “Y” chromosome. M.ale chromosome is therefore XY.half of the male sperms contain X chromosome and the other half is Y chromosome . Each egg of the female contain an X Chromosome. This implies they if an X- sperm fertilizes an X- egg, the offspring will be a female (XX). Otherwise if Y- sperm fertilizes an X -egg,the offspring is a male,having XY genetic constitution
Questions
(1) A man with heterozygous genotype for blood group B marries a woman with heterozygous
A. what percentage of their children be universal donor?
2.The alternative form of a gene that represents constrasting character is a/an (A)allele (B)diploid (C)haploid (D)homologue
(3) If two parents are sickle cell carrier their genotype would be (A) Hb A HbA and Hbs Hbs (b) HbsHbs and Hbs Hbs (c) HbA Hbs and Hb A Hbs (D) Hba HbA and HbA HbA
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