Genes are units of inheritance that determine the characteristic of an individual.
The characteristic of individuals that are controlled by genes include the colour and type of hair, types of ear lobes, being right-handed or left-handed and many more.
genes are found in long molecules called deoxyribonucleic acids (DNA).
DNA molecules are found in chromosomes.
Chromosomes are thread-like structures in the nucleus of a cell.
Each chromosome contains a long DNA molecule enveloped by protein.
Chromosomes exist in pairs, so do genes. Each pair of genes controls one characteristic of an individual.
GENETIC CONCEPT:
Phenotype- characteristic which express
Genotype- a pair of allele
Dominant gene- genes that show their effects whenever they are present
Recessive gene-genes that only show their effects in the absence of dominant genes.
Dominant trait- characteristic which express when the present of dominant gene.
Recessive trait- characteristic which express when the absent of dominant gene.
Heterozygous alelle-different allele (H,h)
Homozygous alelle-same allele (H,H),(h,h)
MANDEL’S FIRST LAW:
Mandel’s First Law describes the monohybrid cross of a pea plant. When a dominant homozygous pure breed was cross by recessive homozygous pure bread the first generations have the same genotype which is heterozygous.
For example, the purple flower is dominant and yellow flower is recessive. A purple flower pure breed (PP) was cross by a yellow flower pure breed (pp). All the first generations were heterozygous (Pp) which express purple flower. This process is explained by the diagram below:
Chromosomes are thread-like structures in the nucleus of a cell.
Each chromosome contains a long DNA molecule enveloped by protein.
Cell growth:
2 types of cell division:
Mitosis-is a cell division that occur in somatic cells.
Meiosis-is a cell division that occur in reproductive organ.
MITOSIS
Definition : Mitosis is a process of cell division which results in the production of two daughter cells from a single parent cell. The daughter cells are identical to one another and to the original parent cell.
In a typical animal cell, mitosis can be divided into four principals stages:
Prophase: The chromatin, diffuse in interphase, condenses into chromosomes. Each chromosome has duplicated and now consists of two sister chromatids. At the end of prophase, the nuclear envelope breaks down into vesicles.
Metaphase: The chromosomes align at the equitorial plate and are held in place by microtubules attached to the mitotic spindle and to part of the centromere.
Anaphase: The centromeres divide. Sister chromatids separate and move toward the corresponding poles.
Telophase: Daughter chromosomes arrive at the poles and the microtubules disappear. The condensed chromatin expands and the nuclear envelope reappears.
Cytokinesis: The cytoplasm divides, the cell membrane pinches inward ultimately producing two daughter cells .
Phases of mitosis:
Interphase
Prophase
Metaphase
Anaphase
Telophase
Importance of mitosis:
To maintain the number of chromosomes.
To maintain genetic materials.
To ensure the body cells are diploid (2n).
Growth, replace damage or death cells
Application of mitosis
Tissue culture
a. isolate tissue from the shoots or roots.
b. transfer the tissue into culture medium.
c. stimulate growth by controlling pH, hormones, temperature.
d. cell replicate and form roots.
2.Cloning
a. nucleus from organism A combine with cell of an organism B.
b. stimulate the cell division.
c. implant embryo into the surrogate mother.
d. an offspring is born.
Advantages of cloning:
1. Produce a large quantity.
2. Maintain the genetic material.
3. Control the quality of crops or livestock.
MEIOSIS
Illustration of the process by which a single parent diploid cell (Both homologous chromosomes) divides to produce four daughter haploids cells (One homologous chromosome of the pair).
Meiosis is thetype of cell division by which gametes cells (eggs and sperm) are produced. Meiosis involves a reduction in the amount of genetic material.
Meiosis comprises two successive nuclear divisions with only one round of DNA replication.
Four stages can be described for each nuclear division.
Interphase: Before meiosis begins, genetic material is duplicated.
First division of meiosis
Prophase 1: Duplicated chromatin condenses. Each chromosome consists of two, closely associated sister chromatids. Crossing-over can occur during the latter part of this stage.
Metaphase 1: Homologous chromosomes align at the equatorial plate.
Anaphase 1: Homologous pairs separate with sister chromatids remaining together.
Telophase 1: Two daughter cells are formed with each daughter containing only one chromosome of the homologous pair.
Second division of meiosis: Gamete formation
Prophase 2: DNA does not replicate.
Metaphase 2: Chromosomes align at the equatorial plate.
Anaphase 2: Centromeres divide and sister chromatids migrate separately to each pole.
Telophase 2: Cell division is complete. Four haploid daughter cells are obtained.
One parent cell produces four daughter cells. Daughter cells have half the number of chromosomes found in the original parent cell and with crossing over, are genetically different.
Meiosis differs from mitosis primarily because there are two cell divisions in meiosis, resulting in cells with a haploid number of chromosomes.
explain the process of human pregnancy or gestation period.
relate basic genetics with breeding in life.
INTRODUCTION
Cell is a basic unit of life. Our bodies and all living things are made up of cells. An understanding of the structure and functions of cells has enabled man to understand about life. By understanding the tiniest part of our life, makes us an individual who can applied knowledge to improve our life.
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2.0 TYPES OF A LASER.
