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Human Biology Form 5 Science

CHAPTER 1 : HERIDITY AND GENETICS

Introduction
  • Genetics : Genetics is defined as the study of heridity and variation.
  • Heridity : It is the transfer of parental characteristics to offfspring from one generatioin to another while  Variation is the difference in characteristics within a given popuulation.

MANDELS FIRST LAW(Law of segregation)

It states that «  genes are responsible for the development of the individual and they are independently transmitted from one generation to another wihout undergoing any change »

SOME TERMS USED IN GENETICS

  • Gametes :  It is a macture sexcell which takes part in a sexual reproduction. It may be either male(sperm) or female( eggcell)
  • Genes : It is the basic unit pf heridity.
  • Allele : It is the different form of the same gene or an allele is one of the different form of the same gene which alter the way in which a particular character such as heigh is expressed.
  • Zygote : A zygote is a single cell that is found as a result of a union a male sexcell and a female sexcell during reprodiction. It contains a diploiod number of chromosomes
  • Homozygous : It is a situation were by there are two similar or identical allele for a given character eg. TT for tall
  • Heterozygous : It is the situation wereby there are two disimilar or unidentical allele for a given character eg. Tt.
  • Phenotype : It is the outward expression or appearance of an organism.
  • Genotype : It is the genetics constitution or genetic makeup of an organism
  • Allelomorphs : It is a pair of genes responsible for a pair of contrasting character like red and white flower colours.
  • Chromosomes : Chromosomes are threadlike material or struction constitsting of nucleic acid and protons located within the nucleus of the cell.
  • Recessive : This is an allele which can not express itself outward in a phenotype but can do so in a homozygous state eg allele for shortness « tt » is recessive for the allele of tall »Tt »
  • Dominant : It refers to a stage in a gene that take autority during crosses
  • Pure breed or pure line : These are parent that have the same characteristics and when cross the offspring have a similar characteristics or trade talll plant cross with another tall plant gives life to tall offsprings TT when criss to TT gives rise to tall offspring
  • Hybrid : Hybrid are organism with a pair of different allele for a particular gene
  • Filiar generation : It is a generation of offspring represented by F1 or F2
  • Linkage : It is an existence of 2 or more allele of on the same chromosome.

Greger mendel is the father of genes. He carry out the process of using a garden pea plant

par Claude Foumtum