Md. Kawsar Ali Hawlader Senior Lecturer Dept. Of Biology Sub:Biology Second Paper

Chapter – 11 Genetics and Evolution

The 1 st law of Mendel and Lethal gene

Learning output  tell the name of the father of genetics  explain the Mendel’s 1 st law  explain the lethal gene. After completing this lesson students should be able to…

Gregor Johhan mendel (1822 to 1884) is the father of genetics.

Mendel’s 1 st law When a pair of alleles is brought together in hybrid union in a monohybrid cross, the members of the allelic pair remain together without mixing, diluting or altering each other and separate or segregate from each other when the hybrid forms gametes.

The example and explanation of Mendel’s 1 st law The law can be explain by crossing between pure black guinea pig and pure brawn guinea pig. Suppose, for the black coloured dominant gene is-B the genotype of black guinea pig is-BB for the brawn coloured recessive gene is-b the genotype of brawn guinea pig is-bb

BbBb BbBbBbBbBbBb BB bb

BbBb BbBb Bb b B BBBb bb

Lethal gene A gene whose expression results in the death of the organism, usually during embryogenesis is known as lethal gene. French scientist Lucien Cuenot in 1905 first discovered the lethal gene in mice.

Explanation of lethal gene Suppose, yellow coloured dominant lethal gene is –Ay agouti coloured recessive gene is-a Crossing of two mice are shown in the Punnett square-

A y a Ay a AyAyAya a aa A y a

Result of crossing Genotype- AyAy : Aya :aa Phenotype- death: yellow: agouti 1 : 2 : 1= 2:1 The result of lethal gene is a deviation of Mendel’s 1 st law.

Group-A Write down the explanation of Mendel’s 1 st law. Group-B Write down the explanation of lethal gene.

BBbb F1 ? F2 ? a.What is allele ? b.What is meant by homozygous? c.Explain the cross up to mentioned generations. d.Analyse the genetic explanation of mentioned law.

HOME WORK Show the cross of Mendel’s 1 st law in a punnett square.