5.1 Concept of Inheritance Based on Mendel’s Experiment

CHAPTER 5 : INHERITANCE

5.1 Concept of inheritance based on Mendel’s eperi!ent

"enetics #t$d% of &enes' heredit%' heredit%' and  and (ariation in (ariation  in li(in& or&anis!s )ased on eperi!ents cond$cted b% "re&or *ohann Mendel

Gregor Johann Mendel 

Gregor Mendel Conducted experiments on pea plants Pisum sativum

+h% Pisum Sativum?

It is easy to grow

Life cycle is short

Pollination of this plant can be easily controlled controlled

 Traits  Traits of this plant can can be easily observed

As a result, Mendel made a statement: ‘ A certain trait that is determined by internal factors that exist in pair of these factors, only one factor (now known as allele) allele ) is carried in every gamete

!his statement is called Mendels "st #aw $ #aw of segregation %:" : &eferred as Mendels Monohybrid 'nheritance &atio

"ENETIC# ,-CA)/AR0

Gene & Alleles Alleles

"ENE#

E(er% &ene sit$ated in specific position referred as loc$s

A stretch of NA 2 RNA that deter!ine a certain traits

nits of inheritance that are passed on to the net &eneration

 ALLELES

"enes that are alleles of one another al3a%s control the sa!e characteristic

"enes fo$nd at the sa!e loc$s on different ho!olo&o$s chro!oso!es are alleles of one

Phenotype & Genotype

Phenotype • expressed trait of an organism • characteristics that are visile! detectale or measurale

Phenotype • can & may chan&e throughout life due to en(iron!ental infl$ences • E"g"  # $air   # $eight  # %ody eight

Genotype • genetic composition of all the cells • depends on the inheritance of genes from its parents

Phenot%pe 4 &enot%pe  en(iron!ent

• E"g"  #Even  # Even though a child has inherited the genes for a ig ody si'e 6&enot%pe7 form his parents! his groth might e stunted 6phenot%pe7 if he does not get suff su fficient icient & alanced food 6en(iron!ent7

()M*+A+, & -ECESS*.E GE+E

(ominant gene • gene that can sho3 the phenot%pic epression for a trait that is under its control in either a homo'ygous / hetero'ygous state

-ecessive Genes • can only sho its phenotypic expression for a particular trait that is under its control in a ho!o8%&o$s state

Genotypic combination

Phenotype (h (hair texture)

CC (homoygous)

Curly hair

Cc (heteroygous)

Curly hair

cc (homoygous)

!traight hair

MENE/’# 9IR#T /A+ M)+)$0%-*( *+$E-*,A *+$E-*,A+CE +CE

Mendel1s 2irst La " Law of segregation " used pure breeding pea plants

Purple PP

3hite pp

Pure %reeding "plants that carries # same alleles for a particular trait " These genes are passed on from the parent to the progeny through selffertiliation only

Purple PP

3hite pp

• Explanation4 ,he inheritance of an organism is determined y &enes &enes that  that exist in pairs (uring the formation of gametes! every gamete only rings ith it one factor from the factors 3hen to alternate for one factor exist in an organism! only the do!inant factor ill e seen as phenot%pe

Male &a!ete

-

r 

9e!ale &a!ete

-

-- 5round6

-r 5round6

r

-r 5 round6

rr 5rin7led6

Punnett s8uare

Exercise 9

2igure shos the inheritance of height in plants" a6 *f , represents represents the the dominant dominant allele allele for tallnes tallness s & t the recessi recessive ve allele for darfness! complete the information given in the figure" 6 *f the 29! generation plants are self:pollinated! dra a genetic diagram to find out the percentage of the offspring of 2 ; generation that ould e a tall plant

• 3hat is the proaility of -r < -r producing rin7led seed=

• 3hat is the proaility of 0y < yy producing green seed=

Mendelian traits in humans

+)+ ME+(EL*A+ ,-A*,S *+ $>MA+

*s it possile for a ron:eyed parents to have a lue:eyed child==

THININ" TIME ;;

MENE/’# #EC-N /A+ ih%brid Inheritance

Crossing of ,all Pea Plants hich have round seeds ith darf pea plants hich have rin7led seeds

 

Gamete

,-

,r

t-

tr

 

Gamete

,-

,,-5tall! round6

,,-r  5,all!round6

,t-5tall!round6

,t-r  5tall!round6

,r 

,,-r  5,all!round6

,,rr  5tall!rin7led6

,t-r  5tall!round6

,trr  5,all!rin7led6

t-

,t-5,all!round6

,t-r  5tall!round6

tt-tt-r  5(arf! round6 5darf!round6

tr 

,t-r  5tall!round6

,trr  5,all!rin7led6

tt-r  5darf!round6

ttrr  5darf!rin7led6

Phenotype

,all/round

,all/rin7led

(arf/round

(arf/rin7led

Genotype 5,otal +umer6

,,-- 596 ,,-r 5;6 ,t-- 5;6 ,t-r 5?6

,,rr 596 ,trr 5;6

tt-- 596 tt-r 5;6

,trr 596

2raction

@/9

B/9

B/9

9/9

2; Phenotype ratio

@

B

B

9

Mendel’s #econd /a3 •  /a3 of independent assort!ent • during gamete formation! each memer of a pair of alleles may comine rando!l% ith either memer of another pair of alleles

Exercise 9