BBT Genetics II

7/25/2019 BBT Genetics II

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Mendelian Genetics

Mendels experiments :

Hypothesis: Natural laws follow mathematical regula To uncover these laws, he realized that he would need to car

uantitative experiments in which the num!ers of o"spring ccertain traits were carefully recorded and analyzed.

#tudy organism: Garden pea, Pisum sativum

$dvantages: #everal properties of this species were particulaadvantageous for studying plant hy!ridization.

%. The species was availa!le in several varieties that had decdi"erent physical characteristics. Many strains of the garden availa!le that varied in the appearance of their height, &oweand pods.

'. The ease of ma(ing crosses. #elf fertilization

)ross* fertilization


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Methodology: #elected Two variants or traits of a character,perform

hy!ridization of these traits using true*!reeding lineschec( the num!er of progenies with a particular trait

$ variety that continues to produce the same trait after seve

generations of self*fertilization is called a true*!reeding line, +e selected characters

Mendel studied these characters !y crossing the varieach other. $ cross in which an experimenter is o!serone character is called a monohybrid cross, also casingle-factor cross.

-hen the two parents are di"erent variants for a givecharacter, this type of cross produces single*charactehy!rids, also (nown as monohy!rids.

Mendel ollowed the /utcome of a #ingle )haracter fGenerations


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Mendels proposals: +is 0rst proposal was that the variant for one characte

dominant over another variant. The term recessive is used to descri!e a variant that is mas(ed

presence of a dominant trait !ut reappears in su!seuent gene -hen a true*!reeding plant with a dominant trait was crossed

!reeding plant with a recessive trait, the dominant trait was alo!served in the % generation. 1n the ' generation, some o"spring displayed the dominant tr

a smaller proportion showed the recessive trait.

#econd proposal2the genetic determinants of traits aralong as 3unit factors4 from generation to generation.

1n % generation the recessive trait was mas(ed !y the presendominant, in the ' it reappeared without any change or !lend

Third proposal 2the factors segregate from each otherthe process that gives rise to gametes

-hen Mendel compared the num!ers of dominant and recessithe ' generation, he noticed a recurring pattern. -ithin expevariation, he always o!served approximately a 5:% ratio !etwedominant trait and the recessive trait.


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Mendels law of segregationstates that:

The two copies of a gene segregate (orseparate) from each other duringtransmission from parent to ospring.

Therefore, only one copy of each gene isfound in a gamete. $t fertilization, twogametes com!ine randomly, potentiallyproducing di"erent allelic com!inations.

-hen an individual possesses twoidentical copies of a gene, the individualis said to !e homozygous with respectto that gene. #o the 6 generation washomozygous

The term genotype refers to the geneticcomposition of an individual.TT and tt

are the genotypes of the 6 *generationin this experiment. % generation is heterozygous, with the

genotype Tt, !ecause every individualcarries one copy of the tall allele andone copy of the dwarf allele.

$lthough these plants are heterozygous,their phenotypes are tall !ecause theyhave a copy of the dominant tall allele.

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BBT Genetics II