PEWARISAN SIFATPEWARISAN SIFAT(HUKUM MENDEL I DAN II)(HUKUM MENDEL I DAN II)

MENDELIAN INHERITANCE

MENDELIAN INHERITANCE

• Mendel mempelajari pada kacang kapri (Pisum sativum) terutama pada variasi bentuk dan warna ditandai dengan hubungan dominan-resesif.

• Mendel mempelajari sifat-sifat tanaman yang dikendalikan gen pada kromosom berbeda.

• Mendel mempelajari pada tanaman menyerbuk sendiri (self pollination).

Hasil Percobaan Mendel pada satu sifat mengarah pd Dominan Sempurna

No Fenotip parental F1 F2

1 Round x wrikled seeds All round 2.96 : 1

2 Yellow x green seeds All Yellow 3.01 : 1

3 Purple x white petals All Purple 3.15 : 1

4 Inflated x pinched pods All inflated 2.95 : 1

5 Green x Yellow pods All green 2.82 : 1

6 Axial x terminal flowers

All Axial 3.14 : 1

7 Long x short stems All long 2.84 : 1

LAWS OF INHERITANCELAWS OF INHERITANCE

• Law of SegregationLaw of Segregation• Law of independent assortmentLaw of independent assortment

1. LAW OF SEGREGATION1. LAW OF SEGREGATION• The Law of Segregation • at the time of gamete formation, members of a

pair of unit characters segregate (separate) from one another and move into different gametes

• Thus parents like this Tt and Tt make these gametes

T t T t

CHROMOSOMAL BASIS OF SEGREGATIONCHROMOSOMAL BASIS OF SEGREGATION

Ova or sperm

• Segregation occurs in meiosis at MI and then at MII

• As a result, the ova or sperm contribute different homologous chromosomes to the progeny

2. LAW OF INDEPENDENT . LAW OF INDEPENDENT ASSORTMENTASSORTMENT

• This law states that at the time of reproduction the members of two or more pairs of unit characters follow the law of segregation independently of each other and segregation independently of each other and assort themselves at random assort themselves at random into the gametes

MEIOSIS MECHANISMS PRODUCE INDEPENDENT ASSORTMENT

• Meiosis I provides the independent assortment of chromosomes and genes into the gametes.

• The homologues are arranged at random at the equatorial plane in Metaphase I

• This results in four different possible combinations of chromosomes and genes in the gametes, in a 1:1:1:1 ratio:

DOING THE CROSS

• Using these laws we can see how Mendel got the 3 tall to 1 short ratio (3:1) among the peas:

B b B b gametes

BB Bb Bb bb offspring

Bb X Bb parents

MONOHYBRID CROSS MONOHYBRID CROSS (CROSS WITH ONLY 1 TRAIT)(CROSS WITH ONLY 1 TRAIT)

DIHYBRID CROSSESDIHYBRID CROSSES

• Dihybrid crossesDihybrid crosses are made when phenotypes and genotypes composed of 2 independent alleles are analyzed.

• Process is very similar to monohybridmonohybrid crosses.

1.Which traits are dominant?2. Did the phenotypes of the P1 generation affect the F1 or F2 generations?

Dihybrid cross - phenotypes

Analysis of dihybrid cross phenotypes(forked-line/probability method)

Trait 1 Trait 2 Combined traits

Since yellow and round are dominant,Let G = yellow, g = green, W = round, w = wrinkled.

Dihybrid Cross: P1 cross

Confirm on your own using a Punnett square!

Dihybrid Cross: F1 cross

Dihybrid Cross: Summary

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Dihybrid Testcross: How to determine the genotype of an individual with

2 traits of dominant phenotype

All yellow All RoundMixed

Dihybrid Testcross: How to determine the genotype of an individual with

2 traits of dominant phenotype

All yellow All RoundMixed

A TEST CROSS• What if you only know

that you have a black and a brown guinea pig (i.e. you don’t know the genotype)?

• Do a test cross• Cross with a known true-

breeding recessive brown guinea pig

• Uji silang digunakan untuk mengetahui genotipe yang disilangkan

BACKCROSS

Backcross atau silang balik adalah persilangan antara keturunan pertama dengan salah satu tetua (parents), Tujuannya untuk memindahkan gen atau sifat tertentu dari salah satu tetua.

Tetua yang memberikan sifat tersebut dinamakan “tetua donor”

BACKCROSS (Silang balik)

P ♀ AA X ♂ aa

BC F1 Aa

aa : tetua donorAA : penerima

P ♀ AA X ♂ aa

BC

F1 Aa

aa : penerimaAA : tetua donor

Pada silang balik, ada tetua donor dan penerima

BACKCROSS

RECIPROCAL CROSSES (Persilangan Resiprok)

P ♀ hh X ♂ HH kuning hijau

F1 Hh (hijau)

F2 1 HH (hijau) 2Hh (hijau) 1hh (kuning)

P ♀ HH X ♂ hh hijau kuning

F1 Hh (hijau)

F2 1 HH (hijau) 2Hh (hijau) 1hh (kuning)

Hasil tidak berbedaArti : Gen pengendali warna ada di dalam inti

RUMUSAN UMUM UNTUK JUMLAH GAMET DAN

TURUNAN DARI n PASANGAN GEN HETEROZIGOT Jumlah

pasangan gen heterozigot

Jumlah genotipe gamet

Jumlah fenotipe turunan

Jumlah genotipe turunan

Jumlah kombinasi gamet yg

mungkin ada

1 2 2 3 4

2 4 4 9 16

3 8 8 27 64

4 16 16 81 256

n 2n 2n 3n 4n