Different crosses performed by Gregor

Mendel

AAPD2BB

Gregor mendel

3 Hypothesis of Mendel

• Hereditary determinants do not “mix” or “contaminate each other”.

• Segregation is the method of separating alleles; they are independent from each other.

• Gametes produced by segregation come together in pairs at random.

Mendelian laws of Inheritance

1. Law of independent assortment-alleles separate independently to each other.

2. Law of segregation-the paired genes separate in the formation of the reproductive cells. It forms together as a zygote.

3 Generalization of Mendel

1. The f1 holds the dominant trait . In crossing a pure breeding variety , only one trait will appear in the f1 and that is the dominant trait.

2. In crosses it doesn’t matter which parent variety contributes the gametes, reciprocal crosses will yield the same result

3. The trait that doesn’t appear in f1 will appear in f2 in a 25% of each progency.

Wild type: common/ dominantMutant: not common/ recessive

2 traits:• Morphological trait

- It is the trait referring to the external or visible characteristics of traits; like phenotype.

• Molecular trait- It is the intrinsic characteristics in

the organism; can’t be seen externally.

Monohybrid cross

• is a method of determining the inheritance pattern of a trait between two single organisms.

• is a cross between parents who are true-breeding for a trait

• Monohybrid inheritance is the inheritance of a single characteristic. The different forms of the characteristic are usually controlled by different alleles of the same gene.

Example:

A normal woman whose parents are both heterozygous normal marries a normal man whose mother is albino and whose father is normal. He has an albino sister. The couple has a normal and albino sons.

a. Construct a pedigree and give the genotypes of all persons involved.

b. If the couple plans to have three more children. What is the probability of having 2 normal and 1 abnormal?

Albinism: recessiveNormal: dominant

A: NORMALa: ALBINISM

a.

b.

n! 3! 3 x 2 x 1

a! (n-a) 1!(2)! 1 x (2 x 1)

3n 2 a 1 = 3 ( ¾ )2 ( ¼ ) = 27/64

Aa x Aa

Albinism = carrier of recessive trait

3

AA AaAa

aa

Dihybrid cross

• is a cross between F1 offspring of two individuals that differ in two traits of particular interest.

• The cross between their offspring is referred to as a dihybrid cross, in which parents are both heterozygous.

• is often used to test for dominant and recessive genes in two separate characteristics. Such a cross has a variety of uses in Mendelian genetics.

Example:

• P1: yellow, round X green, wrinkled

• F1: all yellow, round• F2: 9/16 yellow, round ; 3/16

yellow, wrinkled ; 3/16 green, round ; 1/16 green, wrinkled 

Test cross

• It is a test for genotypes; -heterozygous - 1:1-homozygous – 1:0

• This cross uses the recessive traits.

Example:

1. D x ddDd Dd Dd Dd= DD

2. D x ddDd Dd dd dd= Dd

Trihybrid cross

• The mating of two individuals, organisms, or strains that have different gene pairs that determine three specific traits or in which three particular characteristics or gene loci are being followed.

Example:

23 = 8 * 8 = 64

Fork-line method

MEANING:• The fork line method can be used by

figuring the occurrence of each gene or set of genes to be found in the gamete, and then multiply them together.

• This can be multiplied by figuring each trait or combination of traits separate for both the male and female, or each gene individually regardless of sex.

P1: WWGG * ww gg

F1: Ww Gg * Ww Gg

F2: Ww * Ww Gg * GgWW Ww Ww ww GG Gg Gg gg

Phenotypes:

¾ W ¾ G = 9/16 WG

¼ g = 3/16 Wg

¼ w ¾ G = 3/16 wG

¼ g = 1/16 wg

Phenotypic ratio:9:3:3:1

Genotypes: ¼ GG = 1/16 WW GG

¼ WW 2/4 Gg = 2/16 WW Gg

¼ gg = 1/16 WW gg

¼ GG = 3/16 Ww GG

2/4 Ww 2/4 Gg = 4/16 Ww Gg

¼ g = 2/16 Ww gg

¼ GG = 1/16 ww GG

¼ ww 2/4 Gg = 2/16 ww Gg

¼ gg = 1/16 ww gg

genotypic ratio: 1:2:1:2:4:2:1:2:1

POLYHYBRID CROSS

• Describing an individual, organism, or strain that is heterozygous for more than three specific traits or gene pairs or that is the offspring of parents differing in more than three specific gene pairs.

2 rules in solving probability

• Addition rule- If it is mutually exclusive; the same.

ex: b+gb+gb2+ bg

bg+ g2b2+2bg+g2

• Multiplication rule- If it is independent; it is different.

ex:DdAa * DdAa

DD Aa Dd ddAA Aa Aa aa

(3DD + 1d ) (3A + 1a ) = 9DA