BiLOGY

[Silent Hunter]

hey people what is a test cross in biology inheritance? You do what means what is the procedure? :shock:

 

[Silent Hunter]

SORRY FOR THE WRONG TYPING ITS BIOLOGY

 

[intelnehalem]

A test cross is used to show how specific characters (usually one for OL syllabus) is inherited
Ex for a test cross:
Draw a test cross to show how height is inherited in Pea plants
H- tall allele
h- short allele
Tall (H) is dominant to Short (h)
WE CALL THIS A MONO HYBRID CROSS(ONLY 1 CHARACTER IS SHOWN IN THE CROSS)
We must first begin with identifying the parent's genotype. For this example, we could assume that both parents are pure bred.
One parent- Pure bred Short Pea plant (hh) [ For a recessive allele to bring out its phenotype, both the alleles in the organism has to be the same i.e- Short (Homologous chromosomes) ]
The other parent- Pure bred Tall Pea plant (HH) [Pure bred so both alleles has to be the same - Homologous chromosomes]
Genotypes of parents: HH x hh
Phenotypes of Parents : Tall x Short
gametes: (H) (H) x (h) (h) - GAMETES MUST BE ALWAYS IN A CIRCLE

Resulting (F1) generation genotypes : Hh , Hh , Hh, Hh
Phenotypes : All tall (Tall allele -H is dominant over short allele h (recessive ) so Tall allele is responsible for the phenotypes)
Genotypic ratio: N/A - ALL YOUNG ARE OF THE SAME GENOTYPE
Phenotypic ratio : N/A - ALL YOUNG ARE OF THE SAME PHENOTYPE

Now, we will cross these hybrids (Hh x Hh)

Genotypes of parents: Hh x Hh
Phenotypes of parents: Tall x Tall
Gametes : (H) (h) x (H) (h)
F2 generation genotypes: HH, Hh, Hh, hh
Genotypic ratio : HH:Hh:hh= 1:2:1
Phenotypes of young: Tall, Tall, Tall, Short
Phenotypic ration: Tall:Short= 3:1

This is a brief example. Hope you understood

 

[Silent Hunter]

THanks alot dude......but why you crossed Hh x Hh? in second cross you did

 

[intelnehalem]

THanks alot dude......but why you crossed Hh x Hh? in second cross you did

I did that cross to show how a ratio of 3:1 (Tall:Short) is achieved . Usually questions are based on that.