TEST CROSS
To test whether homozygous or hetero..
Unknown genotype offspring × recessive parent
If heterozygous, result is 1:1
Mendel also worked with two characters on pea plant. He chose color and shape of the seed to explain the inheritance of two genes.
Y – dominant yellow color
y – recessive green color
R – round shape of the seed
r – wrinkled shape of the seed
Phenotypic Ratio:
Round yellow : round green : wrinkled yellow : wrinkled green
9 : 3 : 3 : 1
So, monohybrid ratio phenotype ratio 3:1 is followed in dihybrid cross also.
Both colour 3:1
Shape 3:1
LAW OF INDEPENDENT ASSORTMENT
Segregate and then inheritated seperately
So, equal chance for each gamete to carry an allele, and then express itself in offspring.
CHROMOSOMAL THEORY OF INHERITANCE
- Mendel published his work on inheritance of characters in 1865 but was unrecognized till 1900.
Why remain unrecognised?
1. Lack of communication, not published widely
2. Mendal- 1 gene- controls - 1 character
1gene- 2 alleles- 2 different character
Which do not blend with each other
So, unacceptable.
3. Mathematics and statistics
4. Lack of proof, (regarding factor/gene)
- In 1900, de Vries, Correns and von Tschermak worked independently and rediscovered Mendel’s results.
Imp reason of Rediscovery-- microscopy- cell division- chromosomes
- In 1902, Walter Sutton and Theodore Boveri studied the chromosomal movement during meiosis.
- They observed- behaviour of chromosome is like the behaviour of mendal factors.
- According to this theory, (combination of these 2)
- Genes are located at specific locations on the chromosomes.
- Chromosomes as well as gene both occur in pairs.
- Homologous chromosomes + genes separate during meiosis.
- Fertilization restores chromosome number to diploid condition.
- Chromosomes + genes segregate as well as assort independently.
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