Download Mendel`s Law of Segregation “The two members of a gene pair

Mendel’s Law of Segregation
“The two members of a gene pair segregate from each other into the gametes; so half
the gametes carry one member of the pair and the other half of the gametes carry the
other member of the pair”.
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Allele pairs separate during the formation of gametes and randomly unite at
fertilisation.
He bred; pure tall and pure short pea plants to
generate the tall F1 progeny; he then crossed tall
progeny with themselves and found that the
offspring were 3 tall and 1 short. This led Mendel to
conclude that for short plants to arise from two tall
plants – the tall and short factors must separate
sometime between gamete production and fertilisation. The
molecular mechanism behind this is meiosis – special type of cell
division/replication involved in sexual reproduction.
In human reproduction; meiosis produces four daughter cells – all
with different genetic information. A chromatid is one half of the
two identical copies of a duplicated chromosome which are joined
at the centromere. The centromere is a part of the chromosome that links sister chromatids and
attaches to the spindle during division.
Mendel’s Law of Independent Assortment
“The assortment of the alleles of different traits during gamete formation is totally independent of
their original combinations in the parents”.
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The presence of one allele does not depend on what other alleles are present in the oocyte r
spermatozoa.
Mendel noticed that the height of the plant, colours of the flowers or shape of the seeds had no
impact on one another which led him to conclude that different traits are inherited independently
from one another. This is found to be true for genes that are on different chromosomes, however,
genes on the same chromosome generally do not assort independently from one another. The
molecular principle behind this is also meiosis.
Mendel’s Law of Dominance;
“When two unlike factors responsible for a single character are present in the one individual, one
factor can mask the expression of the other”.
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The phenotype of one allele dominates over the other.
Mendel crossed pure tall plants with pure short plants – all off the F1 progeny were tall. When factors
are mixed, the tall factor dominates over the short factor. The molecular mechanism behind this is
the fact that genes code for proteins. Each gene/allele encodes a protein which is transcribed into
mRNA and translate into protein. Two different alleles at the same locus are the heterozygous
genotype and produce two different protein products. This different protein expression leads to the
development of different phenotypes and the simplest explanation is that one product is nonfunctional.