Heredity-3 Flashcards
what will happen if progeny inherits 1 whole gene set
If progeny plants inherited a
single whole gene set from each parent, then the experiment explained
in Fig. 9.5 cannot work. This is because the two characteristics ‘R’ and
‘y’ would then be linked to each other and cannot be independently inherited.
how do we ensure the stability of dna
This is explained by the fact that each gene set is present, not
as a single long thread of DNA, but as separate independent pieces,
each called a chromosome. Thus, each cell will have two copies of each
chromosome, one each from the male and female parents. Every germcell will take one chromosome from each pair and these may be of either
maternal or paternal origin. When two germ cells combine, they will
restore the normal number of chromosomes in the progeny, ensuring
the stability of the DNA of the species.
is temp imp in detemining gender of offspring
Some rely entirely on environmental cues. Thus,
in some animals like a few reptiles, the temperature at
which fertilised eggs are kept determines whether the
animals developing in the eggs will be male or female. In
other animals, such as snails, individuals can change sex,
indicating that sex is not genetically determined.
explain sex determination in human
Most human chromosomes
have a maternal and a paternal copy, and we have 22
such pairs. But one pair, called the sex chromosomes, is
odd in not always being a perfect pair. Women have a
perfect pair of sex chromosomes, both called X. But men
have a mismatched pair in which one is a normal-sized X
while the other is a short one called Y. So women are XX,
while men are XY. All children will inherit an X chromosome
from their mother regardless of whether they are boys or
girls. Thus, the sex of the children will be determined by
what they inherit from their father. A child who inherits
an X chromosome from her father will be a girl, and one
who inherits a Y chromosome from him will be a boy.
