Principles of Inheritance and Variation 2 Flashcards
define:
i) inheritance
ii) variation
iii) genetics
i)Inheritance is the process by which charcaters are passed down from parent to progeny
ii) Variation is the degree by which progeny differ from their parents.
iii) Genetics is the branch of biology that deals with inheritance as well as variation of characters from parents to progeny.
why did mendel use the pea plant?
i) Easily available on a large scale
ii) many varieties with distinct charactaers
- canbe self pollinated or cross pollinated easily
-have a short lifecycle of 2-3 months and easy to cultivate(annual plant)
- pea seed is large
why were mendels’ expts so successsful
- During Mendel’s investigations into inheritance
patterns it was for the first time that statistical
analysis and mathematical logic were applied
to problems in biology. - His experiments had a large sampling size, which gave greater
credibility to the data that he collected. - Also, the confirmation of his inferences from
experiments on successive generations of his
test plants, proved that his results pointed to
general rules of inheritance rather than being
unsubstantiated ideas. - He studied 1 character at a time and then two characters simultaneously, while predecessors studied many at a time
- He used artificial methods to prevent cross pollination by unwanted pollen grains.
- the studied qualitative characters in a quantitative manner. He maintained statistical records.
what type of experiments did mendel conduct
Mendel investigated
characters in the garden pea plant that were
manifested as two opposing traits, e.g., tall or
dwarf plants, yellow or green seeds.
Mendel conducted such artificial
pollination/cross pollination experiments
using several true-breeding pea lines.
what is truebreeding /pure line
A truebreeding line is one that, having undergone
continuous self-pollination, shows the stable trait inheritance and
expression for several generations.
Mendel selected 14 true breeding pea lines
what are the 7 traits that mendel has considered. Name chromosomes on which the genes are present?
i) Flower colour- purple (dom)/ white-1st
ii) Seed colour- yellow(dom)/ green-1st
iii) Seed shape- ROund( dom)/ wrinkled-7th
iv) Pod colour- green(d)/ yellow- 5th
v) Pod shape-smooth/inflated(d)/ constricted -4th
vi) Flower position- axial(d)/ terminal-4th
vii) height- tall (d)/ dwarf-4th
what is F1 generation or filial one generation?
Mendel took a plants which are true breeding line and self pollinated them.
He collected the seeds produced
as a result of this cross and grew them to
generate plants of the first hybrid generation.
This generation is also called the Filial1
progeny or the F1
. Mendel observed that all
the F1 progeny plants were tall, like one of
its parents; none were dwarf (Figure 5.3). He
made similar observations for the other pairs
of traits – he found that the F1 always
resembled either one of the parents, and that
the trait of the other parent was not seen in
them.
what did he observe in F2 generation
Mendel then self-pollinated the tall F1
plants and to his surprise found that in the
Filial2The
proportion of plants that were dwarf were
1/4th of the F2
plants while 3/4th of the F2
plants were tall.
generation some of the offspring were
‘dwarf. The tall and
dwarf traits were identical to their parental type and did not show any
blending, that is all the offspring were either tall or dwarf, none were of inbetween height
what were mendelian factors
Mendel proposed that something
was being stably passed down,
unchanged, from parent to offspring
through the gametes, over
successive generations. He called
these things as ‘factors’. Now we call
them as genes. Genes, therefore, are
the units of inheritance.
i what are genes? what are alleles?
Genes, therefore, are
the units of inheritance. They
contain the information that is
required to express a particular trait
in an organism. Genes which code
for a pair of contrasting traits are
known as alleles, i.e., they are
slightly different forms of the same
gene.
why is there no blending in filial 2 generation
when the tall and
dwarf plant produce gametes, by the process of
meiosis, the alleles of the parental pair separate or
segregate from each other and only one allele is
transmitted to a gamete. This segregation of alleles
is a random process and so there is a 50 per cent
chance of a gamete containing either allele, as has
been verified by the results of the crossings.
what is a punnett square
It is a graphical
representation to calculate the probability of all
possible genotypes of offspring in a genetic cross.
It is discovered by British scientist RC punnett.
Mendel used maths in biology explain.
Mendel applied statistical analysis and mathematical logic to explaining the results binomial expression (ax +by)2
, that has the gametes
bearing genes T or t in equal frequency of ½. The expression is expanded
as given below :
(1/2T + 1/2 t)
2 = (1/2T + 1/2t) X (1/2T + 1/2t) = 1/4 TT + 1/2Tt + 1/4 tt\
Mendel had obtained the following results, which tallied with his experimental results-
(ax + by)2, where x and y are the two alleles for a character, occurring in a frequency of 50% each, so a and b are the frequency= ½.
(½ T + ½ t)2 = (½ T + ½ t) x (½ T + ½ t)
= ¼ TT + ¼ Tt + ¼ Tt + ¼ tt
= ¼ TT + ½ Tt + ¼ tt
= 1:2:1
what are test crpsses
The cross used to determine the genotype of an organism exhibiting a dominant trait is called test cross. IN this cross, the organism whose genotype is unknown is crossed with a double recessive organism.
If the offpsrings all have dominant trait , then the unknown organism has homozygous dominant
If the offpsrings have 50% dominant trait and 50% recessive trait, then the uknown organism has heterozygous dominant.
to know the genotype of a dominant phenotype, the results in offsprings of F1 tell if the parent was homozygous or heterozygous. Such a cross in which an unknown genotype of a dominant phenotype is crossed with a double recessive is called test cross.
What are reciprocal crosses
A cross, with the phenotype of each sex reversed as compared with the original cross, to test the role of parental sex on inheritance pattern. For example, if the pollen (male) from tall plants is transferred to the stigmas (female) of dwarf plants in one cross, the reciprocal cross would use the pollen of dwarf plants to pollinate the stigmas of tall plants.
Reciprocal cross- tall male x dwarf female
Tall female x dwarf male
