Fundamentals of Genetics
Polygenes influence phenotypes heavily, but don’t entirely decide it. It is a gene whose
individual effect is too small to be observed, but which can act together with others to
produce observable variation. Also: quantitative trait loci (QTLs).
Polygenic inheritance: multiple different allele pairs have a similar and additive effect on a
given trait, for example height and skin color.
Heterozygote for a single gene (A/a) monohybrid.
Heterozygote for a double gene (A/a x B/b) -> dihybrid. A dihybrid cross= (Aa x Bb) x (Aa
xBb)
A seed that is purified for a desirable trait with a view for crossing it with another parent to
create a hybrid is called a parental line.
Mendel’s law of independent assortment:
The law is only valid when dealing with unlinked genes.
You start with the parent cell, this contains 2 chromosomes with Aa and Bb.
This cell goes into meiosis, which separates the cells into 4 versions, these are the
gametes (eggs/sperm).
The versions: AB, Ab, aB and ab (F1).
Each of these combinations has an equal probability of occurring because the allele
you give of one gene has no bearing on the alleles that gametes receive from other
genes.
So the ratio of the F1 will be 1:1:1:1.
Pure lines:
Homozygous.
Are essential for maintenance of stocks for research.
They are made through repeated generations of selfing: in animals, selfing is
accomplished by mating animals of identical genotypes.
Hybrid vigor:
It is the general superiority of multiple heterozygotes. It is the increase in stature,
biomass and fertility.
The F1 is superior to the better of the two parents.
When the hybrid undergoes meiosis, gene assortment breaks up the favorable allelic
combination only a few members of the next generation have the vigor
(health/hardness).
A heteromorphic pair: a chromosome pair with some homology, but are different in size,
shape, or staining properties.
Recombination: the production of new allele combinations.
Meiotic recombination: comparing the inputs with the outputs.
, You cross AB x ab, this cell undergoes meiosis. The 4 outputs are AB, ab and Ab and
aB. These last 2 are recombinants, they are different then the parental line.
Mitochondrial genes play a role in energy production. They regulate cellular metabolism and
play a role in apoptosis.
Chloroplast DNA (cpDNA) is involved in plastid gene expression and photosynthesis.
These two organelle genes are closely spaced and, in some organisms, they contain introns.
Organelle genes have a special mode of inheritance called uniparental inheritance
inherited from one parent, mostly maternal inheritance.
Why only the mother? the egg cell contributes the bulk of cytoplasm, the sperm
cell none. Organelle chromosomes are in the cytoplasm, and therefore the mother
gives all the organelle chromosomes.
Cytoplasmic segregation: organelle populations that contain mixtures of two genetically
distinct chromosomes often show segregation of the two types into the daughter cells after
1 or more cell divisions.
Cytoplasmic mutations in humans:
Sometimes rare disorders transmission only through females and never through
males. This suggests cytoplasmic inheritance and point to a mutation in mtDNA.
mtDNA mostly causes mutations that come to expression in the brain or muscles,
because they require much energy.
mtDNA can change during the lifetime.
Chromosome map: represents the arrangement of genes, shows the gene position (loci).
Reasons to map:
build complex genotypes.
Define the gene at the DNA level (structure and function).
To deduce the evolutionary genetic mechanisms through which genomes diverged.
Polygenes influence phenotypes heavily, but don’t entirely decide it. It is a gene whose
individual effect is too small to be observed, but which can act together with others to
produce observable variation. Also: quantitative trait loci (QTLs).
Polygenic inheritance: multiple different allele pairs have a similar and additive effect on a
given trait, for example height and skin color.
Heterozygote for a single gene (A/a) monohybrid.
Heterozygote for a double gene (A/a x B/b) -> dihybrid. A dihybrid cross= (Aa x Bb) x (Aa
xBb)
A seed that is purified for a desirable trait with a view for crossing it with another parent to
create a hybrid is called a parental line.
Mendel’s law of independent assortment:
The law is only valid when dealing with unlinked genes.
You start with the parent cell, this contains 2 chromosomes with Aa and Bb.
This cell goes into meiosis, which separates the cells into 4 versions, these are the
gametes (eggs/sperm).
The versions: AB, Ab, aB and ab (F1).
Each of these combinations has an equal probability of occurring because the allele
you give of one gene has no bearing on the alleles that gametes receive from other
genes.
So the ratio of the F1 will be 1:1:1:1.
Pure lines:
Homozygous.
Are essential for maintenance of stocks for research.
They are made through repeated generations of selfing: in animals, selfing is
accomplished by mating animals of identical genotypes.
Hybrid vigor:
It is the general superiority of multiple heterozygotes. It is the increase in stature,
biomass and fertility.
The F1 is superior to the better of the two parents.
When the hybrid undergoes meiosis, gene assortment breaks up the favorable allelic
combination only a few members of the next generation have the vigor
(health/hardness).
A heteromorphic pair: a chromosome pair with some homology, but are different in size,
shape, or staining properties.
Recombination: the production of new allele combinations.
Meiotic recombination: comparing the inputs with the outputs.
, You cross AB x ab, this cell undergoes meiosis. The 4 outputs are AB, ab and Ab and
aB. These last 2 are recombinants, they are different then the parental line.
Mitochondrial genes play a role in energy production. They regulate cellular metabolism and
play a role in apoptosis.
Chloroplast DNA (cpDNA) is involved in plastid gene expression and photosynthesis.
These two organelle genes are closely spaced and, in some organisms, they contain introns.
Organelle genes have a special mode of inheritance called uniparental inheritance
inherited from one parent, mostly maternal inheritance.
Why only the mother? the egg cell contributes the bulk of cytoplasm, the sperm
cell none. Organelle chromosomes are in the cytoplasm, and therefore the mother
gives all the organelle chromosomes.
Cytoplasmic segregation: organelle populations that contain mixtures of two genetically
distinct chromosomes often show segregation of the two types into the daughter cells after
1 or more cell divisions.
Cytoplasmic mutations in humans:
Sometimes rare disorders transmission only through females and never through
males. This suggests cytoplasmic inheritance and point to a mutation in mtDNA.
mtDNA mostly causes mutations that come to expression in the brain or muscles,
because they require much energy.
mtDNA can change during the lifetime.
Chromosome map: represents the arrangement of genes, shows the gene position (loci).
Reasons to map:
build complex genotypes.
Define the gene at the DNA level (structure and function).
To deduce the evolutionary genetic mechanisms through which genomes diverged.
