Inheritance Flashcards
(23 cards)
genetics
branch of the biological sciences
that concerns inheritance of traits (heredity)
traits
individual characteristics that can
range from visible to molecular to behavioral
genotype
the alleles of individuals
- genotype and environmental conditions can
both influence the phenotype of individuals
phenotype
observable traits
J. Gregor Mendel
an
Austrian monk who used
experiments with garden
peas to establish rules of
trait inheritance in 1865
- he founded genetics, but his research was ignored until long after his death
mendelian genetics
Mendel chose to
use garden peas
for his research.
- inexpensive
- easy to grow
- many seeds
- visible traits
- mate control
principle of dominance
purebred peas with round seeds were crossed
with purebred peas with wrinkled seeds, while
hybrid offspring were allowed to self-fertilize
monohybrid cross
a breeding experiment between P generation (parental generation) organisms that differ in a single given trait. The P generation organisms are homozygous for the given trait. However, each parent possesses different alleles for that particular trait
dominant gene
particular variant of a gene, which for a variety of reasons, expresses itself more strongly all by itself than any other version of the gene which the person is carrying, and, in this case, the recessive
- RR is homozygous dominant (round seeds),
and individuals make gametes with R allele
recessive gene
a gene whose effects are masked in the presence of a dominant gene
- rr is homozygous recessive (wrinkled seeds),
and individuals make gametes with r allele
principle of segregation
mendel proposed that a parent carries two
of each hereditary factor (gene), and those
factors separate (during meiosis) such that
a gamete will carry only one of the factors.
- uppercase and lowercase letters were used
to represent dominance (RR) and recessiveness (rr)
- Rr is a heterozygote (round seeds due to the
dominance of R alleles), and individuals can
produce gametes that carry the R or r allele
probability rules
addition for two mutually exclusive
events (cannot happen at the same time):
- p(A or B) = p(A) + p(B)
- Multiplication rule for two independent
events (one does not influence the other):
- p(A and B) = p(A) × p(B)
principle of independent assortment
proposes
that genes affecting different traits are passed
down to offspring independently of each other
- purebred peas with yellow and round seeds
were crossed with purebred peas with green
and wrinkled seeds, while hybrid offspring
of that mating were allowed to self-fertilize
heterozygote
Rr is a heterozygote (round seeds due to the
dominance of R alleles), and individuals can
produce gametes that carry the R or r allele
- heterozygotes will express only the dominant
trait according to the principle of dominance
incomplete dominance
incomplete dominance is a non-Mendelian
pattern of inheritance where heterozygotes
express a phenotype that is intermediate to
the phenotypes of homozygous individuals
codominance
another non-Mendelian inheritance pattern
is codominance, where heterozygotes express
both phenotypes of homozygous individuals
- ABO blood types are an example in humans
- Gene ABO is on chromosome 9 and codes for
an enzyme that attaches different sugars (A,
B, or none) to the surfaces of red blood cells
epistasis
an interaction in which one gene
can influence how another gene is expressed
- example is the color of
- labrador retrievers
One gene codes for a protein that is needed
to produce the pigment, and black pigment
(B) is dominant to the chocolate brown (b)
- another gene encodes a protein involved in
depositing the pigment in hair follicles, and
pigment (E) is dominant to no pigment (e)
sex-linked traits
reciprocal crosses switch the phenotypes
of male and female parents, and different
results indicate sex is an important factor
- sex-linked inheritance is caused by genes
located on the sex chromosomes (X or Y)
- X and Y symbols are used with uppercase
and lowercase letters to represent alleles
multiple allelism
the existence of more
than two alleles for a gene in populations
- similar to our ABO gene, there are three
alleles for a gene on the Z chromosome in
pigeons that affects the color of feathers
ZW system
ZW is a genetic sex determination system
used by birds and many other organisms
- males are ZZ and females are ZW, which
is opposite to the XY system in mammals
pedigree
pedigrees are family trees that also provide
information about the inheritance of traits
quantitative analysis
quantitative traits vary on a continuous scale
in populations rather than fall into categories.
- quantitative traits are influenced by multiple
genes (polygenic) and environmental factors
- height
- metabolic rate
- blood pressure
- hair color
extranuclear DNA
mitochondria and chloroplasts contain their
own DNA that is separate from the nucleus.
- human mitochondrial DNA is arranged in a
circle and has only 37 genes, all of which are
essential for normal mitochondrial function.
- mitochondrial DNA is inherited maternally
for most animals, including human lineages
