DAT Bio Genetics Flashcards
Gene
genetic material on a
chromosome for encoding a trait
Locus
location on chromosome where a
gene is located`
Allele
alternative forms of a gene that
allow for differences such as different hair
or fur colors
Homologous chromosomes
a pair of
chromosomes that contain the same
genetic material
i. Each parent contributes one of the
chromosomes in the pair, thus
allowing for different alleles to be
present for each gene
Law of Segregation
one member of
each chromosome pair migrates to an
opposite pole in anaphase I so that each
gamete is haploid
i. Basically, each gamete is left with one
copy of each allele
Law of Independent Assortment
the
migration of homologues within one pair
of homologous chromosomes does not
influence the migration of homologues of
other homologous pairs
Monohybrid cross
two organisms
with variations at one gene of
interest are crossed
Dihybrid cross
two organisms with
variations at two genes of interest
on different chromosomes are
crossed
Test cross
when the genotype of
an organism expressing the
dominant phenotype is unknown,
the unknown organism is crossed
with a homozygous recessive
organism to determine if the
unknown is homozygous dominant
or heterozygous dominant
Punnett squares
technique that
uses probability rules to determine the
outcomes of either monohybrid or
dihybrid crosses and the subsequent
expected frequencies
Incomplete dominance
blending of
expressions of alleles
For example, a red flower and white
flower are crossed to result in a
unique heterozygous pink offspring
Codominance
both of the inherited
alleles are completely expressed
i. For example, blood types A and B
can show as AB if both are
expressed
Multiple alleles
blood groups have
four possible phenotypes, the
codominant A, B, and O, leading to six
possible genotypes and four possible
phenotypes
AA/AO →
type a
BB/BO →
type b
AB →
codominant AB type
OO →
type O
Epistasis
the process in which one
gene affects the phenotypic
expression of a second gene. A
common example of epistasis is fur
pigmentation in mice → one gene
controls the production of pigment by
either turning on or turning off and the
second gene controls the color or
amount of color deposited in the fur.
Therefore, if the first gene codes for
no pigment, then the second gene has
no effect
Pleiotropy -
when a single
gene has more than one phenotypic
expression
Polygenic inheritance
the interaction
of many genes to shape a single
phenotype with continuous variation
such as height, skin color, or hair color
Linked genes
when two or more
genes reside physically close to one
another on the same chromosome and
therefore cannot separate
independently as they are inherited
together
Sex-linked genes
a type of linked gene
that refers to a single gene residing on a
sex chromosome that is inherited
differently in males and females
Sex-influenced genes
these differ
from sex-linked genes in that the
expression of genes can be influenced
by the sex of the individual carrying the
trait
Penetrance
this concept describes the
probability an organism with a specific
genotype will express a particular
phenotype
Complete penetrance means
the
genes for a trait are expressed in all
of the population who have the
gene
Incomplete penetrance means
the
genes for a trait are only expressed
in a percentage of the population
Variable Expressivity
describes the variation or range of
phenotypes for a specific genotype
X-inactivation
during embryonic
development in female mammals, one of
the two inherited X chromosomes does
not uncoil into chromatin, and remains as
a dark and coiled compact body, which is
referred to as a Barr body.
Nondisjunction
describes when one or
more chromosome pairs or chromatids
fail to separate during mitosis. (sister chromatids meiosis ii, homo chromosomes meiosis i)
Mosaicism
a phenomenon that
occurs in cells that undergo
nondisjunction in mitosis during
embryonic development; fraction of
body cells have extra or missing
chromosomes
Polyploidy
when all chromosomes
undergo meiotic nondisjunction and
produce gametes with twice the
number of chromosomes
Point mutation
single nucleotide
change causing either substitution,
insertion, or deletion—the latter two can
cause a frameshift mutation.
transition mutation
conversion of a purine to purine or
pyrimidine to pyrimidine.
transversion mutation
conversion of a purine to pyrimidine
or vice versa.
Aneuploidy
a genome with extra or
missing chromosomes, often caused by
nondisjunction (downs syndrome)
Klinefelter’s Syndrome
(XXY), in
which a male is born with an extra X
chromosome
Chromosomal aberrations
chromosome segments are changed
duplications
chromosome
segments are repeated on the same
chromosome, which can occur from
unequal crossing over
Inversions
chromosome segments
are rearranged in reverse orientation
Translocations
one segment of a
chromosome is moved to another
chromosome.
Chromosomal breakage
spontaneous
or induced breakage of a chromosomal
segment via mutagenic agents or X-rays
Mutagenic agents
include cosmic rays,
X-rays, UV rays, radioactivity, chemical
compounds including colchicine and
mustard gas that can cause genetic
mutations. Mutagenic agents are
generally also carcinogenic
Autosomal recessive conditions (genetic conditions)
Phenylketonuria (PKU), Cystic fibrosis, Tay-sachs
Phenylketonuria (PKU)
inability
to produce the proper enzyme for
phenylalanine breakdown, causing
degradation product
phenylpyruvic acid to accumulate
Cystic fibrosis
fluid buildup in
respiratory tracts
Tay-sachs
lysosome defect in
which cells can’t breakdown lipids
for normal brain function
Autosomal dominant conditions
Huntington’s disease, Achondroplasia, Hypercholesterolemia
Huntington’s disease
nervous system degeneration
Achondroplasia
causes dwarfism
Hypercholesterolemia
excess
cholesterol in blood that
progresses into heart disease
Sex-linked recessive conditions
Hemophilia, color blindness, Duchenne’s Muscular
Dystrophy
Hemophilia
sex-linked recessive
genetic condition causing
abnormal blood clotting
Color blindness
primarily observed in males
Duchenne’s Muscular
Dystrophy
progressive loss of muscle
Chromosomal disorders
changes
to the number or structure of
chromosomes
Down’s Syndrome
trisomy 21
Turner’s Syndrome
deletion of
X chromosome → XO genotype
Cri du Chat
deletion on
chromosome 5
Extranuclear inheritance
extranuclear
genes (genes present in organelles
other than the nucleus) are found in
mitochondria and chloroplasts
Lethal gene
Imagine we cross Aa x Aa,
and get 1 AA, 2 Aa, and 1 aa. If “aa” is
lethal, our genotypic ratio would be AA
and Aa present in a 1:2 ratio.
