Gene Segregation and Interaction (LEC) Flashcards
according to Gregor Mendel (1865) can be analyzed through transmission of visible
characteristics in pea plants.
Genes
Genes according to ___ ___ (1865) can be analyzed through transmission of visible
characteristics in pea plants.
Gregor Mendel
The analysis of genetic crosses depends upon an understanding
of Mendel’s two laws:
principle of segregation
principle of independent assortment
demonstrating that the two members of
a gene pair (alleles) segregate (separate) from each other in the formation of gametes
principle of segregation
indicating that the genes for different traits separate independently
of one another and combine randomly in the formation of gametes during meiosis.
principle of independent assortment
can be defined as the mechanism of how progeny receives genetic information
from the parent.
inheritance
This simply means that due to ___, the members of the same family
possess similar characteristics. I
inheritance
During that period, he chose some distinct characteristics of the peas and conducted some
cross-pollination/ artificial pollination on the pea lines that showed stable trait inheritance
and underwent continuous self-pollination. Such pea lines are called ___ pea line
true breeding
In a monohybrid cross performed by Mendel, he took two pea plants of opposite traits
(one short and one tall) and crossed them. He found the first generation offsprings were tall
and called it __progeny
F1
Then he crossed F1 progeny and obtained both tall and short plants in
the ratio ___ in F2
3:1
Mendel even conducted this experiment with other contrasting traits like green
peas and yellow peas, round vs wrinkled, etc. In all the cases, he found that the results were
similar. From this, he formulated the Laws of __ and __
Segregation and Dominance
states that during the production of gametes, two copies of each
hereditary factor segregate so that offspring acquire one factor from each parent
law of segregation
alternative form of the gene
allele
In other
words, ___(alternative form of the gene) pairs segregate during the formation of gamete.
allele
According to the law of ___, hybrid offsprings will only inherit the dominant trait in the
phenotype
dominance
. The alleles that are suppressed are called as
recessive traits
s while the alleles
that determine the trait are known as the
dormant traits
Another experiment conducted by Mendel is a ___ cross, Mendel considered two traits,
each having two alleles
dihybrid
He crossed wrinkled-green seed and round-yellow seeds and
observed that all the first generation progeny (F1 progeny) were round-yellow. This meant
that dominant traits were the round shape and yellow color. He then self-pollinated the F1
progeny and obtained 4 different traits wrinkled-yellow, round-yellow, wrinkled-green seeds
and round-green in the ratio ____
9:3:3:1
He then self-pollinated the F1
progeny and obtained 4 different traits wrinkled-yellow, round-yellow, wrinkled-green seeds
and round-green in the ratio 9:3:3:1. After conducting for other traits, the results were found
to be similar. From this experiment, Mendel formulated the law of
independent assortment
states that a pair of trait segregates independently of another pair during gamete
formation.
law of independent assortment
As the individual heredity factors assort independently, different traits get ___
opportunity to occur together.
equal
Mendel extended his observations to ___crosses involving three pairs of contrasting
characters.
trihybrid
character where mendel did a monohybrid cross
stem length (short and tall)
characters where mendel did a dihybrid cross
pea shape and pea color
(round, wrinkled)
(yellow, green)
characters where mendel did a trihybrid cross
seed shape (smooth vs wrinkled)
color of cotyledon (yellow vs green)
flower color (violet vs white)
The F1
hybrid produces ___ types of gametes in Mendel’s trihybrid cross
8
These on selfing have equal chances to combine with
any of the 8 types of gametes produced by the other parent resulting in ___ different
combinations.
64
The number of F2 phenotypes resulting from selfing F1 hybrid is a square of the number of
___.
GAMETES
may result to
modified phenotypic ratios deviating from those expected of independently assorting genes
exhibiting complete dominance
gene interaction
involving alleles of a gene
pair
allelic interactions
wherein interaction is between alleles of different genes.
non allelic
– one gene controlling one trait
allelic interactions
allelic interactions include
complete dominance
incomplete dominance
co-dominance
overdominance
dominant lethal
recessive lethal
Heterozygotes are phenotypically identical to the homozygous dominant
complete dominance
f2 phenotypic ratio of complete dominance
3:1
Heterozygotes are phenotypically intermediate between
the two homozygous types
incomplete dominance
f2 phenotypic ratio of incomplete dominance
1:2:1
Heterozygotes
exhibit a mixture of the phenotypic characters of both homozygotes instead of a
single intermediate expression.
co dominance
f2 phenotypic ratio of codominance
1:2:1
Heterozygotes exhibit an exaggeration of phenotypic characters of either
homozygous dominant or homozygous recessive.
overdominance
f2 phenotypic ratio of overdominance
1:2:1
Death of the affected
individual (homozygous dominant or heterozygous) occurs after reproduction
takes place.
dominant lethal
f2 phenotypic ratio of dominant lethal
0:2:1 or 0:1
Effects of recessive genes
are sufficiently drastic to kill the bearers of certain genotypes.
recessive lethal
f2 phenotypic ratio of recessive lethal
1:2:0 or 3:0
– two genes controlling one trait
non allelic interactions
An allele of a gene masks the effect of the allele of the other gene
epistasis
Complete dominance at both gene pairs
but one gene when dominant is epistatic to the
other (A dominant to a; B dominant to b; A epistatic to B and b).
dominant epistasis
f2 phenotypic ratio of dominant epistasis where
Complete dominance at both gene pairs
but one gene when dominant is epistatic to the
other (A dominant to a; B dominant to b; A epistatic to B and b).
12:3:1
Complete dominance at both gene pairs but the first gene when dominant is
epistatic to the second and the second gene, when
homozygous recessive is epistatic to the first (A dominant to a; B is dominant to B; A is epistatic to B and B; bb is epistatic to A_ and aa)
dominant epistasis
Expected F2 phenotypic ratio of Dominant epistasis where
Complete dominance at both gene pairs but the first gene when dominant is
epistatic to the second and the second gene, when
homozygous recessive is epistatic to the first (A dominant to a; B is dominant to B; A is epistatic to B and B; bb is epistatic to A_ and aa)
13:3
Complete dominance at both gene pairs, but
one gene, when homozygous recessive is epistatic or masks the effecr of the o
ther gene (A dominant to a; B dominant to b; aa epistatic to B and b)
recessive epistasis
f2 expected ratio of recessive epistasis
9:3:4
Complete dominance at both gene pairs, but either gene, when dominant
is epistatic to the other (A dominant to a; B
dominant to b; A epistatic to b; B epistatic to a).
duplicate gene action
expected f2 ratio of duplicate gene action
15:1
Complete dominance at both gene pairs,
but either gene when homozygous recessive is epistatic to the effects of the ot
her gene (A dominant to a; B dominant to b; bb epistatic to A
complementary gene action
complementary gene action expected f2 phenotype
9:7
Complete dominance at both gene pairs, new phenotypes are
produced from interaction between dominants and
between both homozygous recessives (A dominant to a; B dominant to b;a in
teracts with B producing new phenotype; aabb also produces a new phenoty
pe)
novel phenotype
novel phenotype f2 phenotype
9:3:3:1
Although individual humans (and all
diploid organisms) can only have two alleles for a given gene, __alleles may exist at
the population level, such that many combinations of two alleles are observed.
multiple
An example of
multiple alleles is the
ABO blood type system
alleles in ABO blood type
IA
IB
i
codes for A molecules on the red blood cells
IA
allele codes for B molecules on the surface of red blood cells
IB
___ allele codes for
no molecules on the red blood cells
i
__ alleles are codominant with
each other in ABO blood group
Ia and Ib
genotype when phenotype is Blood Type A
IaIa or Iai
genotype when phenotype is Blood Type B
IbIb or IBi
genotype when phenotype is Blood Type AB
IAIB
genotype when blood type is O
ii
-chromosome is smaller, and so, very few genes are located
on this chromosome.
Y chromosome
Sex traits can be categorized into three types of inheritance
sex limited
sex linked
sex influenced
s are genes that occur in both sexes
(probably on the autosomes) but are normally expressed only in the gender having the
appropriate hormonal determiner (activator).
sex limited traits
Sex-limited traits are genes that occur in both sexes
(probably on the autosomes) but are normally expressed only in the gender having the
appropriate hormonal determiner (called ____).
activator
Throughout the pedigree the trait appears in
only one sex, but it need not occur in all member of that sex
sex limited traits
The genes for the trait can be
carried and transmitted by the opposite sex although it is not displayed in that sex because of
anatomical or physiological differences.
sex limited traits
s. For instance, barred coloring in chickens normally is
visible only in the ____
roosters
s. For instance, barred coloring in chickens normally is
visible only in the roosters
what kind of sex traits
sex limited traits
would be considered traits like color blindness
and hemophilia. T
sex linked traits
They are said to be linked because more males (XY) develop these traits than
females (XX)
sex linked traits
are autosomal traits that are
influenced by sex
sex influenced traits
The presence of two X chromosomes in females can suppress its expression
when one of them has the genes for the trait and the other does not. Thus, the trait is more
likely to be visible in the male
what kind of sex traits
sex linked traits
If a male has one recessive allele, he will show that trait, but it will take
two recessive for the female to show that same trait.
sex influenced traits
One such gene is male pattern
baldness.
what kind of sex traits
sex influenced traits
A lot of sex-limited traits can determine parental carriers by using a
pedigree
Within a population, there may be a number of alleles for a given ___
gene
Individuals that have
two copies of the same allele are referred to as
homozygous
ndividuals that
have copies of different alleles are known as
heterozygous
If the trait is observed in an individual with only one copy, the allele is said to be ___ ___
autosomal dominant
The phenotype will be observed whether the individual has one copy of the allele
(is heterozygous) or has two copies of the allele (is homozygous)
autosomal dominant
. Individuals with ____
___trait have a 50-50 chance of passing the trait to each of their children.
autosomal dominant
. Individuals with autosomal
dominant trait have a ___ chance of passing the trait to each of their children.
50-50
If the trait is manifested only in an individual has two copies, the allele is said to be
___ ___
autosomal recessive
The phenotype will be observed only when the individual is homozygous
for the allele concerned.
autosomal recessive
An individual with only one copy of the allele will not show the
phenotype, but will be able to pass the allele on to subsequent generations
autosomal recessive
As a result, an
individual heterozygous for an autosomal recessive allele is known as a
carrier
are controlled by genes on the X chromosome.
x-linked inheritance
In females (who
have two X chromosomes), a trait in one of the two copies of the gene in each cell is sufficient
to be manifested in its phenotype.
x-linked dominant traits
In males (who have only one X chromosome), a trait
carried by gene in each cell causes the disorder.
x-linked dominants
While X-linked ___traits are
controlled by recessive alleles on the X chromosome
recessive
In males (who have only one X
chromosome), one copy of the gene in each cell is sufficient to express the phenotype.
X-linked recessive
In
females (who have two X chromosomes), a phenotype will be expressed when both copies of
the alleles are carried by the X chromosome
x-linked recessive
Such conditions is more frequent to be
expressed in males than in females
x-linked recessive
A characteristic of X-linked inheritance is that fathers
cannot pass X-linked traits to their ____
son
if the trait is controlled by a gene located on the Y
chromosome, one of the two sex chromosomes in each of a male’s cell
y-linked inheritance
Because only males
have a Y chromosome, in Y-linked inheritance, a trait can only be passed from father to __.
son
applies to genes in
mitochondrial DNA
mitochondrial inheritance/maternal inheritance
which are structures in each cell that convert molecules
into energy, each contain a small amount of DNA.
mitochondria
Because only egg cells contribute
mitochondria to the developing embryo, only __can pass on mitochondrial mutations to
their children.
female
Conditions resulting from mutations in mitochondrial DNA can appear in every
generation of a family and can affect both males and females, but fathers do not pass these
disorders to their daughters or sons.
mitochondrial inheritance
is the phenomenon wherein several closely related genes stay together during
inheritance through generations without any change or separation
linkage
Linkage was first
suggested by
Walter Sutton
Theodor Boveri
Linkage was first
suggested by Sutton and Boveri (1902-1903) when they propounded the famous “
chromosomal theory of inheritance
who clearly proved and defined linkage on the
basis of his breeding experiments in fruitfully Drosophila melanogaster
Thomas Morgan Hunt
r. In 1911____ and ___proposed chromosome theory of linkage.
Morgan
Castle
In 1911, Morgan and
Castle proposed chromosome theory of linkage. It has the following postulates
1st postulate
Genes are
found arranged in a linear manner in the chromosomes
In 1911, Morgan and
Castle proposed chromosome theory of linkage. It has the following postulates
2nd postulate
Genes which exhibit linkage are
located on the same chromosome
In 1911, Morgan and
Castle proposed chromosome theory of linkage. It has the following postulates
3rd postulate
Genes generally tend to stay in parental combination,
except in cases of crossing over
In 1911, Morgan and
Castle proposed chromosome theory of linkage. It has the following postulates
4th postulate
) The distance between linked genes in a chromosome
determines the strength of linkage.
e. Genes located close to each other show ___linkage
than that are located far from each other
stronger
. Linkage may be classified into
complete linkage
incomplete/partial linkage
It is known to be ____linkage if all meiocytes contains parental types of gametes. There
is complete absence of recombinant types due to absence of crossing over
complete linkage
If some frequency of crossing over also occurs between the linked genes. Recombinant
types are produced.
what type of linkage
incomplete linkage
is constant for any pair of linked loci and
represents the “genetic” distance between them
recombination frequency
is the distance that will generate 1% reco
mbination.
1 m.u (map unit)
1 cM (centiMorgan)
, showing the order of the loci and
the distance between them by observing the number of offspring showing recom
binant phenotypes.
gene map
number of gametic types
gametes formed?
AABbCc
Gametic Types = 2n where n= heterozygous gene/s
= 22 = 2 x 2 = 4
Gametes Formed
ABC
ABc
AbC
Abc
unit hereditary characters occurs in pair,
and that in the formation of gametes
these segregate so that only one
member of the pair goes into a particular
gamete
what law
law of segregation
cross where one character is
observed
monohybrid cross
The unknown genotype is cross
with a known (homozygous
recessive genotype
test cross
. Brown-eye color is dominant over blue-eye color. If a
brown-eyed man, whose father was brown-eyed and
whose mother was blue-eyed, marries a blue-eyed
woman.
What is the probability that they have a child with
brown eyes?
b.What is the percentage of having blue eyes among
the children?
a. 0.5
b. 50%
Genes for different characters are
inherited independently of one another
or that the members of one pair alleles
segregate independently of the other
pairs
law of independent assortment
In cats, again, black color is dominant to a special,
temperature-sensitive albino gene which produces cats
with dark legs, faces and tails (Siamese cats, in case
you don’t recognize it). A short haired (dominant)
Siamese colored female is bred to a long-haired black
male. They have eight kittens: 2 black, short-haired; 2
black, long-haired; 2 Siamese, short-haired; and 2
Siamese, long-haired. What were the genotypes of the
two parents?
Genotypes of Parents
Female: Ssbb
Male: ssBb
check slide 17 for reference
formula for types of gametes
2^n
formula of types of genotypes
3^n
formula of kinds of phenotypes
2^n
given there are 3 heterozygous pairs, compute types of gametes, types of genotypes, and type of phenotypes
8
27
8
Intra allelic interaction
allellic interaction
Inter allelic interaction
non-allelic interaction
non-allelic interaction
Novel Phenotype
Dominant Epistasis
Recessive Epistasis
Complementary Gene Action
Duplicate Gene Action
example of overdominance
Fluorescent pigment in Drosophila
In a recent case in Spokane, Washington, a young
woman accused a soldier of being the father of her child.
The soldier, of course, denied it. The soldier’s lawyer
demanded that blood types be taken to prove the
innocence of his client. The following results were
obtained: Alleged father, Type O. Mother, Type A. Child,
Type AB. The court found the soldier guilty on the basis
of the woman’s remarkable memory for dates and details
that apparently eliminated all other possible fathers.
* What are the possible genotypes for these three people?
* Do you agree with the court’s decision? Why or why not?
Answer to the
questions:
or I
a a. Mother: I i
AI
A
Father: ii
Child: I
AI
B
b. No, there is no possibility
of getting Type AB from the
parents with Type A and Type
O.
check slide 26 for answers
example of recessive lethal
sickle cell anemia
example of dominant lethal
huntington’s disease
view non allellic interactions in ppt
+1
A certain plant may have either single or double flowers:
single flowers when at least one dominant gene of each
of the two different pairs of genes DD and SS are
present, double flowers in the presence of either or both
pairs of the recessive genes. If plants with genotypes
DDss and ddSS are crossed, what would be the
probability of getting double flowers in F2? Single
flowers? What is the gene interaction involved?
Single flower: D_S_ Double flower: dd, ss, ddss
DDss (double) x ddSS (double)
F1 DdSs (Single)
F2 9 D_S (Single)
3 D_ss (Double)
3 ddS (Double)
1 ddss (Double)
Single = 0.56
Answers to Questions:
a. F2 (double flowers) = 0.44
b. Complementary Gene Action
are determined by genes located on
autosomes and express only in one sex
sex limited traits
These traits are responsible considerably
for sexual dimorphism
sex limited traits
is a trait that is
normally limited to females
breast development
sex linked trait that is limited to males
breast development
(both sexes carry the milk controlling genes in ___)
cattle
Gene controlling the trait is
found in autosomal
chromosome.
sex influenced trait
It has a gender preference but express in both gender
sex influenced trait
male pattern blindness is an example of ___
sex influenced trait
Gene controlling the
trait is found in sex
chromosome (X or Y)
sex linked trait
example of x-linked dominant
fragile x syndrome
example of x linked recessive
hemophilia, colorblindness
example of y-linked
hypertrichosis pinnae auris
In humans, hemophilia is a sex-linked recessive trait. If a female who is a carrier for hemophilia marries a male with normal blood clotting, answer the following questions.
a. What fraction of the children will have hemophilia?
b. What percentage of the female children will be carrier/s?
c. What fraction of the male children will have normal blood clotting?
a.1/4
b. 50%
c. ½
is an orderly presentation of family information
pedigree
important in predicting genetic risk
pedigree
identify pedigree symbols
page 31
when people who are related to each other by blood have a sexual relationship or marry each other
Consanguinous mating
first person to be identified to have genetic disorder
proband
dizygous twins are ___ twins
fraternal
monozygous twins are ___ twins
identical
Vertical pattern; multiple generations
affected
Males and females equally likely to
be affected
autosomal dominant
Each child of an affected individual
has a 50% chance to be affected
Every affected child has an affected
parent
autosomal dominant
Horizontal pattern; single generation
affected
Males and females equally likely to be
affected
autosomal recessive
Parents of affected child are unaffected
gene carriers and have a 25%
recurrence risk
autosomal recessive
Unaffected siblings have a 2/3 or 67%
chance to be carriers
autosomal recessive
Children affected individuals are
obligate carriers
autosomal recessive
Females are twice as likely to be
affected than males
x-linked dominant
May be lethal to males and
usually milder in females
x-linked dominant
Affected males pass the genes to
all their daughters
x linked dominant
No male to male transmission
Sons and daughters of affected
female
x linked dominant
condensed, inactive X chromosome found in female cells
x-linked dominant
Males are more often affected
than females
Affected males pass the gene to
all their duaghters and none of
their sons
x-linked recessive
Daughters of carrier have 50%
chance to be unaffected
Sons of carrier females have
50% chance to be affected
x-linked recessive
Affected males in the family are
related to each other through
carrier female
x-linked recessive
Only males are
affected
y-linked (holandric)
Affected males pass
the disease gene to
all their sons and
none to the
daughters
y-linked
y-linked is also called
holandric
are cytoplasmic
organelles important in cellular
respiration
mitochondria
Have their own DNA
mitochondria
mitochondria carries __ genes
37
No recombination happens in this sex linked trait
mitochondrial inheritance
Males and females equally affected and High mutation rate
mitochondrial inheritance
Identify the mode of
inheritance in slide 15
autosomal recessive
Identify the mode of
inheritance in slide 16
x-linked recessive
Contribution of genes and environment is ___
additive
Genes and environment are ___: genes alter the exposure to
relevant environmental factors
correlated
___control sensitivity to the environment
gene
The environment controls ___ ___
gene expression
Individuals
genotype
with the same
can also show
different degrees of the
same phenotype
expressivity
is the degree to
which trait expression
differs among individuals.
expressivity
is the proportion of individuals carrying a particular variant
of a gene (genotype) that also expresses an associated trait
(phenotype)
penantrance
is
in
a
phenotype
variation
(generally
referring to a single trait) which
is caused by environmental
conditions (often,
necessarily, during
but not
the
organism’s development), such
that the organism’s phenotype
matches a phenotype which is
determined by genetic factors.
phenotype
is a situation
organism is determined
only by the environment
where the phenotype of an
not
it
experiences and its genotype,
but also by the environment
and genotype of its mother
maternal effect
demonstrating that genes are located on chromosomes and that nondisjunction (failure of chromosomes to separate during meiosis) can lead to abnormal offspring
Calvin Bridges
pioneered gene mapping by using recombination frequencies to determine the relative positions of genes on chromosomes, a concept that laid the groundwork for modern genetics.
alfred Henry Sturtevant
ho established radiation genetics, demonstrating that X-rays induce mutations and earned him the 1946 Nobel Prize in Physiology or Medicine
Hermann Joseph Muller
types of linkage
complete linkage
incomplete linkage
types of incomplete linkage
single cross over
double cross over
a type of crossover event where one exchange of genetic material occurs between homologous chromosomes
single cross over
efers to two separate crossover events occurring between the same two genes during meiosis, leading to a recombination of the original alleles.
double crossover
is a genetic map
of a species or experimental
population that shows the
position of its known genes or
genetic markers relative to each
other in terms of recombination
frequency, rather than a specific
physical distance along each
chromosome.
linkage map
is the distance that
produces a recombination frequency of 1%;
one map unit
map distance formula
recombinant gametes / total gametes
do problem in slide 30
+1
