Gene Segregation and Interaction Flashcards
can be analyzed through transmission of visible characteristics in pea plants
Genes
Homologus chromosomes combine at ___ stage of meiosis I
pachytene
Segregation of genes commenced at ____
anaphase I
The analysis of genetic crosses depends upon the understanding of Mendel’s two las
Principle of Segregation
Principle of Independent Assortment
demonstrates that two members of a gene pair (alleles) segregate (separate) from each other in the formation of genes
principle of segregation
indicates that the genes for different traits separate independently of one another and combine randomly in the formation of gametes during meiosis
principle of indepdendent assortment
what mathematical tool is used to determine “goodness of fit”
chi-square test
null hypothesis for the observed phenotypic ratio
There is no significant difference between the observed phenotypic ratio and the expected phenotypic ratio
deviatio nformula
d^2 = (O-E)^2
after getting the deviation, what should be done
d^2/E
N is the
total number of observations
degrees of freedom formula
n-1
- Explain Mendelian laws of heredity. Correlate them with the specific events of meiosis (5 pts).
Mendelian laws of heredity propose three laws: law of dominance, where one trait hides the other trait for the same characteristics. Law of segregation, which explains two parents possess traits that only one trait of these individuals can be passed to the offspring. Lastly, the law of independent assortment, that describes alleles of two or more different genes typed into gametes independently.
Law of segregation can be witnessed during meiosis 1, where homologous chromosomes separate, each daughter cells will only have one chromosome per each pair. This process is a basis for the law of segregation.1 In addition, these chromosomes assort independently (law of independent assortation), where one pair of chromosomes does not affect the orientation of the other pair, which leads to an assortment of genes.2
a. Chi square
The Chi-square test is a statistical method used to compare observed and expected values. In genetics, it helps us to decide whether to accept or reject a given hypothesis about genetic inheritance. This test allows us to analyze and interpret the relationship between two genes.
b. Gene segregation
Gene segregation is a process where alleles separate during meiosis to ensure that the parent’s traits are passed down to the offspring. It promotes genetic variation within a population instead of inheriting a blend of the parent’s traits. It can also take place in small populations where individuals share a common ancestry
c. Probability
Probability refers to the likelihood of a specific genetic outcome occurring in offspring. It is used to predict the possible genotypes and phenotypes of offspring based on the genetic makeup of the parents. Probability follows the laws of chance, meaning larger sample sizes tend to yield results closer to predicted ratios (such as Mendel’s 3:1 phenotypic ratio in monohybrid crosses).
d. Random mating
Random mating refers to a reproductive process in which individuals’ pair by chance rather than according to specific genetic traits. This means that everyone in a population has an equal opportunity to mate with any other individual, regardless of genotype or phenotype (if they are compatible for reproduction).
A woman has a rare abnormality of the eyelids called ptosis, which makes it impossible for her to open her eyes completely. The condition has been found to depend on a single dominant gene (P). The woman’s father had ptosis, but her mother had normal eyelids. Her father’s mother had normal eyelids.
a. What are the probable genotypes of the woman, her father, and her mother?
- Since the woman has ptosis, her genotype could be either PP or Pp. But since her mother has normal eyelids (pp), so she must have inherited a ‘p’ allele from her mother. Therefore, the woman’s genotype is Pp.
- The woman’s mother has normal eyelids, meaning she has two copies of the recessive allele, making her genotype as pp.
- The woman’s father has ptosis, so his genotype has at least one ‘P’ allele. His mother had normal eyelids (pp), so he must have inherited a recessive ‘p’ allele from her. Thus, the father’s genotype is Pp.
o The summary of the family’s genotypes are the following:
Woman: Pp
Her father: Pp
Her mother: pp
b. What proportion of their children will be expected to have ptosis if she marries a man with normal eyelids?
Based on the Punnett square above, PP represents children with ptosis and pp represents children with normal eyelids. The genotypic ratio of the woman’s children will be 2:2 or 1:1 and the phenotypic ratio is the same with 2 Ptosis:2 Normal or 1 Ptosis:1 Normal. Therefore, 50% of the children are expected to have ptosis if she marries a man with normal eyelids.
In tomatoes, two pairs of genes affect the color of the ripe fruit as follows: R, red flesh, r yellow flesh; Y yellow skin, y colorless skin. Dominance is complete for red flesh and yellow skin. If the genes are independently segregating, calculate the expected phenotypic ratios from the following crosses:
a. a. Rryy x rrYy
give GR and PR
- Genotypic Ratio = 4:4:4:4 or 1:1:1:1
- Phenotypic Ratio = 4:4:4:4 or 1:1:1:1
b. RrYY x Rryy
give PR and GR
Therefore;
* Genotypic Ratio = 4:8:4 or 1:2:1
* Phenotypic Ratio = 12:4 or 3:1
different alleles are independent of each other in their ___ and ___ patterns
segregation
recombinant patterns
are not merely separate elements producing distinct individual effects, but they could also interact with each other giving entirely different phenotypes
Genes
may result to modified phenoitypic ratios deviating from those expected of independently assorting gens exhibiting complete dominance
gene interaction
heterozygotes are phenotypically identical to the homozygous dominant
complete dominance
one gene controlling one trait
allelic interactions
f2 phenotypic ratio of complete dominance
3:1
heterozygotes are phenotypically intermediate between the two homozygous types
incomplete dominance
incomplete dominance f2 phenotype ratio
1:2:1
heterozygotes exhibit a mixture of the phenotypic characters of both homozygotes instead of a single intermediate expression
co-dominance
expected phenotypic ratio of co-dominance
1:2:1
death of the affected individual (homozygous dominant or heterozygous) iccurs after reproduction takes place
dominant lethal
dominant lethal f2 phenotypic ratios
0:2:1 or 0:1
effects of recessive genes are sufficiently drastic to kill the bearers of certain genotypes
recessive lethal
recessive lethal f2 phenotypic ratio
1:2:0 or 3:0
two genes controlling one trait
non-allelic interactions
an allele of gene masks the effect of the allele of other gene
epistasis
complete dominance at both gene pairst but one gene when dominant is epistatic to the other (A is dominant to a: B dominant to b; A epistatic to B and b)
dominant epistasis
complete dominance at both gene pairs but the first gene when dominant is epistatic to the second and second gene, when homozygous recessive is epistatic to the first (A dominant to a; B dominant b; A epistatic to B and B; bb epistatic to A_ and aa)
dominant epistasis
dominant epistasis f2 expeted PR
12:3:1 or 13:3
complete dominance at both gene pairs, but one gene, when homozygous recessive is epistatic or masks the effect of other gene (A dominant to a; B dominant to b; aa epistatic to B and b)
recessive epistasis
expected PR 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
duplicate gene action PR
15:1
complete dominance at both gene pairs, but either gene when homozygous recessive is epistatic to the effects of the other gene (A is dominant to al B dominant to b; bb epistatic to A)
complementary gene action
complementary gene action PR
9:7
complete dominance at both gene pairs, new phenotypes are produced from interaction between dmoninants and between both homozygous recessives (A dominant to a; B dominant to b; a interacts with B)
NOvel phenotypes
novel phenotypes PR
9:3:3:1
- What is gene interaction? Differentiate allelic from non-allelic interaction (5 pts).
Gene interaction refers to the phenomenon where the expression of one gene is influenced by the presence or absence of another gene. This interaction can occur between genes located at the same locus (allelic interactions) or at different loci (non-allelic interactions) on chromosomes
– occurs between different alleles of a single gene located at the same locus on homologous chromosomes. These interactions can manifest in various forms, including:
allelic interaction
– involves genes that are located at different loci, which may be on the same or different chromosomes
non-allelic interactions
in which one gene masks or modifies the expression of another gene.
epistasis
– in which two or more genes interact to produce a specific phenotype, requiring both to be present for expression.
complementary genes
in which, the genes that contribute to the same trait but may have different alleles may affect the outcome.
duplicate genes
- A woman who is blood type A is married to a man who is blood type B. None of the man’s parents are blood type O. This couple has 4 children with the following blood types: O, AB, AB, B. Give the genotypes of the parents.
In summary:
* The mother’s genotype is AO.
* The father’s genotype is BO.
- Colorblindness in humans is a recessive trait found in the X chromosome. A man and a woman got married and decide to have children. The man is colorblind.
a. Can they have a colorblind daughter? What is the probability?
Possibility 1: Mother is not colorblind and not a carrier (genotype: XX)
The daughters’ genotypes are both XX’. They are both carriers, but are not colorblind. Therefore, the probability of having a colorblind daughter is 0%.
.
- Colorblindness in humans is a recessive trait found in the X chromosome. A man and a woman got married and decide to have children. The man is colorblind.
b. Can they have a colorblind son? What is the probability?
Possibility 1: Mother is not colorblind and not a carrier (genotype: XX)
he sons’ genotypes are both XY, hence they both have normal vision. Therefore, the probability of having a colorblind son is 0%
- Colorblindness in humans is a recessive trait found in the X chromosome. A man and a woman got married and decide to have children. The man is colorblind.
Can they have an offspring who is carrier? What is the probability? What is the gender?
Possibility 1: Mother is not colorblind and not a carrier (genotype: XX)
The daughters’ genotypes are both XX’. Having the chromosome carrying the colorblindness gene makes them carriers. Therefore, the probability of having a carrier offspring is 50%; wherein the probability of a carrier offspring for daughters is 100%.
Possibility 2: Mother is not colorblind but a carrier (genotype: XX’)
- Colorblindness in humans is a recessive trait found in the X chromosome. A man and a woman got married and decide to have children. The man is colorblind.
a. Can they have a colorblind daughter? What is the probability?
The genotype X’X’ indicates colorblindness. The daughters’ genotypes are XX’ and X’X’, indicating that one may have a normal vision, while the other is colorblind. Therefore, there is a 50% chance of having a colorblind daughter.
Possibility 2: Mother is not colorblind but a carrier (genotype: XX’)
- Colorblindness in humans is a recessive trait found in the X chromosome. A man and a woman got married and decide to have children. The man is colorblind.
b. Can they have a colorblind son? What is the probability?
One of their sons exhibit the genotype X’Y; therefore, the probability of having a colorblind son is 50%.
Possibility 2: Mother is not colorblind but a carrier (genotype: XX’)
- Colorblindness in humans is a recessive trait found in the X chromosome. A man and a woman got married and decide to have children. The man is colorblind.
b. Can they have an offspring who is carrier? What is the probability? What is the gender?
One of their offspring exhibits the genotype X’X, indicating that while they have normal vision, one of their chromosomes carry the colorblindness gene. Therefore, there is a 25% chance of having a carrier offspring; wherein the probability of a carrier offspring for daughters is 50%.
- When non-allelic genes interact in a way that one of the genes can hide the expression of the other gene, how is it called? Explain.
The terminology where non-allelic genes interact where one of the gene hides the expression of the other gene is epistasis. According to Ostrander (2025), “epistasis is a circumstance where the expression of one gene is modified (e.g., masked, inhibited or suppressed) by the expression of one or more other genes.”
This is different from the law of dominance, where the process also involves hiding the expression of the other genes, but with the same genes. This happens because of the interaction of two or more genes at different loci (location on the chromosome) . One gene, the epistatic gene masks the phenotypic expression of another gene, hypostatic gene.
- How do gene interactions affect gene expression?
Gene interactions occur when two or more genes influence a single trait or phenotype. Their products interact, affecting gene expression. Epistasis is the mechanism by which one gene (the epistatic gene) masks or modifies the expression of another gene (the hypostatic gene). If two or more genes are required for a particular function, it is called complementation. However, if either gene has a loss-of-function mutation, the function is disrupted. Sometimes, multiple genes have similar functions. If one gene is inactivated, another can compensate, resulting in an observable phenotypic change.
Results of Mendel’s crosses in F2 generation when
Dominant form = 705
Recessive form = 224
3.15:1
Results of Mendel’s crosses in F2 generation when
Dominant form = 6,022
Recessive form = 2,001
3.01:1
genetic makeup of an organism or alleles carried by an individual or arrangement of genes that produces the phenotype
genotype
physical characteristic or appearance of an individual
phenotype
___ parents can only pass one form of an allele to their ofspring
homozygous
___ parents can pass either two forms of an allele to their offspring
heterozygous
the general term for an allele that masks the presence of another allele in the phenotype
dominant allele
the general term for an allele that is masked in the phenotype by the presence of another allele
recessive allele
Mendel went on to examine how the F2 plants passed traits onto successive generations, he found that recessive 1/4 were always true breeding, thus he suggested that there is a 3:1 ratio but it was really a
1:2:1 disguised ratio
in a cross of parents that are pure for contrasting traits, only one form of the trait will appear in the next generation. All offspring will be hybrid for a trait and will have only the dominant trait express the phenotype.
what law
law of dominance
check the label for the f1 and f2 generation for the purple petal
+1
Mendel was able to understand four things about the nature of heredity:
(1) the plants he crossed did not produce progeny of ___ appearance
intermediate
Mendel was able to understand four things about the nature of heredity:
Mendel learned that for each pair of alternative forms of a character, one alternative was not expressed in the F1 hybrids, but it appeared in some ___ individuals
F2
Mendel was able to understand four things about the nature of heredity:
The pairs of ___traits examined segregated among the progeny of a particular cross, some individuals exhibiting one trait, some the other
alternative
Mendel was able to understand four things about the nature of heredity:
These alternative traits were expressed in the F2 generation in the ratio of
3/4 dominant to 1/4 recessive
used to show the possible combinations of gametes
Punnett square
make a punnett square between Pp and Pp
1 PP
2 Pp
1 pp
Mendel’s model has five elements:
Parents do not transmit physiological traits directly to their offspring. Rather, they transmit discrete information about the traits called ___
factors
Mendel’s model has five elements:
Each individual receives two factors that may code for the same trait or two ___ traits for a character
alternative
Mendel’s model has five elements:
Not all copies of a factor are ___
identical
Mendel’s model has five elements:
The two alleles, one contributed by the male gamete and one by the female do/do not influence each other in any way
do not
Mendel’s model has five elements:
the presence of a particular ___ does not ensure that the trait econded will be expressed in an individual carrying that allele
allele
alternative alleles of a character segregate from each other in heterozygous individuals and remain distinct
what Mendel’s Law of Heredity
Segregation
how do we know if it is homozygous (PP) or heterozygous (Pp)?
test cross
mating between an individual of unknown genotype and homozygous recessive individual
test cross
likelihood that a particular event will occur
probability
can be used to predict the outcomes of genetic crosses
principle of probability
what is the probability to have each coin landing heads up
1/8
find the phenotypes of the F1 in the following crosses. Assume that tall (TT) is dominant to dwarf (tt)
TT x TT
GR: 1
PR: 1
find the phenotypes of the F1 in the following crosses. Assume that tall (TT) is dominant to dwarf (tt)
Tt
TT
GR: 2:2 / 1:1
PR: 1 (4 tall)
find the phenotypes of the F1 in the following crosses. Assume that tall (TT) is dominant to dwarf (tt)
TT x tt
GR 1:1
PR: 1 (4 tall)
find the phenotypes of the F1 in the following crosses. Assume that tall (TT) is dominant to dwarf (tt)
Tt
Tt
GR: 2:1:1
PR: 3:1
find the phenotypes of the F1 in the following crosses. Assume that tall (TT) is dominant to dwarf (tt)
Tt
tt
PR: 2:2/1:1
GC: 2:2/1:1
find the phenotypes of the F1 in the following crosses. Assume that tall (TT) is dominant to dwarf (tt)
tt
tt
GR: 1
PR: 1
inheritance of one character is always indepdendent of the inheritance of other characters within the same individual
indepdendent assortment
a modern restatement of Mendel’s Second Law would be that:
Genes that are located on different chromsomes assort independently during meiosis
do a dihybrid cross given
SsYy
SsYy
GR: 4:2:2:2:2:1:1:1:1
PR 9:3:3:1
it states that inheritance of one character is always independent of the inheritance of other characters
law of independent assortment
law of independent assortment is based on ___ ___
dihybrid cross
genes linked on a chromosome can rearrange themselves through the process of ____
crossing over
give the gametes given the parents
Tt
AA
TA, tA
give the gametes
BB cc DD
BcD
give the gametes
Dd EE Aa CC
DEAC
DEaC
dEAC
dEaC
allelic interactions
complete dominance
incomplete dominance
co-dominance
dominant lethal
recessive lethal
non allelic interactions
dominant epistasis
recessive epistasis
duplicate gene action
complementary gene action
novel phenotype
