Gene interactions occur when two or more different genes influence the outcome of a single trait
Epistasis is a phenomenon in which the expression of one gene depends on the presence of one or more modifier genes.
A gene whose phenotype is expressed is called epistatic.
This power point presentation is designed to explain deviation of Mendelian dihybrid ratio due to interaction of genes which may be of following types
1.Two gene pairs affecting same character – 9:3:3:1
2.Epistasis, one gene hides effect of other
a) Recessive Epistasis - 9:3:4
b) Dominant epistasis - 12:3:1
3.Complementary genes - 9:7 ( 2 genes responsible for production of a particular phenotype )
4. Duplicate genes – 15:1 ( same effect given by either of two genes )
5. Polymeric gene action - 9:6:1
6. Inhibitory gene action - 13 : 3
Each interaction is typical in itself and ratios obtained are different
Gene interactions occur when two or more different genes influence the outcome of a single trait
Epistasis is a phenomenon in which the expression of one gene depends on the presence of one or more modifier genes.
A gene whose phenotype is expressed is called epistatic.
This power point presentation is designed to explain deviation of Mendelian dihybrid ratio due to interaction of genes which may be of following types
1.Two gene pairs affecting same character – 9:3:3:1
2.Epistasis, one gene hides effect of other
a) Recessive Epistasis - 9:3:4
b) Dominant epistasis - 12:3:1
3.Complementary genes - 9:7 ( 2 genes responsible for production of a particular phenotype )
4. Duplicate genes – 15:1 ( same effect given by either of two genes )
5. Polymeric gene action - 9:6:1
6. Inhibitory gene action - 13 : 3
Each interaction is typical in itself and ratios obtained are different
Gene interaction -Complementary, Supplementary,Dominant Epistasis, Recessive...Nethravathi Siri
Most of the characters of living organisms are controlled/ influenced/ governed by a collaboration of several different genes. • Numerous deviations have been recorded in which different kinds of interactions are possible between the genes.
Epistasis is a Greek word that means standing over .Bateson used it to describe the masking effect in 1909.
An interaction between a pair of loci in which the phenotype effect of one locus depends on the genotype at the second locus.
Genes whose phenotypes are ;
Expressed,epistatic.
Altered or suppressed hypostatic.
Basics of Undergraduate/university fellows
Complementation between two non-allelic genes (C and P) are essential for production
of a particular or special phenotype i.e., complementary factor.
Two genes involved in a specific pathway and their functional products are required
for gene expression, then one recessive allelic pair at either allelic pair would result in
the mutant phenotype.
When Dominant alleles are present together, they complement each other to yield
complementary factor resulting in a special phenotype.
They are called complementary genes.
When either of gene loci have homozygous recessive alleles (i.e., genotypes of ccPP,
ccPp, CCpp, Ccpp and ccpp), they produce identical phenotypes and change F2 ratio
to 9:7.
This is a very interesting topic in Population Genetics. A mathematics and biology combo of Hardy-Weinberg equilibrium is explained. The history, derivation, condition, merits and demerits of Hardy-Weinberg equilibrium is explained. Hope you all enjoy!!!!
QUANTITATIVE INHERITANCE - KERNEL COLOR IN WHEATNethravathi Siri
Nilsson-Ehle (1909) and East (1910, 1916) documented first significant evidence of
quantitative inheritance by their individual works in wheat.
Their analysis started from one-locus control which continued to two locus control
and concluded at three-locus control.
Gene interaction -Complementary, Supplementary,Dominant Epistasis, Recessive...Nethravathi Siri
Most of the characters of living organisms are controlled/ influenced/ governed by a collaboration of several different genes. • Numerous deviations have been recorded in which different kinds of interactions are possible between the genes.
Epistasis is a Greek word that means standing over .Bateson used it to describe the masking effect in 1909.
An interaction between a pair of loci in which the phenotype effect of one locus depends on the genotype at the second locus.
Genes whose phenotypes are ;
Expressed,epistatic.
Altered or suppressed hypostatic.
Basics of Undergraduate/university fellows
Complementation between two non-allelic genes (C and P) are essential for production
of a particular or special phenotype i.e., complementary factor.
Two genes involved in a specific pathway and their functional products are required
for gene expression, then one recessive allelic pair at either allelic pair would result in
the mutant phenotype.
When Dominant alleles are present together, they complement each other to yield
complementary factor resulting in a special phenotype.
They are called complementary genes.
When either of gene loci have homozygous recessive alleles (i.e., genotypes of ccPP,
ccPp, CCpp, Ccpp and ccpp), they produce identical phenotypes and change F2 ratio
to 9:7.
This is a very interesting topic in Population Genetics. A mathematics and biology combo of Hardy-Weinberg equilibrium is explained. The history, derivation, condition, merits and demerits of Hardy-Weinberg equilibrium is explained. Hope you all enjoy!!!!
QUANTITATIVE INHERITANCE - KERNEL COLOR IN WHEATNethravathi Siri
Nilsson-Ehle (1909) and East (1910, 1916) documented first significant evidence of
quantitative inheritance by their individual works in wheat.
Their analysis started from one-locus control which continued to two locus control
and concluded at three-locus control.
Basics of Undergraduate/university fellows
Epistasis is a Greek word that means standing over.
BATESON used term epistasis to describe the masking effect in 1909
The term epistasis describes a certain relationship between genes, where an allele of
one gene hides or masks the visible output or phenotype of another gene.
When two different genes which are not alleles, both affect the same character in such
a way that the expression of one masks (inhibits or suppresses) the expression of the
other gene, the phenomenon is said to be epistasis.
The gene that suppresses other gene expression is known as Epistatic gene.
The gene that is suppressed or remain obscure is called Hypostatic gene
The classical phenotypic ratio of 9:3:3:1 F2 ratio becomes modified by epistasis.
Biology 103 Laboratory Exercise – Genetic Problems
Introduction
Although the science of genetics has become a highly sophisticated discipline dealing
with the interactions of hereditary factors at the molecular level, it has its roots in the
basic laws of heredity initially discovered and presented by Gregor Mendel more than
one hundred years ago. Mendel's success in discovering these laws was due largely to his
application of the simple rules of mathematical probability - the laws of chance - to his
observations concerning the inheritance of certain characteristics in the garden pea plant.
Reginald Punnett and the Punnett Square
The Punnett square is a diagram used by biologists to determine genotypic probability
within the offspring from a particular genetic cross. The Punnett square shows every
possible genotypic combination of maternal alleles with the paternal alleles for a genetic
cross. Punnett squares only give probabilities for genotypes, not phenotypes. The square
diagram was designed by the British geneticist, Reginald Punnett (1865-1967) and first
presented to the science community in 1905. Punnett’s Mendelism (1905) is considered
the first popular science book to introduce genetics to the public.
Solving Genetic Problems
R
R'
R
RR RR'
R'
RR' R'R'
Maternal alleles
A
A
a
Aa
Aa
Paternal
Alleles
a
Aa
Aa
The first step in solving a genetic problem is to establish the genetic symbols you will use
in your problem solution. Stay consistent by using these same symbols throughout the
problem solving process.
Represent dominant and recessive alleles (different forms of a gene) using traditional
genetic symbols. Dominant alleles should be represented with the capital version of an
alphabetic letter while using the lower case version to show recessiveness. For example:
B = black color, b = white color.
Each individual gene or trait is diploid (2n) in nature and therefore, must be represented
with two alleles. Continuing with the alleles mentioned previously, an individual may
have the genetic makeup BB, Bb, or bb when using those alleles.
Remember that gametes (sperm and egg) are haploid (n) and can only provide one allele
per trait. For example: B or b
An individual’s genotype contains the possible gametes that can be expected to be
produced by that individual. Much of genetics revolves around the probability of the
makeup of gametes. If the individual is homozygous, all of the gametes produced will
possess the same kind of allele. For example, an individual with the genotype BB would
be expected to produce only B gametes and individuals with genotype bb would produce
only b gametes.
If the individual is heterozygous, that is the individual’s genotype contains one dominant
allele and one recessive allele (Bb), the gametes produced will possess one or the other of
the two forms of the gene – B or b. ...
Study Guide Chapter 15 -Chromosomal Basis of Inheritance-Answers.docxhanneloremccaffery
Study Guide Chapter 15 -Chromosomal Basis of Inheritance-Answers
15.1 Mendelian Inheritance and chromosome theory______________________________
1. Thomas Hunt Morgan identified the first solid evidence associating a specific___gene_____ on a specific chromosome.
2. Why did Morgan choose Drosophila as his experimental organism? (List 3 reasons)
They reproduce quickly, a new generation of adults forms every two weeks!
Prolific (single matting = hundreds of offspring)
Only 4 chromosome pairs = simple genetics
3A. The normal phenotype for a character (phenotype most common in nature) is called___wild type_____.
3B. Provide at least two examples this phenotype in Drosophila.
Red eyes
gray body
4A. An alternative phenotype for a character (phenotype not common in nature) is called____mutant____.
4B. Provide at least two examples of this phenotype in Drosophila.
White eyes
Black body
5. Morgan and his students invented a notation to symbolize alleles in Drosophila that differed from the notation Mendel used to represent alleles. Describe how Morgan’s Drosophila characters are named and the symbol used for the allele type.
You can think of Morgan’s wild-type allele as equivalent to the dominant allele in Mendel’s naming system. And you can think of Morgan’s mutant allele as equivalent to Mendel’s recessive allele. So whenever you have one wild-type allele and one mutant allele, that organism will have the wild-type phenotype.
Mendel
Used the first letter of the dominant character name to represent the dominant allele. This letter was capitalized for the dominant allele, lower case for the recessive allele
Ex: purple flower allele dominant to white flower allele: P= dominant allele, p=recessive allele
Morgan
-Used the first letter of the mutant character name to represent the wild-type allele. The letter for the wild-type and mutant alleles are both lower case. The wild-type allele gets a + sign and the mutant does not.
Ex: red eye allele wild-type to white eye mutant: w+ = wild-type allele, w= recessive allele.
6. Morgan and his students invented a notation to symbolize alleles in Drosophila. Which of the following genotypes would produce a fly that is wild-type for eye color (red vs. white eyes)?
w+ w+
w+ w
w w
w+w+ and w+w
7. Morgan performed an experiment that yielded a 3:1 ratio of offspring in the F2 generation; however, only the males of this F2 generation had white eyes.
White- eye females DO EXIST, so why were only white-eye males observed in this cross?
Complete the following chart and describe why Morgan observed these results and how it allowed him to conclusively determine that the gene for eye color was located on the X chromosome.
Morgan’s experiment (see Figure 15.4) Use notation developed by Morgan and his students
If the gene for eye color is located on the X chromosome….
P generation
Red eye Female genotype for eye color = w+w+
White eye Male genotype for eye color= w
F1 generatio.
51
Mendelian Gene cs
Lab 5
52
Lab 5: Mendelian Gene cs
53
Introduc on
In 1866, Gregor Mendel, an Austrian Monk, published a paper en tled “Experiments in plant hybridiza-
on”. It went largely unno ced un l 1900 when it was rediscovered and subsequently became the
basis for what we now refer to as Mendelian Gene cs.
Mendel was the Þrst to recognize:
Inherited characters are determined by speciÞc factors (now recognized these as genes).
These factors occur in pairs (genes).
When both alleles of a gene are the same they are said to be homozygous, while if they are di erent
they are said to be heterozygous. When gametes form, these factors segregate so that each gamete
contains only one allele for each gene. Remember, alleles reside on the chromosomes that are divid-
ing. These original observa ons lead to what we now refer to as The law of segrega on and the law of
independent assortment.
Figure 1: Law of Segrega on
Concepts to explore:
Gregor Mendel
Law of segrega on
Homozygous
Heterozygous
Independent assortment
Dominant vs. recessive
Incomplete dominance
Co-dominance
Genotype
Phenotype
Monohybrid cross
Dihybrid cross
Punne square
Lab 5: Mendelian Gene cs
54
The law of segrega on states that during
meiosis, homologous (paired) chromo-
somes split (Figure 1). The law of inde-
pendent assortment states that during
meiosis, each homologous chromosome
has an equal chance of ending up in ei-
ther gamete, and alleles for individual
genes segregate with the chromosomes
on which they are located (Figure 2).
Using corn as an example (Figure 2):
The large chromosome has the gene for kernel color (Y = yellow, y = blue).
The small chromosome has the gene for kernel texture (S = smooth (green); s = wrinkled (red)).
When a dominant allele is present, that characteris c is expressed, regardless of the second allele. In
this case both the Yy and YY o spring will be yellow.
A recessive allele is only expressed when both alleles are recessive. In this case only the yy combina-
on is blue. The dominant allele is always represented by capital le ers, while the recessive is repre-
sented by lower case le ers.
Genotype refers to the combina on of alleles for a par cular trait. Phenotype refers to the appear-
ance of that combina on of alleles. In our example, the genotype of the diploid cell is Yy, Ss, while the
phenotype is Yellow and Smooth.
Figure 2: Law of Independent Assortment
Figure 3: Monohybrid Cross
Punne Square F1
Lab 5: Mendelian Gene cs
55
Alleles can exhibit incomplete dominance and co-dominance. An example of incomplete dominance is
the cross of two plants, one with red ßowers and one with white, whose o spring have pink ßowers.
In the case of codominance, the same cross would result in red and white striped ßowers.
If we know the genotype of two parents we can.
Similar to Bio 140 lab discussion 2010 ex 1 to 3 (20)
5. TIMING = 24 HOURS
INTERPHASE (18-20 hours)
G1 (10 hours) is typically the longest phase of the cell
cycle since it follows cell division in mitosis; first chance
for new cells have to grow.
S (5 to 6 hours) phase varies according to the total DNA
that the particular cell contains which is fairly constant
between cells and species
G2 (3 to 4 hours)
MITOSIS (2 hours)
the cell makes preparations for and completes cell
division only takes about 2 hours
15. BINOMIAL EXPANSION
Mathematical way to determine or
project combinations
Let a = probability of first event; b =
probability of the alternative event; and
a+b=1
THUS...a 50% probability or chance
that one character will appear over the
other
17. What if you are only after a certain combination?
use of FACTORIAL
P = [n!/x! (n-x)!] pxqn-x
What is the probability is that a monohybrid
cross yielding a litter of four pups will
produce three agouti and one black pup?
B (agouti) and b (black)
P=
n = # trials (births) (4)
s = agouti (p = 3/4 = .75)
t = black (q = 1/4 = .25)
Therefore,
P = [4!/3!1!](.75)3(.25)1 = 0.42
18. MUTUALLY EXCLUSIVE EVENTS
Either one or the other will occur
focus is on the concept of outcome A or B
Example: In rolling a dice: calculate the probability of either two 4s or two
5s
Because these outcomes are mutually exclusive, the sum rule can be used
to tell us that the answer is 1/36 + 1/36 which is 1/18. This probability can
be written as follows:
19. What if: chances of both?
The product rule states that the probability of independent events
occurring together is the product of the probabilities of the
individual events.
consider two dice and calculate the probability of rolling a pair of
4s
The probability of a 4 on one die is 1/6 because the die has six
sides and only one side carries the 4
Therefore, with the use of the product rule, the probability of a 4
appearing on both dice is 1/6 × 1/6 = 1/36
28. DOMINANT EPISTASIS: CASE 1
W is dominant to w (W white)
Y is dominant to y (Y yellow)
W is epistatic to Y and y
In the absence of a dominant allele, the YY or Yy yellow while yy another phenotype which is green)
29. DOMINANT EPISTASIS: CASE 2
If W is white and Y is
WHITE yellow
W is dominant to w
WHITE
Y is dominant to y
YELLOW W is epistatic to Y and y
Y is epistatic to ww
WHITE
W and yy same expression
30. RECESSIVE EPISTASIS
B_: agouti
bb: brown
Presence of one C: allows
pigmentation to occur
Presence of cc: albino
Ratio: 9:3:4 (example:
mouse coat color)
31. DUPLICATE RECESSIVE GENES
W dominant to w
ww epistatic to P
P dominant to p
pp epistatic to W
The presence of at least one dominant allele of each two gene pairs is essential for flower to be purple
Ratio: 9:7 (Sweet Pea flower color)