06. Genetics Flashcards
What is the phenotype ratio of the monohybrid cross?
3:1
What is the phenotype ratio of dihybrid cross?(in independent assortment)
9:3:3:1
What are the conditions we can apply the laws of independant assortment to?
- Genes located on different chromosomes
- genes located far apart on the same chromosome
Name the success of the Mendel’s experiments
- Mendel carried out thousands of genetic crosses of any given kind, closely resembling the
probability predictions . Usually, larger the sample size, closer the results are to the value predicted based on probability. - He kept an accurate record of his results. These records help him to trace the patterns which otherwise would go unnoticed.
- He usually followed up each cross for at least two offspring generation (F1 and F2) helped him to uncover some of the traits hidden in the F1 generation.
- He did a quantitative analysis of the phenotypes of the resulting offsprings.
What are the desirable properties of garden pea plants for the genetic experiment?
- Pea plants are available in many varieties with contrasting traits
- The generation time is short.
‘ - A large number of offspring is produced from each cross.
- Crossing between plants could be strictly controlled (by self/ cross pollination)
What kind of trait is attached/detached ear lobe?
both copies in recessive would result in the attached ear lobe.
What kind of trait is widow’s peak?
This occurs as a result of the recessive allele (ww)
What kind of trait is dimples on cheek?
It is a dominant trait
It often occurs in both of the cheeks
dimple occurring in one cheek is a rare phenomenon
What kind of trait is bent thumb?
What kind of trait is bent thumb?
Having a dominant S would produce the dominant phenotype of the straight thumb
Absence of dominant allele will allow the thumb to bend
What kind of trait is rolling or non rolling of the tongue?
Rolling the tongue into a tube shape is a dominant trait
What does the intrinsic muscles of the tongue allow?
people to fold the tongue into specific shapes
Give an example for incomplete dominance
Mirabilis jalapa ( four’o clock plant)
when red is crossed with white plants, pink plants would be obtained.
What is the crossing of incomplete dominance?
CrCr x CwCw
What is the gentype ratio for incomplete dominance?
1: 2: 3
What is the phenotypic ratio for incomplete dominance?
1:2:1
What is the phenotypic ratio for codominance?
Red:pink:white
1:2:1
What is an example for codominance?
AB blood group system; based on the type of carbohydrate present on the RBC surface
What is the cross of codominance?
IaIa x IbIb
What is the genotype ratio for codominance?
1:2:3
IaIa:IaIb:IbIb
What is the phenotypic ratio of codominance?
1:2:1
A:AB:B
How do we differentiate incomplete dominance from codominance?
incomplete dominance show a different phenotype than both of the parents whereas in codominance, F1 generation shows both the parental traits together.
Name an example for Polyallelism?
ABO blood group system in humans
How is Polyallelism different from codominance?
- IA and IB codes for enzymes that add A and B carbohydrates to the RBC surfaces. The two alleles are further in a codominant relationship
-However, ‘i’ allele results in the lack of these carbohydrates on the RBC surface.
- It is recessive to both of the Ia and Ib alleles.
-Thus, ii would result in a recessive trait of not having either A or B on carbohydrates.
-Iai and Ibi genotypes would result in a dominant phenotype.
What is the cross in Polyallelism?
IaIa x ii = Iai (F1 generation)
IbIb x ii = Ibi (F1 generation)
Then:
Iai x Ibi
What is the genotype ratio of Polyallelism?
IaIb : Iai : Ibi: ii
1: 1: 1: 1
What is the phenotype ratio of the F2 generation in Polyallelism ?
AB : A : B: O
1: 1: 1: 1
What are the blood groups based on the presence of two carbohydrates?
Type A ( Carbohydrate A is present)
Type B ( Carbihydrate B is present)
Type AB ( Both A and B carbohydrates are present)
Type O ( Neither of the two carbohydrates are present)
What are the two main types of epistasis based on the nature of the gene interaction?
- Dominant epistasis
- Recessive epistasis
What is an example of the dominant epistasis?
Plumage colour of the house fowls
What is the nature of the feather colors of the house fowls in the F1 generation?
What is the ratio of the dominant epistasis in the F2 generation?
- All of the feather colors would be white
- The white: coloured fowl ratio would be 13: 3
What is the ratio of the dominant epistasis?
13:3
How is it crossed for the dominant epistasis?
A homozygous, double dominant white house fowl and a homozygous double recessive white house fowl are crossed
How is the colour of the two fowl varieties are determined by?
- Gene C/c is responsible for producing the colour in the feathers. The dominant C produces colour while the recessive c results in the absence of pigmentation.
- Gene I is epistatic to the gene C and it suppresses the expression of the colour. Dominant I allele prevents the production of pigmentation. recessive i is unable to prevent colouration.
What is the cross used in the dominant epistasis?
CCII x ccii - CcIi
then CcIi x CcIi
What makes a species white in dominant epistais?
presence of both C and I
Name an example for recessive epistasis?
Lathyrus (sweet pea) plant containing purple and white coloured flowers
What is the cross used in recessive epistasis?
Purple flower (AABB) x heterozygous recessive flower (aabb)
What is the result of the recessive epistasis?
F1 generation- AABB and aabb produces all purple coloured plants.
F2 generation phenotype ratio- purple: white = 9:7
What is the purple colour of the sweet pea plant in recessive epistasis governed by?
- 2 dominant A and B genes code for the purple colour of sweet pea plants
- A and B alleles code for compounds that are necessary of purple colour. Purple colour will only be present with A and B.
What are the traits involved in polygenic inheritance?
- Height
- skin colour (A, B and C contribute to the dark skin allele contributing 1 unit of phenotype. It is incompletely dominant to a, b and c alleles)
- IQ
Based on the number of genes in determining a polygenic character , what might vary?
- Phenotype combinations
- Genotype combinations
What kind of phenotypes do majority of offspring have?
- Intermediate phenotypes
Give an example genetic linkage?
Inheritance of body colour and wing size of Drosophila flies- wild type flies are found to have gray bodies and normal sized wings.
How is both of the characters determined in gene linkage?
By the genes of autosomal characters
In gene linkage, why does it escape from crossing over and independent assortment?
- That is because some genes coding for a particular character are located on the same chromosome.
2.They are also at a closer distance.
In gene linkage, due to mutation, what happens to the traits?
The body colour of the above traits which are of gray bodies and normal sized wings of wild type become black and wings become vestigial.
What are recessive alleles to the wild type alleles in gene linkage?
Mutant alleles of gene linkage.
Body colour alleles
G- gray
g- black
Wing size alleles
N- normal
n- Vestigial
What was the cross conducted during gene linkage?
Crossing of the wild type alleles with the mutant alleles( to both body size and the wing size)
Followed by a dihybrid cross
What was the cross conducted during gene linkage?
Crossing of the wild type alleles with the mutant alleles( to both body size and the wing size)
Followed by a dihybrid cross
What is the phenotype and genotype ratio during gene linkage?
What kind of genotype did most offsprings have?
Genotype ratio : GgNn: Ggnn: ggNn: ggnn
1: 1 : 1: 1
Phenotype ratio : Gray body normal: Gray body vestigial wings: Black body normal wings: Black vestigial wings
1: 1: 1 : 1
During gene linkage, what happens in some occasions?
They get assorted independently due to crossing over.
The above gene linkage test-cross results in recombinant offsprings in lower frequency.
What is the genotype ratio of monohybrid cross?
1:2:1
What are the examples for human sex linked diseases?
Red-Green color blindness
Hemophilia
Red-Green colour blindness is caused as a result of . . .?
X-linked recessive gene
What is red-green color blindness characterized by?
By the difficulty in perceiving differences between red and green colors
Hemophilia is resulted by…?
X-linked recessive gene
What happens in hemophilia?
One or more proteins required for blood clotting are absent.
Name a risk factor of hemophilia
Severe bleeding during injuries due to delay in clot formation
What are pleiotropic alleles responsible for?
Multiple symptoms associated with certain hereditary symptoms in humans such as cystic fibrosis and sickle cell disease.
sickle cell disease cause?
Alteration in the hemoglobin protein of RBC is the cause for the sickle cell disease. A single gene mutation is responsible for the above condition.
What are the types of individuals of sickle cell variety?
Homozygous recessive individuals
What kind of people experience a low oxygen content in blood?
People living in high altitudes and under higher physical stress
What takes place during sickle cell disease?
Low oxygen content in the blood may induce the sickle cell hemoglobin to get accumulated. It then results in sickle shape in red blood cells.
In sickle cell disease, what takes place?
Sickle cells may clump and clog small blood vessels causing tissue and organ damage in several body parts.
What is cystic fibrosis?
A disease condition causing thicker and stickier mucus than its normal structure
Where does mucus get accumulated in cystic fibrosis?
Pancreas
Lungs
Digestive Tract
Reproductive Organs
what does the accumulation of mucus result in cystic fibrosis?
Lung infections
Respiratory failure
Poor digestion
Infertility
Why does the thickening of mucus occur?
due to excess chlorine secretion of defected chlorine channels of the plasma membrane
why does the defect in the transmembrane chlorine channels occur?
As a result of cystic fibrosis regulator protein (CFTR).
What is the cause for altered CFTR protein?
The mutation of the CFTR gene
What kind of disease is cystic fibrosis?
Autosomal recessive disorder
What is epigenetics caused by?
As a result of switching on and switching off of certain genes by modifying nucleotides of a DNA sequence by methylation and demethylation
What is epigenetics resulted from?
Epigenetics results due to either inherited signals from parents
Due to the environmental factors
How can epigenetics be reversed?
by various external stimuli from the environment
What do some epigenetic influences result in?
Some epigenetic influences result in inappropriate gene expressions leading to cancers.
What is schizophrenia?
Schizophrenia is a mental disorder that occurs due to the genetic defects
What happens during schizophrenia in identical twins?
In some identical twins, only one of them gets schizophrenia and the other does not get it. This is due to two types of expressions for same DNA sequence, called epigenetics.
What is Hardy-Weinberg equilibrium used for?
Hardy-Weinberg Equilibrium is used to assess whether a population is evolving with respect to a particular characteristic/ genetic locus
If the population isn’t evolving, what would the genetic makeup of a trait be like according to Hardy-Weinberg equilibrium?
In 1908 British mathematician G.H. Hardy and German physician W. Weinberg, independently showed that, in a population that is not evolving, allele and genotype frequencies will remain constant from generation to generation.
The genetic makeup of a trait in a population would remain unchanged, if they are not evolving at that genetic locus.
To determine allele and genotype frequency change in consecutive generations what can be drawn according to Hardy-Weinberg equilibrium?
A Punnett-square!
What does P squared determined in Hardy-Weinberg equilibrium?
Frequency of dominant homozygotes
What is denoted by Q squared?
Frequency of
What are the factors affecting Hardy-Weinberg Equilibrium?
- Absence of mutations:
- Occurrence of random mating
- Absence of natural selection
- Size of the population is extremely large
5.Absence of immigration or emigration
What is the importance of plant and animal breeding?
Addressing world food and feed quality needs
Addressing food supply needs for a growing world population
Need to adapt to environmental stresses
Satisfying industrial and other end-use requirements
Developing animal and plant varieties with aesthetic values
What are breeding techniques?
Artificial selection
Inbreeding and out breeding
Hybrid breeding
Interspecific breeding
Give examples for artificial selection
Corn
Give examples for inbreeding
Plants:
Wheat
Oats
Barley
Tobacco
Animals:
Mating of father and daughter, brother and sister or cousins
Give examples for outbreeding
In India zebu breeds of cows and nondescript cows are crossed with exotic breeds like Holstein Fresian, Brown Swiss and Jersey bulls or their semen.
Corn and hemp are cross fertilized.
Give examples for hybrid breeding
Nearly all corn and 50% of rice
Give examples for interspecific breeding
plants :
bread wheats, boysenberries (Rubus ursinus x idaeus)
blackberries (Rubus fruticosus)
European raspberries (Rubus idaeus)
loganberries (Rubus × loganobaccus)
Malus × domestica from Malus × asiatica and Malus pumifolia.
animals:
Mule (male donkey x female horse)
Hinny (male horse x female donkey)
Liger (male lion x female tiger)
zebra/donkey cross called zonkey
zebra/ horse cross resulting in zorse.
Name genetic principles of breeding techniques
Polyploidy
Mutation Breeding
Genetic Modification
Give examples for polyploidy
What is the prerequisite for artificial selection?
*availability of variation with respect to the desirable characters.
*Once a population with a desirable variation is recognized, the best
performing individuals for the desired feature are selected.
What takes place during artificial selection?
*Once a population with a desirable variation is recognized, the best performing individuals for the desired feature are selected.
*The progeny of the selected individuals is
grown further and again screened for the desired feature. This process is repeated sometimes
for many generations, until a uniform plant population is attained *
What are advantages of artificial selection?
*The advantage of selective breeding is that it uses the processes of natural selection, but under
direct supervision from carefully selected animals or plants with the desired traits.
*There are no genetic modifications or other forms of tampering that could potentially harm people and the risk
to the plant or animal is often minimum.
What is a disadvantage of artificial selection?
However, selective breeding among animals can take a long time for the process to work.
What are the disadvantages of inbreeding?
- As a rule, inbreeding increases homozygosis and thus exposes harmful recessive genes which
would have otherwise stay hidden among heterozygotes. - Continued inbreeding, therefore, reduces genetic fitness of the population. As a result, the growth and fertility of the inbred population would go down with adverse effect on their productivity.
- Prevalence of genetic disorders might also increase among the inbred population.
What are advantages of outbreeding?
This allows the desirable characters of the exotic parent, which the indigenous parent does not have, to be transmitted to the progeny.
Name a disadvantage of interspecific breeding?
Often interspecific hybrids are sterile or for some other reason cannot interbreed with the parental
species.
Name some examples for polyploidy
In plants : polyploidy can be induced artificially using antimitotic agent, colchicine.
(widely used principle in plant breeding.)
What are advantages of polyploidy?
*Plant breeding are the increment in plant organs (‘‘gigas’’ effect) caused by the larger number of gene copies. Polyploid individuals may thus exhibit larger organs compared to their diploid counterparts, such as roots, leaves,
tubercles, fruits, flowers and seeds.
*Polyploid plants also have lower growth rates, and tend to
flower later or over a longer period of time than related diploids, which is a desirable feature for
ornamental breeding.
*On the other hand, when the crossing between two species is not possible because of differences in ploidy level, polyploids
can be used as a bridge for gene transferring between them.
*Similarly, the genome doubling in a newly formed sterile hybrid allows the restoration of its fertility.
*The increment in heterozygosity, leading to improving the product quality and increasing the tolerance to both biotic and abiotic stresses.
- Genome redundancy promotes a ‘‘buffering’’ effect in which the deleterious alleles are masked by the extra
copies of wild-type alleles.
What are disadvantages of polyploidy?
*In addition, polyploidy often results in reduced fertility due to meiotic errors, allowing the production of seedless varieties such as the triploid watermelon.
*At the same time, genome redundancy allows functional diversification of redundant gene copies, in which one member of a duplicated gene pair mutates and acquires a novel function, without compromising essential functions.
What are examples for polyploidy
maize, potato and alfalfa
improving the product quality and increasing the tolerance to both biotic and abiotic stresses.
What are the agents that can cause mutations during mutation breeding?
ionizing radiation such as gamma rays, protons, neutrons, alpha and beta particles and chemicals such as sodium azide and ethyl
methanesulphonate.
