Genetic linkage refers to genes that are located close together on the same chromosome tending to be inherited together. Crossing over can break genetic linkage during meiosis by exchanging DNA between homologous chromosomes, producing recombinant gametes with new combinations of genes. The closer genes are on a chromosome, the less likely they are to be separated by crossing over. Crossing over increases genetic variation and plays an important role in plant and animal breeding.
Introduction :
Mendel and subsequent workers assumed that a character was governed by a single gene.
But it was later discovered that many characters in almost all the organisms are governed by two or more genes. Such gene affect the development of concerned characters in various ways.
The phenomenon of two or more gene affecting the expression of each other in various ways in the development of a single character of on organism is known as gene interaction.
Introduction :
Mendel and subsequent workers assumed that a character was governed by a single gene.
But it was later discovered that many characters in almost all the organisms are governed by two or more genes. Such gene affect the development of concerned characters in various ways.
The phenomenon of two or more gene affecting the expression of each other in various ways in the development of a single character of on organism is known as gene interaction.
According to Hardy (England,1908) and Weinberg (Germany,1909), gene and genotype frequency of a Mendelian population remain constant generation after generation unless there is selection,mutation,migration or random drift.
This PPT consists of 15 slides only explaining Pleiotropy. This is a phenomenon when one gene controls more than one trait , the traits may be related .Generally one gene's product acts for many reactions and so can affect more than one trait. Examples can be seen in pea Coloured flower and pigmentation in leaf axil, frizzle trait in chicken, fur colour and deafness in cats,Human pleiotropic traits are PKU,Sickle cell Anaemia. HOsyndrome , p53 gene etc
A chromosome abnormality, disorder, anomaly, aberration, or mutation is a missing, extra, or irregular portion of chromosomal DNA. It can be from an atypical number of chromosomes or a structural abnormality in one or more chromosomes
Maternal effects are the influences of a mothers genotype on the phenotype of her offspring. It results from the asymmetric contribution of the female parent to the development of zygotes.
In terms of chromosomal genes, both male and female parents contribute equally to the zygote. The female parent contributes to the zygotes initial cytoplasm and organelles. Sperm rarely contribute anything other than chromosomes. Therefore zygotic development begins within a maternal medium and hence the maternal cytoplasm directly affects zygotic development.
A complementation test (sometimes called a "cis-trans" test) can be used to test whether the mutations in two strains are in different genes. By taking an example of Benzer's work, complementation has been explained.
According to Hardy (England,1908) and Weinberg (Germany,1909), gene and genotype frequency of a Mendelian population remain constant generation after generation unless there is selection,mutation,migration or random drift.
This PPT consists of 15 slides only explaining Pleiotropy. This is a phenomenon when one gene controls more than one trait , the traits may be related .Generally one gene's product acts for many reactions and so can affect more than one trait. Examples can be seen in pea Coloured flower and pigmentation in leaf axil, frizzle trait in chicken, fur colour and deafness in cats,Human pleiotropic traits are PKU,Sickle cell Anaemia. HOsyndrome , p53 gene etc
A chromosome abnormality, disorder, anomaly, aberration, or mutation is a missing, extra, or irregular portion of chromosomal DNA. It can be from an atypical number of chromosomes or a structural abnormality in one or more chromosomes
Maternal effects are the influences of a mothers genotype on the phenotype of her offspring. It results from the asymmetric contribution of the female parent to the development of zygotes.
In terms of chromosomal genes, both male and female parents contribute equally to the zygote. The female parent contributes to the zygotes initial cytoplasm and organelles. Sperm rarely contribute anything other than chromosomes. Therefore zygotic development begins within a maternal medium and hence the maternal cytoplasm directly affects zygotic development.
A complementation test (sometimes called a "cis-trans" test) can be used to test whether the mutations in two strains are in different genes. By taking an example of Benzer's work, complementation has been explained.
Dihybrid Crosses, Gene Linkage and RecombinationStephen Taylor
For the IB DP Biology course AHL: Genetics unit. To get the editable pptx file, please make a donation to one of my preferred charities. More information at http://sciencevideos.wordpress.com/about/biology4good/
Linkage and crossing over , discovery of linked genes,types of crossing over,significance and difference between linkage and crossing over, complete presentation with suitable examples and figures
Linkage and Crossing over (Sanjay Chetry).pptxsanjaychetry2
Linkage
1. Linkage ensures to keep the genes in a chromosome to inherit together
2. The strength of linkage between two genes is inversely proportional to the distance between them in the chromosome
3. The strength of linkage between two genes increases with the decrease in distance between them.
4. The strength of linkage decrease with increase in distance between the genes.
5. Linkage ensures the maintenance of parental trait in the offspring.
6. Linkage reduces the chance of creation of variability with sexual reproduction.
Crossing Over
1. Crossing over facilitates the separation of genes present chromosome and segregate into different gametes.
2. The chance of crossing over between two genes is directly proportional to the distance between them in the chromosome
3. The chance of crossing over between two genes decreases with the decrease in the distance between them.
4. The chance of crossing increases with increase in distance between the genes.
5. The crossing over causes alterations in the parental traits in the offspring.
6. Crossing over increases the chance of variability with sexual reproduction.
Linkage
Genes far apart on the same assort independently are not linked
The position of the gene – locus
Occurs in the prophase of meiosis 1 where homologous chromosomes break at identical locations and rejoin with each other
Two genes are said to be under linkage, or linked, when they are located on the same chromosome.
Example: peas T=tall; t=short R=red; r=white
Crossing Over
Crossing over is a recombination of genes due to exchange of genetic material between two homologous chromosomes
It is the mutual exchange of segments of genetic material between non-sister chromatids of two homologous chromosomes, so as to produce re-combinations or new combinations of genes.
It occurs in the pachytene stage, at four strand stage with the help of enzymes (endonuclease, exo-nuclease, R-protein or recombinase;
Stern and Hotta,(1969, 1978).
There is breakage of chromatid segments, exchange of nonsister chromatid segments and later their fusion in new places.
Chromosomal crossover, is the exchange of genetic material during sexual reproduction between two homologous chromosomes' non-sister chromatids that results in recombinant chromosomes.
Introduction, Types-somatic and germinal; Mechanism of meiotic crossing oversynapsis, duplication of chromosomes, breakage and union, terminalization;
Cytological basis of crossing over - Stern’s experiment in Drosophila; Creighton
and McClintock’s experiment in Maize; Crossing over in Drosophila, Construction
of genetic maps in Drosophila - two point and three-point crosses; Interference and
coincidence.
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The dimensions of healthcare quality refer to various attributes or aspects that define the standard of healthcare services. These dimensions are used to evaluate, measure, and improve the quality of care provided to patients. A comprehensive understanding of these dimensions ensures that healthcare systems can address various aspects of patient care effectively and holistically. Dimensions of Healthcare Quality and Performance of care include the following; Appropriateness, Availability, Competence, Continuity, Effectiveness, Efficiency, Efficacy, Prevention, Respect and Care, Safety as well as Timeliness.
One of the most developed cities of India, the city of Chennai is the capital of Tamilnadu and many people from different parts of India come here to earn their bread and butter. Being a metropolitan, the city is filled with towering building and beaches but the sad part as with almost every Indian city
Antibiotic Stewardship by Anushri Srivastava.pptxAnushriSrivastav
Stewardship is the act of taking good care of something.
Antimicrobial stewardship is a coordinated program that promotes the appropriate use of antimicrobials (including antibiotics), improves patient outcomes, reduces microbial resistance, and decreases the spread of infections caused by multidrug-resistant organisms.
WHO launched the Global Antimicrobial Resistance and Use Surveillance System (GLASS) in 2015 to fill knowledge gaps and inform strategies at all levels.
ACCORDING TO apic.org,
Antimicrobial stewardship is a coordinated program that promotes the appropriate use of antimicrobials (including antibiotics), improves patient outcomes, reduces microbial resistance, and decreases the spread of infections caused by multidrug-resistant organisms.
ACCORDING TO pewtrusts.org,
Antibiotic stewardship refers to efforts in doctors’ offices, hospitals, long term care facilities, and other health care settings to ensure that antibiotics are used only when necessary and appropriate
According to WHO,
Antimicrobial stewardship is a systematic approach to educate and support health care professionals to follow evidence-based guidelines for prescribing and administering antimicrobials
In 1996, John McGowan and Dale Gerding first applied the term antimicrobial stewardship, where they suggested a causal association between antimicrobial agent use and resistance. They also focused on the urgency of large-scale controlled trials of antimicrobial-use regulation employing sophisticated epidemiologic methods, molecular typing, and precise resistance mechanism analysis.
Antimicrobial Stewardship(AMS) refers to the optimal selection, dosing, and duration of antimicrobial treatment resulting in the best clinical outcome with minimal side effects to the patients and minimal impact on subsequent resistance.
According to the 2019 report, in the US, more than 2.8 million antibiotic-resistant infections occur each year, and more than 35000 people die. In addition to this, it also mentioned that 223,900 cases of Clostridoides difficile occurred in 2017, of which 12800 people died. The report did not include viruses or parasites
VISION
Being proactive
Supporting optimal animal and human health
Exploring ways to reduce overall use of antimicrobials
Using the drugs that prevent and treat disease by killing microscopic organisms in a responsible way
GOAL
to prevent the generation and spread of antimicrobial resistance (AMR). Doing so will preserve the effectiveness of these drugs in animals and humans for years to come.
being to preserve human and animal health and the effectiveness of antimicrobial medications.
to implement a multidisciplinary approach in assembling a stewardship team to include an infectious disease physician, a clinical pharmacist with infectious diseases training, infection preventionist, and a close collaboration with the staff in the clinical microbiology laboratory
to prevent antimicrobial overuse, misuse and abuse.
to minimize the developme
CHAPTER 1 SEMESTER V PREVENTIVE-PEDIATRICS.pdfSachin Sharma
This content provides an overview of preventive pediatrics. It defines preventive pediatrics as preventing disease and promoting children's physical, mental, and social well-being to achieve positive health. It discusses antenatal, postnatal, and social preventive pediatrics. It also covers various child health programs like immunization, breastfeeding, ICDS, and the roles of organizations like WHO, UNICEF, and nurses in preventive pediatrics.
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1. Genetic linkage and Crossing
Over
Prepared by
Samira Fattah
Assis. Lec.
College of health sciences-HMU
Lecture 4
2. Is independent assortment always
the case? No
• Independent assortment states that during gamete
formation, the two alleles for one gene segregate or assort
independently of the alleles for other genes.
• But if two genes are found on the same chromosome, they
will not assort independently, and do not follow Mendelian
inheritance patterns.
• Genes that are inherited together are said to be “linked.”
3. • Genes located on different chromosomes are not linked
This allows independent assortment – in a di-hybrid cross
the traits show the classic 9:3:3:1 inheritance pattern.
• Genes that are located very close together on the same
chromosome may show complete linkage
They may be so close to each other that they cannot be
separated by recombination during meiosis.
4. (c) Genes located far apart on the same chromosome
typically show incomplete (partial) linkage
because they are easily separated by recombination.
5. Genetic linkage is the tendency of alleles that are located close
together on a chromosome to be inherited together
during meiosis.
Genes whose loci are nearer to each other are less likely to be
separated on to different chromatids during chromosomal
crossover, and are therefore said to be genetically linked.
In other words, the nearer two genes are on a chromosome, the
lower is the chance of a swap occurring between them, and the
more likely they are to be inherited together.
6. • William Bateson and Reginald Punnett completed a
study in 1905 that determined the movement of alleles
found on the same chromosome.
• The study used sweet peas, particularly flower colour
and pollen shape, they followed the inheritance pattern.
The discovery of genetic linkage
7. • For flower colour, purple is dominant over red, and
for pollen shape long is dominant over round.
• A cross was performed using a true breeding
purple/long and red/round.
• The F1 generation was 100% purple/long.
8. • Crossing two individuals from the F1 generation
resulted in a F2 generation with four different
phenotypes. (purple/long, purple/round, red/long
and red/round).
• The alleles that created these combinations did not
follow the 9:3:3:1 pattern, but supported the idea
that these alleles did not assort independently and
therefore must be linked.
9.
10. Why Linkage
• Linkage refers to packaging genes onto chromosomes.
• Chromosomes (and therefore linkage) are for
organizing genes for their safe coordinated
transmission from cell to cell( parent to offspring).
11. Types of Linkage
Depending upon the presence or absence of new
combinations or non-parental combinations, linkage can
be of two types:
(i) Complete Linkage:
If two or more characters are inherited together and
consistently appear in two or more generations in their
original or parental combinations, it is called complete
linkage. These genes do not produce non-parental
combinations.
Genes showing complete linkage are closely located in
the same chromosome.
12. (ii) Incomplete Linkage:
Incomplete linkage is exhibited by those genes
which produce some percentage of non-parental
combinations. Such genes are located distantly
on the chromosome. It is due to accidental or
occasional breakage of chromosomal segments
during crossing over.
14. Significance of Linkage
1. Linkage does not permit the breeders to bring
the desirable characters in one variety. For this
reason plant and animal breeders find it difficult
to combine various characters.
2. Linkage reduces the chance of recombination of
genes and thus helps to hold parental
characteristics together. It thus helps organism to
maintain its parental, racial and other characters.
15. • Linked genes are not inherited together every time
Chromosomes exchange homologous genes during
meiosis.
16. Crossing Over and the Inheritance of
Linked Genes
• Linked genes don’t always stay linked.
• These linkage groups can be separated by
crossing over during prophase I of meiosis.
17.
18. • When crossing over occurs, the genes that were
previously linked become unlinked, creating four
different types of chromosomes (gametes).
• The proportions are not equal because crossing over
does not occur in every cell during meiosis.
19. Crossing Over
• A random exchange
of DNA between
two non-sister
chromatids of
homologous
chromosomes.
• Results in
recombination of
genetic material
20. • Prevalence of recombination is dependent on
the distance between linked genes
21. FACTORS AFFECTING CROSS OVER
1. Sex:
there is a tendency of reduction of crossing over in male
mammals.
2. Mutation:
mutation reduces crossing over
3. Temperature:
high and low temperature variations increase the percentage
of crossing over in certain parts of the chromosome.
4. X-ray Effect:
X-ray irradiations increase crossing over near centromere.
5. Age:
older age increases the rate of crossing over.
22. Significance of Crossing-over
1. Produces new combinations of traits.
2. Through crossing over segments of homologous chromosomes
are interchanged and hence provide origin of new characters
and genetic variations.
3. Crossing over plays a very important role in the field of
breeding to improve the varieties of plants and animals.
23. Theories of Crossing Over
(i) Contact First Theory :
According to this theory the inner two chromatids of the
homologous chromosomes undergoing crossing over, first
touch each other and then cross over. At the point of contact
breakage occurs. The broken segments again unite to form
new combinations.
(ii) The Breakage-First Theory :
According to this theory the chromatids under-going crossing
over, first of all break into two without any crossing over and
after that the broken segments reunite to form the new
combinations.
24.
25. Types of Crossing Over
(i) Single Crossing Over:
In this type of crossing over only one chiasma is formed
(a chiasma is the point where two homologous non-
sister chromatids exchange genetic material
during chromosomal crossover in meiosis ) all along the
length of a chromosome pair. Gametes formed by this
type of crossing over are called single cross over
gametes .
26. Types of Crossing Over
(ii) Double Crossing Over:
In this type two chiasmata are formed along the entire
length of the chromosome leading to breakage and rejoin
of chromatids at two points. The gametes produced are
called double cross over gametes.
(iii) Multiple Crossing Over:
In this type more than two chiasmata are formed and
thus crossing over occurs at more than two points on the
same chromosome pair. It is a rare phenomenon.
27.
28. Difference between linkage and crossing
over
Linkage
1. It is tendency of genes on a chromosome to remain
together and passed as such in next generation.
2. It brings more parental types.
3. Strength of linkage between two genes increases if
they are closely placed on a chromosome.
4. It helps to maintain a newly improved variety.
29. Difference between linkage and crossing
over
Crossing over
1. It is exchange of genes or chromosomal parts to
break established linkage and formation of new
linkage.
2. It produces recombination.
3. Frequency of crossing over between two genes
decreases if they are closely placed .
4. It is the source of variation for producing new
varieties.
30. In genetic recombination by crossing over, what is the
difference between parental gametes and
recombinant gametes?
• Parental gametes are the gametes that maintain the
original linkage of genes (alleles) in the chromosome.
• Recombinant gametes are those in which the
original linkage is undone due to exchange of
chromosomal pieces via crossing over during
meiosis.