What is the difference between allele, gene, and trait?

Gene and allele are basically make us who we are. They are genetic sequences of our DNA. Although gene is a more general term than allele. For example, humans have facial hair, which is determined by gene. Hair can be thick or patchy, and that is determined by allele. Alleles determine different traits, which carry different phenotypes. Trait is a physical expression of genes

- Genes are something we inherit from our parents - alleles determine how they are expressed in an individual

- Alleles occur in pairs b ut there is no such paring for genes- A pair of alleles produces opposing phenotypes. No such generalization can be assigned

to genes- Alleles determine the trait we inherit- The genes we inherit are the same for all humans- Alleles determine the different traits which carry different phenotype- Trait does not have homozygous and heterozygous like allele does- Trait us a product of biochemical reactions, whereas allele is a small segment of DNA- Trait is a characteristic of an individual, whereas alleles carry information which is

accountable for a trait of an individual- Alleles are the different cariants of a gene and they occur in pairs

Explain the consequence of a base substitution mutation in relation to the processes of transcription and translation, using the example of sickle cell anemia Sickle cell anemia is a disease passed down through family genetics. Causes and processes:

1. A base substitution mutation happens in a single base in a sequence of DNA. • 6th codon for the beta chain of hemoglobin is changed from GAG to GTG

on the non-coding strand. 2. This changes a single codon in mRNA during transcription.

• From GAG to GUG, resulting in a single amino acid change from glutamic acid to valine (Glu to Val)

DNA Base mutation GAG to GTG (non-coding

strand) mRNA Transcription GAG to GUG Amino acids Translation Glu to Val Consequences: The change in the amino acid alters the structure of hemoglobin causing it to form fibrous, insoluble strands. This causes red blood cells to have a sickle shape.

The insoluble hemoglobin is not able to carry oxygen efficiently, which makes people feel tired. And those sickle cells accumulate in the capillaries and form clots, which blocks blood transportation and supply to vital organs. Sickle cells are also destroyed easier and faster than normal red blood cells and this cases anemia. Anemia is a condition in which the blood has a lower number of red blood cells than the normal level. This is occurred if an individual have two copies of codominant sickle cell allele (homozygotes). However, heterozygous individuals have more resistance to malaria due to the presence of sickle cell allele, which can be an advantage to them.

   

4.2.3 Outline the process of meiosis !

Meiosis involves two divisions. It is preceded by interphase, which includes the replication of DNA (S phase) to create chromosome with genetically identical sister chromatids. !!Meiosis I !

Prophase I !

- chromosome pair up so the chromosomes in each pair are homologous. !

- once paired up, crossing over occurs. !

- Crossing over is the exchange of genetic material between non-sister chromatids. !

- The nuclear member also starts to break down and the spindle microtubules stretch out form each pole to the equator. !

Metaphase I !

- Paired up homologous chromosome line up at equator !

- spindle fibbers attach to the chromosomes !

- one chromosome moved to one pole and other moves to the opposite pole!

Anaphase I !

- homologues chromosome are separated and pull to the opposite poles. !

Telophase I !

- the cells splits into two haploid daughter cells as cytokinesis happens concurrently. !!

Meiosis II!The sister chroma tides are divided into separate cells !

Prophase II !

- spindle fibres reform and reconnect to the chromosomes. !

Metaphase II!

- the chromosomes line up along the equator of the cell !

Anaphase II!

- The sister chromatids split apart and moves to opposite poles !

Telophase II !

- the nuclear membrane reforms around the four sets of daughter chromosomes. !

- the cell spits in two as cytokinesis happens concurrently !

- Cytokinesis then follows to divide the cytoplasm of the two cells and so the result is four daughter cells each with a haploid set of chromosomes. !

!

4.2.4 Explain that non-disjunction can lead to a change in chromosome number,

illustrated by reference to Down syndrome (trisomy 21)

Non-disjunction is a failure of homologous pairs of chromosomes to separate properly

during meiosis.

The failure of the chromosomes to separate may either occur through:

Failure of homologous to separate during Anaphase I (resulting in four affected

daughter cells)

Failure of sister chromatids to separate during Anaphase II (resulting in two

affected daughter cells)

One parental gamete is normal and has a single copy of chromosome 21 but the other

parental gamete has two copies of chromosome 21 as a result of non-disjunction. When

the two gametes fuse during fertilization, it results with a zygote having three copies of

chromosome 21, leading to Down syndrome or trisomy 21.

Genotype:- alleles of an organism.- usually written using upper and lower case letters (e.g. Tt)

Phenotype:- characteristics of an organism.- usually written as a word (e.g. tall)

Dominant allele:- allele which has the same effect on the phenotype whether it is present in the

homozygous or heterozygous state.Recessive allele:

- allele which only has an effect on the phenotype when present in the homozygous state.

Co-dominant alleles:- a pair of alleles that both affect the phenotype when present in a heterozygote.

Multiple alleles:- three or more alleles for a particular gene

Homozygous:- having the two identical alleles of a gene.

Heterozygous:- having two different alleles of a gene.

Locus:- particular position on homologous chromosomes of a gene.

Carrier:- a heterozygous individual that has one copy of recessive allele that causes a genetic disease in individuals that are homozygous for this allele.

Test cross:- testing a suspected heterozygote by crossing with a known homozygous recessive.

Understanding genotype, phenotype and

gametes...

4.3.1.Define genotype, phenotype, dominant allele, recessive allele, co-dominant alleles, multiple alleles, locus, homozygous, heterozygous, carrier and test cross.

Example 1.

Example 2.

(Genotype)(Phenotype)

Heterozygous, since alleles are different (One dominant & one recessive)

Homozygous, since alleles are the same

4.3.4  Describe  ABO  Blood  Groups  as  an  example  of  codominance  and  multiple  alleles  

Blood  Type  • Based  on  4  different  phenotypes  

o A  o B  o AB  o O  

• Combinations  of  3  different  alleles  o IA  o IB  o i  

Phenotypes  are  formed  by  the  following  genotypes:  Phenotype   Genotype(s)  

A   IAIA  or  IAi  B   IBIB  or  IBi  AB   IAIB  O   ii  

Punnett  Squares  

 

 

How does sexual reproduction lead to variation?  

# The sex chromosomes can control gender by referring to the inheritance of X and Y chromosomes in humans  

* Gender in humans is controlled by the 23rd pair of chromsomes  

 Males have one X and one Y (XY) chromosome, while females have two X chromosomes (XX)  

 The female possess two X chromosomes one inherited from the father the other from the mother. 

 The male possess one X chromosome inherited from the mother and the Y chromosome inherited form the father. 

 (The female can provide only one type of chromosome (X). The male however provides sperm cells either with and X or with a Y.) 

 Theoretically this means that in any fertilization there is a P=0.5 ( 50% , 1 in 2) chance of having either a boy or a girl. 

 A Punnett square can be used to predict the chances of the gender of a child.  

# The blood groups of a child also can be controlled from parents.  

 The ABO blood group system is based on 4 different phenotypes (group A, B, AB and O) caused by different combinations of 3 different alleles (IA, IB and i).  

 The alleles IA and IB are codominant, so both will affect the phenotype. The allele i is recessive and will only affect the phenotype when homozygous. 

 

* (So only if two parents are heterozygous, the child is type O.) 

Unit 4 Genetics • Describe the inheritance of color blindness - use a diagram (pedigree) and use the correct

notation. Describe : Give a detailed account. Colorblindness is a recessiv sex linked condition. - Sex linkage refers to a gene/allele/ trait on a sex chromosome. The gene loci is on the non-homologous region of the X-chromosomes. Red Green color blindness is more common in males than in females. - A female has two X chromosomes but a male has one X chromosome. So, males always inherit the colorblind allele from their mothers. Males cannot pass on colorblindness to their sons since the Y-allele does not have any of the colorblindness alleles. XB for normal vision, Xb for clour blindness.

1) Affected father and Unffected mother

XB Y

Xb Xb XB XbY

Xb Xb XB XbY

2) Affected father and Affected mother

XB Y

XB XB XB XBY

XB XB XB XBY

3) Unaffected father and Affected mother

Xb Y

XB XB Xb XBY

XB XB Xb XBY

4.3.8. Describe the inheritance of hemophilia - use a diagram (pedigree) and use the correct notation.

• Hemophilia, like color blindness, is an example of a X-linked recessive condition

• The gene loci for this condition is found on the non-homologous region

of the X chromosome – not present on the Y chromosome

• Males only have one allele for this gene – and can therefore not be a carrier for the condition à this means they have a higher frequency of being recessive and expressing the trait

XH is normal Xh is for hemophilia Males inherit the X-linked recessive condition from their mother – XHY (normal) or XhY (hemophiliac) Females inherit the X-linked recessive condition if they receive a recessive allele for both parents – XHXH (normal) or XHXh (carrier) or XhXh (hemophiliac) The following is part of a family’s pedigree:

4.4.1 Outline the use of polymerase chain reaction (PCR) to copy and amplify minute (little amount of) quantities of DNA !Purpose of PCR: To copy more of the same DNA in order to analyse it when there is not enough - particularly after a body has been found after a while. !Possible sources of DNA: • blood • tissue • hair • semen !Method: • Denaturation: heated and

separated into 2 strands • Annealing: DNA primers attach

to each end of the target sequence

• Elongation: The strands are copied with heat resistant DNA polymerase !Production: 1 cycle produces 2 identical copies of DNA sequence. !Cautions: • Technicians cannot let their own

DNA mix with the original sample !!Works cited: BioNinja. 4.4 Genetic Engineering and Biotechnology. 14 July 2013. 27 February 2014 <http://www.ib.bioninja.com.au/standard-level/topic-4-genetics/44-genetic-engineering-and.html>.

Figure 1 - Process of PCR (BioNinja)

4.4.12 Outline a technique for cloning using differentiated animal cells.

SCNT(Somatic-cell nuclear transfer)1. Take a nucleus from a somatic (body) cell2. Remove the nucleus from an egg cell 3. Replace with the nucleus from the somatic cell4. Give an electric shock to make the cell start dividing5. Grown into a group of cells6. Implant into a uterus where it can grow

Therapeutic Cloning1.Produce and grow human embryos (or cells from the umbilical cord or from aborted fetuses) for a few days into a small ball of cells(cells are not specialized)

2.Through SCNT, the cells grow into any of a large number of different specialized tissues

Bonnie  Poon  12L  

4.4  Genetic  Engineering  and  Biotechnology  

4.4.4  Describe  the  application  of  DNA  profiling  to  determine  paternity  and  also  in  forensic  investigations    

DNA  profiling:  a  technique  by  which  individuals  are  identified  on  the  basis  of  their  respective  DNA  profiles  

1. Collect  DNA  sample  (blood,  saliva,  semen)    2. Amplify  sample  using  the  Polymerase  Chain  Reaction  (PCR)  3. Cut  non-­‐coding  DNA  cut  with  specific  restriction  enzyme  to  generate  

fragment  4. Fragment  lengths  differ  due  to  variable  length  of  individual  Short  Tandem  

Repeats  (STR)  5. Separate  fragments  with  gel  electrophoresis  (as  smaller  fragments  travel  

quicker  through  the  gel)  6. Analyse  DNA  for  applications  

Applications:  

• Paternity  testing    – compare  offspring  DNA  against  potential  father  – children  inherit  allele  from  each  parent  (half)    – thus  children  possess  combination  of  parent  alleles  

• Forensic  investigations    – identify  suspect/victim  based  on  crime-­‐scene  DNA  – suspect  DNA  must  have  complete  match  with  sample  from  crime  

scene  (for  conviction)  

 

4.4.8 Outline a basic technique used for gene transfer involving plasmids, a host

cell (bacterium, yeast or other cell), restriction enzymes (endonucleases) and DNA

ligase.

- Plasmid is a small piece of circular DNA

- Plasmids are circular bits of genetic material carrying 20-30 genes. - Since plasmid replicates, cell is possible to possess several identical plasmids. - Plasmids are used to clone a desired gene.

1. Plasmid removed from the host cell (bacterium of Agrobacterium temefaciens)

2. tDNA is cut by the restriction enzyme. (tDNA is not removed but carrying the foreign gene) 3. Foreign DNA (desired gene) is cut by restricted enzyme. 4. Foreign DNA is inserted to the plasmid. DNA ligase splice the foreign DNA and tDNA together) It

becomes recombinant Ti plasmid. 5. Plasmid with foreign DNA is reinserted into the host cell.

6. The plants cell are grown in culture. 7. Plant is generated.

http://mol-biol4masters.masters.grkraj.org/html/Genetic_Engineering4D-Transformation-Plant_Cells.htm

Host cell - The cell which is to receive the genetic material. Restriction enzymes - Used to cut a desired section of the DNA.