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

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
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
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)
Base mutation
Amino acids
GAG to GTG (non-coding
Glu to Val
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.
4.3.1.Define genotype, phenotype, dominant allele, recessive allele, codominant alleles, multiple alleles, locus, homozygous, heterozygous,
carrier and test cross.
- alleles of an organism.
- usually written using upper and lower case letters (e.g. Tt)
- 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
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
- having the two identical alleles of a gene.
- having two different alleles of a gene.
- particular position on homologous chromosomes of a gene.
- 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
Example 1.
Homozygous, since
alleles are the same
Heterozygous, since alleles are different
(One dominant & one recessive)
Example 2.
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 A B AB O Genotype(s) IAIA or IAi IBIB or IBi IAIB 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 Y
2) Affected father and Affected mother
3) Unaffected father and Affected mother
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
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
• Denaturation: heated and
separated into 2 strands
• Annealing: DNA primers attach
to each end of the target
• Elongation: The strands are
copied with heat resistant DNA
1 cycle produces 2 identical copies
of DNA sequence.
• Technicians cannot let their own
DNA mix with the original sample
Figure 1 - Process of PCR (BioNinja)
Works cited:
BioNinja. 4.4 Genetic Engineering and Biotechnology. 14 July 2013. 27 February 2014
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) cell
2. Remove the nucleus from an egg cell
3. Replace with the nucleus from the somatic cell
4. Give an electric shock to make the cell start dividing
5. Grown into a group of cells
6. Implant into a uterus where it can grow
1.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
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.
Plasmid removed from the host cell (bacterium of Agrobacterium temefaciens)
tDNA is cut by the restriction enzyme. (tDNA is not removed but carrying the foreign gene)
Foreign DNA (desired gene) is cut by restricted enzyme.
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.
Host cell - The cell which is to receive the genetic material.
Restriction enzymes - Used to cut a desired section of the DNA.