unit 3 part 2.

Question 1

define meiosis

Answer 1

the division of a diploid nucelus to preduce foru haploid nuclei

Question 2

what happens before meiosis? in interphase

Answer 2

DNA is duplicated so that sister chromatids are arranged to become homologous chromosomes. these then arrange to form paris called bivalents and are held together by chiasmata

Question 3

what happens in meiosis 1?

Answer 3

prophase 1: Chromosomes condense, nuclear membrane dissolves, homologous chromosomes form bivalents, crossing over occurs.

metaphase 1:
Spindle fibres from opposing centrosomes connect to bivalents (at centromeres) and align them along the middle of the cell

anapahse 1:
Spindle fibres contract and split the bivalent, homologous chromosomes move to opposite poles of the cell

telophase 1:
Chromosomes decondense, nuclear membrane may reform, cell divides (cytokinesis) to form two haploid daughter cells

Question 4

what happens in meiosis 2?

Answer 4

P-II: Chromosomes condense, nuclear membrane dissolves, centrosomes move to opposite poles (perpendicular to before)

M-II: Spindle fibres from opposing centrosomes attach to chromosomes (at centromere) and align them along the cell equator

A-II: Spindle fibres contract and separate the sister chromatids, chromatids (now called chromosomes) move to opposite poles

T-II: Chromosomes decondense, nuclear membrane reforms, cells divide (cytokinesis) to form four haploid daughter cells

Question 5

​Explain how meiosis leads to genetic variation in gametes.

Answer 5

Crossing over in prophase I
Random assortment of chromosomes in metaphase I
Random fusion of gametes from different parents

Question 6

Define non-disjunction.

Answer 6

Nondisjunction is when chromosomes fail to separate properly, leading to gametes with one extra or one missing chromosome. This can lead to down syndrome and other genetic diseases.

Question 7

Describe the two procedures for obtaining fetal cells for production of a karyotype

Answer 7

Chorionic Villi Sampling
Sample of chorionic villus (placenta tissue) is removed via a tube inserted through the cervix.
Approx 1% chance of miscarriage
Done at around 11 weeks

Amniocentesis
Involves the extraction of a small amount of amniotic fluid with a needle
Conducted at 16 weeks
0.5% chance of miscarriage

Question 8

State an example of a dominant and recessive allele found in pea plants.

Answer 8

Dominant trait: flower color: purple, plant height: tall, seed color: yellow, seed shape: round

Recessive trait: flower color: white, plant height: short, seed color: green, seed shape: wrinkled

Question 9

Define codominant alleles.

Answer 9

Co-dominance occurs when pairs of alleles are both expressed equally in the phenotype of a heterozygous individual. Ex. AB blood group

Question 10

Define “carrier” as related to genetic diseases.

Answer 10

An organism that inherits the recessive allele of a gene, but does not show any symptoms of the disease because they also have the dominant (normal functioning) allele.

Question 11

Explain sickle cell anaemia as an example of a genetic disease caused by codominant alleles.

Answer 11

Sickle cells anemia is a rare disease where red blood cells become thin and elongated. If a person has one copy of the sickle cell allele, half of their red blood cells will misshapen. The alleles are codominant since both normal and sickle cell shapes are seen in a heterozygous individual.

Question 12

Define sex linkage + examples

Answer 12

When a gene controlling a characteristic is located on a sex chromosome.
Common examples are colorblindness and hemophilia (both recessive)

Question 13

Use correct notation for sex linked genes.

Answer 13

For sex linked genes, X and Y are used for the notation of whether it is a female or male trait.
The chromosome is written as a subscript.
Xr = red eye

Question 14

List five example genetic diseases.

Answer 14

Cystic fibrosis (autosomal recessive)
PKU (autosomal recessive)

Huntington’s disease (autosomal dominant)

Hemophilia (sex linked recessive, on x Chromosome )
Red-green colorblindness (sex-linked recessive, on the X chromosome)

Question 15

Define monohybrid, true breeding, hybrid, F1 and F2.

Answer 15

Monohybrid - a genetic cross between two individuals tracking one gene of interest
True breeding - organisms that have been bred to have a homozygous genotype
F1 generation - the offspring of the parent generation cross
F2 generation - the result of a cross between two F1 individuals

Question 16

Describe the role of restriction enzymes in nature and in biotechnology applications.

Answer 16

Restriction enzymes are found in bacteria who use the enzymes to break viral DNA into useless fragments. In biotechnology laboratories, restriction enzymes cut DNA into smaller fragments (for example: DNA fingertip)

Question 17

Contrast sticky vs. blunt ends.

Answer 17

When the restriction enzymes cut the DNA directly through the backbones without creating unbonded bases, the cut is said to be “blunt”. However, when a restriction enzyme cuts the DNA through the backbones and along the complementary base, leaving unbonded bases that want to stick back together, the cut is said to be sticky

Question 18

Describe how and why DNA fragments separate during electrophoresis.

Answer 18

A solution of DNA is loaded into the well of an agarose gel. Because DNA is negatively charged (due to its phosphate groups), it can be pulled through the gel by an electric field. DNA fragments move towards the positive electrode, with smaller fragments moving further.

Question 19

Outline the functions of the buffer, marker and loading dye in DNA electrophoresis.​

Answer 19

A buffer contains ions that allow the electrical current to flow through the gel box. Without the buffer, the power source can’t separate the DNA because no electricity is flowing. A buffer contains a PH range that does not damage the DNA.

marker is a sample of DNA fragments cuts into known sizes. The marker acts like a ruler; it is used to compare DNA fragments to the known marker fragment sizes estimate the size of the fragments.

The loading dye is used to add color to the DNA mixture so that one can see them. Similarly to DNA, loading dye is negatively charged and will move towards the positive electrode.

Question 20

State the function of the PCR.

outline the process of PCR

Answer 20

The polymerase chain reaction (PCR) is an artificial method of replicating DNA under laboratory conditions

DNA sample, primers, nucleotides, taq polymerase, mix buffer are added to a PCR tube, which is added to a thermal cycler

Denaturing
1. DNA is heated causing it to sepretae into two strands (denature)

Annealing
1. DNA is cooled off, causing DNA primers to bind to the strands

3. Extension
4. slightly heated again allowing free nucleotides to be added to the strands, resulting in two DNA copies of the ones added in.

Sample is heated up again and process reoccurs.
Each reaction cycle doubles the amount of DNA – a standard PCR sequence of 30 cycles creates over 1 billion copies (230)

Question 21

Outline the process of DNA profiling.​ + uses

Answer 21

• A sample of DNA is obtained.
• A comparison sample of DNA is obtained.
• PCR is used to produce more copies of the DNA
• DNA is cut into fragments by restriction enzymes
• DNA fragments are separated by size via electrophoresis
• Fragments separate into a series of bands
• Bands are compared between different samples
• If banding pattern is the same, then DNA is from the same source
• Children share bands with either one or both parents
• Used for paternity testing, forensic analysis, genetic disease diagnosis and evolutionary analyse

Question 22

Outline the production of embryos via somatic cell nuclear transfer.

Outline the production of Dolly the sheep using somatic cell nuclear transfer.​​

Answer 22

1. Extract somatic cell nucleus from the organism you want to clone.
2. Remove egg cell nucleus from an egg donor.
3. insert somatic cell nucleus in enucleated egg
4. electric shock fuses the cells and starts the development (cell division)
5. Allow blastocyst to develop
6. Implant embryo into a surrogate mother
7. Surrogate gives birth to the clone animal.
   Or
8. Use embryonic stem cells for blastocyst for research or disease treatment.

Question 23

Describe a technique for genetic modification including plasmids, restriction enzymes, reverse transcriptase and ligase.

Answer 23

Gene Isolation
1. Gene vector is isolated (gene: ex.insulin) (vector: plasmid of bacteria cell).

Digestion
2. Both are cut by restriction enzymes at specifc locations.
The gene of interest is inserted into the vector because the ‘sticky’ ends of the gene and vector overlap via complementary base pairing.
Then the gene and vector are spliced together by ligase, by fusing their sugar-phosphate backbones together, to form a recombinant construct.

4. new vector is introduced back into the host bacteria, where it is expressed (ex. to produce insulin.)

Question 24

Describe the process of reproductive cloning via embryo splitting.

Answer 24

A pluripotent embryo (undifferentiated cell) is separated into separate cells which can each develop into separate individuals. Thus, with the correct laboratory equipment, it is possible to separate cells from a growing embryo of an animal, and place the separated cells in the uterus of a female of that species and get artificial twins, triplets and quadruplets, depending on how many cells were separated.

Question 25

Compare therapeutic cloning to reproductive cloning.

Answer 25

The same for both:
Enucleated oocyte is fused with adult cell, resulting from the nuclear transfer a zygote. Development of zygote resulting in a blastocyst.
Reproductive cloning:
Uterine transfer into surrogate resulting in clone

Therapeutic cloning:
Extraction of embryonic stem cell used to differentiate into various tissues.

Question 26

Outline potential environmental, health and agricultural benefits and risks associated with genetic modification of crops.

Answer 26

Benefits
Improved nutritional value of foods
Crops can grow in arid conditions for better yield
GM crops can produce herbicides to kill pests
Reduces economic cost and carbon footprint (less pesticide usage)

Risks
Removal of traits could have unknown effects
Cross pollination could lead to ‘super weeds’
Limit biodiversity
New traits could cause adverse health reactions