Topic 3 - Genetics

Question 1

3.1B - Explain the advantages and disadvantages of asexual reproduction

Answer 1

Asexual reproduction is without fertilisation, producing clones offsprings that are genetically identical to the parent, so no variation.
It is much more faster than sexual reproduction as there is no need to find a mate and because the reproduction is faster.

Question 2

3.2B - Explain the advantages and disadvantages of sexual reproduction

Answer 2

Sexual reproduction involves fertilisation of the female and male gametes.
This combines characteristics from each parent, making offspring different from one another. This is and advantages when there are environment changes.
This is variation, and makes the offspring better suited to the conditions so it can survive and reproduce.
A disadvantage is that a mate needs to be found which can take time.
Also reproduction takes a long time.

Question 3

3.3 - Explain the process of meiosis

Answer 3

This is used to produce gametes.
The gamete making cell is a diploid cell.
Each of the 4 chromosomes replicate and the two copies attach forming an X.
The 4 chromosomes pair up into two cells.
The chromosomes in the two nuclei then split into two more cells.
Meiosis produces four haploid daughter cells with 23 chromosomes.

Each chromosome contains a different version of the same gene, so is genetically different.
Therefore all gametes are different as they are haploid cells made in meiosis.

Question 4

3.4 - Describe what DNA is made up of

Answer 4

Double helix structure - A molecule of DNA has two strands, forming a double helix shape, these two strands are joined by a base.

Complementary base pairing - These bases are adenine, thymine, cytosine and guanine (A,T,C,G).
A always matches with bases T and C always matches with base G, these are complementary base pairs.

Nucleotides - Each base is attached to a sugar which is attached to the phosphate group of the next nucleotide.
This forms the backbone of DNA strands and therefore DNA is made up of many nucleotides making a polymer.

Hydrogen bonding - DNA bases have slight electrical charges, a negatively charged part of a base attracts a positively charged part of another base.
This weak force of attraction is a hydrogen bond.
Adenine and thymine form 2 bonds while cytosine and guanine form 3 bonds.

DNA code - The order of bases in a gene codes the instructions for a specific protein.
Everyone has slightly different DNA . DNA allows scientists to find how people are related.

Question 5

3.5 - What is a gene and a genome?

Answer 5

Genome - the entire DNA of and organism. This is found in most cells.
Gene - a section of DNA that codes for a specific protein. This is found along the genome.
Genes control the order of amino acids.

Question 6

3.6 - Explain how DNA can be extracted from a fruit

Answer 6

Dissolve 3g of salt in 100cm3 of water in a large beaker, the salt makes DNA clump together.
Add 10cm3 of washing liquid and stir till dissolved, this breaks down cell membranes and nuclei.
Mash 50g of kiwi and put it in an empty beaker and add solution made and stir.
Place the beaker in a water bath at 60°C for 15mins.
Filter the mixture and collect the filtrate in a small beaker.
Pour 10cm3 of the mixture in a boiling tube.
Add two drops of protease enzyme solution to break down proteins.
Tilt boiling tube and add cold ethanol. Stop when there is the same amount of ethanol and filtrate.
DNA is insoluble in ethanol and forms a white precipitate.
Leave the tube and let a white layer form, this is the DNA.

Question 7

3.7B - Explain the process of transcription

Answer 7

Space between one gene and another
An enzyme called RNA polymerase attaches to the DNA in front of a gene called the non-coding binding site, where the enzyme separates the two DNA strands.
The enzyme then moves along one DNA strand adding complementary RNA nucleotides.
These nucleotides have the same bases as DNA although uracil is used instead of thymine.
Nucleotides link to form a strand of messenger RNA called mRNA.

Question 8

3.8B - Describe the stages of translation

Answer 8

The mRNA strands travel out the nucleus through nuclear pores. In the cytoplasm mRNA strands attach to ribosomes.
The ribosome moves along an mRNA strand three bases at a time.
mRNA have codons which are grouped into three bases.
At each mRNA codon, a molecule of transfer RNA or tRNA carries a specific amino acid.
The codon joins the anti-codon which joins to the amino acids, they join together to form a protein, many proteins form a polypeptide.

Question 9

3.9B - Describe how genetic variants in the non-coding DNA affects the phenotype

Answer 9

RNA polymerase attaches to DNA bases in front of a gene in the non-coding region.
A mutation in the non-coding region results in RNA polymerase not binding well, reducing transcription.
This can cause tiredness.

Question 10

3.10B - Describe how genetic variants in the coding DNA affects the phenotype

Answer 10

A change in the bases of a gene is a genetic variant or mutation.
It can be caused by DNA not copied properly in cell division and UV rays.
One gene can have many alleles due to mutation, this alleles inherited affect the phenotype.
When there is a change in the base, the codon attracts a different anti-codon, a different amino acid and protein, forming a different polypeptide chain.
This can change a persons phenotype.

Question 11

3.11B - Describe the work of Mendel

Answer 11

Mendel observed many characteristics of pea plants, he wanted to find how they were inherited.
He bred tall pea plants and when its offspring was bred again he got short plants.
He concluded that inherited factors control a plants characteristics. These factors are alleles.
There are two alleles for a characteristic, if they are the same, their offsprings would have the same characteristics as well.

Question 12

3,12/13 - Explain why there are differences in inherited characteristics

Answer 12

Genes for one phenotype can have different instructions creating variations, these different instructions are alleles.
There are two copies of each chromosome in every cells nucleus and two copies of each gene, one copy is an allele.
If both alleles are same the gene is homozygous, if the alleles are different the gene is heterozygous.
The dominant allele is the one chosen for the phenotype while recessive alleles don’t. But two recessive alleles give the phenotype.
Alleles in an organism is the genotype, the characteristics of the alleles is the phenotype.

Question 13

3.14 - What is monohybrid inheritance?

Answer 13

Diagrams that show how a gene is passed through offspring.

Question 14

3.15 - Describe how the sex of offspring is determined

Answer 14

Two chromosomes determine a persons sex, called sex chromosomes and egg cells contain an X while a sperm cell can have an X or Y chromosome.
Punnet squares can work out the probability of sex as well by XX and XY on the boxes.

Question 15

3.16 - What is a pedigree chart?

Answer 15

A chart showing how genotypes and phenotypes are inherited in families.

Question 16

3.17 - Describe the inheritance of the ABO blood groups

Answer 16

There are four groups of blood: A, B, AB and O.
The gene responsible for indicating the group of blood has three alleles. Ia, Ib, Io.
Io is recessive .
IaIb genotype is the blood group AB, both alleles affect the phenotype so they are codominant.

Question 17

3.18B - Explain how sex-linked genetic disorders are inherited

Answer 17

In most pairs of chromosomes, they have the same genes. But males have the Y chromosome which is missing some genes found on the X chromosome.
This means a man will only have one allele for some of all the genes of X, as Y is missing the rest of the chromosomes.
If the allele on a man’s X chromosome causes a genetic disorder, he will develop it.
This is because the man doesn’t have a healthy allele on the other chromosome as it is Y.
In women, they have the healthy allele as they have two X chromosomes, so won’t develop it unless there are two recessive disorder alleles.
There is a higher chance of the disorder developing in man. These are sex-linked genetic disorders.

Question 18

3.19/20/22/23 - What is a mutation

Answer 18

Mutations happen when there is a mistake in cell division copying DNA.
This can happen naturally, but is more likely to happen when there is DNA damage due to UV light and radiation.
A mutation produces an allele that changes how a protein is produced, this affects how the body works and can sometimes be small changes and won’t affect the phenotype.
Most phenotypes depend on multiple genes rather than one gene.

Question 19

3.21 - What is the Human Genome Project?

Answer 19

It was the complete decoded human genome.
This mapped all the complementary base pairs.
It showed that 99% of DNA bases were the same.
Mapping a person’s genome can indicate their risk of developing genetic disorders.
It can also identify which medicines treat a person’s illness the best, as alleles affect how a medicine works.