Topic 3 - Genetics

Question 1

Explain some of the advantages and disadvantages of asexual reproduction

Answer 1

ADVANTAGES:

• only one parent - no need to find a mate so the reproductive cycle is quicker
• offspring are genetically identical. If the organism is in an unchanging environment and the parent is adapted then the offspring will be too

DISADVANTAGES:

• genetically identical offspring means no variation in the population and if the environment changes they may all die

Question 2

Explain some of the advantages and disadvantages of sexual reproduction

Answer 2

ADVANTAGES:

• offspring are genetically different to parents and each other so there is more variation. This means that if the environment changes then some may survive

DISADVANTAGES:

• the organism has to find a mate to reproduce which takes time and energy

Question 3

Explain the role of meiotic cell division

Answer 3

Meiosis creates four daughter cells, each with half the number of chromosomes. Meiosis only happens in gamete producing cells, producing genetically different haploid gametes.

Question 4

What does meiosis produce

Answer 4

It produces four genetically different daughter HAPLOID cells (only one set of chromosomes)

Question 5

Describe the structure of DNA

Answer 5

DNA is a genetic material found in the chromosomes in the nuclei of cells. DNA is a polymer made of many monomers, called NUCLEOTIDES, joined together.

DNA is two strands coiled in a double helix. DNA is made from two genes.

Genes are short pieces of DNA that code for a specific protein.

Strands are linked by a series of complementary base pairs joined together by weak hydrogen bonds (AT , GC)

Nucleotides consist of a sugar and phosphate group with one of the four different bases attached to the sugar

Question 6

Describe what a genome and gene is and how they’re different

Answer 6

A genome is the base sequence of all the DNA in an organism (the entire dna in an organism)

Whereas a gene is a section of a DNA molecule that codes for a specific protein

Question 7

Explain how DNA can be extracted from fruit

Answer 7

DNA can be extracted from fruit by:

1. Grinding the fruit with sand using a pestle and mortar, to separate the cells
2. Adding a detergent to break open the membranes
3. Adding ice cold alcohol so that the dna precipitates out

Question 8

Explain what the order of bases decides

Answer 8

the order of bases in a section of DNA decides the order of amino acids in the protein and that these fold to produce specifically shaped proteins such as enzymes

Question 9

Describe what happens during the stage of transcription in the process of protein synthesis

Answer 9

TRANSCRIPTION takes place in the nucleus.

1. A section of dna is unwound and the two strands separate
2. The enzyme RNA polymerase binds to non coding DNA in front of gene
3. Free complimentary bases pair with the open bases on one DNA strand. The free nucleotides are joined together by the enzyme RNA polymerase to make a strand of complementary mRNA

The base pairs that produce the strand of mRNA are the same as in dna, except the t in dna is replaced with a U in RNA. So A and U pair, and G and C pair.

Question 10

Describe what happens during the stage of translation in the process of protein synthesis

Answer 10

Translation takes place in the cytoplasm when the mRNA strand attaches to a ribosome.

1. The mRNA attaches to a ribosome. Ribosome moves along the mRNA in this direction reading one triplet of bases (codon) at a time
2. TRNA molecules bring amino acids to the ribosome. The amino acid attached to each tRNA molecule depends on the order if bases in the tRNA.
3. Complementary bases of tRNA pair with the bases on the mRNA strand
4. Amino acids that are close together are joined to make an amino acid chain (a polypeptide)
5. TRNA free to collect another amino acid
6. Every protein is formed from a specific number of amino acids in a particular order. The order of the bases in the dna defines the order in which the amino acids are joined together. So one section of dna codes fro one particular protein.

The proteins then fold to produce specifically shaped proteins such as enzymes

Question 11

What does to transcribe mean

Answer 11

To transcribe (translation) means to copy - the base order in dna is copied to make the base order in mRNA. To translate is like changing to another language - translating from bases to amino acids

Question 12

What can the genetic variants affect in the non coding dna (deleted one)

Answer 12

genetic variants in the non-coding DNA of a gene can affect phenotype by influencing the binding of RNA polymerase and altering the quantity of protein produced

Question 13

What can the genetic variants affect in the coding dna

Answer 13

genetic variants in the coding DNA of a gene can affect phenotype by altering the sequence of amino acids and therefore the activity of the protein produced

Question 14

Describe the work of Mendel

Answer 14

Mendel was the first to discover the basics of genetics. He recognised the difficulties of understanding inheritance before the mechanism was discovered

Question 15

What did Mendel experiment and investigate

Answer 15

Mendel cross bred peas to determine which traits were dominant and which were recessive.

Mendels work is important because we set up his experiments scientifically, he used peas because his earlier work showed a repeatable pattern of results. .

Question 16

Explain the terms: chromosome, gene, allele, dominant, recessive, homozygous, heterozygous, genotype, phenotype, gamete and zygote

Answer 16

CHROMOSOME - thin strands of DNA (deoxyribonucleic acid). They are subdivided into genes.
GENE - a short strand of DNA
ALLELE - An allele is a variant form of a gene
DOMINANT - If the alleles of a gene are different, one allele will be expressed; it is the dominant gene
RECESSIVE - Refers to a trait that is expressed only when genotype is homozygous
HOMOZYGOUS - where an individual has inherited the same DNA sequence for a particular gene from both their biological mother and their biological father
HETEROZYGOUS - having two different alleles of a particular gene or genes
GENOTYPE - the genetic constitution of an individual organism (Eg Bb, bb, BB)
PHENOTYPE - the observable physical properties of an organism
GAMETE - Gametes are an organism’s reproductive cells
ZYGOTE - fertilized egg cell that results from the union of a female gamete with a male gamete

Question 17

Explain monohybrid inheritance using genetic diagrams, Punnett squares and family pedigrees

Answer 17

A GENETIC DIAGRAM shows how the parent plants result in different genotypes and phenotypes with arrows showing the different combinations

A PUNNETT SQUARE is a different way of showing the same information about how genotype is inherited and what effect this has on the phenotype (square diagram)

A FAMILY PEDIGREE shows the different members of a family and shows the inheritance of a genetic condition, and which members are recessive and which are dominant

Question 18

Describe how the sex of offspring is determined at fertilisation, using genetic diagrams

Answer 18

The sex of humans is controlled by one pair of sex chromosomes. The genotype XX produces the female genotype and the genotype XY produces the male phenotype.

This can be shown using a genetic diagram or Punnett square to find the probability of male or female.

It shows that there is 50% chance of male nd 50% chance of female.

Question 19

Describe the inheritance of the ABO blood groups with reference to codominance and multiple alleles

Answer 19

I stands for the blood group gene. The superscript shows the allele of that gene. There are other naming systems used.

• I o is recessive to I a and I b because it isn’t expressed in the heterozygote.
• I a and I b are codominant. This occurs when the heterozygous individual shows the effect of both alleles that they carry for the gene

Question 20

Explain how sex linked disorders are inherited

Answer 20

Sex-linked diseases are passed down through families through one of the X or Y chromosomes. X and Y are sex chromosomes. Dominant inheritance occurs when an abnormal gene from one parent causes disease, even though the matching gene from the other parent is normal.

Question 21

What are most phenotypic features a result of

Answer 21

phenotypic features are the result of multiple genes rather than single gene inheritance

Question 22

Describe the causes of variation that influence phenotype

Answer 22

Causes include genetic variation and environmental variation.

Genetic variation - different characteristics as a result of mutation and sexual reproduction

Environmental variation - different characteristics caused by an organism’s environment (acquired characteristics)

Question 23

Explain the effect of a mutation on the phenotype

Answer 23

A MUTATION or GENETIC VARIANT is created if the sequence of bases in a gene is changed. If the amino acid sequence is altered, the activity of the protein produced may also be altered. However :

• most genetic mutations have no effect on the phenotype
• some mutations have a little effect on the phenotype
• a single mutation can rarely significantly affect the phenotype

Question 24

Explain the outcomes of the Human Genome Project and its potential applications within medicine

Answer 24

It’s a collaboration between scientists to decode the human genome (order of bases on all human chromosomes)

The results are being used to develop new medicines and treatments for diseases.

Question 25

Explain the advantages of the human genome project

Answer 25

• alerting people that they are at risk of certain diseases for example cancer or heart disease. The person may be able to make lifestyle changes to reduce the chances of the disease developing
• distinguishing between different forms of diseases such as leukaemia or Alzheimer’s disease, as some drugs are beneficial in some forms of these diseases but not in others
• allowed doctors to tailor treatments for some diseases to the individual, where specific alleles affect how a person will respond to treatment

Question 26

Explain the disadvantages of the human genome project

Answer 26

• people who are at risk of certain diseases may have to pay more to obtain life insurance
• it may not be helpful to tell someone they are at risk of a condition for which there is currently no cure

Question 27

Explain how there is extensive genetic variation within a population of a species

Answer 27

There is usually extensive genetic variation within a population of a species and that these arise through mutations