B6.1 - Genetics

Question 1

What is an asexual reproduction and what is a sexual reproduction?

Answer 1

• Asexual reproduction only involves one parent and the cell divides by mitosis- no fusion of gametes and no exchange in genetic information hence no variation.
• Sexual reproduction involves two games( sperm and the egg) fuse together to form a zygote. The gametes are formed through meiosis. They contain half the number of chromosomes in a normal cell because when the gametes fuse together, the new cell has the right amount of chromosomes.

Question 2

Advantages (2) and disadvantages of sexual reproduction?(3)

Answer 2

Sexual reproduction:
Advantages- Genetic variation and variation gives survival advantage by natural selection if environment changes.
2) Natural selection can be speeded up by humans in selective breeding to increase food population.

Disadvantage;

• time and energy needed to find a mate,
• not possible for isolated populations.
• slower than asexual

Question 3

Advantages and disadvantages of asexual reproduction?

Answer 3

Advantage:
-one parent needed so population can increase rapidly as it is not necessary to find a mate.
-can colonise and exploit a suitable habitat quickly.
Disadvantages:
-no genetic variation.
-more vulnerable to change- decreased survival rate.

Question 4

What are the body cells called and why are they different to gametes?

Answer 4

Body cells are called somantic cells and are diploids which means there are 2 sets of chromosomes whereas gametes have only 1 set( haploids)

Question 5

What happens in the process when cell divides to form gametes?

Answer 5

In meiosis, the genetic info is copied so there are 4 sets of each chromosome instead of 2. Each chromosome formes a pair of chromatids.
2) The cell divides twice to form 4 gametes, each with a single set of chromosomes.

Question 6

What happens to gametes at fertilisation?

Answer 6

Gametes join at fertilisation to restore the normal number of chromosomes and cell divides by mitosis which causes number of cells to increase.

Question 7

Is each gamete similar? Explain why?

Answer 7

Each gamete produced is genetically different from all the others as gametes contain mixtures of original chromatids which produces variation.

Question 8

What sex cells do plants have?

Answer 8

Plants have gametes that are ovum &; pollen

Question 9

When does variation occur?

Answer 9

variation occurs when there are 2 parents as there’ll be some characteristics of both mother and father for there is a mixing of chromosomes.

Question 10

Why do some body cells reproduce asexually?

Answer 10

Some body cells reproduce asexually all the time to divide into 2 identical cells and replace worn out tissue.

Question 11

Describe the process of protein synthesis?(8)

Answer 11

1) DNA unzips and uncoils.
2) Free nucleotides complimenatry base pair with the template of the DNA strand, forming a strand of mRNA.
3) mRNA leaves nucleus as it is a single strand.
^ Transcription.
4)mRNA acts as a messenger to carry cpde between the DNA and the ribosome. Ribsomes bind to the mRNA.
5) Every 3 bases of mRNA is called a codon(triplet) which binds to the anticodon on tRNA( complimentary pairing)
6) Amino acids are binding together at tRNa & form a peptide( protein) bond between amino acids.
7) Long chain of amino acids is called a polypeptide.
8) Amino chain folded and forms bonds to form proteins.

Question 12

Define mutation?

How can mutation be caused?

What are the complimentary base pairing in the mRNA?

Answer 12

Mutations are the changes in the DNA nucleotide in the gene and therefore affects the sequence of bases as it causes a change in the genetic code. It can cause a DNA sequence to code for a protein incorrectly.

-Mutation can be caused by dosage of X-Rays,

-A-U
C-G

Question 13

What are the 3 forms of mutation?

Answer 13

1) Insertion- addition- new bases are inserted into the DNA base where it shouldn’t be and can change the way the groups of 3 bases are read hence they change the amino acids they code for.
2) Deletion- when a random base is deleted from the DNA base sequence and they change the way that the base sequence is read and have a knock on effect further down the sequence.
3) Subsitution- mutations are when a random base in the DNA base sequence is changed to a diff base.

Question 14

What is the definiton of:

• genotype.
• alleles
• phenotype
• homozygous
• heterozygous
• dominant
• recessive?

Answer 14

Genotype- alleles an organism has.
Alles- different versions of a gene that ( may be caused by a mutation)
Phenotype- the appearance of the organism and the expression of alleles.
Homozygous- both the same allele.
Heterozygous- 2 different alleles.
Dominant- allele which is expressed over other alleles- even if only one copy is present.
Recessive- allele that is only eexpressed when both alleles are the same.

Question 15

How can mutations affect a protein? Give examples.

Answer 15

Mutation could cause a change in the shape of the protein hence could affect the ability for it to perform its function.

Mutations occur continiously and most do not alter the protein as some mutations can be silent and not affect the protein.

For eg enzyme’s active site change- its substrate may not longer be able to bind to it.
2) Structural protein could lose their strength is their shape has changed- unable to provide support or strength.

Question 16

What makes up the ‘backbone’ of a DNA?

What decides the order of amino acids in a protein?

Answer 16

The sugar phosphate backbone is made of alternating sugar and phosphate sections that make up a strand of DNA and eace base on one strand joins to the other base on the next strand due to complimentary base pairing.

A- T
C-G

The order of bases in a gene that decides the order of amino acids in a protein. Each amino acid is coded for by a sequence of 3 bases in a gene.

Question 17

What happens after DNA replication?

Give 3 examples of proteins?

Answer 17

After DNA repliciation, differentiation occurs which leads to cell specefic functions due to genos being switched on/off.

1) Enzymes- biological catalysts.
2) Hormones.
3) Structural proteins- collagen.

Question 18

What does a gene simply tells us to do?

Answer 18

Gene simply tells cells in what order to put amino acids together which will determine the type of protein the cell produces and hence what type of cell will be.

Question 19

What is a genome?

Why was genome project first done?

Answer 19

Genome is an entire set of genetic material in an organism and includes all the genetic material found in mitochondria and includes all of the chromosone.

Genome project was first done to discover the sequence of different genos and learn more about the DNA.

Question 20

What are the (4) adv and (3) disadv of the genome project?

Answer 20

Advantages-

1) work on inherited diseases and have to chance to overcome them by either through medicine or repairing faulty genes.
2) Identify gene linked to specefic diseases.
3) see changes in genos for cancer and estabalish a treatment for cancer.
4) understand human evolution and migration.

Disad:

• affects mental health
• expensive
• acess to genos information can affect insurance companies.

Question 21

How can reproduction in plants be sexual?

Answer 21

Sexual- pollen from one flower must move from the stamen to the stigma. Flowers are adapted to attract animal pollinators such as insects or to make it easy for their pollen to be carried by the wind and be caught by another flower. Pollen fused with the egg cell, seeds are formed and helps introduce variation/

Question 22

How can reproduction in plants be asexual?

Answer 22

Asexually- stawberry plants produce runners or bulb division such as daffodils- new plants formed by mitosis and hence there are no variation.

Question 23

How do malaria parasites reproduce sexually & asexually?

What part of the body( be specific) does the parasite reproduce in?

Answer 23

Mosquito bites human -> parasite is transferred.
- Sexually- parasite reproduces when in mosquito but asexually when in human host in the liver and blood cells. The drop in temp between the human body and the mosquito triggers sexual reproduction and the parasite shows lots of variation

Question 24

What is the non-coding DNA involved in?

How can mutations affect the non-Coding DNA?

Answer 24

• Non coding DNA is found to be involved with switching genes, or part of genes, on & off however variation in the non-coding areas of DNA may affect how genes are expressed when then affects the phenotype.
• Mutation in the non-coding DNA will alter how a gene is expressed and therefore affect the phenotype.

Question 25

What is sickle cell disease?

Answer 25

Sickle cell disease is when the RBC are in the wrong shape- sickle shapes- and this can get suck in the arteries which can cause low blood flow and pressures and can advantage down when trapped. They do not carry as much oxygen.

Question 26

How can sickle cell anameia impact malaria?

Answer 26

Sickle cell anaemia means that half the RBS arent the right shapes and thus the shape cannot be affected by the plasmodial of the mosquito; they are able to clot and slow down the blood flow. Sickle-shaped blood cells also
cannot carry blood and their shape leakes nutrients which kills the parasite living on it.

The sickle cell will be destroyed by WBC so it’s an advantage in malaria countries as for sickle cell anameia, there is a higher count of WBC that destroy the affected RBC immediately.

Question 27

Why is colourblindness more apparent in men?

Answer 27

Colourblindness is an inherited disease that is on the X-linked chromosomes; males only one have one X linked chromosomes while females have 2. Hence, in females, a functional gene on only one of the X chromosome is enough to compensate for the loss of another as they have an allele that can correct the faulty gene. Therefore, the mother would not be affected but would be a carrier of the disease. Colourblindness is at the bottom of the X-chromosome which the males do not have another allele to correct.

Question 28

Give a few examples of inherited diseases and state whether they are dominant or recessive?

Answer 28

• Cystic fibrosis- recessive.
• Sickle cell disease- recessive.
• Polydactyl- Dom
• Colour blindness-recessive

Question 29

Why are backup genes needed?

Answer 29

4 gametes produced results in 2 sets of chromosomes produced however we only need 1 set and 1 for backup as we have a 2nd set for same properties so if there was a lethal mutation, our 2nd set of genes would be able to have a chance to correct the faulty genes.

Question 30

How do fungi reproduce sexually and asexually?

Answer 30

• Fungi commonly reproduce asexually and the species release spores which become new fungi when they land in a suitable place. They are genetically identical.
• Sexually- only in response to a condition being unfavourable( eg if it’s dry) and produce spores to introduce variation-> two hyphae from diff fungi join and under meiosis to make haploid spores.

Question 31

How many chromosomes is carried by the human body and how is the sex determined?

Answer 31

-The body carries 23 pairs of chromosomes and 22 pairs only control characteristics, but one of the pairs carries the gene that determines the sex.

Question 32

Describe the structure of the DNA and how is it a polymer?

Answer 32

DNA is a polymer- a long molecule made up of repeating units called nucleotides.

Each nucleotide contains one phosphate, one sugar molecule, and a base. Complimentary bases will pair to the base( A,C, G,T) and a group of 3 bases code for a specefic protein.

It’s found in long strands called chromosomes and they normally come in pairs.

A section on the chromosome is a gene and this is where the genetic information that codes for characteristics is stored. Each gene codes for a specific sequence of amino acids and hence will determine the specific protein made.

Question 33

Explain what is cystic fibrosis?

Answer 33

• It’s a recessive phenotype and is caused by recessive alleles.
• It’s a disorder of the cell membrane that prevents the movement of substances from one side to another. Hence, the mucus made my some cells become very thick and sticky. In the lugs, the respiratory sacs, could become blocked by the thick, sticky mucus and could stop them working properly and can lead to respiratory infections/disorders due to the cilia being unable to remove it as mucus is so sticky.
• also affect the reproductive system and the pancreas.

Question 34

How can cystic fibrosis be treated?

Answer 34

-Physiotherapy, antibiotics or more extreme measure would be lung transplant.

Question 35

Explain what is polydactyl?

Answer 35

Phenotype- extra fingers or toes.

-It’s a dominant allele that means one parent needs to have the condition.

Question 36

What are scientisists trying to do to treat inherited disorders?

Answer 36

-Scientists hope genetic engineering will be the answer, allowing them to replace faulty alleles with healthy ones

Question 37

Spiders produce a protein thread which is extremely strong compared to man made fibres. Explain how genes control the way the protein is made in the spiders body? (4)

Answer 37

1) Gene in the DNA contains bases.
2) The bases code for amino acids in protein.
3) The amino acids are arranged in the correct, specfic order to make the spide protein.

Question 38

1) How do the chromosomes of the body cell compare with the chromosomes in the fertilised egg in which they came? (1)
2) Describe what happens to the chromosome in the nucleus of a body cell when it forms reproductive cells. (4)

Answer 38

1) They are identical as during fertilisation, the correct number of chromosomes are restored.

2) The chromosomes duplicate (1)
b) They divide twice to form four sets (2)
c) The number of chromosomes is halved for each gamete compared to the nu of chromosomes in a body cell. (1)

Question 39

What are the symptons of cystic fibrosis? (2)

Answer 39

• Thicker mucus which is viscous and cillia cannot remove hence there’ll be breathing problems due to trachea being blocked
• Mucus can clog the pancreas which prevents the enzymes from reaching the gut to aid with digestion so difficulty with digestion

Question 40

Define a gene.

Answer 40

Genes are sections of DNA. Each gene is a set of coded instructions for making a particular protein and they are found on long strands called chromosomes.

Question 41

How can you screen for genetic disorders? (3)

What are the risks associated with amniocentesis and chronic villus?

Answer 41

Pre-natal tests:

1) Amniocentesis- removal of fluid from amniotic sac for genetic testing and the fluid contains fetal cells which can be used for genetic testing( usually carried out at 15-16 weeks of pregnancy)
2) Chronic villus- removal of cells from the placenta for genetic testing.(usually carried out between 10-12 weeks)

Both amniocentesis and chronic villus have a risk associated with causing a miscarriage.

3) IVF & Genetic screening- removal of a cell from IVF embryo for genetic testing

Question 42

What are the concerns with embryo screening?

1 adv?

Answer 42

• a healthy fetus may be miscarried in the process to test if they have any genetic abnormalities.
• may give a false positive or negative result which can lead to the termination of a healthy baby or the unexpected birth of a child with a genetic disorder.
• embryo screening also results in the person deciding whether or not to terminate the baby.
• screening is expensive
• genetic screening can lead to the demand of ‘designer babies’.
• adv: it can prevent defective genes from being passed down

Question 43

How do strawberry plants reproduce asexually? (2)

Answer 43

They produce runners to grow in soil

Question 44

What part of the cell does cystic fibrosis affect?

Answer 44

Epithelial cells and goblets produce mucus.

Question 45

Why do we GM potatoes and rice?

Answer 45

Potatoes- starch, resistance

Rice- flooding

Question 46

A gardener wants to produce a new variety of onion. Explain why sexual reproduction could produce a new variety (3 marks)

Answer 46

1) Fertilisation of gametes
2) Leading to a mix of genes
3) One copy of each allele from each parent and meiosis produces variation

Question 47

Describe the function of DNA.(2)

Answer 47

1) It contains the code of the sequence of amino acids forming specific proteins

Question 48

Explain why sexual reproduction is an advantage for bluebells. ( 4 marks)

Answer 48

1) Genetic variation in offspring.
2) so better adapted to survive.
3) and colonise new areas by seed dispersal