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GCSE Biology > Genetics > Flashcards

Genetics Flashcards

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1
Q

Where are chromosomes found?

A

The nucleus.

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2
Q

What does a chromosome consist of?

A

A long strand of DNA

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3
Q

What is a gene?

A

A section of DNA that controls the synthesis of a protein.

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4
Q

Who discovered DNA?

A

James Watson and Francis Crick

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5
Q

What is the term for all of a persons DNA?

A

Genome

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6
Q

How many chromosomes does a person have in each cell?

A

46 (23 pairs)

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7
Q

What is the structure of a chromosome about to divide?

A

Two chromatids joined together at a point called the centromere.

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8
Q

Which chromosomes determine sex?

A

The 23rd pair.

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9
Q

What are the two sex chromosomes?
What is the genotype of a cis male and female?

A

X and Y
Female XX male XY

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10
Q

What is a complete set of chromosomes called?

A

A Karyotype

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11
Q

What causes Down syndrome?

A

An extra chromosome on the 21st pair.

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12
Q

What is the name of the structure that forms the long DNA molecules?

A

Nucleotide

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13
Q

What 3 molecules make up a nucleotide?

A

Phosphate group
Sugar
Base
(Know how to draw this)

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14
Q

What term describes the shape of DNA?

A

Double helix

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15
Q

How are bases linked?

A

Base pairing.
Each base will only pair with their complementary base.

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16
Q

How bases in genes arranged?

A

Each base pairing is arranged differently among different pieces of DNA.

No 2 people have identical sequences of bases (except identical twins)

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17
Q

How does DNA work?

A

It is a code that determines what proteins are made in cells.
By controlling the manufacture of proteins (e.g. enzymes) DNA controls how cells develop and work, and therefore the overall development of an organism.

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18
Q

How does protein synthesis occur?

A

The bases along one side of the DNA (the coding strand) form the genetic code.

They are read in sequences of 3 called base triplets or codons.

Each codon codes for a specific amino acid.

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19
Q

How many amino acids are there?
How many proteins are there?

A

20 amino acids can be arranged in different ways to form the 100,000 known proteins.

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20
Q

What are the two types of cell division?

A

Mitosis and meiosis

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21
Q

Why does cell division occur?

A

So an organism can grow and replace any damaged or worn out cells and tissues.

22
Q

Describe the sequence of mitosis.
Draw a diagram.

A
  1. When a cell is not dividing the chromosomes cannot be seen clearly - they are there, but long, thin and invisible.
  2. DNA replication - each chromosome duplicates by splitting lengthwise, making an exact copy. They are joined together at the centromere and become shorter, thicker, and more visible.
  3. The cells make spindle fibres, which stretch from one end of the cell to the other. Chromosomes line up in the equator.
  4. Spindle fibres get shorter and attach to the centromeres, pulling the two chromatids of the chromosomes apart to the opposite ends of the cell.
  5. Nuclear membranes form around the two groups of chromosomes.
  6. Cytoplasm divides and formation of a membrane gives two identical daughter cells, with exactly the same chromosomes as each other and their parent cell.
23
Q

Describe the sequence of meiosis

A

First division:
1. When a cell is not dividing, the chromosomes can’t be seen clearly - they are there, but are long, thin and invisible.

  1. DNA replication - each chromosome makes an exact copy. The two copies (chromatids) remain joined together at the centromere. Chromosomes become shorter and fatter and can be clearly seen in the nucleus of the cell.
  2. Homologous chromosomes come together, ie maternal chromosome 1 finds paternal chromosome 1.
  3. Chromosomes line up in the centre of the cell and the pairs are pulled apart by spindle fibres to the opposite ends of the cell - this reduces the number of chromosomes.

Second division:
5. New spindle fibres are formed at right angles to original ones. The individual chromosomes line up in the centre of the cells.

  1. Centromeres split this time so the two chromatids separate and are pulled to opposite ends of the cell.
  2. Nuclear membrane forms around the chromatids, and the cytoplasm divides forming four genetically different haploid (n) daughter cells, each with 23 chromosomes.
24
Q

Who was the founder of genetics?

A

Gregor mandel

25
Q

What is a back cross test?

A

Used to work out the genotype of an unknown organism that had the dominant phenotype by crossing it with a homozygous recessive.

If the parent was homozygous dominant all offspring should show the phenotype, and if it was heterozygous some offspring will show the phenotype and some won’t.

26
Q

What is an allele?

A

Different forms of the same gene which produce slightly different characteristics.
E.g. the gene for tongue rolling has two alleles: roller (R) and non-roller (r).

27
Q

How did Mandel work out why young plants and animals resemble their parents?

A

He noticed the peas he was breeding had characteristics that varied widely, like shape, height and colour.

He carried out experiments by crossing plants with characteristics he was interested in, concentrating on one characteristic at a time.

Started with pure breeding plants (homozygous) what were self pollinated. All it’s offspring developed the parent’s characteristics, e.g. only tall plants.

When he crossed this generation with short plants, all the offspring were tall. When this generation was crossed with dwarf plants, there was a mixture of tall and dwarf offspring.

He realised that the peas must be passing on factors (genes) to their offspring. By studying ratios he determined the plants were carrying a pair of genes but only pass on one to each of their offspring.

28
Q

What was Mandel able to deduce about genetics from his experimentation?

A

Certain traits (characteristics) in organisms are determined by factors (genes) within the organism

The factors (genes) for a particular characteristic can be present in two different forms (alleles)

The two factors (alleles) in an individual separate during gamete formation (meiosis)

An understanding of classic monohybrid ratios such as 3:1 and 1:1

29
Q

What are pedigree diagrams?
What are they used for?

A

A diagram that shows the way in which a genetic condition is inherited in a family or a group of biologically related individuals.

Can be used to work out the probability of children inheriting a genetic condition.

30
Q

How is sex determined in humans?

A

Females have the same sex chromosomes, XX
Males have different sex chromosomes, XY

When females form eggs via meiosis, they will all get an X chromosome
When males form sperm via meiosis, they will get an X or a Y chromosome

Sex is determined by whichever type of sperm fertilises the egg, and there is an equal probability of any child being male or female.

31
Q

Why are some conditions sex linked?
Why do they usually affect males?

A

The alleles of the condition are found in the sex chromosomes.

X is a larger chromosome than Y, so Y will not contain all of the same genes as X.
So any recessive condition carried on an X chromosome will show itself in the phenotype, as there is no other allele present.

However, as females have 2 X chromosomes, they can be heterozygous for the condition, meaning they are often carriers but don’t often show any symptoms. They would have to be homozygous for the condition to show symptoms, which is rare.

32
Q

What are some examples of sex linked conditions?

A

Haemophilia
Red green colour blindness

33
Q

What is Haemophilia?

A

Sufferers are at risk of excessive bleeding from small wounds as blood doesn’t clot effectively. Sex linked condition caused by a recessive allele on the X chromosome.

34
Q

What is Cystic fibrosis?

A

Patients have frequent and serious lung infections and problems with food digestion. Caused by a recessive allele so sufferers must be homozygous recessive.

35
Q

What is Huntington’s disease?

A

Affects nerves in the brain, causing brain damage which usually becomes apparent in middle age. Incurable and fatal, caused by a dominant allele.

36
Q

What is a mutation?

A

A change in the amount or composition of DNA
A random mistake in the copying of genetic material, during meiosis and gene formation. If the genome isn’t copied exactly a mutation occurs.

May occur by chance, or can be a result of an environmental factor such as ionising radiation and certain chemicals.

37
Q

What is Down’s syndrome?

A

Caused by the presence of an extra chromosome in set 21, a random chromosome mutation. This is because the gamete (usually female) has 24 chromosomes instead of 23, and when fertilised the new individual having 47 rather than 46.

Causes reduced muscle tone and cognitive development.

38
Q

What is genetic screening?

A

Testing people for a specific allele of a gene, or a faulty chromosome associated with a genetic condition,

Can occur in whole populations, or in targeted group where the probability of the condition is thought to be high (e.g. families who are already affected by the condition).

39
Q

What is Amniocentesis?

A

Genetic screening for Down’s syndrome or other conditions (e.g. CF) carried out in pregnant women.

Involves taking cells from the amniotic fluid, and multiplying them in a lab so chromosomes can be studied for genetic abnormalities.

40
Q

Why is amniocentesis done?

A

Offered to pregnant women who are at greater risk of carrying a child with a genetic abnormality, usually when they are 15 to 20 weeks pregnant.

41
Q

Why may a mother be at greater risk for carrying a child with a genetic abnormality?

A

Have previously carried a child with a genetic abnormality

Have family history of a genetic condition

Possible problems have been identified in earlier medical examinations like blood tests

Older mothers (over 35)

42
Q

What is the risk to Amniocentesis?
How what else can be done to screen for the conditions?

A

1% chance of miscarriage,

Blood test can be done instead, though this is less accurate.

43
Q

What is genetic testing?

A

Having a blood or tissue sample taken to be tested for a particular mutation or if you are at risk of a particular genetic condition.

44
Q

What is genetic counselling?

A

A service that provides information and advice about genetic conditions.

Conducted by healthcare professionals trained in the science of human genetics.

They will discuss the risks, benefits and limitations of genetic counselling, and how the information found from genetic testing could have implications for the whole family.

Often help people with genetic conditions who want to have children, by assessing the risk of passing the condition onto a child.

45
Q

What are some of the ethical issues with genetic screening?

A

Can result in very difficult decisions for potential parents, if the foetus is born with a genetic condition that will cause disability if born alive.

Abortion- foetuses born with a genetic condition that causes disability or death can be aborted. Some argue “yes” as it prevents a child who may die in utero or shortly after birth be in significant pain. Child may have poor quality of life, or a lot of time is needed to care for them at the expense of other children. Some argue “no” as they believe it isn’t morally right to kill a foetus, and they don’t have a say. Abortion is also banned in many religions and countries.

Risks, such as small risk of miscarriage.

Should parents be allowed free choice of screening? Should it be limited by age or family history?

Should it be extended to more serious genetic conditions, or used to predict life expectancy?

Should you be allowed to screen for the sex of a child? Conditions can be sexed linked, or parents may want a specific sex.

Cost of screening compared to cost of treating individuals with a genetic condition.

Should you genetic profile be public? E.g. could it be accessed by employers or insurance companies?

46
Q

What is genetic engineering?

A

Taking a piece of DNA from one organism (the doner) and adding it to the DNA of another (the recipient).

This is usually done in bacteria.

47
Q

Why is bacteria often used in genetic engineering?

A

Bacterial DNA is easily manipulated.
Bacteria reproduce very rapidly, so large amounts are quickly produced.

48
Q

What drugs can be produced from genetically engineering bacteria?

A

Insulin needed to counteract diabetes
Growth hormone to counteract dwarfism
Factor VII, a blood clotting protein for haemophiliacs

49
Q

What are the advantages to producing human insulin by genetic engineering over earlier production methods?

A

Insulin was previously obtained from pigs and cattle, so the amount available was limited by the number of animals brought to the abattoirs for slaughter.

Very slow extraction process and there was risk of transferring infections.

Using animal insulin creates ethical or religious issues for some people.

Animal insulin is different to human insulin and is less effective.

50
Q

What is downstreaming?

A

Following production, the insulin needs to be extracted from the fermenter, purified and packaged before it can be used for medical processes.

51
Q

Why is downstreaming time consuming and expensive?

A

Very small size of microbes and chemicals involved, difficulty in separating.

Insulin from other products; high tech equipment needed; skilled technicians and scientists involved.

52
Q

What is the process of genetic engineering?

A
  1. Remove plasmid from bacteria.
  2. Cut plasmid open using restriction enzyme.
  3. Identify human insulin gene, and remove it using the same enzyme.
  4. Insert this gene into plasmid.
  5. Insert plasmid into bacterium.
  6. Put into growth medium in a fermenter (the fermenter should have adequate oxygen and nutrients for the bacterium to grow and reproduce, and the temperature and pH should be monitored for optimum conditions).
  7. Bacteria containing human insulin gene will replicate.
  8. Insulin is extracted, packaged and purified

GCSE Biology (12 decks)

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