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GCSE Edexcel Biology > Genetics > Flashcards

Genetics Flashcards

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1
Q

What is meiosis?

A

Cell division that produces haploid cells - gametes

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2
Q

What are gametes?

A

Sex cells

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3
Q

What is asexual reproduction?

A

Reproduction from one parent resulting in identical children

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4
Q

What is sexual reproduction?

A

Reproduction from two parents where gametes are fused to produce children with genetic variation

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5
Q

What are the advantages of asexual reproduction?

A

It can produce lots of offspring very quickly (rapid reproductive cycle), so organisms can colonise areas quickly
Only one parent is needed, so organisms can reproduce when conditions are favourable

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6
Q

What are the disadvantages of asexual reproduction?

A

There is no genetic variation between offspring in the population, so whole populations are vulnerable

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7
Q

What are the advantages of sexual reproduction?

A

It creates genetic variation within the population, so different individuals have different characteristics. This protects populations and leads to natural selection

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8
Q

What are the disadvantages of sexual reproduction?

A

It takes longer and uses more energy than asexual reproduction, so organisms produce fewer offspring in their lifetime
It needs two parents to take place, posing problems for isolated organisms. Organisms may have to mate when they find a mate, regardless of the conditions

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9
Q

What happens in meiosis?

A

Two cell divisions producing four haploid cells from one diploid father cell. The four daughter cells have 23 chromosomes in humans. It is used for sexual reproduction and produces gametes.

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10
Q

What are the ‘units’ of DNA called?

A

Nucleotides. They chain together to form DNA, a polymer

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11
Q

What are the components of a nucleotide?

A

An organic base is bonded to a sugar-phosphate backbone, made up of a sugar and a phosphate molecule. The nucleotide is then bonded to another at complimentary bases with a hydrogen bond

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12
Q

What are the organic bases and their pairings?

A

Adenine (A) and Thymine (T)

Cytosine (C) and Guanine (G)

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13
Q

What is a chromosome?

A

A coiled up molecule of DNA, found in the nucleus

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14
Q

What is a gene?

A

A section of DNA that ‘codes’ for a particular protein

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15
Q

What is a genome?

A

All of an organism’s DNA

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16
Q

How would you extract DNA from a fruit?

A

Mash the fruit and put it into a beaker containing a solution of detergent and salt and mix. The detergent breaks down cell membranes and the salt makes the DNA stick together
Filter the mixture to get the froth and insoluble bits of cell out
Add some ice cold alcohol to the mixture. The DNA is not soluble in cold alcohol so will start to come out

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17
Q

What is a codon?

A

A combination of three bases that codes for one amino acid

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18
Q

Where does protein synthesis take place?

A

In the ribosome, found in the cytoplasm

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19
Q

Why can’t chromosomes leave the nucleus?

A

They are too big to get out and they need to be protected from chemical reactions in the cytoplasm

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20
Q

What happens in transcription?

A

The sequence of DNA that contains the gene is unzipped by an enzyme called helicase
An enzyme called RNA polymerase creates the complementary mRNA from the DNA template
The mRNA leaves the nucleus through nuclear pores
The RNA polymerase can make numerous copies of mRNA when the DNA is unzipped

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21
Q

How does RNA differ from DNA?

A

RNA is single stranded and contains the base U instead of T

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22
Q

What happens in translation?

A

mRNA binds to the ribosome
A tRNA molecule carrying a specific amino acid has three free bases that can bind to the codon on the mRNA
The three free bases on the tRNA correspond to the amino acid carried
The ribosome has two sites for two tRNA molecules to attach at a time
One tRNA molecule bonds to the mRNA, then the second. When they are held in place the bond between the first tRNA molecule and its amino acid is broken and a bond is formed between the two amino acids
The ribosome then moves down the mRNA by one codon and the next tRNA with its amino acid binds to the next codon on the mRNA
The process continues until the end of the mRNA molecule

23
Q

What is a polypeptide?

A

A chain of amino acids bonded together to make a protein

24
Q

What are the three types of mutation?

A

Neutral - the amino acid does not change
Beneficial - the organism has a higher chance of survival
Harmful - the organism does not last long enough to reproduce

25
Q

What is a mutation?

A

A random and rare change to an organism’s DNA base sequence

26
Q

How can a mutation in an organism’s coding DNA affect its phenotype?

A

It could change the amino acid the codon codes for, in turn creating a different sequence of amino acids. This changes the shape of the protein and therefore its activity. If it is an enzyme its activity may increase, decrease, or stop. This could change the phenotype. It can be beneficial or harmful but is mire likely to be passed on if it is beneficial

27
Q

How can a mutation in an organism’s non-coding DNA affect its phenotype?

A

RNA polymerase has to bind to non-coding DNA before transcription. A mutation can make it harder or easier for RNA polymerase to bind to it. This in turn affects how much mRNA is transcribed and therefore how much of the protein is produced. Depending on the protein’s function the phenotype of the organism may be affected based on how much of the protein is made.

28
Q

What is an allele?

A

Different versions of a gene, represented by letters in genetic diagrams

29
Q

What is a dominant allele?

A

An allele that masks or overrules others, denoted with capital letters

30
Q

What is a recessive allele?

A

An allele that may be masked by a dominant one, denoted with lowercase letters

31
Q

What does homozygous mean?

A

Having two of the same alleles for a particular gene e.g. TT

32
Q

What does heterozygous mean?

A

Having two different alleles for a particular gene e.g. Tt

33
Q

What does phenotype mean?

A

The characteristic you have e.g. tall or short

34
Q

What does genotype mean?

A

The combination of alleles you have e.g. TT, Tt or tt

35
Q

What are characteristics of chromosomes?

A

23 pairs of chromosomes in each cell
The 2 chromosomes in each pair carry information for the same characteristic
Examples of characteristic include eye colour, hair colour etc.
So each body cell has 2 sets of information for all your characteristics
One set is inherited from your mother; the other is from your father

36
Q

How did Mendel study genetics?

A

He bred pea plants and found that when he crossed pink pea plants with white pea plants all the offspring had pink flowers. The second generation then had one quarter white flowers again.

37
Q

Why did Mendel’s observations happen?

A

In the first generation both parent flowers are homozygous (PP and pp). The children are then all Pp heterozygous; as pink is dominant all are pink. In the second generation one quarter of the plants will be pp so will be white.

38
Q

What is a family pedigree diagram?

A

It shows the occurrence of a trait in an organism and its ancestors from one generation to the next. In genetics, they are often used when discussing genetic disorders.

39
Q

What are the sex chromosomes?

A

X and Y chromosomes that determine whether a baby is a boy or a girl

40
Q

What are sex-linked characteristics?

A

The characteristics that come from X and Y chromosomes

41
Q

What is a blood group?

A

A type of blood based on the presence and absence of antibodies and red blood cell antigens

42
Q

What is codominance?

A

A form of dominance where both alleles are fully expressed

43
Q

What is an antigen?

A

A substance on cells that induces the production of antibodies

44
Q

What is an antibody?

A

A protein used by the immune system to neutralise pathogens by their antigens

45
Q

What is a blood transfusion?

A

When you are given blood from someone else

46
Q

Why does a blood transfusion need to be compatible?

A

A person with a specific antigen on their red blood cells does not possess the corresponding antibody in their plasma. When a patient receives a blood transfusion it needs to be compatible. If it is incompatible, donor antigens react with antibodies in the patient’s plasma. An immune response known as agglutination can occur.

47
Q

What are the blood type phenotypes and genotypes?

A

Phenotypes: A, B, AB, O
Genotypes: IaIa and IaIo, IbIb and IbIo, IaIb, IoIo

48
Q

Are antigens or antibodies in the donor’s blood more important for compatibility?

A

Antigens, as antibodies are diluted by the recipient’s blood, while antigens are found on all cells.

49
Q

What are inherited/ genetic variations?

A

They result from the activity of genes. They are genetically controlled. They cannot be easily altered, e.g. blood group cannot be changed naturally

50
Q

What are acquired characteristics?

A

They result from an individual’s activities, nutrition or from environmental conditions during a lifetime e.g. language, sun tan, obesity, and cuts and bruises. They are not passed on from one generation to the next

51
Q

What is the difference between continuous and discontinuous variation?

A

Discontinuous variation: When variation can easily be broken down into clear discrete categories. They are usually caused by one or two inherited genes e.g. eye colour, sex, blood type
Continuous variation: When variation cannot be broken down into clear discrete categories. They are either caused by environmental factors or lots of different genes all working together or a combination of both e.g. weight, height

52
Q

What are the outcomes of the Human Genome Project?

A

It produced a complete map of the human genome, including the locations of over 20,000 genes. The project has helped to identify about 1800 genes related to disease.

53
Q

What are some medical applications of the Human Genome Project?

A

Prediction and prevention of diseases
Testing and treatment for inherited disorders
New and better medicines

GCSE Edexcel Biology (9 decks)

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