bio topic 3 genetics

Question 1

What are the advantages of sexual reproduction?

Answer 1

Creates genetic variation. If there is an environmental change, at least some individuals will survive. This leads to natural selection and evolution of species to become better adapted to the environment.

Question 2

What are the disadvantages of sexual reproduction?

Answer 2

Takes time and energy. Produces fewer offspring as mate is needed. Two parents required.

Question 3

What are the advantages of asexual reproduction?

Answer 3

Can produce lots of offspring quickly. Organism can rapidly colonise an area. Only one parent needed.

Question 4

What are the disadvantages of asexual reproduction?

Answer 4

No genetic variation. Whole population is affected by environmental change.

E.g. Black Sigatoka affects banana plants, if there is an outbreak, all are affected because none are resistant.

Question 5

What is a zygote?

Answer 5

A fertilised egg cell.

Question 6

Which type of reproduction uses meiosis?

Answer 6

Sexual reproduction.

Question 7

What does it mean if a cell is diploid?

Answer 7

It contains two sets of chromosomes.

Question 8

How many cell divisions happen during meiosis?

Answer 8

2.

Question 9

What cells does meiosis produce?

Answer 9

4 haploid daughter cells.

Question 10

What does meiosis form?

Answer 10

Genetically different haploid gametes.

Question 11

Describe DNA.

Answer 11

A polymer made up of repeating units called nucleotides.

Question 12

What is a gene?

Answer 12

A section of DNA that codes for a specific protein.

Remember: proteins control characteristics!

Question 13

What is an allele?

Answer 13

A version of a gene.

Question 14

Why is DNA described as a double helix?

Answer 14

It is made of two strands which coil to form a double helix.

Question 15

What are DNA strands linked by?

Answer 15

A series of complementary base pairs joined together by weak hydrogen bonds.

Question 16

What do nucleotides consist of?

Answer 16

A sugar and phosphate group with one of the four different bases attached to the sugar.

Question 17

What is a genome?

Answer 17

The entire DNA of an organism.

Question 18

How can DNA be extracted from fruit?

Answer 18

1) Place mashed strawberries in a beaker containing a solution of detergent and salt and mix. 2) Filter to remove insoluble bits of cell. 3) Add ice-cold ethanol. 4) Remove DNA (stringy-white precipitate) using a glass rod.

Question 19

What is the purpose of the detergent?

Answer 19

Breaks down the cell membrane releasing DNA.

Question 20

What is the purpose of the salt?

Answer 20

Makes DNA stick together.

Question 21

How does the order of bases in a section of DNA decide the order of amino acids in the protein?

Answer 21

In the protein-coding region of a gene, the DNA sequence is interpreted in groups of three nucleotide bases, called codons. Each codon specifies a single amino acid in a protein.

Question 22

What do amino acids do?

Answer 22

Fold to produce specifically shaped proteins such as enzymes.

Question 23

What are the two stages of protein synthesis?

Answer 23

Transcription and Translation.

Question 24

Where does transcription happen?

Answer 24

In the nucleus.

Question 25

Where does translation happen?

Answer 25

In the ribosome.

Question 26

What is made in transcription?

Answer 26

mRNA.

Question 27

What is made in translation?

Answer 27

Protein.

Question 28

Describe transcription.

Answer 28

1) DNA helicase unzips DNA (by breaking weak hydrogen bonds) to expose the gene to be copied. 2) RNA polymerase binds to the region of non-coding DNA and moves along the strands of DNA. 3) It uses the coding DNA as a template to make mRNA, base pairing between DNA and RNA ensures that the mRNA is complementary to the gene. 4) Once made, mRNA moves out of the nucleus and joins with a ribosome.

Question 29

Describe translation.

Answer 29

1) Amino acids are brought to the ribosome by tRNA. 2) The order in which amino acids are brought matches the order of base triplets. 3) Complementary codon and anti-codon base pairing ensures amino acids are brought to the ribosome in the right order. 4) Amino acids are joined by the ribosome to make a polypeptide (protein).

Question 30

What word describes an observable characteristic?

Answer 30

Phenotype.

Question 31

What is a mutation?

Answer 31

A change in the base sequence of DNA that may create a new allele (genetic variant).

Question 32

How do genetic variants in the non-coding DNA of a gene affect phenotype?

Answer 32

If a mutation happens in the region where RNA polymerase binds to (in front of a gene), this will affect the ability of RNA polymerase to bind to it. How well it binds affects how much mRNA is transcribed and therefore how much protein is produced, which could affect phenotype.

Question 33

Describe how genetic variants in the coding DNA of a gene can affect phenotype.

Answer 33

Genetic variants in the non-coding DNA may alter the sequence of amino acids, changing the shape of the final protein and so its activity. This could end up changing the activity.

Question 34

What term describes a disorder caused by a faulty allele?

Answer 34

Genetic disorder.

Question 35

What term describes a disorder caused by a faulty allele on a sex chromosome?

Answer 35

Sex-linked genetic disorder.

Question 36

What 3 important conclusions did Mendel reach following his pea experiments?

Answer 36

1. Characteristics are determined by 'hereditary factors' (alleles). 2. One 'hereditary factor' is passed from each parent to the offspring. 3. 'Hereditary factors' can be dominant or recessive.

Question 37

Describe Mendel's pea plant experiment.

Answer 37

1) Crossed pea plants of two different heights, (tall and dwarf) found all offspring produced were tall. 2) Then bred two of these tall offspring together and there was a 3:1 ratio of tall : dwarf plants produced.

Question 38

Why did it take a long time for other scientists to accept Mendel's conclusions?

Answer 38

They didn’t know about DNA or genes. They couldn’t explain the mechanism of inheritance.

Question 39

Define homozygous.

Answer 39

Two alleles for a particular gene that are the same.

Question 40

Define heterozygous.

Answer 40

Two alleles for a particular gene are different.

Question 41

What is a chromosome?

Answer 41

Long, coiled up molecules of DNA.

Question 42

What is a phenotype and genotype?

Answer 42

Phenotype: the physical characteristics of an organism. Genotype: The combination of alleles that control each characteristic.

Question 43

What does it mean if an allele is recessive?

Answer 43

Two copies of the allele must be present for an effect to be seen in the phenotype.

Question 44

What does it mean if an allele is dominant?

Answer 44

One only copy of the allele must be present for an effect to be seen in the phenotype.

Question 45

What type of diagram shows how different combinations of alleles might be inherited in the offspring?

Answer 45

Genetic diagram or Punnett square.

Question 46

Which pair of chromosomes is labelled XX or XY?

Answer 46

23rd.

Question 47

What word describes the likelihood of an event happening?

Answer 47

Probability.

Question 48

What are the two sex chromosomes?

Answer 48

X and Y.

Question 49

List 2 sex-linked genetic disorders.

Answer 49

E.g. colour blindness / haemophilia.

Question 50

How are sex-linked disorders inherited?

Answer 50

A characteristic is sex-linked if the allele that codes for it is located on a sex chromosome. Most genes are carried on X chromosome as it (Y) is smaller. Men only have one allele; the characteristic of this allele is showed even if it is recessive making them more likely to show recessive characteristics for sex-linked genes.

Question 51

Why are males more likely to have sex-linked disorders than females?

Answer 51

Most sex-linked disorders are carried on the X chromosome. Men only have one X chromosome, so will have the disorder even if its recessive.

Question 52

Which of the four alleles for blood group are codominant?

Answer 52

IA and IB.

Question 53

What does codominant mean?

Answer 53

Both alleles are expressed in the phenotype.

Question 54

What does a family pedigree chart show?

Answer 54

How genotypes and phenotypes are inherited in families.

Question 55

What is a genome?

Answer 55

All of the DNA in an organism.

Question 56

What was the aim of the Human Genome Project?

Answer 56

To work out all the bases in the entire human genome.

Question 57

What are the potential medical applications for the Human Genome Project?

Answer 57

- Prediction and prevention of disease – early detection and advice on how to avoid likely problems in lifestyle and diet. - Testing and treatment for inherited disorders – faster detection and treatment. - New and better medicines tailored for people with a genetic variation due to knowledge of common variations.

Question 58

What are the disadvantages of the Human Genome Project?

Answer 58

- Increased stress. - Pressure to not have children. - Discrimination by employers and insurers.

Question 59

Causes of variation that influence phenotype:

Answer 59

- Genetic variation – different characteristics because of mutation and sexual reproduction. - Environmental variation – different characteristics caused by an organism’s environment (acquired characteristics).

Question 60

There is usually extensive __________ variation within a population of a species and these arise through __________.

Answer 60

- Genetic. - Mutations.

Question 61

Most genetic mutations have __ _______ on the phenotype, some mutations have a _______ effect on the phenotype and, _________, a single mutation will significantly affect the phenotype.

Answer 61

- No effect, small, rarely.