3.2 DNA and Inheritance, Natural selection

Question 1

What is an allele?

Answer 1

an alternative version of a gene that cause difference in inherited characteristics such as hair colour

Question 2

What is an anticodon?

Answer 2

part of tRNA that is complementary to a codon on mRNA

Question 3

What is a chromosome?

Answer 3

a long, coiled molecule of DNA that carries genetic information in the form of genes

Question 4

What is codominance?

Answer 4

two different alleles both being expressed in the phenotype

Question 5

What does the term codon mean?

Answer 5

sequences of 3 bases on mRNA which corresponds to a specific amino acid

Question 6

What is deoxyribonucleic acid (DNA)?

Answer 6

double stranded polymer arranged in a double helix
made up of DNA nucleotides that carry the genetic code

Question 7

What does dominant mean?

Answer 7

an allele that is always expressed in the phenotype when in the genotype, denoted by a capital letter

Question 8

What is evolution?

Answer 8

the change in inherited traits within a population over time
modelled by natural selection

Question 9

What is a gene?

Answer 9

a section of DNA that codes for a specific sequence of amino acids that forms a protein and is responsible for a particular trait (phenotype)

Question 10

What is a genome?

Answer 10

the complete genetic material of an organism

Question 11

What is a genotype?

Answer 11

all of the alleles present in an organism

Question 12

What is a haploid?

Answer 12

a ell that contains half the amount of genetic information
human gametes have 23 chromosomes

Question 13

What does heterozygous mean?

Answer 13

when an organism has two different alleles of a gene e.g. Bb

Question 14

What does homozygous mean?

Answer 14

when an organism has two of the same alleles e.g. BB, bb

Question 15

What is meiosis?

Answer 15

a form of cellular division that produces gametes, genetically different haploid cells
4 daughter cells produced over two divisions involving two parent CELLS only occurs in the reproductive and used to produce gametes

Question 16

What is mitosis?

Answer 16

a form of cellular division that produces gametes, genetically identical diploid cells from a single parent CELL
2 daughter cells produced over one division, occurs everywhere in the body and used for growth and repair of cells/tissues

Question 17

What is mRNA?

Answer 17

has a complementary sequence to a sequence of bases on DNA (gene)
made up of codons (3 bases on mRNA)
produced in the nucleus during transcription and travels to the ribosomes for translation (protein synthesis)

Question 18

What is a mutation?

Answer 18

A mutation is a change in the sequence of bases in DNA.

which may result in genetic variations that can produce a slightly different protein and therefore a different phenotype if the mutation occurs in a gene

example being addition, substitution and deletion

Question 19

What is natural selection?

Answer 19

a change in the environment causes an organism with a mutated allele to be at an advantage
they are more likely to survive
reproduce and pass n their advantageous, mutated allele to their offspring
this happens over many generations and results in the mutated allele becoming more frequent in the population at the expense of the previous dominant allele

Question 20

What is a phenotype?

Answer 20

an organisms visual characteristics e.g. hair colour

Question 21

What is protein synthesis?

Answer 21

the formation of a sequence of amino acids and then protein form a gene
involves transcription, the production of mRNA in the nucleus and translation
the production of the sequence of amino acids from mRNA forming a polypeptide chain in the ribosome

Question 22

What does the term recessive mean?

Answer 22

an allele that is only expressed in the phenotype when present with another recessive allele in the genotype (homozygous)
denoted by a lower case letter e.g. b

Question 23

What is a ribosome?

Answer 23

an organelle that is the site of protein synthesis, specifically translation

Question 24

What is RNA?

Answer 24

a single stranded polymer of RNA nucleotides; adenine, uracil, cytosine and guanine, with it being the same as DNA but uracil replaces thymine

two main types, mRNA and tRNA

Question 25

What are sex chromosomes?

Answer 25

a pair of chromosomes that determine the sex of an individual in humans this is the 23rd pair and is XX in females and XY in males

Question 26

What is transcription?

Answer 26

1. The two strands of the DNA helix are unzipped by breaking the weak hydrogen bonds between base pairs. This unwinding of the helix is caused by an enzyme (helicase). 2. The enzyme RNA polymerase attaches to the DNA just before the gene. 3. RNA polymerase moves along the DNA strand. Free RNA nucleotides are attracted to (and form hydrogen bonds with) the exposed DNA strand nucleotides by complementary base pairing. 4. RNA polymerase then catalyses the formation of covalent bonds between the RNA nucleotides to form a strand of mRNA. 5. The newly formed strand of mRNA is now ready to leave the nucleus and travel to the ribosome.

Question 27

What is translation?

Answer 27

1. The mRNA strand travels through the cytoplasm and attaches to the ribosome. The strand passes though the ribosome. 2. For every three mRNA bases the ribosome lines up one complementary molecule of tRNA. We call every three bases on mRNA a codon. The complementary three bases on the tRNA are an anticodon. 3. tRNA molecules transport specific amino acids to the ribosome. The ribosome allows two tRNA molecules to sit next to each other; the ribosome catalyses the formation of a covalent bond (peptide bond) between the two amino acids. 4. Used tRNA molecules exit the ribosome and collect another specific amino acid. 5.A chain of several hundred amino acids forms in the correct order according to the original DNA is then made. This is called a polypeptide --> protein

Question 28

What is tRNA?

Answer 28

a form of RNA that is involved in translation has a complementary anticodon to a codon on mRNA and brings a specific amino acid with is to the ribosome

Question 29

What does the term variation mean?

Answer 29

the differences between individuals due to genes, the environment or a combination of both

Question 30

What is a diploid?

Answer 30

an organism with a full set of chromosomes diploid human cells contain 46 chromosomes

Question 31

What are the 4 DNA nucleotides?

Answer 31

adenine (A) thymine (T) cytosine (C) guanine (G)

Question 32

What are the 4 DNA nucleotides made up of?

Answer 32

a phosphate molecule and deoxyribose sugar

Question 33

Monohybrid cross

Answer 33

a cross between two organisms that is used to investigate the inheritance of a single gene

Question 34

What are mutagens?

Answer 34

chemicals that increase the frequency of mutations in DNA

Question 35

Describe the structure of DNA

Answer 35

double stranded arranged in a double helix paired bases A - T, C - G

Question 36

What is the role of enzyme helicase?

Answer 36

unzip the DNA helix by breaking the weak hydrogen bonds between the base pairs

Question 37

What is the role of the enzyme polymerase?

Answer 37

attaches to the DNA just before the gene RNA polymerase moves along the DNA strand so that free, RNA nucleotides are attracted to (and form hydrogen bonds with) the exposed DNA strand nucleotides by complementary base pairing.

Question 38

What two observations was Darwin's theory based on?

Answer 38

all living things/organisms show variation all living things tend to ever-reproduce

Question 39

What can we deduce from Darwin's theory?

Answer 39

1. Variation occurs due to mutations. These occur randomly and continuously. 2. Some individuals within a population will have features (specialisations) which make them more able to survive in the environment - they might be able to get more food, or have features which mean they can cope with the temperature better. 3. These individuals with better specialisations are more likely to survive to reproduce. 4. They will pass on their advantageous alleles to the next generation. 5. Therefore the offspring will tend to inherit the advantageous characteristics. 6. Less favourable alleles tend to become less common in the population. 7. This repeats for many generations. 8. Over time, the specialisations which help organisms to survive will become more common and the characteristics of a species will change. We end up referring to them as a different species.

Question 40

What is an antibiotic?

Answer 40

chemicals that kill bacteria and do not usually harm animals by targeting structures such as bacterial cell walls, which animals do not contain

Question 41

How has natural selection occurred in response to the overuse of antibiotics? Example penicillin

Answer 41

1. Originally, none of the bacteria were resistant and penicillin was not used 2. Doctors began to use penicillin, which killed the bacteria 3. A chance mutation gave some bacteria resistance to the antibiotic 4. These bacteria were better adapted to an environment in which penicillin was used 5. They survived in greater numbers. As there are fewer non-resistant bacteria there is less competition for resources. 6. So the resistant bacteria reproduce rapidly and passed on the resistance allele 7. This was repeated with each generation of bacteria 8. The proportion of bacteria with the resistance allele increased until most had the allele

Question 42

name the type of organism that makes antibiotics

Answer 42

fungi penicillium bacteria