Biology: Genetics

Question 1

what is a gene?

Answer 1

a section of DNA..

Question 2

what is the locus of a gene?

Answer 2

the position of a gene of particular strand of DNA?

Question 3

how is the genetic code non-overlapping?

Answer 3

the base of a triplet specifying the position of a particular amino acid doesn’t contribute to specifying the positions of other amino acid units. bases don’t overlap between triplets.

Question 4

how is the genetic code degenerate?

Answer 4

all amino acids in a polypeptide are specified by more than one codon.

Question 5

what is the difference between an intron and exon?

Answer 5

introns are non-coding regions of a gene.

exons are the coding regions of a gene.

Question 6

what is the genetic code?

Answer 6

it’s the sequence of bases of all genes in a cell and the information it carries, it’s universal.

Question 7

describe the structure of RNA

Answer 7

• single stranded
• ribose sugar
• thymine is replaced by uricil

Question 8

what are the types of RNA, explain each of them

Answer 8

• mRNA: synthesised in a cell nucleus. it’s complementary to the template strand from which the RNA is formed.
• tRNA: held together by hydrogen bonds within the molecule. amino acid at one end, anticodon on the other. the anticodon is complementary to the mRNA codon.
• rRNA: combines with protein to form ribosomes

Question 9

explain the process of transcription

Answer 9

1) DNA helicase breaks the hydrogen bonds and unzips the DNA structure. this exposes the coding strand and transcribing strand. the transcribing strand carries information used to encode polypeptide synthesis. the sequences which encode polypeptides on the transcribing strand are called exons.
2) RNA polymerase adds more nucleotides onto the growing mRNA strand. bases of the nucleotides are complementary to bases on the transcribing strand. mRNA lengthens in the 5’ to 3’ direction, producing pre-mRNA. the introns and exons are complementary to the introns and exons on the transcribing strand. enzymes called splicosomes remove introns and join exons together, this forms mature mRNA.
3) mature mRNA leaves the nucleus through the nuclear pores.

Question 10

explain the process of translation.

Answer 10

1) a strand of mature mRNA binds to a ribosome. it moves along the strand until it reaches a start codon.
2) tRNA molecules collect amino acids from the cytoplasm.
3) tRNA reaches a start codon, another tRNA molecule binds to the anticodon after that. they’re held in place by the ribosome and a peptide bond forms between the amino acids, a polypeptide forms.
4) it continues to move along until it reaches a stop codon, the bond between the terminal tRNA molecule and the polypeptide is hydrolysed and a polypeptide is released.
5) it’s transported to the Golgi to be packaged

Question 11

what are the 3 types of chromosome mutation?

explain each

Answer 11

deletion: a part of a chromosome is lost
translocation: part of a chromosome moves to another chromosome
inversion: the broken part of a chromosome rejoins it after it rotates 180 degrees

Question 12

describe the process of meiosis

Answer 12

• interphase: genetic material replicated
• prophase: chromosomes condense, nuclear membrane breaks down
• metaphase: chromosomes line up along the middle and attach to spindle fibres
• anaphase: spindle fibres are shortened and chromosomes are pulled apart
• telophase: new nuclear membrane forms.

the process repeats itself and 4 daughter cells are formed as a result.

Question 13

how does crossing over work?

Answer 13

• homologous pairs line up
• the chromatids change position and alleles begin to swap with eachother, chromosomes become twisted.
• the genes are on the same loci, but the chromatid have swapped around, creating different pairs of chromosomes and variation happens as a result.

Question 14

how does random assortment work?

Answer 14

• homologous pairs line up along the equator randomly
• combination of chromosomes pulled to each pole is random
• daughter cells produced are genetically different

Question 15

how do species evolve?

Answer 15

• individuals vary genetically
• resources are finite
• organisms have the potential to over-reproduce but the population usually remains stable
• individuals inherit successful alleles, this is advantageous for them so they live longer and produce offspring which inherit those genes
• ones without the successful alleles die out
• this is called natural selection

Question 16

what is the order of classification

Answer 16

kingdom
 phylum
 class 
order
 family 
genus
 species

Question 17

what is courtship behaviour?

Answer 17

the interaction between males and females of the same species which leads to reproduction

the stimulus triggers a response in the mate

Question 18

what is the purpose of courtship behaviour?

Answer 18

• allows individuals to recognise one another

- promotes pre-zygotic isolation.

Question 19

how can animals be classed using immunological techniques?

Answer 19

• serum taken from sample animal
• injected into rabbit
• the rabbit makes antibodies complementary to that animal’s cells
• serum taken from rabbit
• mixed with serum of other animals, precipitate forms when antibodies bind
• the amount of precipitate formed is proportional to how closely related they are

Question 20

how do you use nucleotides to compare species?

Answer 20

• heat up sample dna strands
• mix to make a hybrid DNA strand
• use radioactive tracers to see how many nucleotides have successfully bound
• this is proportional to how closely related they are