Inheritance topic summary

Transcription (4)

• DNA unzips / separates / one strand copied;

• complementary base pairing;

• template;

• mRNA produced (4)

Translation (6)

• mRNA arrives at ribosome;

• mRNA has codons / is a template;

• ribosome moves along mRNA strand;

• tRNA brings amino acids to ribosome;

• anticodon (on tRNA) binds with codon (on mRNA) / tRNA binds with mRNA;

• amino acid chain produced / amino acid joined / polypeptide (6)

Gene def (2)

• section / length / part of DNA codes for protein / polypeptide;

• form / version / type of gene (2)

Dominant allele def (2)

• present in phenotype / always expressed / homozygote and heterozygote similar;

• expressed when one present (2)

Recessive allele def (1)

expressed only in homozygous

Breeding control (1)

dominant allele cannot be prevented / recessive cannot always be stopped (1)

Codominance def (3)

• both alleles expressed;

• both affect phenotype;

• both show traits (3)

Male sex def (2)

• male;

• XY / different sized chromosomes / heterogametic / has Y (2)

Diploid vs haploid def (2)

• because diploid has two of each chromosome / has 23 pairs / has 46 chromosomes / has 2 sets of chromosomes / eq (1)

• haploid only has one of each pair / would have 23 chromosomes / has one set of chromosomes / would have half the number of chromosomes / eq (1)

Mutation def (4)

• rare / random change to DNA;

• change in gene / allele / genome / code;

• change in nucleotides / bases / triplets;

• change in amino acids / protein / enzyme (4)

Nondisjunction def (3)

• chromosomes fail to separate;

• during meiosis / gamete formation;

• mutation more likely / older gametes (3)

Affect of radiation on butterflies (6)

• more abnormal after 10 months;

• longer exposure to radioactivity;

• offspring more affected than adults 

• passed to offspring; 

• recessive carried by adults;

• carriers mate → abnormal offspring

• other factors / not mutations;

• no control / no baseline;

• radioactivity not monitored;

• sample size unknown (6)

passed to offspring; recessive carried by adults; carriers mate → abnormal offspring (3)

Woodlice rolling adaptation (4)

mutation / variation;

roll up → survive / not eaten; (NAME THE ADAPTATION)

reproduce;

pass on alleles / natural selection (4)

Woodlice camouflage adaptation (5)

variation in shape / colour;

mutation;

not seen / not eaten / camouflaged;

survive;

reproduce / pass on allele / gene / DNA (5)

Human hair loss adaptation (4)

variation in hair;

mutation;

less hair → heat loss / warm climate / chase / clothes;

survive & reproduce / pass on alleles (4)

Bird beak adaptation (4)

variation in beak;

mutation;

long/thin beak → survive;

reproduce / pass on allele / gene / DNA (4)

Natural selection def (3)

mutation;

survive / not killed;

reproduce / pass on DNA / allele / gene (3)

Mark-scheme rules

• NEVER give a mark for “pass on characteristics” on its own (1)

• NEVER give a mark for “size” on its own (1)

• ALWAYS accept the opposite wording (e.g. “bigger” instead of “smaller”) because it shows the same correct idea in reverse – science is right either way (1)