Key terms - Biological genetics

Question 1

homozygous

Answer 1

identical alleles for a specific gene - inherited

Question 2

compound homozygous

Answer 2

individual has the same mutation on both alleles for specific gene - inherited from each parent

Question 3

heterozygous

Answer 3

individual has two alleles inherited form each parent for a specific gene

Question 4

compound heterozygous

Answer 4

individual has two different mutations for the same gene - inherited by each parent

Question 5

hemizygous

Answer 5

individual has only ONE allele for a specific gene on aa sex chromosome

often used for genes located on the X or Y chromosome in individuals with differing sex chromosomes

Question 6

dominant inheritance

Answer 6

when the presence of a single copy of a particular allele is sufficient for expression of the associated phenotype

e.g. a heterozygous individual with a dominant and recessive allele = dominant allele traits are expressed

Question 7

codominance

Answer 7

both alleles in a heterozygous person are expressed fully and at the same time = results in a combined phenotype

neither allele is dominant or recessive

Question 8

wild-type allele

Answer 8

most common/ naturally occurring allele a gene in a population

Question 9

expressivity of a disorder

Answer 9

varying levels of severity

Question 10

penetrance

Answer 10

the probability of a gene being expressed = expression in all of a population equals complete penetrance

• the percentage of individuals who carry the mutation and develop symptoms of the disorder

Question 11

genetic association

Answer 11

the presence of an allele at a higher frequency in unrelated subjects with a particular trait compared to those without that trait

conducted as a case-control study = diseased vs healthy

e.g. presence of an allele higher in those with a disease than without

Question 12

oligo(dT) primer

Answer 12

required in reverse transcription and the synthesis of cDNA from an mRNA template

poly-T primer, complementary to poly-A tail

Question 13

single nucleotide polymorphisms/ SNPs

Answer 13

substitution of a single nucleotide base at a specific position in the genome

mechanism: mismatch repair during DNA replication - mismatch is made, base identified by repair mechanism the wrong base is corrected

effects: influences various traits, susceptibility to disease and drug response, act as genetic markers in association studies

Question 14

STRs (short tandem repeats)/ microsatellites

Answer 14

repetitive DNA sequences repeated in tandem

mechanism: can expand/decrease in length due to polymerase slippage, introduces variation into the number of repeat units

effects: used for DA profiling, forensics, associated with genetic disorders (Huntington’s)

Question 15

copy number variant/ CNV

Answer 15

changes in the number of copies of a particular DNA segment causing structural variations

mechanism: non-allelic homologous recombination in meiosis, causes duplications/ deletions of copies

effects: gene expression, associated with disease and phenotypic variations

Question 16

non-allelic homologous recombination

Answer 16

mechanism behind copy number variation

a form of homologous recombination between two lengths of DNA that have high sequence similarity but aren’t alleles

Question 17

linkage equilibrium

Answer 17

inheritance of alleles at one genetic locus doesn’t affect the inheritance of alleles at another genetic locus

• occurs with genes on different chromosomes, or ones far apart on the same chromosome

Question 18

linkage disequilibrium

Answer 18

inheritance of an allele at one gene locus affects the inheritance of alleles at another genetic locus - occurs with alleles close together on the same chromosome