chapter 12 - mutations and gene pools

Question 1

what is a species

Answer 1

a group of individuals that share many characteristics and are able to interbreed under natural conditions to produce fertile offspring

Question 2

what is an allele

Answer 2

• alternative forms of a gene

- pairs of alleles inherited determines characteristics of an individual

Question 3

what is a population and a geneticist

Answer 3

• P: a group of organisms of the same species, living together in a particular place at a particular time
• G: scientist who specialises in the study of inheritance, consider characteristics of the population as a whole

Question 4

what is a gene pool and allele frequency

Answer 4

• GP: sum of all the alleles in a given population
• AF: how often each allele of a gene occurs in the gene pool for that population
• -> populations that posses characteristic alleles are likely to have different frequencies of various alleles of a gene in their respective gene pool
• -> overtime allele frequencies change (composition of gene pool changes)

Question 5

what is a mutation and types of mutations

Answer 5

• M: when a change in a gene or chromosome takes place leading to new characteristics in an organism, can be harmful or beneficial
• gene mutation: change in single gene
• chromosomal mutation: all or part of a chromosome is affected
• this occurs during the replication of the dna molecule before cell division (mistake will be copied each time dna is replicated)

Question 6

what is a mutagen / mutagenic agent

Answer 6

• environmental factor that increases the rate at which mutations occur
• e.g:mustard gas, formaldehyde, sulfur dioxide, some antibiotics, UV light, radiation, fallout from atomic / nuclear explosions

Question 7

what are somatic and germline mutations

Answer 7

• S: DNA change takes place in body cells, mutation is passed on during mitosis, affects individual, isn’t passed on to offspring
• G: DNA change takes place in sperm / ova (gametes), passed on during fertilisation, individual carries gene but is not usually affected, passed onto offspring (can sometimes be beneficial)

Question 8

what are types and effects of gene mutations

Answer 8

• point mutation (change of a single nucleotide), includes deletion, insertion, substitution)
• change in one DNA molecule can alter protein, have no effect or prevent the production of a protein

Question 9

what are examples of gene mutations

Answer 9

• albinism: missing protein (deletion), absence of pigment in hair (whitish blonde), skin (extremely pale) and eyes (pinkish)
• duchene muscular dystrophy: mutation in mother, passed onto sons, wasting of leg and arm muscles (3-5: apparent, 12-15: bed ridden, 20-25: die due to respiratory failure)
• cystic fibrosis: recessive, occurs on chromosome 7, gene codes for 1480 amino acids (regulate chloride movement), leads to salty skin, persistent coughing, wheezing / pneumonia
• sickle cell anaemia: recessive, sickle shaped RBC (low O2), has a selective advantage (resistant to malaria), involves natural selection

Question 10

what is a lethal recessive allele

Answer 10

• spontaneous abortion or miscarriage, lethal if not masked by a dominant allele
• tay sachs: poor lipid metabolism (missing enzyme), increased fatty acids in NS, develop mental / physical disability, death occurs at early age if they are born

Question 11

what are the types of chromosomal mutations

Answer 11

• deletion: breakage / part of chromosome is lost
• inversion: segment breaks off, flips around and reattaches
• duplication: sequence is repeated
• translocation: involves two chromosomes, not homologous, part of chromosome is transferred to other (similar to crossing over)
• non-disjunction: failure of chromosomes to separate during meiosis, causes gametes to have too trisomy or monosomy
• frameshift mutation: inserting or deleting one or more nucleotides, changes ‘reading frame’, proteins / AA are built incorrectly

Question 12

what are examples of chromosomal mutations

Answer 12

• down syndrome: trisomy 21, nondisjunction, distinct facial appearance, stunted growth, mental disability, partial trisomy 21 can occur (symptoms to small extent)
• patau: trisomy 13, nondisjunction, 1 in 5000 live births (80% die in first month), mental retardation, extra finger, cleft palate / lip, malformations of ears / eyes
• trisomy 16: nondisjunction, most common, more than 1% of pregnancies, spontaneous miscarried in first 3 months
• klinefelter: trisomy X, nondisjunction, XXY, deficiency of male hormones, small testes, infertile, enlarged breasts, little body hair, occasionally mentally retarded
• cri-du-chat: partial monosomy 5, nondisjunction, rare, characteristic cry (cat sound), problems with larynx and NS
• turners: monosomy X, nondisjunction, XO, 1 in 2000 births, infertility, short stature, lack secondary sex characteristics, don’t menstruate
• jacobs: trisomy X, XYY, super male