Patterns of inheritance

Question 1

Physical mutagenic agent

Answer 1

-X rays
-gamma rays
- UV

Question 2

Chemical mutagenic agent

Answer 2

-mustard gas
-amines
-nitrous acid

Question 3

Biological mutagenic agent

Answer 3

-virus
-food contaminant

Question 4

3 types genetic variation

Answer 4

-gene mutations (point and indel)(occur during DNA replication)
-chromosome mutations
-sexual reproduction

Question 5

Chromosome mutations

Answer 5

-Deletion- part of chromosome containing genes is lost
-Inversion- section of chromosome breaks off, rotates 180° then rejoins. Genes too far form regulatory nucleotide to be expressed
-Translocation- piece of chromosome breaks off and attaches to another chromosome
-Duplication-piece of chromosome may be duplicated meaning too many proteins are made, affecting metabolism
-Non disjunction- chromosome fails to separate so one gamete has extra chromosome, can cause down syndrome

Question 6

Aneuploidy

Answer 6

-chromosome number isn’t an exact multiple of the haploid number
-chromosomes fail to separate during meiosis

Question 7

Polyploidy

Answer 7

-when organisms have more than two sets of chromosomes
-found in plants

Question 8

Variation in sexual reproduction

Answer 8

-crossing over in prophase 1
-independent assortment in metaphase and anaphase 1/2

Question 9

Environmental factors that cause variation

Answer 9

-accent
-losing a limb
-scars

Question 10

Variation caused by interaction between genes and enviro

Answer 10

-plants are kept in magnesium insufficient soil
-don’t develop enough chlorophyll
-leaves yellow
-can’t photosynthesise

-height
-weight

Question 11

Test cross

Answer 11

-organism demonstrating a dominant phenotype (TT or Tt)
-crossed with homozygous recessive
-if any offspring have recessive phenotype, the dominant genotype is heterozygous

Question 12

Codominant

Answer 12

where both alleles present in the genotype of a heterozygous individual contribute to the individuals phenotype

Question 13

Dihybrid inheritance

Answer 13

2 different genes are inherited independently of each other and appear on different chromosomes

Question 14

Autosomal linkage

Answer 14

-gene loci present on the same autosome that are often inherited together

Question 15

Epistasis

Answer 15

interaction of non linked gene loci where one masks the expression of the other

Question 16

Recessive epistasis

Answer 16

alleles at first locus are epistatic to those at the second locus which are hypostatic to those at the first locus

Question 17

Complementary gene action

Answer 17

-where genes work to code for 2 enzymes that work in succession, catalysing sequential steps of a metabolic pathway
eg. Allele C =coloured mice
Allele A= agouti
CcAa, CCAa, CcAA= agouti
Ccaa, CCaa= black
ccAA, ccAa= albino

Question 18

Epistasis ratios

Answer 18

-9:3:4 may suggest recessive epistasis
-12:3:1 and 13:3 suggests dominant epistasis
-9:7 and 9:3:4 and 9:3:3:1 suggest complementary gene action

Question 19

Discontinuous variation

Answer 19

-monogenic- determined by alleles of one gene locus (sometimes 2 due to epistasis)
-phenotype classes are distinct categories
-quantitative
-alleles have a large effect on the phenotype
-unaffected by environment
eg. male female, blood group

Question 20

Continuous variation

Answer 20

-polygenic- many genes are involved in determining the characteristic
-smooth graduation between many intermediates
-alleles of each gene may contribute a small amount to the phenotype
-can be affected by the environment
eg height, weight

Question 21

2 factors effecting the evolution of species

Answer 21

Natural selection
Genetic drift

Question 22

3 types natural selection

Answer 22

Stabilising selection- favours intermediate phenotypes eg. child weight favours the middle as too small and too big carry risks
Disruptive selection- favours extreme phenotypes
Directional selection- the environment changes, making one phenotype more advantageous

Question 23

Genetic drift-

Answer 23

a change in the allele frequency within a population by chance over time

Question 24

2 types genetic drift

Answer 24

-Genetic bottleneck- when a population shrinks and then increases again, reducing genetic diversity
-Founder effect- when a new population is established or isolated, with only a small number of people

Question 25

Factors that affect allele frequency

Answer 25

-mutation
-migration
-natural selection
-genetic drift
-non random mating

Question 26

Hardy Weinberg principle assumptions

Answer 26

-population is large enough so sampling errors have minimal effect
-mating is random
-there is no natural selection
-there is no mutation, migration or genetic drift

Question 27

Hardy Weinberg equation

Answer 27

Dominant allele (A) = p
Recessive allele (a) = q
therefore p+q=1
Genotype AA =p^2
Genotype aa = q^2
Genotype Aa= 2pq
therefore
p^2 +2pq + q^2= 1

Question 28

Speciation

Answer 28

-the process by which new species are formed
-this can only happen if the species become isolated into 2 separate populations
-in each location there’s different selective pressures causing the populations to adapt differently
-at times, the populations will be different but still able to inbreed (sub species)

Question 29

2 isolating mechanisms

Answer 29

geographical
reproductive

Question 30

Geographical isolation

Answer 30

-populations are separated by geographical features like lakes, mountains etc.
-isolated populations are subject to different selective pressures, and undergo different changes
-due to natural selection each population become adapted to its environment
-known as allopatric speciation

Question 31

Reproductive isolation

Answer 31

-where biological and behavioural changes lead to isolation
-can be caused by genetic changes which can: prevent gamete fusion, make zygotes less viable or lead to infertile offspring
-can be caused by mutations which can change: courtship behaviours or animal genitalia
-known as sympatric speciation