TASK 2

Question 1

Blending inheritance

Answer 1

• Inheritance of traits from 2 parents (black and blond hair) produces offspring with characteristics that are intermediate
• -> a mixture between traits of the parents (brown hair)

Question 2

Single-gene characteristic

Answer 2

• allelic variation in a single gene accounts for differences in the phenotype

Question 3

Polygenic trait

Answer 3

• multiple genes have one effect
• each (dominant) allele “adds up” to the expression of the trait (if you have many alleles that code for height they add up and contribute to the overall big height)

Question 4

Allele

Answer 4

• Variant form of a given gene

- Different alleles can result in different observable phenotypic traits

Question 5

Homozygous

Answer 5

Having two copies of the same allele (AA or aa)

Question 6

Heterozygous

Answer 6

Having two copies of different alleles (Aa)

Question 7

Dominant allele

Answer 7

A gene that is expressed phenotypically in heterozygous or homozygous individuals

Question 8

Recessive allele

Answer 8

A gene that is phenotypically expressed in the homozygous state
- has its expression masked in the presence of a dominant gene

Question 9

Punnet square

Answer 9

• Square diagram
• used to predict an outcome of a particular cross or breeding experiment + determine the probability of an offspring having a particular genotype (and the resulting phenotype)

Question 10

Degrees of dominance

Answer 10

• Co-dominance (fully red)
• Incomplete dominance
• Complete dominance

Question 11

Co-dominance

Answer 11

• heterozygotes fully express the phenotype of both of their homozygous parents (i.e. red + blue)

Question 12

Incomplete dominance

Answer 12

• Phenotype of the heterozygote is intermediate in form between those of the two homozygotes (i.e. red & blue = lila)
• third phenotype is a combination of the phenotypes of both alleles

Question 13

Linkage

Answer 13

• Tendency of DNA sequences that are close together on a chromosome to be inherited together during meiosis.
• The closer together on a chromosome, the less the chance of recombination between them

Question 14

Mendel’s laws

Answer 14

• Law of dominance
• Law of segregation
• Law of independent assortment

Question 15

Law of dominance

Answer 15

• Recessive allele swill always be masked by dominant ones

- -> only the dominant phenotype will be expressed, while still having a heterozygote genotype

Question 16

Law of segregation

Answer 16

• Allele pairs randomly separate / segregate during gamete formation and randomly unite at fertilization
• each gamete carries only one allele for each gene

Question 17

Law of independent assortment

Answer 17

• When 2 or more characteristics are inherited, individual hereditary factors assort independently during gamete production
• giving different traits and equal opportunity of occurring together (wrinkles or smooth and yellow or green)

Question 18

Quantitative genetics

Answer 18

Branch of population genetics that deals with continuously varying phenotypes as opposed to discretely identifiable phenotypes and gene products (predicting phenotypes which are not either/or)

Question 19

Hardy-Weinberg equilibrium

Answer 19

Model of change in expected frequencies of alleles over generations, states that allele and genotype frequencies in a (perfect) population will remain constant from generation to generation in the absence of other evolutionary influences.

p + q = 1
p(^2) + 2pq + q(^2) = 1

Question 20

Genetic drift

Answer 20

• Variation in the relative frequency of different genotypes in a small population
• due to the chance of disappearance of genes as individuals die or don’t reproduce

Question 21

Heritability

Answer 21

• proportion of the observed phenotypic variation that can be accounted for by genetic variation
• -> calculate the phenotypic correlation between a particular pair of relatives
• 1 = all phenotypic variation explained by genotypic variation
• 0 = none of it is (= environmental effects account for it)

Question 22

Coefficient of relatedness

Answer 22

• probability that 2 individuals share an allele due to common ancestry
• expressed by symbol r
• 0 = unrelated
• 1 = clones/ identical twins
• -> siblings: share no alleles, all alleles, or anywhere in between –> on average share half = r = ½
• -> other family members: easiest to draw a family tree –> count the number of steps between two people

Question 23

Behavioural genetics

Answer 23

• Research that uses genetic methods to investigate the nature and origins of individual differences in behaviour

Question 24

Twin studies

Answer 24

• compare MZ twins and DZ twins
• disentangle genetic, shared + non-shared environment
• MZ have r = 1/100 % same genes
• -> If there’s any difference in phenotypic correlation btw. MZ twins & DZ-twins = impact of the extra half in the coefficient of relatedness

Question 25

Monozygotic twins

Answer 25

= Identical twins

- single fertilised egg splits

Question 26

Dizygotic twins

Answer 26

= Fraternal twins

- Sibling produced by the same pregnancy –> developed from separate eggs (each fertilised by a different sperm cell)

Question 27

Shared environmental influences

Answer 27

Factors that will influence both twins regardless of MZ or DZ like parental social class, parental behaviour, diet available, the school attended, or the house grown up in.

Question 28

Non-shared environmental influences

Answer 28

Influences that are neither shared by MZ nor by DZ twins such as childhood diseases or accidents that affected one twin and not the other like a disease or an accident

Question 29

Falconer’s estimate of heritability

Answer 29

• determine the genetic heritability of a trait based on the differenced between twin correlations (correlation of MZ twins being higher than the one of DZ twins)

2 * (r(monozygotic twins) – r (dizygotic twins) = estimated heritability

Question 30

ACE models

Answer 30

• Epidemiological model
• states that individual differences in a phenotype are accounted by A (additive genetic factors), C (common environmental factors), and E (specific environmental factors)

Question 31

Epistatic effects

Answer 31

• Epistasis = the phenotypic expression of a gene at one locus alters that of a gene at another locus
• -> gene that affects another is “epistatic” to that other gene (e.g. Labrador fur)
• Modifies 9:3:3:1 ratio
• ACE models = due to interactions between alleles at different loci

Question 32

Narrow-sense heritabilities

Answer 32

Estimates of variance based on additive genetic effects (A) (study designs include only A, C, and E) = h2

Question 33

Broad-sense heritabilities

Answer 33

Estimates of variance that include epistatic effects (all genetic factors) = H2

Question 34

Complex traits

Answer 34

• Trait that does not follow Mendelian inheritance patterns

- likely derived from multiple genes and exhibits a large variety of phenotypes

Question 35

Pleiotropy

Answer 35

One gene has multiple effects

Question 36

Dominant effects

Answer 36

• due to interaction between pair alleles at one loci

Question 37

Adoption studies

Answer 37

• disentangle genetic & environmental sources

- Kids get genetic contribution from one set of parents + shared environment from another

Question 38

Mendelian diseases

Answer 38

• Lethal recessives = recessive alleles that cause death of an organism that carries it
• individual carrying a single recessive deleterious allele will be healthy and can easily pass the deleterious allele into the next generation (big influence individual level)
• -> Not a problem when population is large as then they’re rarely expressed (small influence population level)
• -> Reason to avoid inbreeding

Question 39

Neutral theory of molecular evolution

Answer 39

• amount of divergence between the DNA sequences of any 2 populations/ species reflects the time since their common ancestor (= molecular clock)

Question 40

Recombination

Answer 40

• during meiosis paired chromosomes line up next to one another –> exchange DNA –> sequence that was originally found on chromosome A is now found on chromosome B
  = crossing over
• Parental type offspring: inherit phenotype that matches either of the parents
• Recombinants: offspring with new combination