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Genetics > Inheritance > Flashcards

Inheritance Flashcards

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Biology 101 flashcards
1
Q

homozygote

A

gene with two identical alleles (PP, pp)

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2
Q

heterozygote

A

gene with two different alleles ( one of them is dominant -> visible and the other recessive (Pp)

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3
Q

First Mendelian Law :

Law of Segregation

A

The two alleles for the heritable characteristic segregate during gamete formation (meiosis) and end up in different gametes

-> If two hetereozygote individuals are crossed with one another ( F1 genertaion)

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4
Q

allele

A

alternative form of gene that accounts for variations in inherited characters
example
gene : hair colour
allele1 blond; allele2 brown

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5
Q

Punnet Square

A

predicts allele composition

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6
Q

true-breeding

A

p generation are both homozygote (PP and pp)

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7
Q

ratio in f1 and f2 generation after true breeding

A

f1 : Pp Pp Pp Pp (4:0)

f2. PP Pp Pp pp (3:1)

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8
Q

Law of Independent Assortment

A
  • Each pair of alleles segregats independently of each other pair during gamete formation
  • each gene has an independent biologically effect
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9
Q

Law of Dominance

A

recessive allele will be always masked by dominant allele

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10
Q

Mendelian Disease -> lethal recessives

A

Lethal recessives - recessive allele that causes death of an organism that carries it

  • an individual carrying a aingle recessive deleterious allele will be healthy and can easily pass the deleterious allele into next generation as long as population is large as then -> rarely expressed

REASON TO AVOID INBREEDING

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11
Q

co-dominant genes

A

fully express the phenotype of both of homozygous parents

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12
Q

Complete dominance

A

dominant allele completely masks the recessive one

- one copy of the dominant allele is enough to produce some enzyme

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13
Q

Incomplete dominance

A

heterozygous phenotype intermediate between the two homozygous phenotypes

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14
Q

Co-dominance

A

two allels each affect the phenotype in seperate, distinguishable way , both phenotypes are fully expressed
eg blood group

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15
Q

Pleiotropy

A

one gene affects multiple phenotypic characteristics

-> causes multiple disesase eg albinism

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16
Q

Epistasis

A

the phenotypic expression of a gene at one locus alters the that of a gene at another locus

  • > the gene that affects another is ‘epistatic’ to that other gene
  • > modyfies 9:3:3:1 ratio
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17
Q

Quantitative characters

A

classification is impossible as they vary along a continuum ( eg skin colour)

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18
Q

Polygenic Inheritance

A

additive effect of multiple genes on a single phenotypic character
Eg AABBCC -> darkest
AaBbCc -> middle
aabbcc-> lightest ( majority of the population is in the middle)

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19
Q

Norm of reaction for a genotype

A

genotype is generally not associated with one definite phenotype but rather with a range of phenotypic possibilities ( broadest for polygenic characteristics)

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20
Q

Multifactorial characters

A

refers to both genetic and environmental factors ; collectively influence phenotype

21
Q

Linkage

A

when two genes lie on the same chromosome

closer together -> greater linkage

22
Q

Variation

A
  • provides raw material for natural selection
  • interplay between environment and genotype will determine which genetic combinations persist over time
  • if new arised traits better suit for a given environment , organisms possessing those will thrive and leave more offspring -> next generation: generation again shuffled
23
Q

Hardy Weinberg - conditions

A 
1 no mutation in gene pool 
2 random mating
3 extremely large population size 
4 no gene flow ( from and to other populations) -> no migration 
5 no selection
24
Q

Hardy Weinberg Principle

A

the frequencies of alleles and genotypes in a population will remain constant from generation to generation provided that only Mendelian segregation adn recombination of alleles are at work -> equilibrium

25
Q

HW - theorem

A

p = frequency of one allele q= frequency of the other allele
p+q=1
p2+2pq+q2=1

26
Q

HW and natural selection

A

NS occurs when the frquencies change a

27
Q

Equilibrium

A
  • if expected frequencies are same as actual frequencies

- some genes can be in equilibrium while other at same time arent

28
Q

Genetic Drift

A
  • the smaller a population the more frequencies will fluctuate
  • new mutations can fluctuate all the way till point where everyone has it -> muations becomes fixed
  • the number of new mutation arising is greater the greater the population
29
Q

Neutral Theory of Molecular Evolution

A

amount of divergence between the dna sequences of two populations reflects their time since their common ancestor -> molecular clock

  • accounts for much of the functionless molecular change not phenotype
30
Q

Heritability (h2)

A

proportion of the observed phenotypic variation between individuals that can be accounted for by genetic variation
-> soil example demonstrates this

31
Q

misunderstanding of heritable

A

Heritable does not mean ‘‘genetically’’ determined

32
Q

Environmental variation

A

Environmental variation changes the heritability -> as environmental variation becomes higher heritability goes down
NECESSARY for evolutionary change

33
Q

Schizophrenia

A

risk of developing schizophrenia increases systematically as a function of the degree of genetic similarity -> pattern of affected individuals does not conform to Mendelian proportions

34
Q

genes with additive gene effect ( neither dominant nor recessive)

A

leads to normal distribution in population

35
Q

phenotypic variation

A

genetic variation + environmental variation

36
Q

Coefficient of relatedness (r)

A

probability that any particular allele in individual A is identical by descent ( derived from same immediate source) as the allele in individual B

r = 0 -> unrelated 
r = 1 -> identical twins
37
Q

coefficient of relatedness between siblings

A

humans are diploid organisms ( receive one 1/2 maternal and one 1/2 paternal gene)
siblings could share no alleles ( in case they got in both case the opposite of the half gene) ; all allels ( both siblings got same set of genes from parents) or anywhere inbetween , thus average 0.5

38
Q

Monozygotic Twins

A

identical r = 1

39
Q

Dizygotic Twins

A

no more related than normal siblings r=0.5

40
Q

Non-shared environmental influences

A

any phenotypic difference bw Monozygotic Twins that must be due to NSE eg accident, disease -> thus
estimate of impact = 1-rmz

41
Q

Shared environmental influences

A

eg parental social class, behavior, scool, household

estimate of its effect = rmz-heritability of the trait

42
Q

Falconers Estimate of Heritability

A

equiation to estimate the heritability of traits ( mainly used in twin studies)

h*2 = 2 x rmz -rdz

43
Q

ACE model components

A

A - heritability
C - effect of shared environment
E - effect of non-shared environment

-> C tends to be much less important than E but it is often underestimated

44
Q

ACE Model

A

it relies on assumption that genetic effects accumulate in an additive manner -> r =1 is twice the effect of r = 0.5

45
Q

Adaptation studies

A

helps distangle genetic and environmentalsources

  • kids get genetic contribution from one set of parents and the shared environment from another
  • > test correlation between kids and their biological parents and adopted parents ; or biological siblings adopted into different families
46
Q

selection vs evolution

A

selection : individuals that are well adapted on average survive longer
evolution : over time selected characteristics will increase in frequency in the population

47
Q

mechanisms of evolution and HW

A

correspond to violations of different Hardy-Weinberg assumptions. They are: mutation, non-random mating, gene flow, finite population size (genetic drift), and natural selection.

48
Q

genetic hitchhiking

A

when an allele changes frequency not because it itself is under natural selection, but because it is near another gene that is undergoing selective pressure ( in linkage with that gene)

Genetics (5 decks)

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