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A-Level Biology > 6.1.2 Genetic inheritance > Flashcards

6.1.2 Genetic inheritance Flashcards

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1
Q

monogenic definition

A

determined by a single gene

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2
Q

gene locus definition

A

position of gene on a chromosome

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3
Q

heterozygous definition

A

having different alleles for the same gene locus on a pair of homologous chromosome

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4
Q

homozygous definition

A

having same alleles at the same gene locus on a pair of homologous chromosomes

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5
Q

true-bred definition

A

homozygous

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6
Q

dominant definition

A

masks the effects of recessive alleles

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7
Q

recessive definition

A

masked by dominant alleles

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8
Q

F1 definition

A

first generation of offspring (to original parents)

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9
Q

F2 definition

A

second generation (offspring of F1)

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10
Q

continuous variation features

A

no defined categories
there is a range (any value is possible)
caused by more than one gene and often environment
greater number of gene loci contributing to characteristic, greater range in variation
quantitative

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11
Q

discontinuous variation features

A

discrete categories with no intermediates
usually caused by one gene
genes at different loci may interact to influence one characteristic and cause discontinuous variation
no/very little environmental effects cause it
qualitative

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12
Q

polygenic definition

A

caused by more than one gene

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13
Q

epistasis definition

A

expression of one gene is affected by expression of one or more independently inherited genes

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14
Q

environmental factors that influence variation

A

diet in animals leads to changes in mass (malnutrition)
language
scars
plants grown in too little light experience etiolation (rapidly growing stems, weakened cell walls, chlorosis)

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15
Q

chlorosis definition

A

lack of chlorophyll

the environmental factors prevent the expression of genes for chlorophyll production

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16
Q

different blood groups phenotypes

A

A
B
AB
O

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17
Q

sex linkage definition

A

when a gene is present on one of the sex chromosomes

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18
Q

why sex chromosomes are not fully homologous and its impact

A

Y chromosome lacks many genes that code for characteristics on X chromosome
men can neither be homozygous nor heterozygous for these genes
men more likely to have genetic diseases linked to genes on these chromosomes

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19
Q

Haemophilia in genes

A

found on X chromosome but not Y

functional:faulty allele = X^H:X^h

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20
Q

colour blindess

A

gene causing red-green colour blindness
found on X but not on Y chromosomes
functional/faulty allele: X^B/X^b

21
Q

autosome definition

A

non-sex genes

22
Q

autosomal linkage definition

A

linkage when 2 or more genes on the same chromosome are inherited together (they dont undergo independent assortment in metaphase 1)

23
Q

epistasis definition

A

interaction of non-linked genes (on different chromosomes) where one masks the expression of the other

24
Q

epistasis effect on number of phenotypes

A

epistasis reduces number of phenotypes in F2 generation and reduced variation

25
Q

epistatic alleles definition

A

alleles masking the effect of the alleles on the other gene

26
Q

hypostatic alleles definition

A

alleles whose effect is being masked

27
Q

recessive epistasis definition

A

when homozygous recessive alleles of gene locus 1 are epistatic to both alleles on gene locus 2 (hypostatic)
9:3:4 ratio

28
Q

dominant epistasis definition

A

where dominant alleles of gene locus 1 are epistatic to both alleles on gene locus 2 (hypostatic)
12:3:1 or 13:3 ratio

29
Q

epistasis by complementary gene action definition

A

when 2 different genes work together to express phenotypes

9:7 or 9:3:4 phenotypic ratio

30
Q

what a non 9:3:3:1 phenotypic ratio means for 4 phenotypes for 2 genes/traits

A

autosomal linked and crossing over will have occurred
further apart the gene loci for linked genes, the more likely crossing over is and higher the number of recombinant phenotypes

31
Q

natural selection/evolution method

A

V: individuals of a population of same species have different characteristics due to genetic variation
O: overproduction of offspring
S: selection pressure kills individuals with less advantageous characteristics die
S: those with more advantageous characteristics survive
AR: those who survive are more likely to reproduce and advantageous alleles are passed onto their offspring

32
Q

Hardy Weinberg assumptions

A 
large population
no genetic drift
random mating
no natural selection 
no mutation
no migration
33
Q

2 types of natural selection

A

stabilising selection

directional selection

34
Q

stabilising selection features

A

occurs when organisms’ environment doesn’t change
favours intermediate phenotype (over extremes)
reduces variation in a population (e.g. those with short/long fur in constant temperatures selected against, mid length fur will survive, higher frequency of alleles for mid length fur)

35
Q

directional selection features

A 
occurs when environment changes
favours new (extreme) phenotype
causes change in population’s mean phenotype
36
Q

genetic drift definition

A

random changes in alleles frequency in small populations

37
Q

genetic drift features

A

only small populations as each individual forms a larger proportion of gene pool and greater effect on gene pool
not due to natural selection, chance only
population alleles can drift from original, could lose alleles from gene pool

38
Q

2 types of genetic drift

A

genetic bottleneck

founder effect

39
Q

genetic bottleneck features

A

an event reduces numbers of a population
some alleles lost from population at random
genetic variation reduced -> genetic drift

40
Q

founder effect features

A

small number of individuals from an original larger population
establish a new population
some alleles lost from population at random (these could be advantageous)
genetic variation reduced -> genetic drift

41
Q

speciation definition

A

splitting of a population of a species into 2 isolated population that overtime undergo genetic changes, resulting in reproductive isolation and the formation of 2 different species

42
Q

allopatric speciation mechanism

A

populations are physically separated e.g. by water/mountains/fences
barrier prevents gene flow between populations
genetic changes occur in species (caused by genetic drift, mutations or natural selection (different pressures in different areas))
populations become so genetically different they can no longer interbreed (reproductively isolated)
new species has been formed

43
Q

sympathetic speciation mechanism

A

several things can lead to individuals in a population become reproductively isolated:
• behavioural changes (sleep patterns, courtship behaviours)
• biological changes (size differences, genitalia differences)
• genetic changes (change in chromosome number, prevents zygote viability)
populations can no longer interbreed to produce fertile offspring, new species been formed

44
Q

artificial selection definition

A

selective breeding of organisms in order to produce desired phenotypes in an organism (often to benefit to humans)
humans choose parents with desired phenotypes and therefore desired alleles and interbreed them to produce offspring with higher frequency of these phenotypes, repeated over many generatjons

45
Q

stages of artificial selection

A

male and female with desired characteristic chosen and bred together
some of the offspring will carry all of the desired characteristics of the mother and father
choose the offspring with the all of the desired characteristics and breed together
repeat

46
Q

inbreeding features

A

genetic diversity decreases with each generation, individuals become more and more related
likelihood of unintentionally selecting 2 copies of a harmful recessive allele increases in small gene loci
…

47
Q

hybrid vigour definition

A

outcross individuals belonging to 2 different varieties to obtain individuals heterozygous at many gene loci

48
Q

how/when gene has multiple alleles

A

when it has 3 or more alleles

A-Level Biology (24 decks)

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