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IB Biology 22-24 > Topic 10: Genetics and Inheritance > Flashcards

Topic 10: Genetics and Inheritance Flashcards

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1
Q

List two causes of variation within a gene pool. [2]

A
  • Mutation
  • Sexual reproduction / random fertilization
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2
Q

Describe how variation contributes to evolution by natural selection. [3]

A
  • Variation: different phenotypes between individuals in a population/species
  • Competition for survival
  • Some individuals have more advantageous characteristics
  • Favourable characteristics passed on to next generation
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3
Q

Outline causes of speciation. [3]

A
  • Divided gene pool
  • Reproductive isolation
  • Due to temporal/behavioural/geographical isolation
  • Different natural selections or selective pressures
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4
Q

Discuss the role of genes and chromosomes in determining individual and shared character features of the members of a species. [7]

A

Genes

  • mutation causes genetic differences
  • genes have multiple alleles
  • different alleles give different characteristics
  • alleles are dominant or recessive
  • both alleles influence the characteristic with co-dominance
  • all members of a species are genetically similar
  • genes inherited from parents
  • not all genes are expressed (epigenetics/methylation/acetylation)

Chromosomes

  • same locus
  • same number of chromosomes within a species
  • some individuals have an extra chromosome
  • X and Y chromosomes determine the gender
  • independent assortment gives new combinations of genes
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5
Q

Outline the process of speciation [4]

A
  • splitting of a species
  • reproductive isolation
  • temporal/behavioural/geographical isolation
  • polyploidy
  • gene pools separated
  • gradualism: changes accumulating over long periods
  • punctuated: changes over a short time
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6
Q

Outline how reproductive isolation can occur in an animal population. [3]

A
  • sympatric or allopatric
  • temporal: different populations reproduce at different times, e.g. different flowering patterns
  • behavioural: different in courtship/mating rituals
  • geographical: populations separated by natural or man-made barriers, e.g. mountains
  • polyploidy
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7
Q

Describe the process of crossing over. [2]

A
  • occurs in prophase I
  • homologous chromosomes line up and form bivalents
  • breaking and rejoining of chromatids
  • exchange of DNA between non-sister chromatids
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8
Q

Explain the reason for linked genes not following the pattern of inheritance discovered by Mendel. [2]

A
  • linked genes are on the same chromosome
  • Mendel’s genes were on different chromosomes
  • inherited together, no independent assortment
  • only separated by crossing over, fewer recombinants
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9
Q

Outline the processes that occur during the first division of meiosis. [6]

A
  • PMAT
  • chromosome number halved (diploid to haploid)
  • homologous chromosomes pair up to form bivalents
  • crossing over between non-sister chromatids
  • nuclear envelope breaks down at end of prophase I
  • bivalents align on the spindle equator in metaphase I
  • spindle fibres attach to centromeres
  • homologous chromosomes pulled to opposite poles in anaphase I
  • nuclear envelopes reform in telophase I
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10
Q

Compare the information that could be deduced when the genotypes are presented as AaBb or AB/ab. [2]

A
  • both indicate the same phenotype
  • AB/ab indicates linked genes
  • AB/ab indicates genes located on the same chromosome
  • no independent assortment unless crossing over occurs
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11
Q

Deduce one possible recombinant offspring of individual AB/ab after a test cross. [1]

A

Aabb or aaBb

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12
Q

Deduce the reason for the person developing as a female. [1]

A

No Y chromosome

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13
Q

The probability of extinction of a species increases if the population is small with low genetic variation.

State two processes that cause population size to decrease. [2]

A
  • mortality (diseases, natural disasters, predation)
  • emigration
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14
Q

Explain how meiosis promotes variation. [3]

A
  • in prophase I, crossing over between homologous chromosomes
  • in metaphase I, random alignment of bivalents along spindle equator
  • second division of meiosis separates alleles further
  • combinations of alleles in gametes is unlimited (2^n)
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15
Q

Outline the inheritance of haemophilia in humans. [2]

A
  • sex-linked on the X chromosome
  • recessive alleles
  • more common in males
  • heterozygous females are carriers
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16
Q

Using an example, describe polygenic inheritance. [3]

A
  • more than one gene contributes to some characteristics
  • as the number of genes increases, so do phenotypes
  • continuous variation
  • e.g. human skin colour due to differing amounts of melanin
17
Q

Describe the causes of Down syndrome. [5]

A
  • non-disjunction
  • during meiosis
  • chromosomes fail to separate in meiosis I
  • some gametes have an extra chromosome
  • individual has 47 chromosomes
  • trisomy 21
  • increased probability with mothers of older age
18
Q

Describe how human skin colour is determined genetically. [5]

A
  • polygenetic inheritance
  • many genes contribute
  • due to the amount of melanin in the skin
  • combination of alleles determines the phenotype
  • continuous variation
  • phenotypes do not follow Mendel’s ratios of dominant/recessive
  • environment affects gene expression
19
Q

Explain the causes of sickle-cell anaemia. [8]

A
  • gene mutation
  • due to base substitution
  • changes code on DNA
  • change in transcription
  • DNA changes from CTC to CAC
  • change in translation/polypeptide chain
  • tRNA adds the wrong amino acid to the chain
  • glutamic acid replaced by valine
  • produces abnormal haemoglobin
  • abnormal erythrocyte shape
  • lower ability to transport oxygen
20
Q

Explain, using a named example, how polygenic inheritance gives rise to continuous variation. [2]

A
  • e.g. human skin colour (amount of melanin varies)
  • controlled by alleles from more than three genes
  • alleles are co-dominant
  • many possible combinations
21
Q

Describe the inheritance of colour blindness in humans. [3]

A
  • sex-linked
  • gene on the X chromosome
  • more common in males
  • allele is recessive
  • heterozygous females are not colour blind, homozygous females are colour blind
22
Q

Outline the relationship between Mendel’s Law of Independent Assortment and meiosis. [6]

A
  • independent assortment of unlinked genes
  • unlinked genes located on different chromosomes
  • genes inherited independently
  • presence of one allele does not affect presence of other allele
  • seen in dihybrid crosses
  • phenotypic ratio 9:3:3:1 in double heterozygous cross
  • ratio shows equal probability of all genes
  • random orientation of homologous chromosomes
  • orientation of one bivalent does not affect orientation of other bivalents
  • occurs in meiosis I, metaphase
23
Q

Outline the formation of chiasmata during crossing over. [5]

A
  • chiasmata formed during prophase I of meiosis
  • pairing of homologous chromosomes
  • chromatids break
  • non-sister chromatids exchange alleles
  • X-shaped structure formed
  • chiasma formed at position of crossing over
  • chiasmata becomes visible when homologous chromosomes unpair
  • chiasma holds chromosomes together until anaphase
24
Q

Explain the cause of sickle cell anemia and how this disease affects humans. [8]

A
  • base substitution mutation from GAG to GTG
  • mutation of a subunit of hemoglobin
  • mRNA copies DNA mutation, substitutes wrong amino acid in hemoglobin
  • glutamic acid substituted by valine
  • causes distorted hemoglobin protein (Hb^S)
  • causes distorted/sickling shape change of red blood cells
  • block capillaries, block blood flow
  • cannot carry enough oxygen for the body
  • homozygous leads to severe anemia
  • heterozygous has less anemia
  • heterozygous provides protection against malaria
25
Q

Outline the inheritance of blood types in the ABO blood system in humans. [4]

A
  • i, I^A, and I^B are alleles
  • I^A/I^B are dominant, i is recessive
  • Group A: I^A i or I^A I^A, Group B: I^B i or I^B I^B, Group O: ii
  • I^A and I^B co-dominant, so Group AB: I^A I^B
  • one allele inherited from each parent
26
Q

Explain how genetic variation between the individuals in a species can be generated. [7]

A
  • mutation
  • base substitution/change to base sequence of gene
  • new alleles formed
  • radiation/mutagens increase the chance of mutation
  • meiosis
  • new combinations of genes produced by crossing over
  • independent assortment of homologous chromosomes/bivalents
  • gametes from two parents combined in sexual reproduction
  • random fertilization
  • natural selection differs in reproductively isolated populations
  • disruptive selection causes phenotypes to diverge
27
Q

Outline one method that has been used successfully to clone an adult animal. [3]

A
  • nucleus removed from egg cell
  • body/somatic cells removed from donor
  • enucleated egg and donor cell fused (egg cell nucleus replaced by body cell nucleus)
  • resulting embryo implanted in uterus of surrogate

IB Biology 22-24 (13 decks)

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