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Biology Module 6 > Genetics > Flashcards

Genetics Flashcards

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1
Q

whats a genotype

A

genetic makeup of an organism

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2
Q

whats a phenotype

A

visible characteristic of an organism

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3
Q

what are the causes of phenotypic variation

A

genetic factors
- gene mutations
- chromosome mutations
- sexual reproduction
environmental functions
- variation caused solely by the environment
- variation caused by the environment interacting with genes

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4
Q

what is a mutation

A
  • change to genetic material, this may involve changes to the structure of DNA or changes to the number or gross structure of the chromosomes
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5
Q

what are the different types of mutagenic agents

A
  • physical agents
  • chemical agents
  • biological agents
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6
Q

what are some physical agents

A
  • x rays
  • gamma rays
  • UV light
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7
Q

what are some chemical agents

A
  • benzopyrene
  • mustard gas
  • nitrous acid
  • aromatic amines- in dyes
  • reactive oxygen species - free radicals
  • colchicine
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8
Q

what are some biological agents

A
  • some viruses
  • transposons - jumping genes, remnants of viral nucleic acid that have become incorporated into our genomes
  • food contaminants such as mycotoxins from fungi, contaminated nuts, chemicals in charred meat and alcohol
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9
Q

what are the mutations that occur in gamete formation

A
  • persistent - they can be transmitted through many generations without change
  • random - they are no directed by a need on the part of the organism in which they occur
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10
Q

when do chromosome mutations occur

A

they occur during meiosis

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11
Q

name some chromosome mutations

A
  • deletion
  • inversion
  • translocation
  • duplication
  • non-disjunction
  • aneuploidy
  • polyploidy
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12
Q

describe deletion

A
  • part of a chromosome containing genes and regulatory sequences is lost
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13
Q

describe inversion

A
  • a section of a chromosome may break off, turn through 180 degrees and then join again although all the genes are still present some may now be too far away from their regulatory nucleotide sequences to be properly expressed
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14
Q

describe translocation

A
  • a piece of one chromosome breaks off and then becomes attached to another chromosome this may also interfere with the regulation of the genes on the translocated chromosomes
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15
Q

describe duplication

A
  • a piece of a chromosome may be duplicated, over expression of genes can be harmful because too many of certain proteins or gene regulating nucleic acids may disrupt metabolism
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16
Q

describe non-disjuction

A
  • one pair of chromosomes or chromatids fails to separate leaving one gamete with an extra chromosome, when fertilised by a normal haploid gamete the resulting zygote has one extra chromosome,
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17
Q

describe aneuploidy

A
  • the chromosome number is not an exact multiple of the haploid number for that organism, sometimes chromosomes or chromatids fail to separate during meiosis
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18
Q

describe polyploidy

A
  • if a diploid gamete is fertilised by a haploid gamete the resulting zygote will be triploid, the fusion of two diploid gametes can make a tetraploid zygote
  • many cultivated plants are polyploid
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19
Q

describe how sexual reproduction leads to genetic variation

A
  • meiosis produces genetically different gametes, during meiosis
  • allele shuffling during crossing over in prophase 1
  • indepednent assortment of chromosomes during metaphase/anaphase 1
  • independent assortment of chromatids during metaphase/anaphase 2
  • random fusion of gametes creates more genetic diversity
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20
Q

describe how variation is caused solely by the environment

A
  • speaking with a particular regional dialect - learn to speak by listening to other people
  • losing a digit or limb or having a scar following an injury
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21
Q

describe how variation is caused by the environment interacting with genes

A
  • if plants are kept in dim light after germination, then there leaves do not develop enough chlorophyll and are yellow or yellow white
  • the plant is described as chlorotic or suffering from chlorosis and the plant cannot photosynthesise
  • chlorotic plants have the geneotype for making chlorophyll but environmental factors are preventing the expression of these genes
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22
Q

what is an allele

A

a version of a gene

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23
Q

what is heterozgous

A

having different alleles at a particular gene locus on a pair of homologous chromosome

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24
Q

what is homozygous

A

having identical alleles at a particular gene locus on a pair of homologous chromosome

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25
Q

what is monogenic

A
  • determined by a single gene
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26
Q

what is dominant

A
  • the phenotype always shows if its present
27
Q

what is recessive

A
  • the phenotype is only present if the dominant allele is not
28
Q

what is test crossing used for

A
  • the organism exhibiting the dominant phenotype but of an unknown genotype is crossed with an individual showing the recessive phenotype, therefore being homozygous recessive genotype
  • if any of the offspring have the recessive phenotype then the dominant phenotype organism is heterozygous
29
Q

what is dihybird

A
  • this involves two gene loci
30
Q

from the results of mendels dihybird cross what did mendel deduce

A
  • the alleles of the two genes are inherited independently of each other so each gamete has one allele for each gene locus
  • during fertilisation any one of an allele pair can combine with any one of another allele pair
31
Q

what are the probability of occurring in F2 generation in a dihybrid cross

A
  • 9:3:3:1
32
Q

what is co dominance

A
  • this is where both alleles present in the genotype of a heterozygous individual contribute to the individuals phenotype
33
Q

what is multiple alleles

A
  • characteristic for which there are three or more alleles in the populations gene pool
  • three or more alleles at a specific gene locus
34
Q

what do human blood groups demonstrate

A

codominance

35
Q

describe how human blood groups demonstrate co dominance

A
  • the four blood groups A, B, O, AB are determined by three alleles of a single gene on chromosome 9
  • the gene encodes an isoagglutinogen I on the surface of erythrocytes
  • the alleles present in the human gene pool are Ia, Ib, Io, Ia and Ib are both dominant to Io which is recessive
  • Ia and Ib are codominant and will both contribute to the phenotype
  • any individual will have only two of the three alleles within their genotype
36
Q

describe how coat colours in rabbits are codominant

A
  • the coat colours in rabbits are
  • wild type coat colour called agouti, each hair has a grey base, a yellow band and a black tp
  • albino - the condition where no pigment develops and the fur is white
  • chinchilla - hairs are silvery grey as they lack the yellow band
  • himalayan white - but with black feet, ears and tail
  • these coats are determined by one gene that has 4 alleles
  • agouti C is dominant to all other alleles
  • chinchillia Cch is dominant to himalayan Ch
  • albino c is recessive to all other alleles
37
Q

what is sex linkage

A

these are genes present on (one of) the sex chromosomes

38
Q

what are non sex chromosomes called

A

autosomes

39
Q

what are the male sex chromosomes

A

XY

40
Q

what are the female sex chromosomes

A

XX

41
Q

describe the human chromosome X

A
  • contains over 1000 genes that are involved in determining many characteristics or metabolic functions not concerned with sex determination and most of these have n partner alleles on the Y chromosome
  • if a female has one abnormal allele on one of her X chromosomes she will probably have a functioning allele of the same gene on her other X chromosome whereas if a male inherits from his mother an X chromosome with an abnormal allele for a particular gene they will suffer from the genetic disease as they will not have a functioning allele for that gene
  • males cannot be heterozygous or homozygous for X linked genes
42
Q

name some sex linked diseases

A
  • haemophilia A
  • colour blindness
  • cat coats
43
Q

described haemophilia A as a sex linked disease

A
  • a person with haemophilia A is unable to clot blood fast enough
  • one of the genes on the non-homologous region of the X chromosome codes for a blood clotting protein called factor 8, a mutated form of the allele codes for non-functioning factor 8
  • a female with one abnormal allele and one funcitoning allele produces enough factor 8 to enable her blood to clot normally when required but the female is a carrier for the disease, if a female passes the X chromosome containing the faulty allele to her son they will have non functioning allele for factor 8 on his Y chromosome therefore he will suffer from haemophilia A
44
Q

describe colour blindness as a sex linked disease

A
  • one of the genes involved in coding for a protein involved in colour vision is on the X chromosome but not the Y chromosome
  • a mutated allele of this gene may result in colour blindness - an inability to distinguish between red and green, a female with one abnormal allele and one functioning allele will not suffer from colour blindness, but a male with an abnormal allele on his X chromosome will not have a functioning allele on his Y chromosome and will therefore suffer from red-green colour blindness
  • the inheritance pattern is the same as for haemophilia A, that of a recessive sex linked disorder
45
Q

describe sex linkage in cats

A

one of the genes C for coat colour in cats is sex linked, it is on the non-homologous region of the X chromosome

  • the allele Co produces orange fur
  • the allele Cb produces black fur
  • these alleles are codominant as cats with the genotype expressing Co and Cb are tortoiseshell and have patches of black fur and patches of orange fur, both the organge and black alleles contribute to the phenotype but the orange allele is only expressed in cells where the x chromosmes bearing the black coat colour allele is inactivated and vice versa
  • male cats may be either black or ginger but not tortoiseshell as they only have one X chromosome
46
Q

what is inactivation of x chromosomes in female mammals

A
  • in every female cell nucleus one X chromosome is inactivated
  • determination of which member of the pair of X chromosomes becomes inactivated is random and happens during early embryonic development
47
Q

describe co dominant inheritance in animals

A
  • coat colour in shorthorn cattle is an example of codominant inheritance, the one gene for coat colour has two alleles Cr and Cw
  • cattle that are homozygous for the red-coat allele have a red chesnut coat
  • cattle homozygous for the white coat allele have a white coat
  • heterozygous cattle - genotype CrCw - have both a red and white hairs - a roan coat
48
Q

MN blood groups codomiance

A
  • the MN blood group system is controlled by a single gene with two alleles Gm and Gn
  • the gene codes for a parituclar protein on the surface of erythrocytes, the Gm codes for one version and Gn for another
49
Q

sickle cell anaemia codominance

A
  • sickle cell anaemia is caused by a mutation in the gene that codes for the B globin chain of haemoglobin, the mutant allele is given the symbol HbS and the normal allele is given the symbol HbN
  • in heterozygous poeple at least half the haemoglobin in their red blood cells is normal and half is abnormal, however heterozygous people do not suffer from sickle cell anaemia
  • if we consider the type of haemoglobin as the phenotype then these alleles are considered as codominant
  • however if we take sickle cell anaemia to be the phenotype then the hb5 allele is considered to be recessive as this disorder has a recessive inheritance pattern
50
Q

describe codominance inheritance in plants

A
  • some type of camellia have red flowers and some have white flowers
  • if these two types are crossed the offspring will have red and white spotted flowers
  • both alleles of the gene for petal pigment, Pr and Pw are expressed in the phenotypes of the heterozygotes
51
Q

what is autosomal linkage

A

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

52
Q

linked genes are not free to undergo…

A

independent assortment, they are usually inherited together as a single unit this is because the chromosome is the unit of transmission during sexual reproduction

53
Q

describe inheritance of autosomally linked genes with no crossing over

A
  • if linked genes are not affected by crossing over of non sister chromatids during prophase 1 of meiosis then they are always inherited as one unit
54
Q

define epistasis

A

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

55
Q

describe the example of inheritance of autosmally linked genes with crossing over

A
  • no 9:3:3:1 ratio
  • produces recombinant gametes (lowest number) by crossing over during meiosis 1
  • the further apart the two gene loci are on a chromosome the greater the chance of recombinant gametes forming
56
Q

when can we use the chi-squared test

A
  • have a strong biological theory to use to predict expected values
  • the data is in categories
  • the sample size is large
  • the data are only raw counts
  • there are no zero scores in the raw count data
57
Q

describe epistasis

A

interaction of non-linked gene loci where one makes the expression of the other

58
Q

is epistasis sorted indepedently

A

because the gene loci are not linked they assort independently during gamete formation
- epistasis reduces the number of phenotypes produced in the F2 generation of dihybird crosses and therefore it reduces genetic variation

59
Q

describe recessive epistasis

A
  • the homozygous presence of a recessive alllele at the first locus prevents the expression of another allele at a second locus
  • the alleles at the first locus are epistatic to those at the second locus which are hypostatic to those at the first locus
60
Q

describe an example of recessive epistasis

A

an example is the inheritance of flower colour in salvia

  • two gene loci A/a and B/b on two different chromosomes are involved
  • if a pure breeding pink flowered varaiety of saliva which has the genotype AAbb is crossed with a pure breeding white flowered variety which has the genotype aaBB all of teh offspring has purple flowers and their genotype is AaBb
  • interbreeding members of the F1 generationr esults in plants that bear purple, pink and white flowers in the ration of 9:3;4
  • the homozygous aa is epistatic to both alleles of the B/b gene, neither the allele B for purple nor the allele b for pink, when in a homozygous state, can be expressed if no dominant allele A is present
61
Q

describe an example of dominant epistasis

A
  • the inheritance of feather colour in chickens is an example of dominant epistasis
  • interaction between two gene loci I/i and C/c
  • hypostatic gene C/c codes for coloured feathers
  • the I allele of the epistatic gene I/i prevents the formation of colour even if one C allele is present
  • individuals carrying at least one dominant allele I have white feathers even if they also have one dominant allele for coloured feathers
  • birds that are homozygous for the recessive allele, c, are also white as this mutated allele does not cause pigment to be made
  • pure breeding white leghorn chicken have the genotype IICC
  • pure breeding white wyandotte chickens have the genotype iicc
  • if IICC is crossed with iicc the offspring is all white and they are heterzyogous IiCc
62
Q

describe coat colour in mice (epistasis)

A
  • in mice the gene locus C/c determines that the coat will have colour, but the recessive genotype cc no pigment develops
  • A/a determines what colour is seen by determining the distribution of pigment
  • dominant allele A produces an agouti colour
  • the recessive allele a when homozygous produce black fur
  • if there are two cc alleles no colour will develop as no pigement to be distributed
63
Q

describe flower colour in sweet peas (epistasis)

A
  • two gene loci, A/a and B/b may yield results if one gene locus codes for an enzyme that catalyses the production of a colourless intermediate product from a colourless precursor substance, and the second gene locus codes for an enzyme that catalyses the production of a purple pigment from the intermediate production
  • A-B- = purple
  • A-bb = white
  • aaB- = white
  • aabb = white
64
Q

describe combs of domestic chickens (epistasis)

A

two gene loci, P/p and R/r interact with each other to affect comb shape
- effect of P/p alleles depends upon which R/r alleles are present in the birds genotype
- P-R- = walnut comb
- ppR- = rose comb
- P-rr = pea comb
- pprr = single comb
-

Biology Module 6 (13 decks)

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