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BMS2042 > TOPIC 1: MENDEL AND EXTENSIONS TO MENDEL > Flashcards

TOPIC 1: MENDEL AND EXTENSIONS TO MENDEL Flashcards

WEEKS 1 AND 2

1
Q

What is transmission genetics?

A
  • How genes are transmitted from parents to offpring
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2
Q

What is a monohybrid cross?

A
  • One pair of contrasting traits by mating two TRUE bred organisms from TWO parents strains each exhibiting the CONTRASTING characteristics.
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3
Q

What does P1 mean?

A
  • The Parental generation
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4
Q

What does F1 mean?

A
  • The first filial generation (Offspring)
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5
Q

What does F2 mean?

A
  • The second filial generation (offspring from the F1)
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6
Q

What does the 3:1 ratio mean for the monohybrid cross?

A
  • That both of the parents are heterozygous and 3/4 looked like F1 plants and 1/4 had the contrasting trait that wasn’t present in F1
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7
Q

What are Mendels’ 3 postulates?

A
  • Unit Factors in pairs
  • Dominance/recessiveness
  • Segregation
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8
Q

What is mendels first postulate and what does it mean?

A

“Genetic characters are controlled by unit factors existing in pairs in individual organisms”

  • One unit factor (gene) exists and there are 3 possibilities
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9
Q

What is Mendels second postulate and what does it mean?

A
  • “When two unlike unit factors responsible for a single character (phenotype) are present in a single-individual, one-unit factor is dominant to the other, which is said to be recessive”
  • Trait expressed in the F1 is controlled by the dominant factor e.g. Tall stems are dominant over short stems
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10
Q

What is Mendel’s third postulate and what does it mean?

A
  • “During the formation of gametes, the paired unit factors separate, or segregate, RANDOMLY so that each gamete receives one or the other with equal likelihood”
  • Gametes of TALL plants ALL receive one tall unit factor from SEGREGATION and the same with dwarf plants
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11
Q

What are alleles?

A
  • Alternative forms of a single gene
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12
Q

What is the genotype?

A
  • When alleles are written in pairs e.g. Dd –> also describes whether an individual is haploid or diploid
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13
Q

What does it mean to be TRUE BRED?

A
  • The individual is HOMOZYGOUS for the gene
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14
Q

What is a test cross and when is it performed?

A
  • When an organism expresses the dominant phenotype but has an UNKNOWN genotype is crossed with a HOMOZYGOUS RECESSIVE individual
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15
Q

When do we find a 9:3:3:1 ratio?

A
  • when there has been a DIHYBRID CROSS for two heterozygous parents
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16
Q

What is mendels 4th postulate?

A
  • “During gamete formation, segregating pairs of unit factors assort independently of each other”
  • ALL possible gametes should be formed in equal frequency
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17
Q

What are the patterns to look for in an autosomal recessive inheritance? (5 things)

A
  • Affected people usually born to UNAFFECTED PARENTS (asymptomatic carriers)
  • Appears EQUALLY in males and females
  • Increased incidence of consanguinity
  • SKIPS generations
  • After the birth of each child, the subsequent child has a 25% chance of being affected
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18
Q

What are 3 patterns to look for in autosomal dominant inheritance?

A
  • Affected person usually has AT LEAST ONE affected parent
  • Affects EITHER sex
  • Child with ONE affected parent and ONE unaffected parent has a 50% chance of being affected
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19
Q

What are 5 things to look for in an X-linked recessive inheritance pattern?

A
  • Affected MALES usually born to unaffected PARENTS
  • Affects mainly MALES
  • MOTHER usually asymptomatic carrier
  • NO-MALE-MALE TRANSMISSION
  • Females can be affected IF the father is affected AND mother is a carrier OR from NON RANDOM X-INACTIVATION
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20
Q

What is a trait?

A
  • A characteristic of an organism e.g. seed colour
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21
Q

What is a phenotype?

A
  • Appearance of an organism e.g. yelow seat coat
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22
Q

What is a gene?

A
  • Unit of heredity (region of DNA) influencing a trait e.g. gene for seed colour
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23
Q

What is an allele?

A
  • An alternative version of the same gene
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24
Q

What is a locus?

A
  • Specific place on a chromosome occupied by a gene
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25
Q

What does homozygous mean?

A
  • An organism possessing two of the SAME alleles at a locus
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26
Q

What does heterozygous mean?

A
  • An organisms possessing two DIFFERENT alleles at a locus
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27
Q

What is the principle of independent assorment?

A
  • Genes encoding different characteristics SEPARATE and assort INDEPENDENTLY to one another when they do not locate close together on the same chromosome
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28
Q

What is the principle of segregation?

A
  • Two alleles of the same gene encoding one characteristic still have to be segregated from each other during the formation of gametes
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29
Q

What is consanguinity?

A
  • Increases the chance that a mating couple will both carry the SAME disease causing mutation
  • e.g. Cousins
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30
Q

What is the product rule?

A
  • The Pr of INDEPENDENT events occurring together is the product of the probabilities of the individual events
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31
Q

What is the sum rule?

A
  • The probability of either two mutually exclusive events occurring is the SUM of their INDIVIDUAL probabilities.
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32
Q

In dominant diseases, is the homozygous individual affected more than the heterozygous?

A
  • YES! –> the majority
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33
Q

Can the effects of recessive genes be detected in heterozygotes and why/why not?

A

YES!

-Because they can result in reduced levels of enzyme -

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34
Q

What is the definition of codominance?

A
  • Both alternative traits are visible in the heterozygotes and NEITHER phenotpye is dominant
  • Phenotypic expression of TWO DIFFERENT alleles for a locus
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35
Q

What is the ratio for two heterozygotes who have children and there is codominance?

A
  • 1:2:1
36
Q

What is a classic example of codominance?

A
  • ABO blood groups with the A and B (not with O-that is recessive)
37
Q

In the ABO blood groups, what is an example of a null mutant and what does this mean?

A
  • ii (O) is a null mutannt –> means that there is no enzyme activity and NO extra antigens
38
Q

Is the ABO locus polymorphic?

A
  • YES!
39
Q

What is OVERDOMINANCE?

A
  • A heterozygote advantage where heterozygotes have characteristics that are BETTER for survival/reproductive success in environment than EITHER homozygote
    e. g. Sickle cell anaemia for malaria
40
Q

What are mutations called when there is no previous family history of the disease?

A
  • De novo mutations
41
Q

What is an example of inheritance where they can be from a new mutation?

A
  • Autosomal or X-linked dominant
42
Q

What is mosaicism defined as in general?

A
  • Present in individuals or tissue of AL LEAST 2 CELL LINES that differ genetically but are derived from a SINGLE zygote
43
Q

Where is somatic mosaicism present and where is it NOT?

A
  • In some tissues of body but NOT IN GAMETES
44
Q

Where is a germline mutation restricted to?

A
  • The gamete lineage
45
Q

Which patterns of inheritance is mosaicism present in?

A
  • Autosomal and X-linked dominant diseases
46
Q

What is a lethal allele?

A
  • An allele that has the potential to cause death of an organism, sometimes in utero
47
Q

Are lethal alleles the result of mutations in essential genes?

A
  • YES
48
Q

In lethal alleles, what can the Mendelian 1:2:1 genotype and 3:1 phenotype appear as instead?

A
  • 2:1 ratio instead
49
Q

Which disease is an example of a lethal allele?

A
  • Rett Syndrome -abnormality in the regulation of genes in the brain
  • Lethal in males as it is X-linked dominant
50
Q

What is penetrance?

A
  • The Pr that a gene will have any phenotypic expression at all
  • Some individuals might have the same genotype as others in family but NOT express the phenotype or have a LESS SEVERE phenotype
51
Q

What is incomplete penetrance?

A
  • Someone who has the disease causing genotype and doesn’t have symptoms of disease at all, but can pass it onto the NEXT generation
52
Q

What is a penetrance of under 100% termed as?

A
  • Reduced penetrance
53
Q

Is there such thing as age-dependent penetrance?

A
  • YES!

- e.g. BRCA1 and BRCA2

54
Q

Is penetrance an all-or-none phenomenon?

A
  • YES!

- One either has the phenotype or doesn’t

55
Q

What is variable expression defined as?

A
  • The SEVERITY OF EXPRESSION of the phenotype among individuals with the SAME disease causing genotype.
56
Q

What can the severity of expression of the phenotype be modified by?

A
  • X-chromosome inactivation
57
Q

What is the definition of pleiotropy?

A
  • Where ONE mutation has MULTIPLE effects

- Most mutations are pleiotropic

58
Q

What is allelic heterogeneity?

A
  • Where many different mutations within a given gene/locus can be seen in different patients with a certain genetic condition
59
Q

What is LOCUS heterogeneity?

A
  • Where the SAME clinical phenotype can result from mutations at any one of the several different loci that lead to a disease (may be from epistasis)–> gene A and B with similar function in different pathways that afect the SAME phenotype
60
Q

What is anticipation?

A

-Where a genetic trait becomes more strongly expressed at an EARLIER STAGE as it is passed from generation to generation

61
Q

Which types of mutations is anticipation common in?

A
  • Dynamic mutations
62
Q

What do dynamic mutations cause in terms of the DNA?

A
  • Expansion of trinucleotide repeats in tandem with a gene or DNA segment –> dynamic mutation is trinucleotide repeat that expands during gametogenesis and interferes with gene expression
63
Q

Can the number of unstable repeat expansions affect the severity and the age of onset of diseases causes by dynamic mutations?

A
  • YES!!!
64
Q

What is an example of a human trinucleotide repeat expansion inside and outside a coding region respectively?

A
  • Huntingtons disease (expansion of CAG triplet-autosomal dominant) and Friedreichs ataxia
65
Q

What is complementation?

A
  • When organisms that are HOMOZYGOUS for mutations that show the SAME phenotype but are in DIFFERENT genes are crossed together and the progeny are WILD TYPE thus COMPLEMENTATION
66
Q

What occurs when complement fails?

A
  • When organisms that are HOMOZYGOUS for mutations that show the SAME phenotype and are in the SAME GENE are crossed together and the progeny is MUTANT thus FAIL TO COMPLEMENT (no active protein)
67
Q

Which condition can complementatino occur in?

A
  • Deafness (mating between two homozygotes for the recessive deafness trait)
68
Q

What is the common ratio for complementary gene action?

A
  • 9:7 ratio
    e. g. colour in sweet peas (two true breeding white varieties produced pruple peas)
  • Purple 9: White 7
69
Q

What is complementary gene action AKA duplicate recessive epistasis?

A
  • Where there needs to be a dominant allele for each gene to produce the trait
    e. g. C dominant to c and P dominant to p
  • If EITHER cc or pp will be white there needs to be a DOMINANT ALLELE for both genes to be purple
70
Q

What is the common F2 ratio for recessive epistasis?

A
  • 9:3:4
71
Q

What is epistasis?

A
  • When the phenotpye produced by a mutant allele of one gene (the epistatic allele) masks or BLOCKS or MASKS the PHENOTYPE produced by the alleles of another gene.
72
Q

In what form does a recessive epiatatic allele have to be in to block or mask the phenotypic effects of alleles of other genes?

A
  • Only when it is HOMOZYGOUS
73
Q

Are genes in the same pathway or a different pathway for the producing trait in recessive epistasis?

A
  • Same pathway
74
Q

What is the common ratio for dominant epistasis?

A
  • 12:3:1
75
Q

What is dominant epistasis?

A
  • Where a dominant allele at one loci masks an allele at the second loci
76
Q

What is an example of dominant epistasis?

A
  • Where one homozygous white squash is crossed with one homozygous green squash regardless of the second allele
  • F1 are ALL white
  • F2 then have the 12 white : 3 yellow: 1 green
77
Q

What is the common ratio for duplicate genes?

A
  • 15:1
78
Q

What is duplicate gene inheritance and an example?

A
  • Where EITHER the A or B allele is required

- In Shepards purse weed–> Dominant allele of EITHER = Triangular shape thus 15 triangular and 1 ovate (ttvv)

79
Q

What are two examples of the environment affecting the phenotypic expression of a phenotype?

A
  1. Temperature –> coat colour with artic fox

2. Chemicals –> PKU –> loss of enzyme to metabolize Phe (change physical environment to remove Phe from diet)

80
Q

What is the process of imprinting?

A
  • Where for some human genes, one of the alleles is TRANSCRIPTIONALLY INACTIVE (no mRNA), depending which parent from whom the allele was received
  • transcriptionally silenced genes are ‘imprinted’
81
Q

What is a feature of imprinted alleles?

A
  • Heavily methylated or have chromatin modifications in chromatin of SPECIFIC histone types –> epigenetic changes
82
Q

What is an example of imprinting alleles?

A
  • 15q11-q13 deletion
  • From FATHER–> PWS syndrome –> SNRPN and NDN paternally expressed–> must eat all the time
  • From MOTHER–> ANgelman syndrome –> UBE3A expressed maternally
83
Q

What is an example of sex influenced characterisitcs?

A
  • Baldness –> autosomal dominant in males and recessive in females
84
Q

What are sex influenced characterisitcs?

A
  • Inherited characteristics that are conditioned by the SEX of the individual e.g. baldness dominant in males
85
Q

What are sex-LIMITED characterisitcs and an example?

A
  • Where the characterisitc only appears (or develops) in ONE OF THE SEXES
    e. g. Ovary development in females and sperm in males
86
Q

Does sex-influenced mean sex-linked?

A

-NO!

87
Q

Which type of sequencing is the most cost effective?

A
  • Targeted sequencing (if you have a family history)

BMS2042 (11 decks)

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