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Genetics > Exam 3 Mapping and Pedigree > Flashcards

Exam 3 Mapping and Pedigree Flashcards

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1
Q

Chiasma

A

a point of contact between two paired chromosomes during meiosis from which crossing over and the exchange of genetic material can occur

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2
Q

Crossing over

A

The actual physical process of reciprocal exchange of chromosome segments at corresponding positions along homologous chromosomes. A process that involves symmetrical breaking and rejoining of segments.

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3
Q

Coupling

A

two wild-type alleles are on one homologous chromosome and the mutant alleles are on the other

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4
Q

Repulsion

A

each chromosome has one wild type allele and one mutant allele

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5
Q

Test cross

A

involves the breeding of a heterozygous individual with a homozygous recessive individual, in order to determine the zygosity of the former by analyzing proportions of the offspring and their phenotypes

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6
Q

Genetic Map

A

a representation of the genetic distance separating nonallelic genes in a linkage structure

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7
Q

Linkage analysis

A
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8
Q

Inheritance of genes is

A

on the same chromosome

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9
Q

Mendel’s Laws

A

1st law- segregation
2nd law-independent assortment

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10
Q

Mendel’s first Law

A

Segregation
individuals possess two alleles and a parent passes only one allele to their offspring

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11
Q

Mendel’s second law

A

independent assortment
the inheritance of one pair of genes is independent of the inheritance of the other pair

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12
Q

Chromosome theory of inheritance ideas

A
  1. Genes reside on chromosomes
  2. genes and chromosomes show parallel behavior
  3. Genes and chromosomes occur in pairs, 2 alleles of a gene pair are located on homologous sites on homologous chromosomes
  4. during meiosis due to pairing and subsequent segregation of homologous chromosomes genes also segregate
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13
Q

Chromosome theory of inheritance main idea

A

chromosomes are the carriers of genetic heredity and genes are situated on chromosomes

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14
Q

Genetic Linkage

A

when two genes are located on the same chromosome they exhibit linkage

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15
Q

Recombination

A

a process by which segments of DNA are broken and recombine to produce new combinations of alleles

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16
Q

Where does recombination usually take place

A

Anaphase 1 during meiosis

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17
Q

The recombination process

A

created genetic diversity at the level of the genes that reflects differences in the DNA sequences of different organisms

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18
Q

Complete linkage

A

when the genes are located close to one another on the same chromosomes and no recombinants are produced

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19
Q

Incomplete linkage

A

when genes are on the same chromosome but are far enough apart that some recombination occurs, but they do not assort independently

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20
Q

Linked genes segregate

A

together

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21
Q

In a testcross at least one heterozygous individual of the progeny are expected to

A

display at least one of the original parental phenotypes

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22
Q

In a testcross independent assortment produces what type of ratio

A

1:1:1:1
50% parental (non-recombinants)
50% nonparental (recombinants)

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23
Q

Why, when, how, and where does mitotic recombination occur

A

repair of breaks
interphase
different mechanisms
common fragile sites in the genome

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24
Q

Parental ‘Non-recombinant’ Gametes

A

the progeny of a cross (or genotype of the gametes) that have combinations of alleles that are like the one or the other of the parents

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25
Q

Non-parental ‘Recombinant’ Gametes

A

the progeny of a cross (or genotype of the gametes) that have non-parental combinations of alleles. These gametes result from processes of genetic recombination

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26
Q

If two genes are completely linked will they assort independently

A

No

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27
Q

If two genes are not linked they will assort

A

independently

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28
Q

No crossing over means

A

alleles of linked genes do not assort independently
genes segregate together such that gametes are the same as parents

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29
Q

Gene linkage is broken so recombinants are changed chromosomes

A

crossing over

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30
Q

If two genes are incompletely linked the parental gametes will be at a

A

higher frequency

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31
Q

Recombination frequency equation

A

of recombinant progeny over total # of progeny X 100

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32
Q

A coupling phase of linkage

A

when like alleles, dominant or recessive, are linked

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33
Q

Linkage types- Alleles in Coupling

A

recombinants- less frequently occurs- always lesser number
nonrecombinants- larger number

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34
Q

In Repulsion

A

when dissimilar alleles (e.g. dominant for one gene and recessive for the other) are linked

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35
Q

Outcome of independent assortment

A

25%
25%
25%
25%

36
Q

outcome of complete linkage (coupling)

A

50%
50%

37
Q

Linkage with crossing over (coupling)

A

> 50%
<50%

38
Q

Goodness of fit

A

theoretical relation based on expected progeny ratio that when calculating degrees of freedom no parameters are estimated

39
Q

Independence

A

based on only observed progeny ratio

40
Q

a chi-squared test can be used to

A

determine in genes are linked

41
Q

Number expected formula for testing independent assortment using chi-squared test

A

(row total X column total) over grand total

42
Q

1% recombination equals

A

1 centimorgan

43
Q

Genetic mapping

A

the process of determining the relative positions of nonallelic genes on the chromosomes of a species using genetic crosses to locate genes on chromosomes relative to one another

44
Q

steps to desining a genetic map

A
  1. design crosses involving traits of interest
  2. observe progeny ratios
  3. determine whether or no the genes are linked (chi-squared test vs. expected ratio)
  4. determine recombination frequencies
  5. determine the linkage arrangement (coupling or repulsion)
  6. position genes on chromosomes in a way that best suits the data
45
Q

When genes are linked, the parents are

A

always the most frequent classes while recombinants are the least frequent classes because they result from recombination

46
Q

In a double cross over, progeny reflect

A

nonrecombinant gametes

47
Q

Recombination frequency formula

A

sum of recombinants over sum of progeny times 100

48
Q

Multiple crossovers

A

effect on progeny outcomes

49
Q

Three point test cross

A

a test cross involving three linked genes in a small region of the chromosome
it is a testcross of a trihybrid

50
Q

Steps to determining gene order for a 3-point cross

A
  1. identify the nonrecombinants progeny (two most numerous progeny)
  2. identify the double-crossover progeny (two least numerous progeny)
  3. compare the phenotypes of the double-crossover progeny with the phenotypes of nonrecombinant progeny. should be alike in two characteristics and different in one. the characteristic that differ between the double-crossover and the nonrecombinant progeny is encoded by the middle gene
51
Q

Coefficient of coincidence

A

the ratio of observed double crossovers to expected double crossovers

52
Q

interference

A

degree that one crossover interferes with other crossovers

53
Q

how to calculate interference

A

take the percentages and multiply them
take that times the total progeny
divide the number of observed crosses by the expected double cross overs
1- the number gotten in the previous step

54
Q

Genetic linkage mapping process

A
  1. find sets of related patients
  2. assemble patients into pedigrees
  3. genotype patients and other family members
  4. find genotypes that are inherited with the disease
  5. identify the region where they are located
55
Q

Logarithm of odds (LOD)

A

estimation of the probabilities of obtaining the observed results under the assumption of linked genes with defined recombination or independent assortment. the ratio of these two probabilities is the LOD score

56
Q

In general, LOD scores of 3 or higher indicate

A

linkage

57
Q

Genome wide association

A

the nonrandom association between a trait and alleles at many loci throughout the genome

58
Q

haplotype

A

a specific set of linked alleles along a chromosome

59
Q

linkage disequilibrium

A

the nonrandom association between alleles at two or more loci in a general population

60
Q

Single nucleotide polymorphism (SNP)

A

positions in the genome where a single nucleotide varies across individuals

61
Q

GWAS Process

A
  1. goal is to identify genomic regions associated with a phenotype
  2. fit a statistical model at each SNP in the genome
  3. use fitted models to test null hypothesis: no association with SNP and phenotypes
62
Q

Features of a haplotype

A

a haplotype is a particular pattern of sequential SNPs found on a single chromosome
Haplotype has a block-wise structure separated by recombination spots
within each block, recombination is rare due to tight linkage and only very few haplotypes

63
Q

Non-variable region

A

area with very little variation
blank spots on chromosomes

64
Q

Why is linkage disequilibrium so useful in GWAS studies

A

determines the extent to which association mapping can be used in species

65
Q

what do linkage disequilibrium measure

A

the degree to which alleles at two loci are non-randomly associated

66
Q

Pedigree

A

a pictorial diagram of the family history, that outlines the inheritance of one or more traits

67
Q

Proband

A

first affected person that comes to the attention of the geneticist

68
Q

Autosomal dominant trait facts

A

both sexes equally
both sexes transmit to offspring
affected individuals have an affected parent
affected parent is heterozygous, Aa, and the other parent is unaffected 1/2 of the offspring will be affected
unaffected parents don’t transmit the trait

69
Q

Autosomal recessive trait facts

A

both sexes equally
skips generation
affected individuals born to unaffected parents
if both parents are heterozygous, Aa, then about 1/4 of the offspring will be affected
more frequent occurrence with inbreeding

70
Q

On average each person is a carrier for how many recessive diseases

A

20

71
Q

consanguineous

A

denoting people descending from the same ancestor
inbreeding

72
Q

how are consanguineous breedings useful in genetics

A

help find recessive traits

73
Q

IBD

A

identity by descent
segments are the same inherited over generations

74
Q

X-linked recessive trait facts

A

more males than females are affected
affected sons born to unaffected mothers
half of a carrier mother’s sons are affected
never passed from father to son
all daughters of affected father are carriers

75
Q

X-linked dominant trait facts

A

males and females are usually affected, often more females than males are affected
affected male parent passes the trait to all daughters and no sons
does not skip generations
affected mothers if heterozygous pass the trait to half the sons and half the daughters

76
Q

Y-linked traits

A

transmitted from father to son
only males
does not skip generations

77
Q

Genetic mosaicism

A

individuals whose cells hold different genetic constitutions- 30% of cells

78
Q

Dizygotic

A

twins arise when two different eggs are fertilized by two different sperm
50%

79
Q

Monozygotic

A

twins arise when one egg fertilized by one sperm splits in early development into two embryos
100%

80
Q

Concordance

A

the percentage of twin pairs that are concordant (both twins pairs have the trait) for a trait

81
Q

Why is adoption useful for studying the influence of genes and the environment?

A

Identical twins with the same genetics can be raised in different environments to determine what is affected by genes vs. environment

82
Q

Genetic Counseling

A

a process of communication where patients are provided information relevant to the transmission of heritable disorders

83
Q

Genetic testing methods used today

A

maternal blood screening
non-invasive prenatal screening
presymptomatic
pharmacogenetic
newborn

84
Q

Interpreting genetic test is complicated by

A

the presence of multiple causative mutations, incomplete penetrance, and influence of environmental factors

85
Q

Genetic information nondiscrimination act

A

a law that prohibits health care insurers from using genetic information in making decisions about providing health care coverage and rates

Genetics (5 decks)

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