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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
Non-parental 'Recombinant' Gametes
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
26
If two genes are completely linked will they assort independently
No
27
If two genes are not linked they will assort
independently
28
No crossing over means
alleles of linked genes do not assort independently genes segregate together such that gametes are the same as parents
29
Gene linkage is broken so recombinants are changed chromosomes
crossing over
30
If two genes are incompletely linked the parental gametes will be at a
higher frequency
31
Recombination frequency equation
of recombinant progeny over total # of progeny X 100
32
A coupling phase of linkage
when like alleles, dominant or recessive, are linked
33
Linkage types- Alleles in Coupling
recombinants- less frequently occurs- always lesser number nonrecombinants- larger number
34
In Repulsion
when dissimilar alleles (e.g. dominant for one gene and recessive for the other) are linked
35
Outcome of independent assortment
25% 25% 25% 25%
36
outcome of complete linkage (coupling)
50% 50%
37
Linkage with crossing over (coupling)
>50% <50%
38
Goodness of fit
theoretical relation based on expected progeny ratio that when calculating degrees of freedom no parameters are estimated
39
Independence
based on only observed progeny ratio
40
a chi-squared test can be used to
determine in genes are linked
41
Number expected formula for testing independent assortment using chi-squared test
(row total X column total) over grand total
42
1% recombination equals
1 centimorgan
43
Genetic mapping
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
steps to desining a genetic map
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
When genes are linked, the parents are
always the most frequent classes while recombinants are the least frequent classes because they result from recombination
46
In a double cross over, progeny reflect
nonrecombinant gametes
47
Recombination frequency formula
sum of recombinants over sum of progeny times 100
48
Multiple crossovers
effect on progeny outcomes
49
Three point test cross
a test cross involving three linked genes in a small region of the chromosome it is a testcross of a trihybrid
50
Steps to determining gene order for a 3-point cross
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
Coefficient of coincidence
the ratio of observed double crossovers to expected double crossovers
52
interference
degree that one crossover interferes with other crossovers
53
how to calculate interference
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
Genetic linkage mapping process
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
Logarithm of odds (LOD)
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
In general, LOD scores of 3 or higher indicate
linkage
57
Genome wide association
the nonrandom association between a trait and alleles at many loci throughout the genome
58
haplotype
a specific set of linked alleles along a chromosome
59
linkage disequilibrium
the nonrandom association between alleles at two or more loci in a general population
60
Single nucleotide polymorphism (SNP)
positions in the genome where a single nucleotide varies across individuals
61
GWAS Process
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
Features of a haplotype
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
Non-variable region
area with very little variation blank spots on chromosomes
64
Why is linkage disequilibrium so useful in GWAS studies
determines the extent to which association mapping can be used in species
65
what do linkage disequilibrium measure
the degree to which alleles at two loci are non-randomly associated
66
Pedigree
a pictorial diagram of the family history, that outlines the inheritance of one or more traits
67
Proband
first affected person that comes to the attention of the geneticist
68
Autosomal dominant trait facts
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
Autosomal recessive trait facts
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
On average each person is a carrier for how many recessive diseases
20
71
consanguineous
denoting people descending from the same ancestor inbreeding
72
how are consanguineous breedings useful in genetics
help find recessive traits
73
IBD
identity by descent segments are the same inherited over generations
74
X-linked recessive trait facts
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
X-linked dominant trait facts
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
Y-linked traits
transmitted from father to son only males does not skip generations
77
Genetic mosaicism
individuals whose cells hold different genetic constitutions- 30% of cells
78
Dizygotic
twins arise when two different eggs are fertilized by two different sperm 50%
79
Monozygotic
twins arise when one egg fertilized by one sperm splits in early development into two embryos 100%
80
Concordance
the percentage of twin pairs that are concordant (both twins pairs have the trait) for a trait
81
Why is adoption useful for studying the influence of genes and the environment?
Identical twins with the same genetics can be raised in different environments to determine what is affected by genes vs. environment
82
Genetic Counseling
a process of communication where patients are provided information relevant to the transmission of heritable disorders
83
Genetic testing methods used today
maternal blood screening non-invasive prenatal screening presymptomatic pharmacogenetic newborn
84
Interpreting genetic test is complicated by
the presence of multiple causative mutations, incomplete penetrance, and influence of environmental factors
85
Genetic information nondiscrimination act
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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