Human Genetics Exam 2

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89 Terms

1

define dysmorphology

the study of human congenital malformations and birth defects

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2

dysmorphology combines knowledge of:

  • genetic principles

  • developmental mechanisms

  • natural history of congenital abnormalities

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3

what are common dysmorphologies related to Down Syndrome?

  • upslanting palpebral fissures

  • flattened nasal bridge

  • brushfield spots

  • low-set, small, folded ears

  • short neck

  • epicanthal folds

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4

what is the dysmorphology term for a child’s head being either to large or small

microcephaly and macrocephaly

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5

define hypertelorism

eyes are too far apart

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6

define hypotelorism

eyes are too close together

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7

define telecanthus

the inner corners of the eye are displaced laterally

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8

define epicanthal folds

folds of skin overlapping the inner canthi

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9

define blepharophimosis

small eye openings

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10

define prognathia

jaw protrudes out

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11

define retrogneathia

jaw retracts

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12

define micrognathia

small jaw

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13

define polydactyly

extra digits

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14

define syndactyly

fused digits, deficiencies, abnormal creases

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15

define brachydactyly

short digits

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16

define arachnodactyly

long digits

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17

define oligodactyly

missing digits

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18

what enzyme converts testosterone to dihydrotestosterone

5a-reductase

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19

what type of inheritance does Guevedoces display

autosomal recessive

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20

Guevedoces is primarily what type of mutation?

missense

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21

Pseudoautosomal regions (PAR1 and PAR2) make up __-__% of the chromosome

5-10%

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22

What is the other 95% (not PAR1 and PAR2) of the male chromosome referred to as

Male Specific Region

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23

what does the SRY gene code for

transcription factor protein - stimulates male development and sends signals to gonads to degenerate female structures

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24

define pronucleus

the sperm/egg nucleus after sperm has entered the ovum at fertilization but before fusion of the pronuclei

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25

what are sex-limited traits

traits that affect a structure or function occuring only in one sex - may be autosomal or X-linked

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26

examples of sex limited traits

  • beard growth

  • milk production

  • preeclampsia in pregnancy

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27

what are sex-influenced traits

allele is dominant in one sex but recessive in the other - difference in expression can be caused by hormonal differences between sexes

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28

sex-influenced trait examples

pattern baldness in humans - heterozygous male is bald, heterozygous female is not

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29

what is the paternal age effect?

increased risk of health disorders in children with older fathers

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30

examples of disorders that display the paternal age effect:

  • achondroplasia

  • crouzan syndrome

  • multiple endocrine neoplasia 2

  • pfeiffer syndrome

  • thanatophoric dysplasia

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31

how many possible combinations of maternal chromosomes via independent assortment

2²³ = ~8,000,000

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32

What is the MHC

Major Histocompatibility Complex - codes for proteins to help the immune system identify foreign antigens

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33

what is another name for the MHC

HLA region - Human Leukocyte Antigen

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34

where is the MHC located

Located on the short arm of chromosome 6

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35

functions of the MHC

  • presentation of intracellular and extracellular pathogens

  • inflammation

  • neural development

  • potentially related to mate selection

  • environmental factor responses

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36

What are the three regions of MHC called

Class I, Class II, Class III

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37

Describe Class I region of MHC

  • expressed on nearly all nucleated cells

  • presenting endogenous (intracellular) peptides to CD8+ T cells

  • genes: HLA-A, HLA-B, HLA-C, etc

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38

CD8 cell function

directly kill infected immune cells

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39

describe class II region genes of MHC

  • expressed on antigen presenting cells (APCs)

  • presenting exogenous (extracellular) peptides to CD4+ T cells

    • adaptive immunity

  • genes: HLA-DP, HLA-DQ (two letters = class 2)

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40

describe class III region genes of MHC

  • expression affects inflammation and immunity

    • complement proteins and cytokines

  • supports both innate and adaptive immunity

  • genes: Complement component 4 (C4), TNF-a/b, etc

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41

____ genes are the most polymorphic genes in the human genome

MHC

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42

what does high allelic diversity allow for

better immune recognition but complicates transplantation compatibility

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43

what is the most polymorphic gene in the human genome

HLA-B

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44

True/false: certain MHC alleles may confer resistance or susceptibility to autoimmune responses

true

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45

which type of selection maintains MHC diversity and why?

balancing selection - prevents any single allele from becoming fixed or lost in a population

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46

_____ genotypes can present a wider variety of pathogen-derived antigens

heterozygous - harder for antigens to escape immune detection

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47

does infectious disease promote or inhibit HLA diversity

promote

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48

what is a haplotype

a set of genes or genetic markers that are inherited together from one parent

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49

siblings have a ___% chance of a full HLA match

25%

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50

mismatched HLA alleles can lead to ____________ or organ rejection

graft-versus-host-disease - transplanted immune cells (graft) attack the recipient’s (host) healthy tissues

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51

what is linkage disequilibrium

the nonrandom association of alleles at different loci in a population

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52

define cytogenetics

the study of chromosomes and their abnormalities

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53

Benefits of using Fluorescent in situ hybridization

  • sequence and chromosome specific places in DNA

  • simultaneous assessment of multiple genetic targets in an intact cell

  • relatively easy interpretation

  • easy to perform

  • short time-to-result

  • quantitates genetic changes cell-by-cell

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54

abnormal chromosomes account for at least __% of spontaneous abortions

50%

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55

nondisjunction during meiosis I results in

both homologs in one gamete

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56

nondisjunction during Meiosis II results in

both sister chromatids in one gamete

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57

frequently seen trisomies:

21, 18, 13

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58

Describe Trisomy 18

  • Edward’s Syndrome

  • commonly do not survive

  • mental and physical disabilities

  • oddly clenched fists

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59

Describe Trisomy 13

  • Patau Syndrome

  • very rare and generally do not survive past 6 months

  • serious mental and physical disabilites

  • eye fusion

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60

name ways you can diagnose aneuploidies

  • standard cytogenic

  • QF-PCR (quantitative fluorescenting)

  • NIPT (noninvasive prenatal testing)

  • serum and ultrasound screening

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61

Describe Klinefelter syndrome

  • 85% nondisjunction

  • XXY

  • common cause of male infertility

  • incomplete sexual development, rudimentary testes and prostate, long limbs, large hands and feet, breast tissue development

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62

Describe Jacob’s Syndrome

  • XYY aneuploidy

  • 96% are phenotypically normal

  • modest phenotypes - great height, acne, speech and reading disabilities

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63

describe XXYY syndrome

  • arises due to unusual oocyte and sperm

  • more severe behavioral problems than Klinefelter’s - OCD, learning disabilities

  • infertile and treated with testosterone

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64

Describe Turner Syndrome

  • XO

  • 99% of fetuses die in utero

  • features: short stature, webbing at the back of neck, incomplete sexual development, impaired hearing

  • individuals who are mosaics may have children

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65

Triplo-X Syndrome

  • few modest effects on phenotype

  • tallness, menstrual irregularities, and slight impact on intelligence

  • X inactivation of two X chromosomes occurs

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66

Reciprocal Translations

  • two non-homologous chromosomes exchange parts

  • usually healthy because they have the normal amount of genetic material

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67

Robertsonian Translocation

  • two nonhomologous, acrocentric chromosomes break at the centromere and the long arms fuse

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68

is nondisjuction more common in males or females

females

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69

what do mitochondrial genomes code for

polypeptides required for mitochondrial respiratory chain

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70

what type of diseases result from mitochondrial mutations

  • monogenic disorders that affect the nervous system, muscles, heart, and endocrine organs

  • mutations with milder contribution to common complex traits and late-onset disorders

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71

does mtDNA contain introns?

no

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72

is there recombination in mtDNA

no

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73

what makes mtDNA easily mutable

high exposure to free radicals

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74

how many copies of DNA do each mitochondrion contain

2-10

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75

functions of the mitochondria

  • cellular metabolism

  • intracellular calcium signalling

  • biogenesis of iron-sulfur clusters

  • apoptotic cell death

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76

define heteroplasmy

mosaicism for mitochondrial DNA variants, usually within a single cell

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77

levels of heteroplasmy can vary:

  • between cells in the same tissue or organ

  • from organ to organ in the same person

  • between individuals in the same family

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78

what is leber optical atrophy and what can it be the result of

impaired vision - mitochondrial disorders

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79

describe Leber Hereditary Optic Neuropathy (LHON)

painless, progressive loss of central vision - degeneration of retinal ganglion cells and their axons, leading to acute loss of central vision

missense mutations - low penetrance with males more likely to become blind

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80

Describe myoclonic epilepsy with ragged red fibers (MERRF)

  • tRNA mutation

  • progressive epilepsy and dementia, onset late childhood-adulthood

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81

are mtDNA point mutations or mtDNA deletions inherited

point mutations

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82

are mtDNA point mutations or mtDNA deletions homoplasmic

point mutations

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83

describe Friedreich’s Ataxia

  • triplet/trinucleotide repeat disorder

  • results in cell death, in particular of neurons, heart muscle, and beta cells in pancreas

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84

5 hardy weinburg assumptions

  • infinite number of individuals in the population

  • random mating

  • no new mutations

  • no migration

  • no natural selection

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85

what is genetic load

collection of recessive deleterious alleles in a population

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86

describe population bottlenecks

occurs when a large population is drastically reduced in size - Ashkenazi Jews

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87

Founder Effect

all individuals in a population with a certain illlness have the same mutation - BRCA1 breast cancer among Ashkenazi Jewish people

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88

describe balanced polymorphism

harmful recessive alleles are replaced by new mutation, and persistence in heterozygotes - sickle cell

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89
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