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Flashcards in Genetics Deck (63)
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1

Genes

Hereditary units of DNA transmitted from one generation to another; code for proteins

2

Locus

The specific location of a gene on a chromosome vs. genetic marker isn’t as exact (zone of a chromosome)

3

Alleles

Different versions of a gene; humans have 2 alleles for each autosomal gene

4

Chromosomes

Structure composed of genes located in nucleus of a cell

5

Homologous chromosomes

Have the same genes at the same loci, one maternal and one paternal

6

Genome

The genetic information contained in the cells, on the chromosomes, for a particular species

7

Mutation

A change in some part of the DNA code. Can be:
-Spontaneous
-Induced by exposure to mutagenic chemicals or radiation

8

Autosome

Any chromosome that is not a sex chromosome (humans have 22 pairs of autosomes)

9

Haploid number

the number of chromosomes in sex cells/gametes (n=23)

10

Diploid number

the total number of chromosomes in somatic cells (2n=46)

11

Somatic chromosomes

Autosomes

12

Sex chromosomes

Allosomes
-Males have one morphologically dissimilar pair (heteromorphic), labeled X and Y. Genetic factors on the Y determine maleness
-Females have two morphologically similar X's

13

Karyotype

The characterization of the chromosomal complement of an individual or a species, including number, form, and size of the chromosomes.

14

Mitosis

-The process by which all somatic cells replicate and become descendants of one original cell
-One exact copy of each chromosome is made and distributed through the division of original cell into two daughter cells

15

Meiosis

-The process by which gamete cells are produced (egg and sperm)
-Resulting gametes have 23 new chromosomes, with new combos of the original maternal and paternal copies
-Occurs only in specialized germ cells of gonads
-2 consecutive cell divisions producing cells with half the original chromosome number
--> Diploid 2n-->haploid n

16

Genotype

All of the alleles of an organism
-Homozygous: contains the same allele @ a single locus
-Heterozygous: contains 2 different alleles @ a single locus

17

Phenotype

a measurable trait an organism has
-i.e. hair color, eye color, blood type

18

Dominant allele

Phenotype can be seen in both the heterozygote and homozygote

19

Carrier

Heterozygous individual with a recessive alley that's hidden from phenotypic view by the dominant, normal allele
Ex: Cystic Fibrosis

20

Recessive allele

Produces this phenotype only when its paired allele is identical

21

Single Gene Disorders (Mendelia Disorders) Classification

-Autosomal or x-linked
-Dominant or recessive pattern

22

Mendel's Principle of segregation

One parent has 2 copies of a gene for trait, but transmits o only one via a gamete

23

Codominance

When two alleles for a trait are equally expressed
Ex: AB blood type

24

incomplete dominance

Heterozygotes have phenotypes that have both alleles visible as a blend (makes a third phenotype)
Ex: wavy hair, skin color

25

Pentrance

The probability that individuals in a population who have a particular gene combination will show the condition

26

Genetic marker

Sequence of DNA with a known location on a chromosome

27

Expression

The components of the phenotype that are exhibited in an individual
Ex: Myotonic muscular dystrophy- Two ppl carrying the this gene may express it differently (one has cataracts, the other has grip myotonia)

28

Anticipation

Genetic disease that increase in severity or have earlier onset with each successive generation
Ex: Huntingtons dz

29

Aneuploidy

Abnormal number of chromosomes
-Most common abnormality

30

Balanced chromosomal abnormalities

No net less or gain of chromosomal material, length is still the same
Types:
-Balanced translocation
-Inversion

31

Balanced translocation

Rupture of a chromosome resulting in the pieces "re-sticking" in the wrong combinations

32

Inversion

A chromosome piece is lifted out, turned around, and reinserted

33

Unbalanced chromosomal abnormalities

Additional or missing information
-Deletion
-Insertion (can be beneficial or lethal)

34

Unbalanced translocation

Tends to arise as an offspring of a balanced carrier

35

Robertsonian translocation

-involve 2 out of chromosomes 13, 14, 15, 21, and 22
-All acrocentric
-The bigger chromosome can produce an unbalanced gamete
-Chromosome 21= Down syndrome

36

What are the functions of a three-generation pedigree?

-Making a diagnosis
-Deciding on testing strategies
-Establishing the pattern of inheritance
-Identifying people at risk
-Educating the patient
-Determining reproductive options

37

Consultand

-The person seeking genetic advice
-Represented by an arrow on pedigree
-Can be healthy or a person with a condition

38

Proband

The affects individual

39

Characteristics of Autosomal Dominant (6)

1. Vertical pattern- Transmission passes from parent to offspring
2. Multiple generations affected
3. Variable expressivity- Affected individuals in same family may show varying degrees of phenotypic expression (severity)
4. Reduced Penetrance-Some with the genetic mutation may not show phenotype, making it appear that it "skipped" a generation
5. Males and females affected equally
6. Male-to-Male transmission can be seen

40

Autosomal Dominant

-65% of human monogenic disorders
-Mutations in a single allele can cause dz
-Affected individuals are HH or Hh

41

Autosomal Recessive

-25% of human monogenic disorders
-Two copies of diseased allele required for expressing the phenotype

42

Characteristics of autosomal recessive (5)

1. Horizontal inheritance-multiple affected offspring
2. Higher associated with consanguinity- closer relatives having children with each other
3. Males and females affected equally
4. Inheritance is from both parents, each being heterozygote/carrier
5. Each offspring has a 25% chance of being affected and a 50% chance of being a carrier

43

X-linked

-5% of human monogenic disorders
-Males are hemizygoes (heterozygous) for mutant allele the x
-->only have one x and don't have another x to overshadow it or cover it
-No male to male transmission is possible: Dad only gives his Y to his son (no x)

44

Multifactorial/Complex Disease

-Caused by interactions of variations in multiple genes and environmental factors
-Identified for complex conditions such as: Cancer, DM, asthma, heart dz, mental illness, cleft lip/cleft palate

45

Down syndrome

-Trisomy 21 (95%)
-Most common non-lethal trisomy
- 4% Roberstonian translocation
-Prenatal Testing: Quad screen & nuchal translucency (thickness of the skin
-Intellectual disability
-cardiac/GI defects, hearing loss, visual problem
-increased risk for alzheimer dz (half of adults)

46

Trisomy 18

-Edwards Syndrome
-2nd most common autosomal trisomy (after 21)
-Club foot (Rocker bottom feet)
-Low set ears, small jaw, development delay, kidney/GI/heart defects
-IUGR: Intrauterine growth restriction (retardation)
-High mortality rate

47

Trisomy 13

-Patau Snydrome
-Cleft lip/palate, polydactyly
-High mortality rate
-Most cases=3 copies of chromosome 13

48

Cri-du-Chat Syndrome

-Deletion of PART of short arm of chromosome 5
-Partial monosomy (when only a portion of a chromosome has one copy instead of two)
-Cat-like-Cry from abnormal larynx development
-Intellectual disability, wide set eyes, low ears

49

Klinefelter's Syndrome

-47XXY
-Occurs during gametogenesis
-Most common sex chromosome aneuploidy in males
-Affects male physical and cognitive development (becomes more apparent after puberty): Hypogonadism, Gynecomastia (development of breast), reduced body hair

50

Turner syndrome

-45X: Affects development in female
-Gonadal Dysgenesis (non-functional ovaries)
-Short stature, broad chest, webbed neck
-Amenorrhea, infertility

51

Huntington's Disease

-Neurodegenerative Dz: Progressive brain disorder
-HD Gene on chromosome 4 that codes for "Huntington" protein
-CAG Trinucleotide Repeat (36-120 repeats)
-Most cases are inherited: Autosomal dominant
-Genetic anticipation
-Early signs: Depression, irritability,
-Adult onset: genetic defect is latent for 3-5 decades
-Causes Chorea (involuntary jerking movements)
-ONLY human disorder of complete dominance

52

Alzheimers Disease

-Neurodegenerative dz
-Formation of plaques and tangles
-Most common form of dementia in older individuals
-Two forms of AZ dz:
1. Sporadic AZ (late onset)= Most cases, after age 65, chromosome 19 APOE gene increases risk
2. Familial AZ (early onset)= Rare, before age 65, autosomal dominant

53

Hereditary Breast and Ovarian Cancer

Two major cancer susceptibility genes:
1. BRCA1- Chromosome 17
2. BRCA2- Chromosome 13
-Mutated gene increases risk
-Autosomal dominant

54

Colorectal Cancer

-Diet, smoking and obesity increase risk more than genetics
Types of colorectal cancer:
1. Familial
-May be due to chance alone
-Shared exposure to a carcinogen or diet/lifestyle
-Combo of gene mutations/environment
2. Hereditary
-->Familial Adenomatous Polyposis (FAP)=less than 1%
-Hundred/thousands of polyps
-Autosomal dominant
-APC gene on chromosome 5
-Develops in 20's
-100% risk of developing CA before age 50
-->Nonpolyposis Colorectal Cancer (HNPCC)=Lynch Syndrome
-2-3% of all colorectal cancers
-Autosomal dominant
-Small number or no polyps
-50% chance in Women
-70% chance in Men
-Regular colonoscopy starting @ age 25 for relatives or beginning 5 years younger than affected family member
-Associated with formation of other cancers

55

Chronic Myelogenous Leukemia

-Myeloproliferative disorder
-More common in men (55 yrs)
-Translocation between chromosome 9-22
-Philadelphia chromosome 22
=Causes body to make too many WBC's (non-functional)- Takes up bone marrow space for healthy WBC's
-Fever, night sweats, fatigue
-Slow onset, progressive

56

Hemophilia

-Mutation on F8/F9 gene o x chromosome
-Males mainly affected
-Hemophilia A: F8 Gene= Most common
-Hemophilia B: F9 Gene= Christmas disease
-Hemarthrosis (popcorn)
=spontaneous bleeding into a joint

57

Sickle Cell Disease

-Mutation on HBB gene
-Autosomal RECESSIVE
-Atypical Hemoglobin molecules=Crescent shaped break down prematurely
-Anemia, infections, SOB, fatigue
-Common in specific areas

58

Cystic Fibrosis

-Autosomal RECESSIVE
-Mutation in the CFTR gene that codes for chloride channels in epithelial cells
-Water balance in secretions is disrupted= Thick, sticky mucus obstructing in airways in lungs and ducts of pancreas
-Failure to thrive, poor growth
-Meconium ileum (popcorn)
-->newborn intestinal obstruction due to thick fecal waste products
-Pulmonary dz= Most common cause of morbidity
-->pulmonary systems can't defend against pathogens well
-->Chronic sinus infections common in CF pt's (this isn't normal in kids)
-Sweat Chloride test

59

Marfan Syndrome

-Autosomal dominant
-Mutation on FBN1
-Defects in connective tissue (hyper flexible joints)
-Tall, long arms, arm span>height
-Dislocated lens of eye (popcorn)
-Aoritic aneurysm/dissection (popcorn)
-Advised to avoid sports, caffeine, decongestion to avoid increased stress on CV system

60

Neurofibromatosis Type 1

-Autosomal Dominant
-NF1 gene on chromosome 17=tumor suppressor gene
-Growth of neurofibromas on nerves of skin and brain
-Cafe-au-lait spots=Hyperpigmented skin
-Crowe sign= axillary/inguinal feckling
-Lisch nodule in eye

61

Polcystic Kidney Disease

-Fluid filled sacs in kidneys
-Can't filter blood properly
-->Kidneys enlarge and can fail
-HTN, back pain, hematuria, UTI's, kidney stones
-Increased risk of aortic/brain aneurysm
-Two forms:
1. Autosmal Dominant= more common, develop in adulthood
2. Autosmal Recessive= RARE, lethal early in life

62

Teratology

Study of abnormal development

63

Teratogens

-Anything capable of disrupting embryonic or fetal development and producing malformations
-Critical period for teratogenic effects is 3-16 weeks gestation
-Timing of exposure determines which systems are affected