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Anatomy > ANA 209 Human Genetics > Flashcards

ANA 209 Human Genetics Flashcards

1
Q

definition of heredity

A

passing of a trait from parent to offspring

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2
Q

What is genetics

A

the study of heredity

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3
Q

what is the law of segregation?

A

The law of segregation states that during the production of gametes, alleles segregate from each other during meiosis, so that offspring acquire one factor from each parent
Also known as the first law of inheritance

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4
Q

What is the law of dominance?

A

states that hybrid offspring will only exhibit the dominant trait in the phenotype

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5
Q

What is the law of independent assortment?

A

states that alleles will assort independently of one another during gamete formation
2nd law of inheritance

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6
Q

Gene

A

Basic unit of heredity

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7
Q

Allele

A

variation of a gene

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8
Q

Homozygous

A

an individual with 2 identical alleles

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9
Q

Heterozygous

A

an individual with 2 different alleles

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10
Q

Genotype

A

the composition of alleles in an individual

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11
Q

Phenotype

A

The physical appearance of an individual

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12
Q

Gene locus

A

a specific position on a chromosome where a gene is located

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13
Q

cytogenetics

A

the study of chromosomes

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14
Q

Chromosome

A

a thread-like structure consisting of DNA

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15
Q

Chromatid

A

A chromatid is one of the two identical halves of a chromosome that has been replicated in preparation for cell division.

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16
Q

Parts of a chromosome

A

Chromatid
centromere
telomere

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17
Q

Telomere

A

A telomere is a region of repetitive DNA sequences at the end of a chromosome

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18
Q

Genome

A

Genetic material of an organism

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19
Q

Types of chromosomal abnormalities

A
  1. Numerical abnormalities
  2. Structural abnormalities
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20
Q

What is continuous variation?

A

Continuous variation is the type of genetic variation showing an unbroken range of phenotypes in a population

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21
Q

What is discontinuous variation?

A

discontinuous variation is where the different types of variations are placed into discrete categories.
It cannot be measured or quantified
It is caused by a small number of genes. The environment has little or no effect e.g. blood group and eye color

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22
Q

Incomplete dominance

A

Both alleles of a gene at a locus are partially expressed, often resulting in an intermediate phenotype of e.g skin and hair

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23
Q

Based on the position of centromere and length of chromosomal arms, the chromosomes are classified into 4 groups:

A

(1). Telocentric chromosomes
(2). Acrocentric chromosomes
(3). Sub-metacentric chromosomes
(4). Metacentric chromosomes

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24
Q

Describe a Telocentric chromosome

A
  1. Centromere is located at the proximal end (tip/telomere) of the chromosome
  2. Long rod-like
  3. Appear as an ‘i’ shaped strcutre in metaphase stage
  4. Only had one chromosome arm (q arm)
    5.very rare, reported in very few speciea
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25
Q

Describe Acrocentric chromosomes

A
  1. Very short p arm and vert long q arm
  2. Appears as a ‘J’ shaped structure in metaphase
  3. Acrididae group (grasshoppers) show this type of chromosomes
  4. Aka sat chromosomes
  5. In humans Chromosomes 13,15,21, and 22 are sat-acrocentric
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26
Q

Describe Sub-metacentric chromosomes

A
  1. Centromere is located near the center (not the exact center) of the chromosome
  2. Unequal arms (small p and large q)
  3. Appears ‘L’ shaped during metaphase
  4. Majority of human chromosomes are sub-metacentric
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27
Q

Describe metacentric chromosomes

A
  1. Centromere at the exact center
  2. 2 equal size arms
  3. Primitive type
  4. Seen in amphibians
  5. Seen in humans in chromosome 1 and 3
  6. Appear ‘V’ shaped during metaphase
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28
Q

Types of chromosomal abnormalities (based on type of change)

A
  1. Structural changes: Any change which alters the basic chromosome structure is known as a structural change.
  2. Numerical changes
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29
Q

Types of Structural changes in chromosomal abnormalities

A

Deletions
Duplications
Translocations
Inversions

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30
Q

What is deletion?

A

A portion of the chromosome is missing or deleted. The chromosome becomes shorter due to the loss of one or more genes.
Large deletions will most probably be lethal
Smaller deletions may allow survival
E. coli: deletions of up to 1% have been observed in living cells
D. melanogaster : deletions of up to 0.1% observed

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31
Q

What is duplication?

A

A portion of the chromosome is duplicated, resulting in extra genetic material.

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32
Q

Give examples of deletions in humans

A
  1. Cri-du-chat syndrome
    Microdeletion of chromosome 5
  2. Di-George syndrome
    Micro deletion of chromosome 22
  3. Schizophrenia & Obsessive Compulsive Disorder
    Micro deletion of chromosome 22 associated
  4. Angelman syndrome
    Micro deletion of chromosome 15
  5. Prader-Willi syndrome
    Micro deletion of chromosome 15
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33
Q

What is Cri-du-chat syndrome?

A

1st autosomal deletion on chromosome 5
Characteristic cat-like cry, which disappears with age
Microcephaly (small head)
Severe mental retardation
Congenital heart disease
Hypertelorism (widely separated eyes)
Low birth weight and poor growth
Severe cognitive, speech, and motor delay
Behavioral problems
Excessive drooling

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34
Q

What is Prader-Willi Syndrome

A

Lack of muscle tone in newborn
Poor swallowing reflex
As adult - gross obesity
Mean I.Q. ~ 50
Microdeletion of 15

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35
Q

What is Cri-du-chat syndrome?

A

1st autosomal deletion described
Characteristic cat-like cry, which disappears with age
Microcephaly (small head)
Severe mental retardation
Congenital heart disease
Hypertelorism (widely separated eyes)
Low birth weight and poor growth
Severe cognitive, speech, and motor delay
Behavioral problems
Excessive drooling
Deletion in chromosome 5

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36
Q

What is Angelman Syndrome

A

Developmentally delayed
Jerky movements
Stiff, fixed smile
Uncontrolled laughter
Abnormal E.E.G., epilepsy
Microdeletion of 15

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37
Q

What is translocation?

A

A portion of one chromosome is transferred to another chromosome. There are three main types of translocation.
Simple translocation- In simple translocation, segment from one chromosome will break and attached to another chromosome.
Reciprocal translocation- In a reciprocal translocation, segments from two different chromosomes have been exchanged.

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38
Q

What is Robertsonian translocation?

A

Robertsonian translocation- In a Robertsonian translocation, an entire chromosome arm has attached to another at the centromere.
Loss of chromosomal segment.

39
Q

What is an isochromosome?

A

Centromere of the chromosome divides transversely instead of longitudinally
One arm is missing and the other arm duplicated

40
Q

What is a ring chromosome?

A

Occurs due to loss of both the ends of a chromosome
The broken ends rejoin to form a ring-like chromosome
Rare anomaly

41
Q

What are the two types of robertsonian changes in chromosomes?

A

Fusion: 2 chromosomes join to form one
Fission: One chromosome split to form 2

42
Q

What is inversion?

A

A portion of the chromosome has broken off, turned upside down, and reattached. As a result, the genetic material is inverted.
An inversion is produced when there are two breaks in a chromosome and the intercalary segment reunites in reverse order i.e., the segment rotate by 180°.

43
Q

Types of inversion

A

Pericentric inversion- If the inverted segment includes the centromere, the inversion is called pericentric inversion

Paracentric inversion- If it does not include centromere the inversion is called paracentric inversion.

44
Q

Codominace

A

Both alleles are expressed in the offspring e.g. ABO blood grouping

45
Q

Causes of variation

A

Crossing over
Recombination
Mutation
Environmental effects

46
Q

What are heteroploids?

A

Individuals possessing the variant chromosome numbers

47
Q

Types of heteroploidy

A
  1. Aneuploidy
  2. Euploidy
48
Q

Aneuploidy

A

•It involves addition or deletion of one or few chromosomes to the usual diploid set of chromosomes.
•Aneuploid changes in chromosome number do not involve the whole genome

49
Q

Types of Aneuploidy

A

Hypoploidy: Monosomy (2n-1) Nullisomy (2n-2)
Hyperploidy Trisomy (2n+1) Tetrasomy (2n+2)

50
Q

Hypoploidy

A

They arise by the loss of one chromosome from the diploid set i.e., 2n-l.

51
Q

Describe monosomies of chromosomes

A

•Presence of only one member of a chromosome pair in a karyotype
•More detrimental than equivalent trisomy
•Can involve autosomes or sex chromosomes
•Usually abort spontaneously
•Monosomy of X chromosome results in XO condition called Turner syndrome

52
Q

What is Turner syndrome?

A

•Chromosome complement: 45,XO
•Phenotype: Female
•Incidence: 1:5000-8000

53
Q

Features of Turner syndrome

A

•Short statured female
•Sexual infantilism with primary amenorrhoea and sterility
•Short, webbed neck
•Prominent ears with defective hearing
•Small mandible
•Defective vision
•Epicanthal folds
•Low posterior hair line
•Cubitus valgus
•Broad chest with widely spaced nipples
•Cardiovascular anomalies
•Hyperconvex finger nails
•Pigmented nevi
•Sex chromatin negative

54
Q

What is amenorrhea going

A

Absence of menstruation due to underlying disease or condition

55
Q

What is cubitus valgus?

A

Cubitus valgus is a deformity in which the forearm is angled out away from the body when the arm is fully extended.

56
Q

Nullisomy

A

These arise by the loss of a particular pair of chromosomes i.e., 2n-2.

57
Q

Trisomy

A

These arise by addition of an extra chromosome to the normal diploid set with the genetic formula, 2n + 1.

58
Q

Examples of trisomy if sex chromosomes

A

•Klinefelter syndrome
•Triple X syndrome
•Double Y syndrome

59
Q

What is Klinefelter syndrome?

A

*Chromosome complement: 47,XXY
*Phenotype: Male
*Incidence: 1:1000

60
Q

Features of Klinefelter Syndrome

A

Tall stature; thin build; long lower limbs
•Testicular atrophy
•Female pattern of pubic hair
•High pitched voice
•Infertility (aspermatogenesis)
•Gynaecomastia
•Low level of intelligence
•Serum testosterone levels low to normal
•FSH and LH levels very high
•Sex chromatin positive

61
Q

What is Testicular atrophy?

A

Testicular atrophy refers to the shrinking of testicles

62
Q

Triple X syndrome (superfemale)

A

•Chromosome complement: 47,XXX
•Phenotype: Female
•Incidence: 1:1000

63
Q

Features of triple X syndrome

A

•Normal in appearance
•Difficulty in speech, learning and emotional responses
•Mild mental retardation in 15-25% cases
•Two sex chromatin Barr bodies
•Infertility
•Wide-set eyes
•Amenorrhoea
•Expressionless face
•Enamel hypoplasia
•Deficient language skills
•Delayed development of motor skills

64
Q

What is enamel hypoplasia?

A

Dental enamel hypoplasia is an enamel defect characterized by thin or absent enamel

65
Q

What is a Barr body?

A

the inactive X-chromosome in the somatic cells of mammalian females

66
Q

Double Y syndrome

A

•Chromosome complement: 47,XYY
•Phenotype: Male
•Incidence: 1:1000

67
Q

Features of double y syndrome

A

•Normal in appearance
•Tall stature
•Aggressive behaviour
•Problems in motor and language development

68
Q

Tetrasomy

A

•These arise by the addition of an extra pair of chromosome to the diploid set with a chromosomal formula 2n + 2.
•By this a particular chromosome is represented in four doses instead of normal two.

69
Q

Euploidy

A

addition or loss of complete one set (n) or more than one set of chromosomes

70
Q

Types of Euploidy

A

Monoploidy: Presence of a single copy of a single genome is known as monoploidy, denoted by x.

Polyploidy: Organisms having more than two normal sets of chromosomes (2n) are called polyploids.

Organisms with three sets of chromosomes (2n + n) = 3n, are triploids.
•Those with four sets of chromosomes (2n + 2n) = 4n, are tetraploids and those with five sets (2n + 3n) = 5n, are pentaploids and so on.

71
Q

Mechanism of polyploidy

A

(a)Failure of pulling apart of 2 chromatids to opposite ends after metaphase stage of mitosis.

(b)Reduplication of chromosomes without dissolving of nuclear membrane.

(c)Failure of cytoplasmic division.

72
Q

Types of polyploids

A

*Autopolyploids and allopolyploids

73
Q

Autopolyploidy

A

Autopolyploids are those polyploids which have same basic set of chromosomes multiplied.
For instance, if a diploid species has two similar sets of chromosomes (AA), an autotriploid will have three similar sets (AAA) and an autotetraploid will have four such sets (AAAA).

74
Q

Allopolyploidy

A

*Allopolyploids are those polyploids which contains two or more distinct (different) genomes.
* If we double the chromosome number in a F1 hybrid (AB) which is derived from two distinctly different species, the resulting polyploidy will be allotetraploid (AABB).
*common wheat is an allohexaploid having genome configuration AABBDD (three distinct species).

75
Q

Mechanism of Aneuploidy

A

Non-dysjunction: failure of separation of chromosomes during cell division.
•Formation of 2 types of gametes (both abnormal)
•Fusion of either of these abnormal gametes with a normal gamete can result in trisomy or monosomy
•May involve autosomes or sex chromosomes

76
Q

Examples of trisomy’s of autosomes

A

*Trisomy 13 or D-trisomy (Patau syndrome)
*Trisomy 18 or E-trisomy (Edward syndrome)
*Trisomy 21 or G-trisomy (Down syndrome)

77
Q

Trisomy 13 (Patau Syndrome)

A

•1st described by Bartholin (1657) & redefined by
Patau (1960).

•Chromosomal complement: 47,XX,+13 (female) or
47,XY,+13 (male)

•Phenotype: Male or female

•Incidence: 1:12,000 (increases with the age of
mother)

78
Q

Features of Patau syndrome

A

Mental deficiency
•Low birth weight
•Abnormal development
of frontal lobe
•Absence of corpus callosum
•Hypoplasia of cerebellum
•Sloping forehead
•Scalp defects
•Malformed ears
•Congenital heart defects
•Renal tract anomalies
•Microphthalmia
•Bilateral cleft lip/palate
•Polydactyly with
rudimentary digits
•Rocker-bottom heel

79
Q

Trisomy 18 (Edward Syndrome)

A

•Chromosomal complement: 47,XX,+18 (female) or
47,XY,+18 (male)

•Phenotype: Male or female

•Incidence: 1:8000

80
Q

Features of Edward Syndrome

A

•Mental deficiency
•Growth retardation
•Prominent occiput with elongated head
•Webbing of the neck
Short sternum
Micrognathia

•Low-set malformed ears
•Ventricular septal defects
•Renal anomalies
•Clenched fists with overlapping of fingers
•Hypoplastic nails

81
Q

Micrognathia

A

Micrognathia is a condition in which the mandible is undersized (madibular hypoplasia)

82
Q

What is hypoplasia?

A

Hypoplasia is the incomplete development or underdevelopment of an organ or tissue.

83
Q

Trisomy 21 (Down Syndrome)

A

•Chromosomal complement: 47,XX,+21 (female) or 47,XY,+21 (male)
•Phenotype: Male or female
•Incidence: 1:800 (increases with the age of mother)

84
Q

Features of Down Syndrome

A

•Short height
•Severe mental deficiency with decline in the IQ with age
•Brachycephaly with flat face and occiput
•Flat and low nasal bridge
•Upward slant to palpebral fissures

•Malformed large ears
•Epicanthal folds of the eyes
•Brushfield spots in iris
•Renal anomalies
•Prominent and protruding tongue (scrotal tongue)
•Simian crease
•Clinodactyly of 5th digit

85
Q

What is Brachycephaly?

A

is an infant skull deformity characterized by a shortened anteroposterior skull length and a widened biparietal diameter (a flattened area at the back of the skull)

86
Q

What is simian crease/ single palmar crease

A

A single palmar crease (simian crease) is a single line that runs across the palm of the hand. People most often have 3 creases in their palms.

87
Q

What are Brushfield spots?

A

Brushfield spots are small, white or greyish/brown spots on the periphery of the iris in the human eye due to aggregation of connective tissue, a normal constituent of the iris stroma

88
Q

What is clinodactyl?

A

Fingers curving to one side

89
Q

What are the palpebral fissures?

A

The palpebral fissure is the area between the open eyelids.

90
Q

What is the occiput?

A

Back of the head

91
Q

What is microphthalmia?

A

Microphthalmia is when one or both of a baby’s eyes are small

92
Q

What is a ventricular septal defect (VSD)?

A

A ventricular septal defect (VSD) is a hole in the heart. It’s a common heart problem present at birth (congenital heart defect)

93
Q

What are hypoplastic nails?

A

the nails in young children, especially the toenails, may be unusually small and underdeveloped

Anatomy (17 decks)

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