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From Flashcardlet > Human Genetics chapter 6 > Flashcards

Human Genetics chapter 6 Flashcards

0
Q

Metacentric

A

Describes a chromosome that has a centrally placed centromere and equal arm lengths

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1
Q

Centromere

A

A region of a chromosome to which spindle fibers attach during cell division. The location of a centromere gives a chromosome it’s characteristic shape.

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2
Q

Submetacentric

A

Describes a chromosome whose centromere is placed closer to one end than the other, unequal length arms

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3
Q

Acrocentric

A

Describes a chromosome whose centromere is placed very close to, but not at, one end.

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4
Q

Sex chromosomes

A

In humans the X and Y chromosomes that are involved in sex determination.

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5
Q

Autosomes

A

Chromosomes other than the sex chromosomes. In humans, chromosomes 1 to 22 are Autosomes.

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6
Q

Telomere

A

Short repeated DNA sequences located at each end of chromosomes

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7
Q

How to determine a gene locus

A

Address includes (EX. 1q2.4) p= short petit arm (always on top) q=long arm (always on bottom)

  1. Chromosome 1
  2. The arm (p or q)
  3. The region
  4. The band
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8
Q

G- banding (giemsa-stained)

A
  1. Identifies areas of low gene density

2. Stains areas rich in A’s and T’s

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9
Q

Karyotype

A
  1. A complete set of chromosomes from a cell that has been photographed during cell division (metaphase) and arranged in a standard sequence (according to size and centromere location)
  2. Identifies chromosome number
  3. sex chromosome content
  4. presence or absence of individual chromosomes
  5. nature and extent of detectable structural abnormalities.
  6. Chromosome painting makes identifying occurrences straightforward
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10
Q

Symbols of Abnormalities

A
  1. t= translocation (non homologous swapping)
  2. Del= deletion of segments on the chromosome
  3. Dup= duplication of chromosome segment
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11
Q

Amniocentesis
When?
Why do it?

A
  1. A method of sampling the fluid surrounding the developing fetus by inserting a hollow needle and withdrawing suspended fetal cells and fluid; used in diagnosing fetal genetic and developmental disorders; usually performed in the 16th week of pregnancy.
  2. Restricted to certain circumstances because of risk factors
  3. When the mother is over age 35 (high risk of chromosome abnormalities increase at this age)
  4. Mother has already had a chromosome aberration (deviation from normal)
  5. When either parent carries one or more structurally abnormal chromosomes
  6. Mother carries a disorder caused by a gene on X chromosome
  7. Couple has previous miscarriages or unexplained fertility problems
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12
Q

Chorionic villus sampling(CVS)

A

A method of sampling fetal chorionic cells by inserting a catheter through the vagina or abdominal wall into the uterus. Used in diagnosing biochemical and cytogenetic defects in the embryo. Usually performed in the eighth or ninth week of pregnancy.

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13
Q

Euploidy

A

Normal diploid number in somatic cells and haploid number in gametes

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14
Q

Polyploidy
Why does it occur?
Give examples

A
  1. A chromosomal number that is a multiple of the normal haploid chromosomal set.
  2. Occurs from errors in meiosis during gamete formation, events at fertilization, errors in mitosis after fertilization
  3. These become Triploid (3n) or Tetraploidy (4n)
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15
Q

Triploidy
Why does it happen?
Is it lethal?

A
  1. A chromosomal number that is three times (3n) the haploid number, having three copies of all Autosomes and three sex chromosomes.
  2. Most common form of polyploidy (15%-18% of miscarriages)
  3. Lethal condition
  4. 75% have two sets of paternal chromosomes (69, XYY) arising from dispermy (two sperms in one egg)
16
Q

Tetraploidy

Why does it happen?

A
  1. A chromosomal number that is four times the haploid number, having four copies of all Autosomes and four sex chromosomes
  2. 5% of miscarriages, rare in live births
  3. Results from failure of cytokinesis in first mitotic division after fertilization
  4. Results from changes in number of gene copies not mutation.
17
Q

Aneuploidy
Ex.?
Which type of chromosome is more affected?

A
  1. Aneuploidy Changes the number of individual chromosomes in the set
  2. EX. Monosomy 2n-1, trisomy 2n+1
  3. Aneuploidy of the sex chromosomes more common than autosomal aneuploidy
18
Q

Nondisjunction

A
  1. The failure of homologous chromosomes to separate properly during meiosis or mitosis (anaphase)
  2. Most common cause of aneuploidy
19
Q

Monosomy

Is it lethal?

A
  1. one member of a chromosomal pair is missing; having one less than the diploid number (2n-1)
  2. Lethal
20
Q

Trisomy

Lethal?

A
  1. Addition of one chromosome to a diploid set (2n+1)

2. Common, trisomy 21 can live into adulthood

21
Q

Trisomy 21

A
  1. A diploid involving the presence of an extra copy of chromosome 21, resulting in Down syndrome
  2. 1 in 800 live births
  3. Wide, flat skull, folds in the corners of eyelids, spots in irises
  4. Mental retardation, heart defects, growth and behavior problems
  5. Develop leukemia and Alzheimer’s more often
  6. Few reach the age of 50
  7. Leading risk factor is maternal age, significantly women over 35
  8. Maternal age leading factor, by age 35 1 in 111
  9. Non disjunction in 94% of the time in the mother for trisomy
22
Q

Turner syndrome

A
  1. A monosomy of the X chromosome (45,x) that results in female sterility.
  2. Short, wide chested, undeveloped ovaries, puffy hands and feet
  3. No mental retardation, 1 in 10,000 births
23
Q

Klinefelter syndrome

Why does it happen?

A
  1. Aneuploidy of the sex chromosomes involving an XXY (males) chromosomal constitution
  2. Fertility problems
  3. 1 in 1,000 male births
  4. Results from maternal non disjunction
  5. More X chromosomes more phenotypic symptoms
24
Q

XYY Karyotype

Normal?

A
  1. Aneuploidy of the sex chromosomes involving an XYY chromosomal constitution
  2. 1 in 1,000 male births
  3. Phenotypically and socially normal
25
Q

Cri du chat syndrome

A
  1. A delation of the short arm (p) of chromosome 5
  2. Infants have cat like cry
  3. Facial abnormalities
  4. Severe mental retardation
26
Q

Uniparental disomy (UPD)

A

A condition in which both copies of a chromosome are inherited from one parent.

27
Q

How many chromosomes does a fruit fly have? Corn?

A
  1. 8

2. 20

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