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Genetics > Chapter 8 > Flashcards

Chapter 8 Flashcards

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Biology 101 flashcards
1
Q

Chromosome mutation

A

Variations in chromosome number and or structure do periodically arise

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2
Q

Chromosome morphology

A

Position of the centromere on the chromosome

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3
Q

Metacentric

A

centromere in middle of chromosomes

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4
Q

Submetacentric

A

centromere so placed that it divides the chromosome into two arms of unequal length

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5
Q

Acrocentric

A

centromere is very close to one end of chromosome

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6
Q

Telocentric

A

centromere is placed very close to the end of the chromosome

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7
Q

Karyotyping

A
  • Chromosomes prepared from actively dividing cells
  • Halted in metaphase preventing from going into anaphase

-Chromosomes arranged according to size

-helps identify abnormalities

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8
Q

Three processes of mutation

A
  • Chromosome rearrangements: structural
  • Aneuploidy: Number of chromosomes altered ( one or more individual chromosomes are added or deleted)
  • Polyploidy: Number of chromosomes ( seen in plants One or more complete sets of chromosomes are added, 3n,4n…)
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9
Q

Chromosome Rearrangements do..

A

Alter the structure of the chromosomes.

deleted or duplicated chromosomes

Double-stranded breaks in DNA often cause cell death.

Mechanisms help repair breaks, but they are sometimes incorrect! (Leads to chromosome rearrangement!)

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10
Q

Four basic types of rearrangements:

A

1.Duplications
2.Deletions
3.Inversions
4.Translocations

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11
Q

Chromosome rearrangements are

A

chromosome mutations that change the structures of individual chromosomes.

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12
Q

Chromosome rearrangement can also arise through

A

errors in crossing over or when crossing over occurs between repeated DNA sequences.

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13
Q

Chromosome Duplication

A

Tandem – duplicated segment immediately adjacent to the original segment (i.e. AB CDEFEFG)

Displaced duplication – duplicated segment is some distance from the original (either on the same or different chromosome) (i.e. AB CDEFGEF)

Reverse duplication – duplicated region is inverted

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14
Q

segmental duplications

A

duplications greater than a thousand base pairs.

Most segmental duplications are intrachromosomal (two copies found on the same chromosome) but others are interchromosmal (two copies found on different chromosomes).
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15
Q

Effects of Chromosome Duplication

A

When an individual has a duplication on one chromosomes (heterozygous for duplication) – pairing can arise at prophase I of meiosis.

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16
Q

Chromosome Deletions

A

loss of a chromosomal segment (i.e. AB CDEFG undergoes deletion EF to become AB CDG)

Large deletions easily detected - chromosome is noticeably shorter!

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17
Q

Effects of Deletions

A

Phenotypic consequences depend on which genes are located in the deleted region!

If deletion includes centromere – chromosome will not segregate in meiosis or mitosis.

Many deletions are lethal in the homozygous state - essential genes in that region are lost.

Imbalances in gene product may occur.

Expression of a normally recessive gene may occur (pseudodominance).

Some genes require two copies for normal function. When a single copy of a gene is not sufficient to produce a wild-type phenotype, that gene is said to be haploinsufficient.

18
Q

Inversion

A

chromosome segment is inverted – turned 180 degrees. (i.e. and inversion in ABCDEFG could be ABCFEDG)

19
Q

Paracentric inversion –

A

does not include the centromere (i.e. AB*CFEDG)

20
Q

Pericentric inversion

A

– does include the centromere (i.e. AC*BDEFG)

21
Q

Effects of Inversions

A

An inversion may break a gene into two parts.
One part may move to a new location, destroying the function of that gene!

Many genes are regulated in a position-dependent manner – if position changes, their expression may be altered – referred to as position effect.

22
Q

Inversions in meiosis

A

Individuals homozygous: no problems arise during meiosis

Individuals heterozygous:
Homologous sequences align only if the two chromosomes form an inversion loop

23
Q

Nonreciprocal translocation

A

– genetic material moves from one chromosome to another without any reciprocal exchange.

Consider AB CDEFG and MN OPQRS;
if EF moves and creates chromosomes AB CDG and MN OPEFQRS

24
Q

Reciprocal translocation

A

– two way exchange of segments between chromosomes
Consider AB CDEFG and MN OPQRS;
If EFG exchanges with QRS, so now - AB CDQRS and MN OPEFG

25
Q

Translocation

A

a segment of a chromosome that moves from one chromosome to a nonhomologus

26
Q

Effects of Translocations

A

Translocations can physically link genes that were formally located on different chromosomes.

New linkage may affect gene expression

The chromosome break that brings about translocations may take place within a gene and disrupt its function.

27
Q

Robertsonian translocation

A

– long arms of two acrocentric chromosomes become joined to a common centromere through a translocation.

28
Q

Fragile Sites

A

– Sites that develop constrictions or gaps when the cells are grown in culture and are prone to breakage under certain conditions.

29
Q

Common sites

A

– present in all humans and are normal features of chromosomes.

30
Q

Rare sites

A

– found in few people and exhibit Mendelian inheritance.

31
Q

Copy-number variations

A

– the number of copies of a particular gene varies from person to person

32
Q

Structural variants

A

– chromosome rearrangements and copy number variations

33
Q

Aneuploidy

A

change in the number of individual chromosomes

34
Q

Polyploidy

A

– increase in the number of chromosome set

35
Q

Causes of aneuploidy:

A

Deletion of centromere during mitosis and meiosis

Robertsonian translocation

Nondisjunction

36
Q

Types of Aneuploidy

A

Nullisomy: loss of both members of a homologous pair of chromosomes; 2n − 2
i.e humans 2n = 46, nullisomic zygotes has 44 chromosomes.

Monosomy: loss of a single chromosome; 2n − 1

Trisomy: gain of a single chromosome; 2n + 1

Tetrasomy: gain of two homologous chromosomes; 2n + 2

37
Q

Effects of aneuploidy in humans

A

Turner syndrome; XO
Klinefelter syndrome; XXY

Autosomal aneuploids:
Trisomy 21: Down syndrome

38
Q

genetic mosaicism

A

Regions of the tissue with different chromosome constituents

39
Q

Autopolyploidy

A

Accidents of mitosis or meiosis that produce extra sets of chromosomes, all derived from single species

40
Q

Allopolyploidy

A

Hybridization between two species, the resulting polyploid carries chromosome sets derived from two (or more) species

41
Q

The significance of polyploidy:

A

Increase in cell size
Larger plant attributes
Evolution: may give rise to new species

Genetics (19 decks)

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