topic 6 chromosomes Flashcards

1
Q

how can they be altered

A

• Description of completement of chromosomes
• Alterations -
Loss of whole chromosome or a major part =
reduced viability of a gamete

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
2
Q

what is aneuploidy

A

• Aneuploidy
○ Unbalanced chromosome complement
○ Fertilization of gametes in which nondisjunction occurred
§ Offspring with abnormal number of a chromosome
○ A trisomic zygote has 3 copies
A monosomic zygote only has one copy of a particular chromosome

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
3
Q

downsyndrome ex

A
• Down syndrome 
		○ Trisomy of chromosome 21 
		○ Most common human chromosome abnormality - 1 in approx 800 births 
		○ Frequency of having a down syndrome child increases w age of mother - correlation not explained
		○ Above 35 it increases 
		○ Paper in 2009 
		○ Mean maturnal age vs birth year 
		○ oogenesis
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
4
Q

describe oogenesis

A

• Begins in embryo
• Primordial germ cells become oogonia (both diploid)
• Oogonium:
○ Multiples by mitosis
○ Begins meiosis
Stops at prophase I - primary oocyte - @ puberty influence of FSH initiates division - secondary oocyte - arrested @ metaphase - ovulation completes maturation

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
5
Q

oogenesis down syndrome possible connection?

A
  • As a result, an egg produced by a 15 yr old is 15, therefore, one by 45 is 45 years old - bc meiosis stops at birth for eggs
    • Theory for down syndrome - multiple stops - halting at prophase 1 and metaphase 2 might be connected to disjunction at chromosome 21 - older age accelerates this chance
    • Up to 37 - mostly MM1 error
    • Past - mostly MMII
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
6
Q

maternal age connection to trisomy 21? is it confirmed?

A

• Likelihood of a chromosomal disorder caused by
an error in cell division increases with maternal
age
Allen et. al. (2009). Human Genetics Vol. 125
Significant association between advanced maternal age
and chromosome 21 nondisjunction was restricted to
meiotic (meiosis I & Il) errors in the ovum
Increased proportion of MMI cases among women < 15
& those 40-45 years of age
• Prevalence also known to vary by race/ethnicity
○ African: 7.3, White: 9.2, Hispanic: 11.8
○ Could be other mechanisms involved!
• Conclusion: jury is still out

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
7
Q

describe turner syndrome

A
  • Monosomy of X chromosomes (XO)
    • Sterile female
    • 1 in 5,000 female births
    • Also has common characteristics
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
8
Q

describe klinefelter syndrome

A
  • Ex. 3 klinefelter syndrome
    • Sex chromosomes - 2 X and one Y
    • Extra X in a male
    • Trisomy of sex chromosomes
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
9
Q
For alterations in the sex chromosomes in 
e 
which parent did nondisjunction occur? 
XO
XXX
XXY
XYY
A

• 1st either
• 2nd either
• 3rd either
4th father only

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
10
Q

what is polyploidy? how does it happen

A
• More than 2 sets of homologous chromosomes 
	• 
	• Many species of plants 
Fewer species of animals Failure of reduction 
division in meiosis 
produces unreduced 2N 
gametes => 3N zygote
	• 
	• Results in aneuploid gametes
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
11
Q

what is autopolyploids

A

c Autopolyploids
Multiple chromosome
sets originating from
within one species

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
12
Q

what is allopolyploid

A
Allopolyploids 
Multiple chromosome 
sets originating from 
two or more species 
Between closely 
related species
	• 
	• Allopolyploid - usually results in hybrids
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
13
Q

polyploidy in plants result

A
• Polyploids are often larger 
	& have larger component 
	arts than their relatives 
	• Epidermal leaf cells of tobacco plants 
Increase of cell size (evident 
in stoma size) with increase 
of ploidy 
x 2. grapes 
	• Tetraploid grapes are larger than diploid
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
14
Q

how can polyploidy occur in animals? ex?

A

• Via parthenogenesis
○ Flatworms, leeches, brine shrimps
○ Female doesn’t need sperm to multiply
• Salmonids

• Hybridization - are polyploid, all female for the minnows
Polyploid frogs & toads may participate in sexual
reproduction but salamanders & lizards are
parthenogenetic
Sterility of triploids has been commercially exploited
2N oysters become unpalatable during breeding season
3N’s are sterile; hence palatable year-round

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
15
Q

4 types of alternations to chromosome structure? what leads to them

A
Breakage of a 
chromosome leads to 
four types of changes in 
chromosome structure 
Deletion 
Removal of a segment 
Duplication 
Repetition of a segment 
Inversion 
Reversal of segment 
orientation within a 
chromosome 
Translocation 
Segment moving from one 
chromosome to another
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
16
Q

ex of chromosome alteration

A
• Certain cancers, including 
	chronic myelogenous 
	leukemia (CML), are 
	caused by translocations 
	of chromosomes 
Abnormally short 
chromosome 22 — the so- 
called "Philadelphia 
chromosome" & 
abnormally long 
chromosome 9 
Reciprocal translocation in 
a single blood cell 
precursor leading to all 
abnormal descendent cells 
	• Chromosome 9 and 22 leading to the formation of a short chromosome 22
17
Q

Human chromosome mutations: overall incidence?

A

• Surprisingly frequent in human sexual reproduction
○ Relevant cellular processes prone to high level of error
• Approx. 15% of conceptions abort spontaneously
○ 50% show chromosomal abnormalities
• 0.6% of live births also show abnormalities
○ From aneuploidy and rearrangements
• Study by griffiths

○ Suggests there is a strong incidence of abnormailities

18
Q

ex kayotype difference in deer but still look similar

A
2n=46 vs 2n=8 
i666Äapid and 
number reduction in Munoac Deer Inferred from 
.Mitochondria1 DNA Phylogeny. Evole. 
Karyotypic evolution in Muntjac proceeded 
via reduction in 2N number 
Rate of change in chromosome number in 
e 
Muntjac is one of the fastest among 
vertebrates 
e Involves many fusion
19
Q

summary

A

e Mutations are random; do not depend on their role in
advantage or disadvantage
Rate of mutation, by itself, quite low; but total input of
e
genetic variation by mutation has significant contribution
in evolutionary process
o Polyploidy, translocations, fusions, or fissions of
chromosomes are extremely important for evolution of
chromosome number
e Mutations of karyotype include polyploidy & structural
rearrangements
Many of them may have reduced fertility in heterozygous condition
Related species may differ strikingly in karyotype but not
in phenotype