Lecture 4, 5, 6, 7 & 8 Flashcards
(85 cards)
1
Q
Locus
A
the specific place on a chromosome where a gene is located
2
Q
each individual has 2 alleles, however…
A
there can be many different alleles in the population (sometimes >100)
3
Q
Mitosis (x4)
A
- 1 division
- 2 identical daughter cells
- Somatic cell
- For growth and repair
4
Q
Meiosis (x3)
A
- 2 divisions
- 4 haploid daughter cells
- for the production of sperm/egg/gametes
5
Q
heteromorphic chromosomes
A
different looking chromosomes
6
Q
What did the Datura plants show
A
Are aneuploidy- addition of new chromosomes created different looking plants -> chromosomes = different and carry genes
7
Q
What did Morgans data show
A
That linked genes in a dihybrid may be present in 2 configurations:
- Cis configuration
- Trans configuration
8
Q
Cis Configuration
A
(adjacent) the 2 dominant alleles are present on the same homolog
9
Q
Trans Configuration
A
(opposite) the 2 dominant alleles are on different homolog
10
Q
Result from dihybrid crosses & linkage (ratios)
A
- 2 equally frequent NON-RECOMBINANT classes totaling GREATER than 50%
- 2 equally frequent RECOMBINANT classes totalling LESS THAN 50%
11
Q
What is the relationship between distance and amount of crossing over and recombination
A
- further apart = more crossing over & higher recombination number
- closer together = less crossing over, very low recombination number
12
Q
Morgan suggested that recombination is bought about by…
A
Chiasma formation
13
Q
When does Chiasma formation occur
A
during zygotene/pachytene of meiotic prophase 1
14
Q
What is Chiasma
A
Sites of crossing over
15
Q
Morgan’s Data
A
homozygous recessive X homozygous dominant
=heterozygous
F1: heterozygous X homozygous(tester) = F2 ( P, P, Recombinant, recombinant)
16
Q
INTERchromosomal recombination
A
the genes are on DIFFERENT chromosomes resulting in EQUAL frequencies of recombinant and partenal classes
p: 1/4
p: 1/4
r: 1/4
r: 1/4
1: 1:1:1 ratio
17
Q
INTRAchromosomal recombination
A
Mediated by CHIASMA FORMATION where the RECOMBINANT classes are LESS frequent.
p: >1/4
p: >1/4
r: < 1/4
r: <1/4
18
Q
Bivalents are…
A
paired homologous chromosomes. Formed during recombination
aka Tetrad
contain 4 chromatids or 2 pairs of sister chromatids
19
Q
Frequency of recombination =
A
total n# of recombinant gametes / total n# of parental gametes x 100/1
20
Q
Recombinant frequencies can’t be greater than:
A
50%
21
Q
The further apart genes are, the closer or further the recombination frequency gets to 50%
A
Closer
22
Q
Relative position and physical position are or are not the same
A
are not necessarily the same
23
Q
mu =
cM =
A
map units
centimorgans
24
Q
1mu or 1cM is defined as:
A
the distance between genes for which 1 product of meiosis out of 100 is recombinant
25
1cM = recombination frequency of __%
1%
26
If all progeny of a test cross have EQUAL amounts of recombinant and nonrecombinant then is..
Independent assortment on different chromosomes
27
If all progeny of a test cross do NOT have equal amounts of recombinant and nonrecombinant then...
recombination is occuring on the same chromosome
28
Why is genetic mapping not efficient. What is more efficient
- several 2-point crosses have to be carried out
- double crossovers are missed
- three-point test cross is more efficient
29
In recombinant chromosome resulting from double crossing what gene(s) are altered
Only the middle gene is altered
30
linkage group =
chromosome
31
Crossing over occurs how many times in a chromosome
1-3 times
32
Frequency of progeny for parental type, for single crossing over and double crossing over types
parental type = highest number
single crossing over = medium number
double crossing over = lowest number
33
Frequency of progeny for parental type, for single crossing over and double crossing over types
parental type = highest number
single crossing over = medium number
double crossing over = lowest number
34
To determine the gene order in a three-point cross:
compare the highest number (nonrecomninant progeny) and the lowest number (double-crosing over). They should be alike in 2 characteristics and differ in 1 characteristic. This different one is encoded by the middle gene
35
Expected frequencies of double crossing over =
(recombinant f x recombinant f ) x total gametes
36
Interference=
| % expected of double crossover progeny were not observed because of interference
1 - Coefficient of coincidence
37
Interference=
1 - Coefficient of coincidence
38
I =0
I = 1
I <1
I =0 no interference (equal expected and observed)
I = 1 complete interference (no observed db cross)
I <1 fewer recombinants that expected
39
each meiocyte produces:
a linear array of 8 ascospores called an octad (octad of 4 spore pairs)
40
Why cant centromeres be mapped
because they show no heterozygosity (variation)
41
However in ______ you can map the centromere
Fungi
42
Centromere mapping involves:
estimating the distance from a locus to the centromere
43
What are the 2 patterns of alleles observed in the tetrad or octad
4:4 or 2:2:2:2
44
How do you get the 4:4 allele pattern
First division segregation (M1 pattern). Arises when there is no crossing over between the gene and the centromere
45
How do you get the 2:2:2:2 allele pattern
Second division segregation (M2 pattern). Arises when there is a crossover between the gene and teh centromere
46
- There are __ different spore arrangements/patterns from the 4:4 and 2:2:2:2 allele pattern
- What are they?
- What ones are Recombinants
- How do they arise
```
.Six
AAAAaaaa
aaaaAAAA
AAaaAAaa (recombinant)
aaAAaaAA (recombinant)
AAaaaaAA (recombinant)
aaAAAAaa (recombinant)
```
Arise as the centromeres attach to the spindle at random
47
How to calculate map distance of gene from centromere?
| Very Important
Sum of the total of 2nd division (recombinants) / total Octads x100/1
This tells us that a crossover occurs in _% of meioses
Divide by 2 to get the map distance as half of the products of meiosis didn't recombine
48
Crossing over is a ___ and ____ process of chromatids
How was this found out?
The Harlequin chromosomes also showed this...
break and rejoining.
Found out by McClintock & Creighton using 'marked' chromosomes in maize: segment and knob- all recombinants had either the segment OR the knob
Tease and Jones - the harlequin chromosomes. Corissing over between light and dark stained non-sister chromatids, showed there is a physical exchange of chromatid segemts
49
What did the Harlequin Chromosomes show?
Tease and Jones. Showed that crossing over occured at the FOUR CHROMATID STAGE, by proving that chiasmata were the crossing over site.
- Observed chromosomes at diakinesis (prophase 1)
- Only possible for tetrads to contain FOUR dfferent allele combinations if crossing over occurs at the 4 chromatid stage
50
Multiple crossovers can include more/less/same than two chromatids
Multiple crossovers can include MORE than 2 chromatids
51
Double crossover can involve THREE chromatids. This means______, not just _______, chromatids can cross.
non-adjacent, adjacent
52
Crossing over can only occur between __ chromatids at any one time.
2
53
What does polyethylene glycol do?
Fuse the membrane of a human fibroblast and mouse tumor cell
54
What is a heterokaryon?
A hybrid cell that contains 2 nuclei
55
What is somatic cell hybridization
the fusion of different cell types
56
In ahuman-mouse comatic cell hybrid who's chromosomes are lost
Humans
57
In situ hybridisation is a method for:
Determining the chromosomal location of the gene through molecular analysis.
can be used for diagnostic purposes
58
How does In situ hybridization work?
- Require a probe thats single stranded, fluorescent and complementary for the gene.
- You denature the target chromosome so it becomes single stranded
59
What chromosome is associated with Down Syndrome
21
60
What is Philadephia chromosome
In chronic myelogenous leukemia (CML) there is a translocation between chromosome 9 and 22
61
What does CML stand for
Chronic myelogenous leukemia
62
What are genetic markers?
Are variable genes with easily observable phenotypes (blood types, seed shape)
63
Types of DNA markers (x4)
Minisatellite marker: based on variation in the number of tandem repeats 15-100 bp long
Microsatellite markers: based on variation in the number of a 2-6 bp sequence
Both loci have the same repeat unit just different number of repeats
Single nucleotide polymorphism (SNPs): are positions in the genome where people differ in a single nucleotide base
Restriction fragment length polymorphism (RFLPs) is a SNP that alters a restriction enzyme recognition site
64
What method/approach was used in the discovery of the genes responsible for Huntingtons disease
Linkage analysis using DNA markers
65
What are the 2 type of chromosomal mutations
structural and number
65
What are the 2 type of chromosomal mutations
structural and number
66
Changes in chromosomal number are refereed to as
polyploid changes
66
Changes in chromosomal number are refereed to as
polyploid changes
67
Structural mutations involve...
novel sequence rearrangements within 1 or more DNA molecule
67
Structural mutations involve...
novel sequence rearrangements within 1 or more DNA molecule
68
Why are chromosomal mutations important x5
- understand how genes work together
- insights into meiosis and chromosome architecture
- tools for genomic manipulation
- cause of genetic diseases
- insights into evolutionary processes.
68
Why are chromosomal mutations important x5
- understand how genes work together
- insights into meiosis and chromosome architecture
- tools for genomic manipulation
- cause of genetic diseases
- insights into evolutionary processes.
69
Types of chromosomal mutations x3
- loss of genetic material
- gain of genetic material
- relocation of genetic material
69
Types of chromosomal mutations x3
- loss of genetic material
- gain of genetic material
- relocation of genetic material
70
What causes loss of genetic material (x2)
- deletion
| - missing chromosome
70
What causes loss of genetic material (x2)
- deletion
| - missing chromosome
71
what causes a gain in genetic material (x2)
- duplication
| - extra chromosome
71
what causes a gain in genetic material (x2)
- duplication
| - extra chromosome
72
What causes relocation of genetic material (x2)
- Translocation
| - inversion
72
What causes relocation of genetic material (x2)
- Translocation
| - inversion
73
How do you form a deletion?
A chromosome segment can be lost
73
How do you form a deletion?
A chromosome segment can be lost
74
How do you form a duplication?
a section can be doubled
84
How do you form a duplication?
a section can be doubled
85
Haplotypes
- determine gene position
| - combination of alleles that are located closely together on the same chromsome ( often inherited together)
