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Genetics > Lecture 4: Meiosis, Recombination, and Linkage > Flashcards

Lecture 4: Meiosis, Recombination, and Linkage Flashcards

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1
Q

How are chromosomes numbered?

A

Order of decreasing size

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2
Q

How many BPs per chromosome?

A

50-250 M

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3
Q

2 categories of DNA sequences? How much DNA does each account for?

A
  1. Unique sequence: 50%

2. Repetitive DNA: 50%

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4
Q

2 types of repetitive DNA?

A
  1. Clustered repeats

2. Dispersed repeats

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5
Q

What are pseudogenes?

A

Vestigial copies of genes that are rarely expressed

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6
Q

Other name for clustered repetitive DNA sequences?

A

Satellite DNA

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7
Q

How many times are satelittle DNA repeats repeated?

A

6 to several hundred

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8
Q

What are satellite DNA repeats useful for?

A
  1. Gene mapping
  2. Tracking alleles in families
  3. Cancer diagnosis
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9
Q

What are the 2 most common dispersed repeats in the human genome? Describe each.

A
  1. SINE: short interspersed nuclear element: 280 bp sequence present 1.5 million times (13% genome)
  2. LINE: long interspersed nuclear element: 6000 bp sequence present about 100,000 times (20%)
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10
Q

What can dispersed DNA repeats cause?

A

Chromosomal rearrangements: deletions, duplications, inversions, translocations

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11
Q

4 phases of the cell cycle?

A
  1. G1
  2. S
  3. G2
  4. M
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12
Q

What is the interphase of the cell cycle?

A

G1, S, G2

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13
Q

What are the 2 parts of the M phase of the cell cycle?

A
  1. Mitosis (nuclear division)<

2. Cytokinesis (cytoplasmic division)

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14
Q

During which cell cycle phases does the cell have a 4N genetic content?

A

From S until M

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15
Q

Why do extremely unlikely events occur during mitosis?

A

Because it happens 10 times over a human lifetime!

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16
Q

5 phases of mitosis? Describe each.

A
  1. Prophase: Chromosomes contract and coil and each consists of a pair of sister chromatids held together at the centromere
  2. Metaphase: Nuclear membrane dissolves and chromosomes align at equatorial plane
  3. Anaphase: Sister chromatids separate to poles
  4. Telophase: Nuclear membranes encompass chromosomes
  5. Cytokinesis divides cytoplasm among daughter cells
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17
Q

What happens during meiosis?

A

Cell undergoes two divisions without intervening S phase, thereby generating haploid gametes

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18
Q

What is a common error during meiosis? What does this lead to?

A

Errors in segregating chromosomes ==> Nonfunctional gametes, abortive embryos, cytogenetic abnormalities

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19
Q

10 phases of meiosis? Give the genetic material amount in each

A
  1. Prophase 1: 4n
  2. Metaphase 1: 4n
  3. Anaphase 1: 4n
  4. Telophase 1: 4n
  5. Cytokinesis: 2n
  6. Prophase 2: 2n
  7. Metaphase 2: 2n
  8. Anaphase II: 2n
  9. Telophase II: 2n
  10. Cytokinesis: 1n
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20
Q

What does n mean?

A

Number of chromosomes

1n: 23 chromosomes
2n: 46 chromosomes
4n: 46 chromosomes with 2 chromatids each

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21
Q

Difference between meiosis metaphase 1 and mitosis metaphase?

A

Homologous chromosomes are in two different planes and are getting separated in meiosis metaphase 1 VS in mitosis metaphase all of the chromosomes are in one plane and the sister chromatids are being separated

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22
Q

Describe prophase I.

A

Parental homologs form synaptic complex called a bivalent or tetrad

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23
Q

What is meiosis 1 referred to as?

A

Reduction division

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24
Q

What does meiosis 2 resemble?

A

Mitosis

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25
Do centromeres separate during metaphase 1?
NOPE
26
What does it mean for a cell to go from diploid to haploid?
46 to 23 chromosomes
27
2 methods for reassortment of parent genes in gametes?
1. Independent assortment of maternal and paternal homologs derived chromosomes at meiosis 1 2. Recombination between parental homologs at prophase of meiosis I
28
How many combinations possible for independent assortment of maternal and paternal homologs?
8M combinations
29
How many recombination events during a single meiosis? More common in spermatocytes or oocytes?
50 per spermatocytes 1.9 x higher in oocytes
30
What does recombination between parental homologs generate?
One recombination event generates 2 recombinant and 2 nonrecombinant gametes (.
31
What can increase the likelihood of recombination between genes?
The further the genes are from each other
32
What does it mean for genetic loci to co-segregate? What is another term for this?
It means they recombine in less than 50% of gametes They are said to be linked
33
How to estimate the % gametes with recombination between 2 loci?
1 centimorgan (cM) is the genetic distance between two loci that yields recombination in 1% of gametes
34
What are the 2 types of genetic traits? Define each and provide 2-3 examples each.
1. Mendelian trait: single gene (achondroplasia and Pompe syndrome) 2. Quantitative trait: multiple genes (BP, height, MS)
35
2 other names for quantitative genetic traits?
Polygenetic = complex traits
36
Main example of Mendelian trait?
Neurofibromatosis Type 1 (Nf1)
37
Goal of gene mapping?
Find a gene responsible for a disease or trait
38
Inheritance pattern for Nf1?
Autosomal dominant
39
2 types of tumors found in Nf1 patients?
1. Benign cutaneous | 2. Plexiform along nerve
40
Strategy for old school mendelian traits gene mapping?
Identify a physical marker (polymorphism) that is inherited (cosegregates) with the disease in a pedigree
41
During mendelian traits gene mapping, how can you determine if 2 genes are linked?
Every affected individual with disease has the allele for another random gene TO BE VERIFIED
42
What could explain not all affected individual with disease being heterozygous for another random gene but the genes still being linked?
Meiotic recombination between homologs
43
What is the LOD score? How can it determine gene linkage?
Statistical measure of the likelihood of odds that the observed marker is indeed linked and not inherited with disease by chance LOD≥ 3 indicates significant likelihood that two loci are linked
44
5 types of polymorphisms used for mendelian traits gene mapping? Describe each.
1. Restriction fragment length polymorphism (RFLP) 2. SNPs: single nucleotide polymorphisms present is at least 1% population 3. SNVs: single nucleotide variation seen in a single individual or family (less than 1% of pop) 4. Tandem repeats (microsatellites): variations in the number of short repeats at a particular site 5. Copy Number Variations (CNVs): duplications or deletions, often 1000 to several million bp
45
2 ways to disease gene map mendelian traits in the genomic era?
1. Find a sequence variant co-segregating in a pedigree | 2. Find different variants in the same gene shared in multiple kindreds
46
Which type of trait is often impact by the environment?
Quantitative traits
47
How do you gene map for quantitative traits?
GWAS (genome-wide association study) used to identify loci contributing to trait ==> take a huge group of patients and non-patients and compare 100,000 SNPs in their DNA in a Manhattan plot
48
3 values of GWAS style studies?
1. Precision medicine 2. Disease risk and prevention 3. Insight into disease mechanisms
49
Do gametes form before or after gonad formation?
Before
50
What type of sperm cells enters the embryonic gonad?
Primordial germ cells
51
5 stages of sperm cell development? Provide quantity of genetic material. How long does this take?
1. Primordial germ cell 2. Spermatogonia: 2n 3. Primary spermatocyte: 4n 4. Secondary spermatocyte: 2n 5. Spermatid: 1n 6. Spermatozoa: 1n TOTAL: 64 DAYS
52
What is special about spermatogonia?
They can undergo mitosis or meiosis
53
5 stages of egg development? Provide quantity of genetic material and meiosis stage.
1. Primordial germ cell 2. Primary oocyte: 4n - ARRESTED IN MEIOTIC PROPHASE 1 PRIOR TO PUBERTY 3. Secondary oocyte: 2n + Polar body: 2N - MEIOSIS 1 COMPLETED WITH OVULATION 4. Mature egg: 1n + Polar body: (from secondary oocyte) 1N - UPON COMPLETION OF MEIOSIS 2 WITH FERTILIZATION
54
What egg stage is ovulation?
Secondary oocyte
55
What determines if the secondary oocyte becomes a mature egg?
Fertilization
56
How many gametes do you obtain per meiosis in males?
4
57
How many games do you obtain per meiosis in females?
1
58
What can explain the unequal cytoplasm partition during female gamete development?
Cells need all the nutrients they can get while they are traveling through the Fallopian tube
59
Are the patterns of chromosomal segregation similar or different in male and female gametes? Explain.
SIMILAR
60
Can female oocytes divide as true stem cells?
Unknown
61
Can male spermatogonia divide as true stem cells?
YUP
62
Does mitosis maintain genetic constitution during cell division?
YUP

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