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

Lecture 4: Meiosis, Recombination, and Linkage Flashcards

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Biology 101 flashcards
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
Q

Do centromeres separate during metaphase 1?

A

NOPE

26
Q

What does it mean for a cell to go from diploid to haploid?

A

46 to 23 chromosomes

27
Q

2 methods for reassortment of parent genes in gametes?

A
  1. Independent assortment of maternal and paternal homologs derived chromosomes at meiosis 1
  2. Recombination between parental homologs at prophase of meiosis I
28
Q

How many combinations possible for independent assortment of maternal and paternal homologs?

A

8M combinations

29
Q

How many recombination events during a single meiosis? More common in spermatocytes or oocytes?

A

50 per spermatocytes

1.9 x higher in oocytes

30
Q

What does recombination between parental homologs generate?

A

One recombination event generates 2 recombinant and 2 nonrecombinant gametes (.

31
Q

What can increase the likelihood of recombination between genes?

A

The further the genes are from each other

32
Q

What does it mean for genetic loci to co-segregate? What is another term for this?

A

It means they recombine in less than 50% of gametes

They are said to be linked

33
Q

How to estimate the % gametes with recombination between 2 loci?

A

1 centimorgan (cM) is the genetic distance between two loci that yields recombination in 1% of gametes

34
Q

What are the 2 types of genetic traits? Define each and provide 2-3 examples each.

A
  1. Mendelian trait: single gene (achondroplasia and Pompe syndrome)
  2. Quantitative trait: multiple genes (BP, height, MS)
35
Q

2 other names for quantitative genetic traits?

A

Polygenetic = complex traits

36
Q

Main example of Mendelian trait?

A

Neurofibromatosis Type 1 (Nf1)

37
Q

Goal of gene mapping?

A

Find a gene responsible for a disease or trait

38
Q

Inheritance pattern for Nf1?

A

Autosomal dominant

39
Q

2 types of tumors found in Nf1 patients?

A
  1. Benign cutaneous

2. Plexiform along nerve

40
Q

Strategy for old school mendelian traits gene mapping?

A

Identify a physical marker (polymorphism) that is inherited (cosegregates) with the disease in a pedigree

41
Q

During mendelian traits gene mapping, how can you determine if 2 genes are linked?

A

Every affected individual with disease has the allele for another random gene

TO BE VERIFIED

42
Q

What could explain not all affected individual with disease being heterozygous for another random gene but the genes still being linked?

A

Meiotic recombination between homologs

43
Q

What is the LOD score? How can it determine gene linkage?

A

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
Q

5 types of polymorphisms used for mendelian traits gene mapping? Describe each.

A
  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
Q

2 ways to disease gene map mendelian traits in the genomic era?

A
  1. Find a sequence variant co-segregating in a pedigree

2. Find different variants in the same gene shared in multiple kindreds

46
Q

Which type of trait is often impact by the environment?

A

Quantitative traits

47
Q

How do you gene map for quantitative traits?

A

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
Q

3 values of GWAS style studies?

A
  1. Precision medicine
  2. Disease risk and prevention
  3. Insight into disease mechanisms
49
Q

Do gametes form before or after gonad formation?

A

Before

50
Q

What type of sperm cells enters the embryonic gonad?

A

Primordial germ cells

51
Q

5 stages of sperm cell development? Provide quantity of genetic material. How long does this take?

A
  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
Q

What is special about spermatogonia?

A

They can undergo mitosis or meiosis

53
Q

5 stages of egg development? Provide quantity of genetic material and meiosis stage.

A
  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
Q

What egg stage is ovulation?

A

Secondary oocyte

55
Q

What determines if the secondary oocyte becomes a mature egg?

A

Fertilization

56
Q

How many gametes do you obtain per meiosis in males?

A

4

57
Q

How many games do you obtain per meiosis in females?

A

1

58
Q

What can explain the unequal cytoplasm partition during female gamete development?

A

Cells need all the nutrients they can get while they are traveling through the Fallopian tube

59
Q

Are the patterns of chromosomal segregation similar or different in male and female gametes? Explain.

A

SIMILAR

60
Q

Can female oocytes divide as true stem cells?

A

Unknown

61
Q

Can male spermatogonia divide as true stem cells?

A

YUP

62
Q

Does mitosis maintain genetic constitution during cell division?

A

YUP

Genetics (5 decks)

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