BIOL 2100 Exam 3 Notes

BIOL 2100- Exam 3 Notes

Chapters 2-8

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Chromosomes and Cellular Reproduction - Chapter 2

Binary fission - literal separation of the cell into 2 halves

Archea → prokaryotic

Viruses are neither prokaryotic nor eukaryotic

What are viruses and are they alive

Prokaryotic cells

  • Simple division; separation of a replicated circular chromosome

  • Origin of replication; they have 1

  • High rate of replication

Eukaryotic cells

  • Homologous pairs

Diploid → 2 sets of genetic information

Haploid → 1 set of genetic information

  • Humans have 46 chromosomes, 23 pairs of chromosomes

  • Gametes are haploids

Chromosome structure

  • Centromere - attachment point for spindle microtubules

  • Telomeres are tips of a linear chromosome

  • Origins of replication are where DNA synthesis begins

If a chromosome does not have a kinetochore

  • Spindle microtubules would not attach to the chromosome

  • Chromosomes would not be drawn into the newly formed nucleus

  • The resulting daughter cells would be missing a chromosome

The Cell Cycle

Interphase → an extended period between cell divisions, DNA synthesis, and chromosome replication phase

M phase → mitotic phase

Phase checkpoint → key transition points; cells cannot move forward unless checkpoint permits them to

*G phase stands for growth phase*

g1 - g2 is interphase

Mitosis

Spindle microtubules are made up of proteins called tubulin subunits, these can assign polarity to the spindle microtubules

Genetic consequences of the cell cycle

  • Cycle produces 2 genetically identical cells

  • Newly formed cells contain a full complement of chromosomes

  • Each newly formed cell contains approximately half the cytoplasm and organelle content of the original parental cell

*know this about the cell cycle*

Sexual reproduction and genetic variation

Meiosis is the production of haploid gametes

Fertilization is the fusion of haploid gametes

Genetic variation is the consequence of meiosis

Meiosis

  1. Interphase - dna replication and chromosome replication

  2. Meiosis I, separation of homologous chromosome pairs, reduction of chromosome number - reductional

  3. Meiosis II, separation of sister chromatids, known as equational division - equational

Meiosis I

  • Prophase I

  • Synapsis; close pairing of homologous chromosomes

  • Tetrad; closely associated four sister chromatids of two homologous chromosomes

  • Crossing over; crossing over of chromosome segments from the sister chromatid of the other synapsed chromosome - exchange of genetic information

Metaphase I - random alignments of homologous pairs

Anaphase I - separation of these homologous chromosomes

cohesions- proteins that hold the chromatids together and are the key to the behavior of chromosomes in mitosis and meiosis.

shugoshin protects cohesion from degrading

how does shugoshin affect sister chromatids in meiosis I & II

Anaphase I → protects cohesion at centromeres, during anaphase II, shugoshin breaks down

Meiosis in animals:

Spermatogenesis → male gamete production

Oogenesis → female gamete production

during the second half of male & female gamete production, both become haploid. (2n → n)

Chromosome Variation - Chapter 8

Karyotyping - chromosomes prepared from actively dividing cells

Halted in metaphase

Chromosomes are arranged according to size

*the 23rd & 24th are the sex chromosomes*

Types of Chromosome Mutations

Chromosome rearrangements

  • Alter the structure of chromosomes

Aneuploidy

  • Alters the number of chromosomes for one type of chromosome

Polyploidy

  • One or more complete sets of chromosomes are added

Unbalanced gene dosage

  • Pseudodominance - recessive gene is expressed due to gene deletion

Effects of deletions

  • Imbalances of gene product

  • Expression of a normally recessive gene(pseudo dominance)

  • Haploinsufficiency

Types of inversions

  1. Paracentric inversions

  • Centromere does not move due to inversion

  1. Pericentric inversions

  • One that involves a shift in location of centromere, arm length changes

Inversions in meiosis

  • No issues occur in individual homozygous

  • Individual heterozygous

  1. Only align if inversion loop is formed

  2. Demonstrates reduced recombination as it is formed from a nonviable offspring

  3. Have abnormal gametes formed in pericentric inversions

← paracentric inversion

pericentric inversion→

Translocations

  1. Robertsonian

  2. Reciprocal

  3. Nonreciprocal

Robertsonian translocation - involves 2 acrocentric chromosomes and 2 breakage events, exchange in chromosomal arms occurs, forming one metacentric chromosome with abnormally long arms, and one chromosome with very short arms, and major pieces missing

Variations in copy number are aneuploidy and polyploidy

Causes of aneuploidy

  1. Deletion of a centromere

  2. Robertsonioin translocation

  3. Nondisjunction during mitosis and meiosis

Nondisjunction → improper separation of chromosomes or chromatids in anaphase; this dictates the # of chromosome copies each cell gets

Types of aneuploidy

  1. Nullisomy → loss of both members of homologous chromosomes; 2n-2

  2. Monosomy → loss of a single chromosome; 2n-2

  3. Trisomy → gain of a single chromosome; 2n + 1

  4. Tetrasomy → gain of 2 homologous chromosomes; 2n + 2

Effects of aneuploidy

In plants, mutants could be trisomics

In humans

  • Sex chromosome aneuploids

1. Turner syndrome, XO

2. Klinefelter, XXY

Autosomal Aneuploids

Trisomy 21 → Down syndrome

Primary Down syndrome → 75% nondisjunction in egg formation

Familial Down syndrome → Robertsonian translocation between chromosomes 14 & 21

In humans

  1. Autosomal aneuploidy

  2. Aneuploidy & maternal age →


Causes of aneuploidy

  • Uniparental disomy → both chromosomes inherited from the same parent

  • Mosaicism(nonapparent chromosomal defect)& nondisjunction in mitotic division

  • Genetic mosaicism of the sex chromosome produces a gynandromorph

Polyploidy

→ can arise through nondisjunction in mitosis or meiosis

The presence of more than 2 sets of chromosomes

  1. Autopolyploidy is from a single species

  2. Allopolyploidy is from two species


The significance of polyploidy → increases cell size, can cause larger plant attributes, can give rise to new species through evolution


←Meiosis - autotriploid (3 sets of chromosomes) homologous chromosomes can or can not pair in 3 ways






Mendelian Genetics - Chapter 3

Used pisum satvium (peas) to experiment → never looked at plant chromosomes

  • Observed seed color

  • Seed shape & coat color

  • Pod color & shape

  • Flower position and stem length


Mendel conducted his experiments between 1856 through 1863


Monohybrid cross → cross between 2 parents that differ in a single characteristic

  1. Conclusion 1 = two genetic factors encode character

  2. Conclusion 2 = two genetic factors (alleles) separate when gametes are formed

  3. Conclusion 3 = the concept of dominant & recessive traits

  4. Conclusion 4 = two alleles separate with equal probability into gametes


Principal of segregation (mendels first law)→ each individual diploid organism possesses two alleles for any particular characteristic, they segregate when gametes are formed, and one allele goes into each gamete


The concept of dominance → one allele is typically shown over another the “dominant” allele


Sutton ⇒ chromosomal theory of hereditary


Law of segregation

  1. Each individual organism possesses two alleles encoding a trait; before meiosis*

  2. Alleles separate when gametes are formed; anaphase I*

  3. Alleles separate in equal proportions; anaphase I*


Law of independent assortment - the way 2 different traits get distributed (not related to one another)

  1. Alleles at different loci separate independently; anaphase I ∫


∫ This is assuming crossing over occurs, if crossing over does not occur, then segregation & independent assortment may also occur in anaphase II


Monohybrid crosses reveal the principle of segregation & the concept of dominance

  • Tested the theory of inheritance of dominant traits using backcrosses

  • Predicted the outcomes of genetic crosses through punnet squares


Dihybrid cross → involves examining 2 traits at a time

  • This relates back to the principle of independent assortment

  • Related independent assortment to meiosis Ω

  • Gametes located on different chromosomes will sort independently


Ω at the end of anaphase I, each daughter chromosome will get its own full set of chromosomes, and genes on each different pair of chromosomes will sort independently, thereby giving different outcomes


chi-square goodness of fit test →

  • indicates the probability that the difference between the expected & observed value is due to chance


∑(O-E)2 ⁄E - Goodness of Fit Equation

 If the chi-square value is greater than 0.5, it indicates that the probability difference expected is due to chance


Chapter 4 - Sex determination & inheritance of sex-linked characteristics


there are several different mechanisms of sex determination; x& y pair up


sex determination 

Alternate between haploid & diploid states


hermaphroditism → both sexes are seen in the same organism

  • Monecious has both

  • Diecious is one of the two


XX-XO system:

XX- female 

XO - male

grasshoppers


XX-XY system

XX - female

XY - male

mammals


 There also exists the ZZ-ZW system 

  • ZZ are males

  • ZW are females

  • ⇐ Found in birds, reptiles, snakes, butterflies, amphibians, & fish

Haplodiploid system

  • Haploid set- male

  • Diploid set - female

  • Bees, wasps, and ants

Gene sex-determining system

  • No sex chromosomes, only the sex-determining genes

  • Plants, protozoans, & fish

Environmental sex determination

  • Limpet’s neck position ⇒ 

  • Turtle temperature




Sex determination in drosophila melanogaster

 Uses genic balance system

X:A ratio; (x is the number of chromosomes, a is the haploid set of autosomes)


Metamales and metafemales are low viability, these tend to not rise from the larvae.




In humans

  1. Turner syndrome - XO, 1/3000 female births

  2. Klinefelter - XXY, XXXY, XXXXY, or XXYY; 1/1000 male births

  3. poly-X females; 1/1000 every female births

The role of sex chromosomes

  • The X chromosome contains genetic information essential for both sexes, one copy of X at least is required

  • The male determining gene is located on the Y chromosome, A single Y produces a male phenotype

  • Absence of Y results in a female phenotype

In males

  • sry(sex determining region)

  • Androgen-insensitivity syndrome

    • Caused by a defective androgen receptor


Dosage compensation ⇒ the amt of protein produced by x-linked genes & random inactivation in two sexes


Lyon hypothesis →

Within each female cell, one of the two chromosomes is inactivated.

need one functioning X chromosome


Tortoise-shelled cats are a result of random x-inactivation; this occurs in 2 steps

  1. Cell assess # of present X chromosomes

  2. One X chromosome is picked to stay active, whereas the others become inactivated


all cells contain all chromosomes


Calculating recombinant frequency can be done by:

(number of recombinant progeny) / (total number of progeny) * 100%


Nonrecombinant ratio is 1:1:1:1


Mapping techniques

molecular markers

  • rflps (restriction fragment length polymorphism)

Genome-wide association studies (gwas)

  • Association within populations

  • haplotype

  • Linkage disequenceilibrium

Physical mapping

  • Somatic cell hybridization

  • Deletion mapping

  • Physical mapping through molecular analysis

    • Fluorescent In Situ Hybridization (FISH)

      • Fluorescent probe binds to complementary regions of the target gene, & targets specific dna sequences for genetic diagnosis (alexa-fluor 488)


eggs are single-cell


Levels of recombination vary between the species, chromosomes of a single species, and between males and females