Genetics Lectures 18 and 19

Cytology

Study of cells

Karyotype

Chromosomes arranged by size; Largest is chromosome 1, second largest is chromosome 2

Chromosomes arranged by size; Largest is chromosome 1, second largest is chromosome 2

SKY

Spectral Karyotyping - uses single stranded fluorescently labeled DNA probes to unique. regions of the chromosomes

Change in Chromosome Numbers: Euploidy, Aneuploidy

Euploidy - Changes in WHOLE chromosome set - size may change, but general shape and proportions stay the same

Aneuploidy - Changes in PARTS of chromosome sets - Shape and proportions are generally altered in very specific ways

Euploid; haploid, diploid = normal

Haploid (n) - half the number of chromosome sets (gametes)

Diploid (2n) - two copies of each chromosome

Euploidy; Aberrant = not normal

polyploidy - more than two chromosome sets

Triploid (3n) - three copies of each chromosome set

Tetraploid (4n) - four copies of each chromosome set

Haploid vs. Monoploid

Haploid - # of chromosomes found in gametes following meiosis

Monoploid - organism has the haploid # of chromosomes (1n) one set of genetic information - breed through cloning

Parthogenesis

asexual reproduction in which offspring develop from unfertilized eggs.

Automixis through mitosis

Apomixis is a combination of meiosis and mitosis

Animals : Aberrant Euploids or Polyploids

Not very common in animals; most often seen in non-vertebrates

Rarely occurs in humans - most often results in miscarriges

Plants ; Aberrant Euploids or Polyploids

Pervasive - present everywhere

Can arise spontaneously in plants but is also a key mechanism in plant breeding

Most of the time display some kind of variation in morphology related to parents

Aberrant or Euploids or Polyploids

Often a correlation between numbers of chromosome sets and size of the organism

Colchicine - microtubule inhibitor

Autopolyploids

Having more than one set of chromosomes originating within a species

• offspring with polyploidy karyotypes may be viable and able to self-fertilize themselves

Unreduced gametes with six chromosomes each ; Tetraploid 4n = 12

Triploids - 3n ; makes triploid then one splits normally the other does not; makes an aneuploid

Allopolyploids

Unreduced gametes with four chromosomes → unreduced gametes with seven chromosomes

Embryoids

Pluripotent stem cells (haploid content)

Applications of Polyploidy

Increased yield

Increased aesthetics

Triticale yield of wheat

hardiness of rye

Self-fertilizing crop

Aneuploidy definition new:

Chromosome number differs from a normal individual by PART of a chromosome set

Generally, the chromosome set differs from the normal individual by only one chromosome or by a small number of chromosomes

Chromosome numbers can either by greater or smaller than normal individual

2n-1 = Monosomic in autosomes = lethal in utero

2n+1 = Trisomic

XXY,XYY,XXX,XO Sex Chromosomes

Aneuploidy full form

All cells in the organism display the aneuploidy, either gain or loss of a chromosome

Partial form - Aneuploidy

All cells in the organism diplay the aneuploidy however, you do not have complete gain or loss of a chromosome, only part of the chromosome is changed (addition or loss of a p or q arm)

Mosaic form

Not all cells display the Aneuploidy

Disjunction

The normal segregation of homologous chromosomes during either mitosis or meiosis

• Normal process (evenly split chromosomes)

Non-disjunction

Abnormal segregation of homologous chromosomes

• First chromosome split and the other one instead of splitting goes one way or the other (completely to one side)

• One haploid minus one n-1

• And n+1 One has too much information and one doesn’t have enough

Organism will show the abnormality

Monosomic in Sex chromosomes

Turners Syndrome [XO] - Single X (Why Men cannot have it)

Only affects women

Generally, very mild developmental and cognitive effects

Sterile (not able to produce or fertilize) due to improper development of the ovaries

Treatable with hormone therapy

AUTOSOMES = LETHAL IN UTERO - only happens on allosomes

Trisomic Chromosomal Complement (autosome and sex chromosomes)

Occurs in both autosomal and sex chromosomes

Can occur with any chromosome - Trisomy 16 is the most common (miscarriage)

Most severe phenotypic effects with Autosomes - Edwards syndrome (18) can be full form, partial form or Mosaic form, Downs syndrome (47, +21) full form (95%) vs. Mosaic (2-3%) vs. Translocation

Sex chromosome (allosomal) trisomys can be relatively symptom free - XXY Klinefelter’s Syndrome

You see these more often then monosomic because you have more genes than you are supposed to (2n+1)

Gene balance

Additions or subtractions of single chromosomes to the karyotype of an organism produce a greater impact on phenotype than whole genome changes in ploidy

Increased Abnormalities

Gene product - copy number of the gene

Normal physiology - normal gene balance

Changes in gene product = physioloigcal imbalances

Edwards Syndrome

An extra copy of all or part of Chromosome 18

• Very short life spans

• Seen more in males than females

• “Rocker feet” and “curled hands”

Full form, partial form, and mosiac form

Downs Syndrome

An extra copy of chromosome 21 (47, +21)

Most common aneuplopidy in America

Maternal age relationship - Depends on what age you have a child can affect if they get this or not

Full form (95%) and mosiac form (25%)

Klinefelter Syndrome

(47, XXY)

An extra X chromosome in males

Usually not diagnosed because you look normal

Treatment with testosterone

Full form or Mosaic

Jacobs Syndrome

(47, XYY)

An extra Y chromosome

Major symptom is increased height and size

Refered to as super male

Triplo-X-Syndrome

(47, XXX)

An extra X chromosome in females

Slightly larger

X chromosome inactivation - one crumbles up into an R body

(the epigenetic process in female mammals where one of the two X chromosomes in every cell is transcriptionally shut down)