Week 4 2nd half

What is Aneuploidy

When there is 1 extra or 1 less chromosome

(not like 2n or n)

What are examples of Aneuploidy

• Monosomy (2n-1)

• Trisomy (2n+1)

• Tetrasomy (2n+2)

What is Euploidy, Monoploid, Polyploidy

• Euploidy is when an organism has the normal amount of chromosomes (2n in humans)

• Polyploid is when an organism has more than 2 sets of chromosomes (3n, 4n, etc)

• Monoploid is when an organism only has 1 set of chromosomes (1n)

What is Trisomy

2n+1 , viable in humans

What is Monosomy

2n-1 chromosomes (not possible in humans)

How can you tell when a disorder is aneuploidy vs euploidy/polyploidy

• “___somy” is aneuplody

• “__ploidy” is euploidy/[polyplody

What is nondisjunction

When chromosomes don’t seperate

What happens when nondisjunction happens in meiosis 1

A homologous chromosome does not separate

• 1 cell gets both homologous chromosomes and the other get neither

• At the end of meiosis, 2 gametes have n+1 and 2 gametes have n-1

After fertilization, monosomy (2n-1) and trisomy (2n+1) occur

What happens when nondisjunction happens in meiosis 2

Sister chromatids don’t separate

• There are 2 normal gametes, 1 gamete (n-1) and 1 gamete (n+1)

Why is aneuploidy usually harmful

When you have an extra or missing a chromosome, it causes a change in protein levels

Is monosomy or trisomy more lethal in humans

Monosomy is much more lethal.

Trisomy 21 (down syndrome), Trisomy 18, etc are non-lethal.

Is aneuploidy dangerous in sex chromosomes

It is less lethal than somatic chromosomes aneuploidy.

OY (no X chromosome) is not viable

XO, XXY, XXX, and XYY are all viable

Why can humans tolerate extra X chromosomes

Because of X activation

What is X-inactivation

In Females, 1 X chromosome is randomly and permanently turned off. The inactive X becomes a Barr body. This continues for all somatic cells in the organisms.

When and where does X-inactivation occur

It starts in the early embryo (about 800 cells) stage, this does not occur in gametes.

How are females mosaics

Since the X chromosome that inactivates is random, different cells have different genes active on 1 or the other X chromosome. (50/50 average)

What is mosaicism

It is when an organism has 2 or more genotypes in it. (Maybe from a mutation)

Where are genes not repressed during X-inactivation

At the telomeres, the ends of the chromosome

How are extra X chromosomes different in flies and humans

Humans silence extra X chromosomes, but flies don’t but the male produces double the gene products to compensate

How do mosaics change based on when in fertilization they occur

The earlier the mutation occurs, the larger the amount of cells affected (50/50)

What is a gynandromorph

Happens when a female fly (XX) loses an X chromosome during mitosis and the final organism is a gynandromorph. Has equal male and female tissue.

What are the 2 types of gynandromorph

• Bilateral (symmetrical)

• asymmetrical

What is a chimera

When 2 zygotes come together and result in less than 1 genotypes

What is the main difference between a mosaic and Chimera

• A mosaic is made of 1 zygote, has a mitotic error

• A chimera is made of 2 zygotes, causes from fusion

Why are Triploids sterile

Since there are 3 copies of each chromosome, this causes the organism to have messy pairing and separation and uneven.

How are triploids created

when a diploid and tetraploid are crossed

How are tetraploids made

When the chromosomes don’t segregate(separate) or when 2 diploid embryos come together.

What is haplodiploidy

Includes ants, bees, wasps

(Males develop from unfertilized eggs (Haploid) and girls develop from fertilized eggs (diploids))

What is parthenogenesis

Reproduction without fertilization

What is an example of parthenogenesis

The Komodo dragon female has the ZW sex chromosomes. They can create ZZ or ZW offspring. (WW is lethal)

Why are mules sterile

Because they have 63 chromosomes (32 from horse, 31 from donkey) so they cannot pair up during meiosis.