Genetics Clemson

Changes in the number of individual chromosomes

Loss of chromosome that lost its centromere
Robertsonian translocation
nondisjunction

In meiosis it only effects daughter cells of that division
in mitosis it effects all future daughter cells that can result in mocaism

Type of aneuploidy that results in loss of both members of a homologous pair (2n-2) not survivable in humans

Loss of a single chromosome, Turner's is the only survivable human form (2n-1)

Gain of a single chromosome (2n+1)

Gain two homologous chromosomes (2n+2)

Can manage aneuploidy in sex chromosomes, which is more tolerable than somatic chromosomes

Only can happen in humans on smaller chromosomes, like chromosome 21

Caused by a Robertsonian translocation in which the long arm of chromosome 21 is translocated the short arm of chromosome 14; tends to run in families.

trisomy that is resolved by a loss of a chromosome during embryogenesis. (review)

Occurs when both chromosomes are inherited from one parent (can occur from trisomic rescue)

Organism can have normal tissues and tissues with chromosome abnormalities depending on when nondisjunction happens

Can happen from errors in meiosis
events at fertilization
errors in mitosis after fertilization

simultaneous fertilization of egg with two sperm

All chromosome sets are from the same species

Chromosome sets are from different species

a polyploid that has two extra sets of chromosomes, identical to the normal haploid complement of the same species.

When X chromosome is taken out it breaks before it can be karyotyped, results from an increase in trinucleotide repeats, can lead to elongated face,

number of repeats increases in future generations causing symptoms to be worse. Prevelant with huntingtons disease

increase in number of copies of a gene, increase amount of gene product being created

Related genes that all do slightly different jobs that were formed by gene duplication

Duplicated genes that are non functional

Generated first map of chromosome based on recombination frequency in 1911

Suggested that chromosomes segregated together and that those closely linked rarely recomb

new combinations of alleles

offspring whose genes are not recombinant, same as parental genes

Genes that are linked often travel together in meiosis, leading to an overrepresentation of parental alleles, recombinants still exist but because of crossing over

Heterozygous to homozygous recessive are seen to note recombination rates.
- equal representation between parental and recombinant are expected

On the same chromosome super close together so recombination and crossing over is super unlikely
All parental is expected

genes on same chromosome, but some distance apart, allows some recombination.
Crossing over gives recombinants.

Postulated that the frequency of recombination could be used to determine the physical separating two genes on a chromosome.

Can result in complete loss of genetic information

Some genes are flipped to the opposite order

Chunk of chromosomal information ends up on a nonhomologous chromosome.

balance of gene product must be maintained for some pathways.
duplications can result in abnormal phenotype.

gene product can be imbalanced
recessive alleles on undeleted chromosomes can be represented (pseudodominance)

expression of a normally recessive allele owing to a deletion on the homologous chromosome

The appearance of a mutant phenotype in an individual cell or organism that is heterozygous for a normally recessive trait, not enough gene product to produce expected phenotype

does not include centromere

includes centromere

Matching up of base pairs despite a chromosome being inverted, can result in loss of centromere if crossing over takes place
one chromosome is acentric, and cannot move, the other forms a dicentric bridge.
when lined up i metaphase 1 they begin to separate and the bridge eventually snaps

still forms an inversion loop, centromere is part of the region that got flipped around ***

Translocation in which the long arms of two acrocentric chromosomes become joined to a common centromere, resulting in a chromosome with two long arms and usually another chromosome with two short arms.

the tiny recombinant of P arms is usually lost

segregation in meiosis ends up being a problem
- 4 chromosomes can end up trying to line up together
3 ways they can separate
-adjacent segregation
-adjacent 2 segregations
-Alternate segregation
Adjacent 1 and 2 are missing gene information, but alternate segregation can result in viable gametes

two crossover events happen near each other, the first one pushing the second one away to a undetectable point

Wild type alleles on one chromosome, mutant alleles on the other

Each chromosome has one wild type and one mutant allele

maize; cytological markers and 2 linked genes
- Showed crossing over results from a physical exchange between homologs
- Used a physical knob as a marker to see when translocation occured

A group of alleles of different genes on a single chromosome that are closely enough linked to be inherited usually as a unit

media that contains the minimal nutrients needed for growth

has anything and everything bacteria might desire.
- bacteria may die on minimal media but will grow on complete media

Wild type bacteria that can synthesize all compounds needed from simple ingredients.
- can grow on minimal media, selective media, or complete media

Minimal media + other components
or complete media -1 or more components

conjugation
transformation
transduction

small circular DNA molecules that replicate separately from the bacterial chromosome

Physical connection between bacterial cells, one donates a piece of its genome

One cell dies, the other takes fragments of its DNA

Viruses carry DNA from one bacterium to another

Cells that have it are F+ and can undergo conjugation with cells that are F-, making them into F+ cells

plasmid that can integrate into bacterial chromosome

high frequency of recombination; sex factor gets incorporated into the bacterial genome so when conjugation bridge forms, the whole bacterial chromosome duplicates and attempts to transfer over, many times conjugation bridge breaks before all of it can get over

Consequences
- regions of homology in bacterial chromosome that transferred over can trade out a good allele for a bad one
- recipient cell remains F-, F factor ends up breaking down

have plasmid separate from bacterial chromosome that has some bacterial chromosome information

Recipient cell receives part of bacterial chromosome with F factor because it was not excised precisely, becomes diploid for certain genes but remains haploid over all

gene mapping by interrupted conjugation, time it takes for certain genes to cross between the bridge during conjugation