Monday - March 31st, 2008

 

3-31-08

 

Hemophelia -

Blood clotting disorder - (typically boys as its X recessive)

Talked about XY in mammals and ZW in birds

Autosomes - chromosomes that are not sex chromosomes. (majority of chr.)

talked about X-inactivated chromosomes = Barbodies.

look at the edge of a nuclei, and see there's a black little dot on the rim = That's a bar body, and only in Females

 

In tortoise shelled cats - big orange kitty patches - That inactivation happened earlier.

"Happens early in embryonic development"

---

Most autosomes have 100's to 1,000's of genes.

How can you tell if two genes are linked together on the same chromosome?

(used during genetics test)

Answer: By their inheritance pattern.

 

if genes were not linked, the ratio we'd see would be...a 1:1:1:1: -- all are equally likely if unlinked

KNOW FOR EXAM!

(sidenote: however, what we see in the F2 generation is that we normally see tons of Parental type, and fewer non-parental type)

 

If genes are linked on same chromosome, then most of the offspring will have the parental Phenotypes.

Inherited together most of the time.

 

Recombinant offspringcome from crossing-over betweent he genes. Crossing over gives us new gene combinationsthat now are inherited together (linked). Genetic recombination

(underlines used as synonyms)

 

Recombination Frequency:

To determine how often crossing over occurs

Equal to:           (total # of recombinant individuals)  / (total # of individuals)  * 100   == Percent recombination.

 

If 2 genes are close together, the closer this number will be to zero.

(because its less likely they'll be  a crossover between the two genes)

 

The further apart these 2 genes are, the more likely it will be that a crossover will occur.

 

So, the maximum number that we can detect is 50% recombination.

1% recombination= equal to = 1 cM centiMorgan)= also called = 1 Map Unit

 

Recombination Frequencies - use to construct genetic map = linkage map .

Map of genes on the chromosomes in terms of order and recombination between the genes.

 

 

A-B = 20 map units apart = 20% recombint

A - C = 8 map units apart

B -C = 12 map units apart

   (------8------)    (------------12----------)

A -------------C------------------------B

(------------------20-------------------------)

 

More combination to b & c on purple slide.

So less combination between C & D than any other 

 

Changes in chromosome number:

Mistakes --> genetic disorders

1.) Aneuploidy= ("not true ploidy") one or more too many / too few chromosomes  (n+1 ; n-1 ;)

in humans (normal = 23) we'd see aneuploid gametes are 22 or 24

the usual cause is non-disjunction during meiosis. (disjunction = separating,it means not-separating-properly)

 

most common aneuploidy of autosomes = trisomy 21 aka downs syndrome

three copies of #ch 21.

1/700 births in US.

2n = 47 (instead of 46)

 

Sex Chromosome Aneuploidy:

its better tolerated than autosomal - usually sterile. Some effects on intelligence, but not so much.

 

X0 = Turner's Syndrome  (one x chromosome, and usually sterile)

XXY = Klinefelter's Syndrom (also usually sterile, but have mostly male sex characteristics) a male with a barbody

XXX = normal phenotype (not so severe reproductive repercussions than other types)

 

2.) Polyploidy: More than two whole SETS of chromosomes (as opposed to just a lingering one or two)

Rare in animals - but common in Plants --> and is beneficial!

Bananas - triploid - 3n --> sterile

Potatoes - tetraploid - 4n --> sterile

Bread wheat - hexaploid - 6n -->

 

Causes problems in meiosis during homologous synapsis stage, so reproduction is probably not gonna happen

Bananas - asexual - apparently there's a disease and unless we get it underway, in 20 years, we'll have no bananas.

 

-caused by failed cell division - either mitosis, or meiosis

 

Abberations of chromosome structure.

4 main types

• duplication: segment of a chromosome is duplicated.
• deletion: segment of a chromosome is missing. (so all its data is competely lost)
• inversion: segment of a chromosome is inverted (flipped over, reversed).
• translocation: pieces of chromosome exchanged between non-homologous chromosomes

 

caused by errors in meiosis I in crossing over - it can also happen when chromosomes are damaged by radiation, or chemicals.

(high levels of X-rays, gamma rays, etc - can lead to cancer, or passed onto next generation)