13-Chromosomes

What is the chromosome theory of inheritance?

genes are on chromosomes are specific loci and chromosomes undergo segregation and independent assortment

What organism did Thomas Morgan study?

fruit fly

what were the advantages of using fruit flies?

-inexpensive, easy to maintain

-100s of offspring every 2 weeks

-many identifiable traits

-easy to control matings

- 4 pairs of chromosomes ( 3 pairs of autosomes, 1 pair of sex chromosomes)

what was the ratio Morgan found?

3:1

wild type flies had ____eyes and mutant flies had _____ eyes

red-dom; white-rec

a gene is given a _____ for the 1st mutant observed

symbol

what was discovered in the F2 generation in Morgan's experiment?

all the white-eyed flies were male

what were the conclusions of Morgan's experiment?

eye color is loaded on the X chromosome; no corresponding locus on Y

what was important about Morgan's work?

he discovered that a specific gene is carried on a specific chromosome and genes on sex chromosomes exhibit unique inheritance patterns

what are autosomes?

non-sex chromosomes; homomorphic

what are sex chromosomes?

major sex-determining genes + other types of genes; heteromorphic; happen during meiosis

what happens during meiosis in sex chromosomes?

synapse (come together) and crossing-over can occur

sex-linked gene can be found where?

on a sex chromosome

Are males heterogametic or homogametic?

heterogametic (XY)

Are females heterogametic or homogametic?

homogametic (XX)

what is a x-linked gene?

genes on the X chromosome

what is a sex-linked trait?

trait whose allele is located on the X chromosome

What is X-inactivation and it's steps?

X inactivation is when the X chromosome compacts into a Barr body and genes within become unexpressed. The Barr body lies along the nuclear envelope, and is more likely in females.

inactivation occurs by using _____ methylation and ________ proteins

DNA; histone

What is a Barr body?

Inactivated X chromosome; very dense/stains darkly

what are linked genes?

genes on the same chromosome

what does linkage mean?

The tendency of genes that are located close to each other on a chromosome to be inherited together during meiosis and appear in the same gamete

what does linkage violate?

law of independent assortment

what is complete linkage?

linkage between genes that are located close together on the same chromosome with no crossing over between them

what is incomplete linkage?

linkage between genes that exhibit some crossing over

how can linkage be determined?

test cross results

genetic recombination

new combination of genes produced by crossing over and independent assortment

in complete linkage what do the offspring look like?

parental generation

in unlinked linkage what do the offspring look like?

Not exactly identical due to recombination