Chromosome theory of inheritance
genes have specific loci along chromosomes and chromosomes undergo segregation and independent assortment
Name two alleles located on Chromosome 11
Student choice
one example: ALD
If you crossed an F1 plant from pg. 241 with a plant that is recessive for both genes (rryy). what would be the phenotypic ratio?
1:1:1:1
Why did Thomas Hunt Morgan choose the fruit fly for his experiments?
prolific breeders, two-week generation, chromosomes could be seen with a light microscope
What is meant by wild type?
the character most commonly observed in natural populations.
ex. red eyes
In contrast, a mutant phenotype would be white eyes.
Why did Morgan see males who were white-eyed in the F2 generation?
White is recessive. He discovered this in the F1 generation.
There is no corresponding allele on the Y chromosome so if the white allele is on the X, cannot be masked.
What is a sex-linked gene?
Located on either X or Y chromosome.
If X- linked, on X.
If Y-linked, on Y
What does the SRY gene control? Where is it located?
SRY stands for sex-determining region of Y is required for the development of testes.
If absent, ovaries will develop in an XY individual*.
*Assuming the WNT4 gene is active.
Why are X linked diseases more common in males?
Males inherit a Y from their father and an X from their mother. If mom passes a recessive allele for hemophilia, for example, there is no corresponding allele to mask the recessive allele.
Females need to inherit 2 recessive alleles for hemophilia to be affected by the disease.
If a carrier female has children with a colorblind male, what is the chance that their sons have the disorder?
50%
Hint: look at the boys only. 1/2 of the boys are colorblind.
What is a Barr body?
The inactive X in each cell of a female.
Females have 2 X. If both were active, there would be twice as many of the proteins encoded by the one X in males.
In early development, almost all of one X chromosome in each cell in females becomes inactivated.
How do you think this happens?
Hint: What can you add to DNA to make it inactive? Take a look at page 245.
Is it possible to have a tortoiseshell cat? Why or why not?
No. not usually. It would have to be a Klinefelter Male!
Males only have on X. There are no Barr Bodies. If males inherit a black allele on the X, then they will only have black patches.
What are linked genes?
genes located near each other on a chromosome
Which other gene do you see linked to BRCA1?
How are parental offspring different from recombinant offspring?
Take a look at page 248.
Parental types = inherit a phenotype that matches either of the parents
Recombinants: new combinations of seed shape and color.
What is the null hypothesis of the cross?
GgNn X ggnn?
1:1:1:1
This is the expected ratio for the test cross.
See pg. 247.
Is this what happened? Why or why not?
Take a look at page 249.
If you were to draw a gene map for alleles body color and wings, how many map units would these genes be apart?
17 map units.
Recombination frequency is 17%.
What is nondisjunction?
members of a homologous pair do not move apart in Meiosis I or sister chromatids do not separate during Meiosis II.
Which is more harmful to gamete formation?
Take a look at Figure 12.13 on page 252
monosomy
missing chromosome
ex. Turner Female 45 X
trisomy
Extra chromosome
ex. Down Syndrome 47 XX +21
deletion
chromosomal fragment is lost
duplication
extra copy of a piece of a chromosome
inversion
a chromosomal fragment attaches in reverse order
translocation
a fragment joins a nonhomologous chromosome
Take a look at the chromosome. Which type of alteration is shown?
Translocation
