Ro_Lecture3

Ro_Lecture3 - Sex-linked Although these were convincing...

Info iconThis preview shows pages 1–9. Sign up to view the full content.

View Full Document Right Arrow Icon
1 Sex-linked Although these were convincing correlations, actual proof of the chromosome theory required the discovery of sex linkage. Remember, Mendel had found that reciprocal crosses produce equal results with respect to the progeny. In general geneticists confirmed his results. However exceptions did arise. The most famous exception was that discovered by Tomas Hunt Morgan in the fruit fly Drosophila melanogaster. Drosophila eyes are normally bright red. Morgan discovered an exceptional white-eyed male. He performed the following crosses:
Background image of page 1

Info iconThis preview has intentionally blurred sections. Sign up to view the full version.

View Full DocumentRight Arrow Icon
2 Bridges assumed that XXX and Y0 progeny die and the only two viable progeny types were XXY and X0 In this model sex is determined by the number of X chromosomes rather than the presence or absence of the Y chromosome This model makes a strong prediction that is genes reside on chromosome the exceptional red-eyed males should be X0 and the exceptional white eyed females should be XXY. (something to think about: What classes of progeny would be expected from the cross X w X w Y x X W Y ?)
Background image of page 2
3 Bridges and Triploids White X w X w Y red X W Y
Background image of page 3

Info iconThis preview has intentionally blurred sections. Sign up to view the full version.

View Full DocumentRight Arrow Icon
4 Triploidy Species that are triploid, reproduce asexually (plant species) What are the consequences of triploidy during mitosis and meiosis? Haploid Diploid Triploid Mitosis
Background image of page 4
5 Meiosis and triploids 4N 3N 3N 2N Triploids produce unbalanced gametes MeiosisI This is for one chromosome. If there are n chromosomes in an organism, then balanced gametes (equal copies of all chromosomes) is very rare.
Background image of page 5

Info iconThis preview has intentionally blurred sections. Sign up to view the full version.

View Full DocumentRight Arrow Icon
6 Seedless watermelons Triploidy is useful in agriculture. Polyploid plants are bigger than diploid plants Biological control: Triploid carp- eat weeds in waterways but are unable to replicate and compete with beneficial fish species. Take a diploid watermelon species and add colchicine- disrupt microtubules and induce tetraploids Cross a tetraploid with a diploid Triploid watermelon produced. This grows and when it produces seeds these are aneuploid (white seeds) Tetraploid parental lines normally have a light rind without stripes. By contrast, the diploid parent almost always has a fruit with a striped rind. The resulting hybrid triploid seedless melon will inherit a striped pattern.
Background image of page 6
7 And triploid toads Triploid toads Nature Genetics 30, 325 - 328 (2002) Tetraploid green toads reproduce through diploid eggs and sperm cells. A new taxon was discovered at an isolated site in the Karakoram mountain range. Every wild toad caught (n=131) from eight localities was triploid Did not find a single diploid or tetraploid Batura toad. Both males and females were found 3N female 3N male N elimination N eliminatio 2N 2N 4N 2N N 3N
Background image of page 7

Info iconThis preview has intentionally blurred sections. Sign up to view the full version.

View Full DocumentRight Arrow Icon
8 Sex in organisms Under the microscope Bridges examined the cytology of the exceptional progeny and found the following: Sex chromosomes and sex linkage: In Drosophila, it is the number of X's that determine sex while in mammals it is the presence or absence of a Y chromosome that determines sex. Species
Background image of page 8
Image of page 9
This is the end of the preview. Sign up to access the rest of the document.

Page1 / 36

Ro_Lecture3 - Sex-linked Although these were convincing...

This preview shows document pages 1 - 9. Sign up to view the full document.

View Full Document Right Arrow Icon
Ask a homework question - tutors are online