DNA IDENTITY AND DISEASE

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Y-chromsome ANALYSIS:

By the end of this lecture aim is to :

1) Evaluate the use of Y -chromosome markers to identify individuals

2) Discuss how alterations to the T-chromosome can be linked to pathologies

3) explain how the amelogenin is used to differentiate the males and females

5)describe how Y-STR and Y-SNP are being used to type individuals for genealogy studies

STR DETECTION:

-needs a detection method which can distinguish 2-4 bases difference

-capillary electrophoresis

Y CHROMOSOME structure

1) Contains 78 protein coding genes

2) encodes 27 proteins

3) HEMIZYGOUS ( has no partner)

DISORDERS ASSOCIATED WITH Y-CHROMOSOME:

1) Infertility ( De novo deletion of q-arm ( long arm) , sometimes due to recombination.

2) rare single gene abnormality in USP9Y

Y- chromosome azoospermia:

1) infertility

2) Y chromosome infertility by azoospermia (

there is Mild, severe and moderate types of azoospermia:

Syndromes related to Y chromosome

1) 46, XX testicular disorder of sex development

translocation of the SRY gene onto an X chromosome. Foetus with affected X chromosome will develop as a MALE

2) 48, XXYY syndrome

Extra X and Y chromosomes in a male's cells. Interferes with male sexual development and reduces levels of testosterone

3) 47, XYY syndrome

One X chromosome and 2 Y's in each cell for a total of 47 chromosomes. Associated with tall stature, learning difficulties

6) 46, XY/47, XYY mosaicism

Y-chromosome in FORENSICS:

Y-chromosome typing:

1) sexual assault

2) amelogenin deficient males

3) paternity testing

4) missing persons

5) migration and evolutionary studies

6) historical and geneological research

Differential extraction of samples

Remove a

portion of

the mixed

stain

Perpetrator’s sperm mixed with victim’s epithelial cells

Add SDS, EDTA and proteinase K

(cell lysis buffer),Incubate at

37 degrees and centrifuge

sperm

pellet

REMOVE

supernatant = FEMALE FRACTION

Add SDS, EDTA and proteinase K + DTT

DTT lyses

sperm

heads = sperm pellet = MALE FRACTION

Differentiating between males and female samples:

1) large amounts of cells- chromosome analysis ( KARYOTYPING)

2) bodies ( small particles seen in serology)

3) typing for genes specific to Y-chromosome ( NRY or MSY region)

4) Y-STR

5) Y-SNP

6) Genes which vary between X and Y chromosome e.g. Amelogenin

What is Amelogenin?

Gene occurs in male and female

for X chromsome - 103 bp

for Y chromsome- 109 bp

Why do male profiles have both 103 and 109 bp fragments?

Ans: Because they have X and Y chromosomes together whereas females only have XX chromosomes

The structure of Amelogenin (AMEL) , the Y -chromosome is much smaller (50Mb) than the X chromosome (154 Mb).

Y chromosome markers:

1) Amelogenin is useful to determine if a sample is from a female or male

2) Other Y chromosome STR markers are utilised to identify individuals

3) for mixed samples where the DNA from the male is virtually undetectable ( sexual assault) - y chromosome testing may yield a profile

Y-STR

DYS38911

DYS385

DYS393

DYS19

Y-SNP

single nucleotide polymorphisms (SNP)

very low mutation rates

for example: M11, M119 , M130 etc and SRY+ 465 and TAT

Geneology testing

1) significant amount of interest by public to find out about their ancestors '' who do you think you are''

2) surname mapping can be linked to the Y chromosome: