Lecture 7

Question 1

What system of sex determination do mammals use and what do birds use?

Answer 1

Mammals
X/Y system - male XY female XX
Sex depends on nature of sex chromosome carried by male gamete
Birds
Z/W system - ZZ male ZW female
Sex depends on nature of chromosome carried by female gamete

Question 2

How is sex determined in insects such as grasshoppers, bees and ants?

Answer 2

Haplo-diploid system
X0 (hemigametic) - male
XX (homogametic) - female
Only one type of sex chromosome 
Males develop from unfertilised eggs females from fertilised ones

Question 3

What gene in humans has been identified as to being the possible gene for the male phenotype?

Answer 3

SRY gene on the Y chromosome
(Sex determining Region on Y)
Gene product initiates series of events that start male development

Question 4

What are sex linked genes?

Answer 4

Genes found on a sex chromosome
X linked on X chromosome
Y linked on Y chromosome
Many X linked genes
Very few Y linked genes
X linked genes never pass from father to son
Y linked genes alway pass from father to son

Question 5

Name some X linked traits that can be inherited

Answer 5

Haemophillias A and B
Duchenne muscular dystrophy
Red/green colour blindness

Question 6

What are the 2 components of prokaryotic and eukaryotic genomes?

Answer 6

Chromosomal DNA
Extra-chromosomal DNA
- plasmids in prokaryotes
- mitochondrial and chloroplast DNA in eukaryotes

Question 7

Features of mitochondrial and chloroplast DNA

Answer 7

Both double stranded circular DNA molecules
- mitochondrial DNA ~ 13-18x10^3 base pairs
- chloroplast DNA ~ 130-150x10^3 base pairs
Encode products used within each organelle
Some components though are encoded within the nuclear genome
Inheritance of mt and cp DNA is only maternal
- inherited through cytoplasm of female gamete

Question 8

What diseases result from mutations in mitochondrial or chloroplast DNA?

Answer 8

Hereditary optic neuropathy (blindness)

Affected mother passes mutant DNA to all her offspring and thus all are affected

Question 9

When genotypic sex established?

Answer 9

At conception