U2L9 Flashcards
Mendelian inheritance has its physical basis in the
Behaviour of chromosomes
What exhibit unique patterns of inheritance?
Sex linked genes
Why are linked genes inherited together?
Because they are located near each other on the same chromosome
What causes genetic disorders?
Alterations of chromosome number or structure
What does the chromosome theory of inheritance state?
- Mendelian genes have specific loci (positions) on chromosomes
- chromosomes undergo segregation and independent assortment
What discovery of Morgan’s helped develop the chromosome theory of inheritance
His discovery of a trait that correlated with the sex of flies
What two varieties of sex chromosomes are found in humans?
A larger X chromosome and a smaller Y chromosome
What do the ends of Y chromosomes have?
Regions homologous with corresponding regions of X chromosome that allows the two to behave as homologues during meiosis in males
What does the SRY gene do?
On Y chromosome and codes for a protein that directs development of male anatomical features
True or false: the X chromosome has genes for many characters unrelated to sex
True
True or false: The Y chromosome mainly encodes genes related to sex determination
True
For a recessive X linked trait to be expressed:
- Females need two copies of the allele (homozygous)
- Males need only one copy of the allele (hemizygous)
Examples of some disorders caused by recessive alleles on the X chromosome?
Colour blindness
Duchenne muscular dystrophy
Hemophilia
Sex chromosomes in chickens?
ZW: female
ZZ: males
What is X inactivation in female mammals?
One of the two X Chromosomes in each cell is randomly inactivated during embryonic development
What does an inactive X condense into?
A Barr body
If a female is heterozygous for a particular gene located on the X chromosome, she will be…
A mosaic for that character
Define parental types
Offspring with a phenotype matching one of the parental phenotypes
Define recombinant types
Offspring with non parental phenotypes (new combinations of traits)
What is the frequency of recombination observed for any two genes on different chromosomes?
50%
Why did morgan propose the idea of crossing over of homologous chromosomes?
Discovered that gene linkage was incomplete due to observing recombinant phenotypes and proposed that some process must be breaking the physical connection between genes on the same chromosome
What can lead to miscarriages?
Large scale chromosomal alterations such as changes in number or structure
Define meiotic nondisjunction
Pairs of homologous chromosomes do not separate normally during meiosis, as a result one gamete receives two copies of a chromosome and the other receives 0
Aneuploidy
results from fertilization of gametes in which nondisjunction occurred - offsprings have an abnormal number of a chromosome
