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Applied Biology - Week 5 - Lecture 1 (Linked genes tend to be inherited…
Applied Biology - Week 5 - Lecture 1
Locating genes along chromosomes
A genes location can be seen by tagging isolated chromosomes with a fluorescent dye
Mendelian inheritance has its physical basis in the behaviour of chromosomes
chromosomes have Mendel's heritable factors (genes)
Correlating behaviour of a Gene's Alleles with Behaviour of a Chromosome Pair
Sex-linked genes exhibit unique patterns of inheritance
In humans and other animals there is chromosomal basis of sex determination based on X and Y
A gene located on a sex chromosome is called a sex-linked gene
Y linked chromosomes passes only from father to son, deletions are a frequent cause of male fertility
X linked recessive disorders are much more common in males than in females
e.g. Red-green colour blindness, Maemophilia
X inactivation in female mammals
one of two chromosomes in each cell is randomly inactive during embryonic development
if female is heterozygous for a gene located on x chromosome then she will be a mosaic for that character
Other animals have different methods of sex determination
Linked genes tend to be inherited together because they are located near each other on the same chromosome
Each chromosome has 100 or 1000's of genes
Genes located closely together tend to be linked
Genetic Recombination and Linkage
The genetic findings of Mendel and Morgan relate to the chromosomal basis of recombination
Recombination of unliked genes = independent assortment of chromosomes
Recombination of Linked Genes: Crossing Over
Morgan discovered that genes can be linked, but linkage is incomplete, because come recombinant phentoypes were observed
Breaking this connection between genes on the same chromosome was the crossing over of homologous chromosomes
New combinations of Alleles: Variation for Normal Selection
Recombination generates new allele combinations
Random fertilisation further increases variation combinations
This abundance of genetic variation underpins how natural selection works
Mapping the distance between genes using recombination data
Such genes are physically linked, but genetically unlinked and bave as if found on different chromosomes
Alterations of chromosome number or structure cause genetic disorders
Large scale alterations can cause abortions or developmental disorders
Plants tolerate genetic changes better than animals do
Abnormal Chromosome number
Nondisjunction = homologous chromosomes do not separate normally during meiosis
Aneuploidy = fertilisation of gametes where nondisjunction occurred
Monosomic zygote = has only one copy
Trisomic zygiote = three copies
Polyploidy = organism with more than tow complete sets of chromosome
Triploidy = three sets of chromosomes
Tetraploidy = four sets of chromosomes
Common in plants, not in animals
Polyploids are more normal in appearance then aneuploids
Alterations of chromosome structure
Deletion
Duplication
INversion
Translocation