Chromosomal Theory Of Inheritance And Sex Linked Genes Flashcards
Explain what are holing Oue chromosomes
Diploid organisms have 2 set of chromosomes; two of each kind
Each member of a pair carries the same genes ( though possibly different alleles) and are referred to as homologous chromosomes
On the 23 pairs of chromosomes that human possess how many are sex chromosomes ? What about the others
1 pair of chromosomes (sex chromosomes)
The 22 other pairs (autosomes) carry genes necessary for normal development
What do sex chromosomes carry
They carry the genes for the sex determination of an individual and control the development of most of the secondary sexual characteristics
They also carry genes for other characteristics
What are the kinds of sex chromosomes existing in mammals ?
X and Y chromosome
Female carry to X
Mâle carry one X and One Y
Sex chromosomes behave as homologous pairs in males and females
How is sex determined
Females are homozygous XX and all their gametes (ova) carry a X chromosome
While male are heterozygous XY and 50% of their gametes (sperm) carry a X chromosome and the other 50% carry a Y
XX gives a daughter
XY gives a son
What are the sex determination patterns in other organisms ( Birds, Grasshoppers and bees)
Birds
Male are homozygous ZZ
Females are heterozygous ZW
Grass hoppers
Females are homozygous XX
Males are XO ( absence of one chromosome)
Bees
Have no sex chromosomes
Females are diploid (develop from fertilized eggs)
Males are haploid
Develop from unfertilized eggs
What happens during embryonic development in mammalian females
One X chromosome is randomly inactivated and in each cell the inactive c condenses in a compact object called a Barr body
Why does a X chromosome becomes inactive in mammalian females
Dosage compensation : ensures a equal level of expression for the sex chromosomes despite a differing number of chromosomes in males and females
How are called genes located on sex chromosomes
Sex linked gene ( their is a few on the Y and most are on the X)
How many alleles do females and males possess for each characteristic
2 for females and 1 for males
Females can be homozygous or heterozygous
Males are only hemizygous
Who suggested the central role for chromosomes and announced a paper for the rediscovery of mendel’s work
Carl Correns
Who proposed the chromosomal theory of inheritance and what was it based on
Walter Sutton
And it was based on observations that similar chromosomes paired with one another during meiosis
What does the chromosomal theory of inheritance states
- genes have specific positions on chromosomes
- it is the chromosome that undergo segregation and independent assortment
Who proposed the first solid evidence associating a specific gene with a specific chromosome and what was his experiment based on
Thomas Hunt Morgan
Experimented on fruit flies
Why did Morgan choose fruit flies
Easy to breed
Breed at a high rate
Have a relatively short life cycle
Only four pairs of chromosomes
In Morgan experiments what are wild types and mutents
Wild types : term used to describe the phenotype/genotype in most natural populations of drosophila (fruit flies )
- special notation for fuit flies ++
Mutants
Natural variants
Mutant alleles are designated by symbols that are typically abbreviations of the mutant name
