BIOLOGICAL INHERITANCE |
SPECIAL CASES
LOCATION OF GENES
Thomas Hunt Morgants theory about the role of chromosomes in inheritance.
DETERMINING SEX
Sexual reproduction in animal is possible because.
SEX CHROMOSOMES
The chromosomas common to both sexes - AUTOSOMES
XX/XY
System
ZZ/ZW System:
INHERITANCE LINKED TO SEX
When a trait is controlled by a gene located on the X chromosome it is said to be linked to the X chromsome.
A female that is heterozygous for a recessive trait can pass the affected allele on to ther offspring.
- Multiple alleles; more than 2 alleles for a trait.
- Gene interaction: a pair of alleles influence the expression of another different pair of alleles.
- Lethal genes: this cause death and modify the normal proportions of phenotypes and genotypes in the offspring.
- Quantitative inheritance: these different traits only vary slightly from each.
LOCATION OF GENES
Thomas Hunt Morgants theory about the role of chromosomes in inheritance.
- Genes are located on chromosomes. Each gene is made up of a segment of DNA.
- Each gene has a specific place on a chromosome.
- The two alleles which determine a spscific trait are located on two chromosomes which are the same size and shape. These are called homologus chromosomes.
DETERMINING SEX
Sexual reproduction in animal is possible because.
- males - sperm
- females - ova
SEX CHROMOSOMES
The chromosomas common to both sexes - AUTOSOMES
XX/XY
System
- The female has 2 identical chromosomes (x).
- The male has X and Y.
- The Y chromosome only has genes that take part in the DEVELOPMENT of male.
- The X chromosome carries genes that are not related to sexual differences.
- maleY: male
- male X: female
- The sex of mammals and some fish and amphibians is determinated by this system.
ZZ/ZW System:
- ZZ - males
- ZW - females
- Birds and reptiles
- Symilar to the XX/XY system
- Only X sex chromosomes
- XX - female
- XY - male
- O - lack of second X
- male determine the sex.
- in some insects
INHERITANCE LINKED TO SEX
When a trait is controlled by a gene located on the X chromosome it is said to be linked to the X chromsome.
A female that is heterozygous for a recessive trait can pass the affected allele on to ther offspring.