BIO 30 Reviewer For 2nd EXAM

BIO 30 Lect 4

Linkage

• linear arrangement of non-allelic genes on the same chromosome

• genes do not assort independently

• genes can be separated by crossing-over.

X-Linked Mutants

• % recombination is used as a measurement of distance

• one map unit or 1 cM (centimorgan) is the distance that gives 1% recombinatio

Linkage Map

• linear arrangement of non-allelic genes on the chromosome

• distance between genes is based on % recombinatio

Sex Llinkage

sex chromosomes carry other genes aside from genes for sex determination

X-Linked inheritance

• it be due to sex-linked recessive genes

Y-Linked Inheritance

genes on the Y chromosome

shows holandric transmission

father to son transmission

Webbing of toes, Hypertrichosis

Examples of the Y-LInked Traits

colorblindness, hemophilia, absence of central incisors, congenital deafness, congenital cataract

Examples of X linked inheritance

Genetic sex determination, environmental Sex Determination, Chromosomal sex determination

types of sex determination

Genetic Sex Determination

a. Specific genotypes

-Neurospora

- Chlamydomonas

b. multiple alleles

e.g. in Hymenopterans

9 alleles

heterozygous: female

homozygous: male

c. multiple genes

- e.g. in Boniellia

Environmental sex determination

it is a sex determination that has example of: Coral reef fish (Labroides dimidiatus)

- e.g. in marine worms

- if free swimming at larval stage (female)

- larva attached to female adult becomes male due to the masculinizing hormones secreted by female

chromosomal Sex Determination

it has an example of:

• Mc Clung 1900

• association of sex characteristics with a particular chromosome

Mary Lyon, 1961

she compose Lyonization or X-inactivation