Chromosomal Inheritance

chromosome theory of inheritance

1. genes have specific loci along chromosomes

2. chromosomes undergo segregation and independent assortment

3. autosomal and sex chromosomes

sex-linked gene

any gene that is located on a sex chromosome

barr body

inactive X chromosome; regular gene dosage in females during embryonic development; ex. allele for fur color is on X, only female cats can be tortoiseshell or calico

what chromosome is required for development of testes

Y chromosome

SRY gene

sex-determining region of Y

what happens if genes are found on different chromosomes / far apart on the same chromosome

assort independently and are said to be unlinked

what happens if genes are close together on the same chromosome

said to be linked

recombination frequency

a way to see if two genes are linked and how tightly by using data

genetic reconstruction

production of offspring with combination of traits different from each parent

parental types

offspring looks like parents

recombinants

different from parents

what if results do NOT follow mendel’s law of independent assortment

the genes are probably linked

the further apart 2 genes on same chromosome

higher the probability of crossing over and higher the recombination frequency

recombination frequencies can be used to build

linkage maps

genomic imprinting

process by which only one copy of a gene in an individual is expressed, while other copy is suppressed

gene expression is silenced by the addition of what to the DNA during gamete formation

methyl groups (methylation)

what happens if some irregular genes are located in organelles

will be passed onto children if the mother has it; but not the father

what can cause alterations to chromosomal numbers

physical or chemical disturbances or errors during meiosis

nondisjunction

members of a pair of homologous chromosomes do not move apart properly during meiosis I or sister chromatids fail to separate during meiosis II

nondisjunction explained simply

one gamete receives two of the same type of chromosome and the other gamete receives no copy

aneuploidy

abnormal number chromosomes in a pair. ex. monosomic trisomic

polyploidy

having 2+ complete sets of chromosomes

what are the types of alterations of chromosomal structure

1. deletion

2. duplication

3. inversion

4. translocation

deletion

chromosome fragment is lost; can lead to missing certain genes

duplication

a “deleted” section could become attached to as an extra segment to a sister chromatid

inversion

a fragment may reattach in reverse orientation

translocation

fragment joins a nonhomologous chromosome