Ch.15: Chromosomes and Inheritance Flashcards
Mitosis and meiosis were first described in
late 1800s
The chromosome theory of inheritance states:
Mendelian genes have specific loci (positions) on chromosomes
Chromosomes undergo segregation and independent assortment
The behavior of chromosomes during meiosis was said to account for Mendel’s
law of segregation and law of independent assortment
an embryologist
Particular genes are on particular chromosomes
Still didn’t know about DNA
Thomas hunt morgan
What did Morgan worked with?? It is a model organisms that has certain characteristics that are easily observed such as eye color
fruit flies
Several characteristics make fruit flies a convenient organism for genetic studies:
They breed at a high rate
A generation can be bred every two weeks
They have only four pairs of chromosomes
or normal, phenotypes
Types that were common in the fly populations
wild type
Traits alternative to the wild type are called
mutant phenotypes
In one experiment, Morgan mated male flies with white eyes (mutant) with female flies with red eyes (wild type)
The F1 generation all had red eyes
The F2 generation showed the 3:1 red:white eye ratio, but only males had white eyes
Morgan determined that the white-eyed mutant allele must be located on the ____________
x chromosome
A gene located on either sex chromosome is called a
sex-linked gene
Some disorders caused by recessive alleles on the X chromosome in humans:
Color blindness
Duchenne muscular dystrophy
Hemophilia
For a recessive sex-linked trait to be expressed
A female needs two copies of the allele
A male needs only one copy of the allele
sex-linked recessive disorders are much more common in
males than females
The production of offspring with combinations of traits differing from either parent
gene recombination
Offspring with a phenotype matching one of the parental phenotypes are called
parental types
Offspring with nonparental phenotypes (new combinations of traits) are called
recombinant types or recombinants
3 types Types of Chromosomal Alterations
Nondisjunction
Aneuploidy
Alteration of Chromosome Structure
pairs of homologous chromosomes do not separate normally during meiosis
As a result, one gamete receives two of the same type of chromosome, and another gamete receives no copy
nondisjunction
results from the fertilization of gametes in which nondisjunction occurred
Offspring with this condition have an abnormal number of a particular chromosome
aneuploidy
zygote has only one copy of a particular chromosome
monosomic
zygote has three copies of a particular chromosome
trisomic
is an aneuploid condition that results from three copies of chromosome 21
downs syndrome
the result of an extra chromosome in a male, producing XXY individuals
klinefelter syndrome
Monosomy X, called ______ _______, produces X0 females, who are sterile; it is the only known viable monosomy in humans
Only possible because it occurs on sex chromosomes
Turners syndrome
is a condition in which an organism has more than two complete sets of chromosomes
Triploidy (3n) is three sets of chromosomes
Tetraploidy (4n) is four sets of chromosomes
common in plants not animals
polyploidy
Breakage of a chromosome can lead to four types of changes in chromosome structure:
Deletion removes a chromosomal segment
Duplication repeats a segment
Inversion reverses a segment within a chromosome
Translocation moves a segment from one chromosome to another
The syndrome cri du chat (“cry of the cat”), results from a specific deletion in
chromosome 5
are genes found in organelles
Mitochondria and chloroplasts carry small circular DNA molecules
extranuclear genes or cytoplasmic genes
Extranuclear genes are inherited
maternally because the zygote’s cytoplasm comes from the egg.
What are some examples of Some defects in mitochondrial genes prevent cells from making enough ATP and result in diseases that affect the muscular and nervous systems
mitochondrial myopathy and Leber’s hereditary optic neuropathy
