Biology 1115 Chapter 15
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Biology 1115 Chapter 15
chromosomal basis inheritance
The chromosomal basis of inheritance
Where are genes located?
Explain how the behaviour of chromosomes during meiosis accounts for Mendel's two laws of inheritance.
Law of segregation: when
homologous chromosomes separate
Law of independent assortment
: the way homologous chromosomes
line up at the metaphase plate independently
which gives a variety of gametes
Who was Thomas Hunt Morgan?
he provided the
first solid evidence associating a specific gene with a specific chromosome
by experimenting on fruit flies
What are 3 characteristics that 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 4 pairs of chromosomes
In Morgan's experimental evidence, the
that were common in the fly population was called?
In Morgan's experimental evidence, traits that were
alternative to the wild type
How did Morgan's findings support the chromosome theory of inheritance?
Morgan determined that the white-eyes mutant allele must be located on the
Where are the sex linked chromosomes located?
How are the X and Y sex chromosomes homologous?
ends of the Y chromosome
have regions that are homologous with the X chromosomes
What is the
It's a gene on the Y chromosome that codes for the
development of testes
A gene located on either sex chromosome is called?
True or false. The sex chromosomes have genes for many chromosomes
unrelated to sex
In humans, sex-linked usually refers to a gene the?
What are 3 disorders caused my
in humans? Who are these more common to?
Duchenne muscular dystrophy
more common to
Why are sex-linked recessive disorders much more common in males than in females?
this is because a
female need two copies
of the allele and
male needs only one copy
of the allele, that's why it's more common in males
What is the X inactivation in mammalian females?
one of the 2 X chromosomes in each cell is
randomly inactivated during embryonic development
What happens to the inactive X chromosome?
it condenses into a
, which is no longer functional
If a female is
for a particular gene located on the X chromosome, what happens to her character?
she will be
for that character
What are linked genes?
genes located on the
that tend to be
Morgan noted that the flies body colour and wing size
did not assort independently
and reasons that?
they were on the
the production of offspring with combinations of traits differing from either parent
Define parental types.
offspring with a phenotype matching one of the
Define recombinant types or recombinants.
Offspring with nonparental phenotypes (
new combinations of traits
What does a
50% frequency of recombination
it's the frequency of recombinants observed for any two genes on
Morgan proposed that some process must sometimes
break the physical connection
between genes on the same chromosome, what was this mechanism?
of homologous chromosomes
In a genetic map, the further apart two genes are? (2)
higher the probability that a crossover will occur
between them and therefore the
higher the recombination frequency
Genes that are far apart on the
can have a recombination frequency of what?
what happens in
pairs of homologous chromosomes do
not separate normally
What can result from nondisjunction?
one gamete can receive two of the same type of chromosome and the other gamete receives no copy
Define aneuploidy. What happens to the offspring with this condition?
results from the
of gametes in which
offspring have an abnormal number of a
what is a monosomic zygote?
of a particular chromosome
what is trisomic zygote?
of a particular chromosome
is a condition in which an organism has
more than two complete sets
define triploidy and tetraploidy.
: 3 sets of chromosomes
: 4 sets of chromosomes
Polyploidy is more common in?
which are more normal in appearance, aneuploidy or polyploidy?
Breakage of chromosomes can lead to 4 types of changes in chromosome structure, what are they?
: removes a chromosomal segment
: repeats a segment
: reverses a segment within a chromosome
: moves a segment from one chromosome to another
What is down syndrome?
that results from
three copies of chromosomes 21.
What is the correlation between down syndrome of child and mother's age?
frequency of down syndrome increases with the age of the mother
what is klinefelter syndrome?
result of an
extra chromosome in a male
, producing XXY individuals.
what is monosomy X (turner syndrome)?
produce X0 females, who are sterile.
would you expect females with trisomy X to exhibit major phenotypic differences from normal females?
no because one X will become dysfunctional and form a Barr body
What are the 2 normal exceptions to Mendelian genetics?
1. genes located in the nucleus
2. genes located outside the nucleus
what is genomic printing?
genomic printing involves the
silencing of certain genes
that are "stamped" with an imprint during gamete formation
it appears that genomic imprinting is the result of?
addition of CH3 of DNA
normal development requires that embryonic cells have ______________ of certain genes.
exactly one active copy
what are extranuclear or cytoplasmic genes?
genes found in organelles in cytoplasm
Extranuclear genes are inherited ___________. Why?
because zygote's cytoplasm comes from the egg