5.3 Inheritance Patterns for Linked Genes Flashcards
What is the chromosome theory of inheritance?
states that genes are located at specific positions on chromosomes, and the segregation and assortment of these chromosomes during meiosis is responsible for
inheritance patterns
Define the term “gene locus.”
gene locus (plural gene loci) is a site on a chromosome that a specific gene occupies
What are sex chromosomes?
XX and XY chromosomes
Define the term “genetic linkage.”
ability for several genes on the same chromosome to be inherited together
Where are the oldest individuals located on a pedigree?
left most side
Gene loci far apart =
regular meiosis
Gene loci close together =
linked genes
Recombination frequency
Scientists can look at the frequency with which certain genes turn up together
Genetic mapping
diagram used to show relative locations and distances of genes on a chromosome
Sex-linked trait
Any gene located on a sex chromosome
Give 2 examples of recessive x-linked disorders
Hemophilia and red-green colour blindness
What is SRY?
“sex determining region” on the Y chromosome
How are chromosomes related to the
inheritance of traits?
segregation and assortment of chromosomes during meiosis is responsible for inheritance patterns
How is distance between gene loci related to
genetic linkage?
gene loci close together = alleles stay together=linked genes
gene loci far apart = new combo of alleles=regular meiosis
Describe two differences between X and
Y chromosomes in humans
females have 2 X chromosomes, males have 1 X and 1 Y (hemizygous for x-linked traits)
What is the relationship between alleles and
gene loci?
The alleles of a gene reside at the same
location, or locus, on homologous chromosomes.
What inheritance pattern would you expect
to see for a Y-linked trait in humans?
-females wouldn’t get it (don’t have Y)
-also would be hemizygous in males (only 1 Y)
-no carriers
Which human chromosome carries most of the
genes for sex-linked traits?
X chromosome
Male birds have two Z chromosomes (ZZ),
while female birds have a Z chromosome and a
W chromosome (ZW). Suggest why birds would
make poor model organisms for understanding
the inheritance of human sex-linked traits
-birds use different chromosome letters for sex
chromosomes than humans do, which would make it
confusing
when you have only one x allele what is that called
hemizygous
in a pedigree, what do the circles symbolize
females
in a pedigree, what do the squares symbolize
males
what do the shaded shapes represent in a pedigree
affected
chromosome theory of inheritance
-genes are located at specific positions on chromosomes
-segregation and assortment of these chromosomes during meiosis is responsible for inheritance patterns
-Meiosis explains Mendel’s laws
gene locus
Gene locus: a site on a chromosome that a specific gene occupies
gene loci
The alleles of a gene reside at the same _____, or locus, on ____________
location; homologous chromosomes
Homologous chromosomes bear either the same alleles (_______) or different ones (______) at a particular locus
homozygous; heterozygous
Linkage
Occurs when one gene affects the expression of another
Independent Assortment
-One gene doesn’t affect the other—they act independently
-The chance of having one characteristic would be unrelated to having another characteristic—it is random
-Each allele has the same chance of being expressed in the gametes
Independent Assortment
The chromosomes assort independently during meiosis, producing 4 _________ in the gametes
possible genotypes
genetic linkage
Genetic linkage: is the ability for several genes on the same chromosome to be inherited together
Genes close together are less likely to assort _____, one will affect the other
independently
true or false: Women are more likely to get affected by a y-linked disorder
false (females don’t have a Y chromosome, so we would never get affected by the disorder)
if you have an affected female(x-linked disorder), what must that mean about her parents?
-father-must be affected (hemizygous)
-mother-carrier or affected
gene loci far apart=
reg. meiosis
gene loci close together=
alleles linked –> related
The distance between loci is directly related to ________
genetic linkage
scientists can look at the frequency with which certain genes turn up together, this value is called the ______________
recombination frequency
recombination frequency
Can be used to map the distance between gene loci on a chromosome – smaller recombination frequency = closer together
genetic mapping
Genetic mapping: a diagram used to show relative locations and distances of genes on a chromosome
how frequently something will recombine with the other gene because they’re so close to one another
recombination frequency
Any gene located on a sex chromosome is called a
sex-linked trait
Females would have to inherit 2 copies of a _____ allele to be affected (XrXr)
recessive
Males would only need ____ copy to be affected (XrY)
one
most sex linked traits occur on the __ chromosome
X (X-linked)
Affects 4-8% of males and 0.4% of females
–>which sex-linked disorder is this?
Red-Green Colour Blindness
1 in 1000 babies (most boys)
Hemophilia
hemophilia
“bleeder disease”
Blood fails to clot normally
name 2 recessive x-linked disorders
red-green colour blindness
hemophilia
Sex-linked disorders are more common in
males
If males inherit the X-linked trait from ____, it will be expressed (XrY)
mom
Females need to inherit __ copies in order to be affected (XrXr)
2
y-linked disorders
mutations on the Y chromosome
what does SRY stand for and where is it located?
SRY – “sex determining region” on the Y chromosome
sex determining region
-Gene for testis-determining factor
-A mutation in this region results in XY females with disorders in the development of the reproductive system
A female carrier for haemophilia has children with an unaffected male.
What proportion of their daughters will have haemophilia?
How many will be carriers?
What proportion of their sons will have the disorder?
0% of the daughters will be affected
50% of the daughters will be carriers
50% of the sons will have the disorder
A female carrier for haemophilia has children with an affected male.
What proportion of their daughters will have haemophilia?
How many will be carriers?
What proportion of their sons will have the disorder?
What are the chances of having a son who is also a haemophiliac?
50% of their daughters will have the condition
The other 50% will be carriers
50% of the sons will have the disorder
50% chance of having a son X 50% chance of having the disorder = 25%
