Download Genetics Notes: Sex-linked Inheritance

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Genetics Notes: Sex-linked Inheritance
___-____ traits (controlled by genes) are located on the sex chromosomes
Sex chromosomes are ____ and ____
XX = genotype for ______________
XY = genotype for _______
Many sex-linked traits carried only on the ____-chromosome
Human Chromosomes:
There are ____ pairs of human chromosomes (total 46)
The first 22 pairs of chromosomes are called _______________ and
carry genes that code for all physical traits. Autosomes are chromosomes
not associated with ______________ characteristics.
The 23rd pair is called the _____ chromosomes and determines the sex of
the human (male or female)
Sex chromosomes –________ ________ (determine sex)
____ – female
____ - male
Genotypes for sex-linked traits:
Alleles for sex-linked traits are written as _____________ on the ____chromosome. (The Y-chromosome will not carry the allele)
In humans, sex-linked disorders are usually passed-on from ________ to
________ by a defective gene on the X-chromosome.
Examples of sex-linked traits in humans:
Red-Green ___________________________
___________________________________
Duchenne ______________ _____________ (DMD)
Practice Problem 1: Eye color in fruit flies is sex-linked
XRY (red-eyed male) x XrXr (white-eyed female)
Remember: the Y-chromosome in males does not carry traits.
1
Genotypes
XRXR
XRXr
XrXr
XRY
XrY
Xr
Phenotypes
_____-eyed female
Red-eyed _______________ female
____________-eyed female
____________-eyed male
____________-eyed male
Xr
XR
Note: Separate males and females
when giving phenotypic percents
Genotypes: ________ and ________
Phenotypic Percent: _______ Red-eyed carrier
females
_______ White-eyed males
Y
Sex Determination:
When a male and a female have a child, there is always a ____% chance the
child will be __________ and a _____ chance the child will be _______.
Cross a Male (XY) with a female (XX)
X
X
Genotypes: _____, _____
Genotypic Percents: ____% , ____%
Phenotypes: _________, ________
Phenotypic Percents: ____% , ____%
X
Y
Colorblindness:
____________________________ is a sex-linked trait that affects the
ability to see colors correctly.
Red-Green colorblindness is the most common form and afflicts mostly
__________.
Affected people are unable to see the colors red and green normally.
This disorder is given to a son by his _____________.
Practice Problem 2
XB = not colorblind
Xb = colorblind
Parent Genotypes: (Male) XBY
x
XB Xb (female)
XB
Y
XB
Xb
Phenotypic Percents:
_____% Normal visioned females
_____% Carrier females
_____% Normal visioned males
_____% Colorblind males
2
Hemophilia:
Hemophilia is a rare, inherited bleeding disorder in which the __________
doesn’t ________ normally.
Persons who inherit the sex-linked ________________ gene lack a
clotting factor to prevent bleeding.
A hemophiliac may bleed for a longer time than others after an injury.
Even simple cuts may be a serious problem for hemophiliacs.
Sometimes people with hemophilia need injections of a clotting factor or
factors to stop bleeding.
About _____________ people in the United States have hemophilia.
Each year, about ______ babies are born with the disorder.
Hemophilia is an X-linked recessive disorder that affects one in 10,000
__________ and very few females
Since females have ______ ____-chromosomes, they may be __________
of the gene.
Carriers of the gene do ______ show symptoms of the disorder, however,
the defective gene may be passed from a mother to her son.
The ______, who inherits his X-chromosome from his ____________, will
have the disorder because he has only ______ X-chromosome.
Hemophilia Practice Problem 3:
Cross a normal carrier woman with a normal male.
What are the possible genotypes & phenotypes or their children?
P1 generation: ____________ (female) x ________ (male)
_____
XH
Y
______
Genotypes:_________, ________,
_________, ________
Phenotypes: ___% _________ females
___% _________ females
___% ___________ males
___% ___________ males
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Duchenne Muscular Dystrophy
Definition - One of nine types of muscular dystrophy, a group of genetic,
degenerative diseases primarily affecting ____________ ____________.
Cause - An absence of dystrophin, a ___________ that helps keep ______
cells intact.
Onset – Early childhood- about ____-____ years.
Symptoms - Generalized weakness and _______ wasting first affecting the
muscles of the hips, pelvic area, thighs and shoulders. Calves are often
enlarged.
Progression - DMD eventually affects all voluntary muscles, and the ______
and __________________ muscles. Survival is rare beyond the early 30s.
Inheritance - ____-__________ recessive. DMD primarily affects _____,
who inherit the disease through their ______________. Women can be
________________ of DMD but usually exhibit no symptoms.
Duchenne Muscular Dystrophy Problem 4:
Mother is a carrier for Duchene’s Muscular Dystrophy and the father is
normal. What are the genotypes of mom and dad? What are the phenotypes
of the offspring?
P1 generation: __________ (female) x ________ (male)
XD
Xd
XD
Phenotypes: ____% Normal females
____% Carrier females
Y
____% Normal males
____% DMD males
,
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