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Name: Per: Date: 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 3 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 , 4