Presentation on theme: "Tracing the Inheritance of the Human Y Chromosome"— Presentation transcript:
1 Tracing the Inheritance of the Human Y Chromosome Women have sex chromosomes of XX, and men have sex chromosomes of XY.Which of a man's grandparents could not be the source of any of the genes on his Y-chromosome?Father's Mother.Mother's Father.Father's Father.Mother's Mother, Mother's Father, and Father's Mother.Mother's Mother.
2 Tracing the Inheritance of the Human X Chromosome Women have sex chromosomes of XX, and men have sex chromosomes of XY.Which of a women's grandparents could not be the source of any of the genes on either of her X-chromosomes?Mother's Father.Father's Mother.Mother's Mother.Father's Father.Mother's Mother and Mother's Father
4 Is there a special pattern of inheritance for genes located on the X or Y chromosome? Yes, they are called sex-linked genes.More than 100 sex-linked genetic disorders have been mapped on the X chromosome.Y chromosomes are smaller than X chromosomes and appear to only contain a few genes.
5 Red-Green Colorblindness The most common type of red-green color perception defect is due to a mutation on the X-chromosome (i.e. a red-green color blind allele). X-linked red-color blindness is a recessive trait. Females heterozygous for this trait have normal vision. The color perception defect manifests itself in females only when it is inherited from both parents. By contrast, males inherit their single X-chromosome from their mothers and become red green color blind if this X-chromosome has the color perception defect.
6 HemophiliaHemophilia in humans is due to an X-chromosome mutation. What will be the results of mating between a normal (non-carrier) female and a hemophilac male?half of daughters are normal and half of sons are hemophilic.all sons are normal and all daughters are carriers.
7 Chromosomal Disorders In some disorders, entire chromosomes, or large segments of them, are missing, duplicated, or otherwise altered.The most common error is nondisjunction, when homologous chromosomes fail to separate during meiosis.If nondisjunction occurs, the number of chromosomes in the gametes can be abnormal, and a disorder may result.
8 Homologous chromosomes fail to separate NondisjunctionSection 14-2Homologous chromosomes fail to separateMeiosis I:NondisjunctionMeiosis IIGo to Section:
9 Homologous chromosomes fail to separate NondisjunctionSection 14-2Homologous chromosomes fail to separateMeiosis I:NondisjunctionMeiosis IIGo to Section:
10 Homologous chromosomes fail to separate NondisjunctionSection 14-2Homologous chromosomes fail to separateMeiosis I:NondisjunctionMeiosis IIGo to Section:
12 Down’s Syndrome Occurs in 1/800-1,000 births Caused by nondisjunction Trisomy 21 = three copies of chromosome 21
13 Frequency of Down Syndrome Per Maternal Age Age (years)Frequency of Fetuses with Down Syndrome to Normal Fetuses at 16 weeks of pregnancyFrequency of Live Births of Babies with Down Syndrome to Normal Births----1 / 12501 / 14001 / 11001 / 900321 / 750331 / 4201 / 625341 / 3251 / 500351 / 2501 / 350361 / 2001 / 275371 / 1501 / 225381 / 1201 / 175391 / 1001 / 140401 / 75411 / 601 / 85421 / 451 / 65431 / 351 / 50441 / 301 / 4045 and older1 / 201 / 25Return to Prenatal Testing for Down Syndrome Return to Down Syndrome: Health Issues Homepage
14 Down’s SyndromeThe image shows a karyotype of a person with Down’s Syndrome, Trisomy 21
15 Sex Chromosome Disorders Turner’s Syndrome (XO)underdeveloped ovaries, short stature, webbed neck, and broad chest. Individuals are sterile, and lack expected secondary sexual characteristics. Mental retardation typically not evident.
17 Sex Chromosome Disorders Klinefelter’s Syndrome (XXY)Nondisjunction in malesSome development of breast tissue, little body hair is present; typically tall, with or without evidence of mental retardation. Males with XXXY, XXXXY, and XXXXXY karyotypes have a more severe presentation, and mental retardation is expected.
19 Some Autosomal Disorders in Humans Type of DisorderDisorderMajor SymptomsDisorders caused by recessive allelesAlbinismLack of pigment in hair, skin, and eyesCystic FibrosisExcess mucus in lungs, digestive tract, liver; increased susceptibility to infections; death in childhood unless treatedPhenylketonuriaAccumulation in brain cells; lack of normal pigment; mental retardationTay-Sachs DiseaseLipid accumulation in brain cells; mental deficiency; blindness; death in early childhoodDisorders Caused by dominant allelesAchondroplasiaDwarfism (one form)Huntington’s DiseaseMental deterioration and uncontrolled movements; appears in middle ageDisorders caused by codominant allelesSickle Cell AnemiaSickled red blood cells; damage to many tissues