Lecture 6 Flashcards
What are some Y-linked diseases?
Male infertility, excessive hair on the ear pinna (Hypertrichosis pinnae), retinitis pigmentosa, XYY syndrome
XYY Syndrome
Genetic condition in which a human male has an extra male (Y) chromosome, giving a total of 47 chromosomes instead of the usual 46; occurs in about 1/1000 male births
X-Linked Recessive Inheritance
Mode of inheritance in which a mutation in a gene on the X chromosome causes the phenotype to be expressed in males (they would be necessarily hemizygous for the gene mutation because they have one X and one Y chromosome)
Dosage Compensation
Inactivation of 1 X chromosome to compensate for different X dosage between the sexes
Lyon Hypothesis
Named after Mary Lyon, suggested that dosage compensation in mammals is by inactivation of all but one X chromosome in cells with more than 1 X chromosome; the Barr body, visible in some female mammalian cells, is an inactivated X chromosome
Mosaicism
Condition in which cells within the same person have a different genetic makeup
Ex: When different X chromosomes are inactivated in neighboring cells
Xic
X inactivation centers; they are counted and if there are 2 or more, Xist (Xi specific transcript) is turned on and its RNA product coats one of the X chromosomes - randomly determined; additional proteins recognize the inactive X and cause condensation and permanent inactivation; this process is undone during meiosis
Most Common X-Linked Recessive Disorders
Red-Green color blindness, hemophilia A/B, duchenne muscular dystrophy, beckers muscular dystrophy, X-linked ichthyosis, X-linked agammaglobulinemia (XLA), and glucose-6-phosphate dehydrogenase deficiency
Genetic Linkage
Tendency of alleles that are located close together on a chromosome to be inherited together during meiosis; linked genes will segregate together and not obey Mendel’s 2nd law
Linkage Disequilibrium
Non-random association of alleles at different loci; loci are said to be in linkage disequilibrium when the frequency of association of their different alleles is higher or lower than what would be expected if the loci were segregating independently
What happens when the SRY gene is translocated to the X chromosome in female genotypes?
Some male sex characteristics are present, such as underdeveloped external genetalia
Polygenic Traits
Traits that are produced by the interplay of many sets of genes
Non-Mendelian Inheritance
Refers to any pattern of inheritance in which traits do not segregate in accordance with Mendel’s laws
Complete Dominance
Phenotype of the heterozygote is the same as the phenotype of one of the homozygotes
Incomplete Dominance
Phenotype of the heterozygote is intermediate (falls within the range) between the phenotypes of the 2 homozygotes
Codominance
Phenotype of the heterozygote includes the phenotypes of both homozygotes
Penetrance
Percentage of individuals having a particular genotype that express the expected phenotype
Expressivity
Degree to which a character is expressed
Complete Penetrance
Everyone who inherits the disease causing alleles has some symptoms
Incomplete Penetrance
Some individuals do not express the phenotype even though they inherit the alleles; an example is polydactyly
Variable Expression
Symptoms vary in intensity in different people; for example, two extra digits versus three extra digits in polydactyly
Lethal Allele
Causes death at an early stage of development, and so some genotypes may not appear among the progeny
Gene Interaction
Effects of genes at one locus depend on the presence of genes at other loci; can produce novel phenotypes
Gene Interaction with Epistasis
One gene masks the effect of another gene
Blood Type A
Genotype: AA or AO
Antigen Type: A
Antibodies Made: Anti-B
Can Receive Blood From: A or O
Blood Type B
Genotype: BB or BO
Antigen Type: B
Antibodies Made: Anti-A
Can Receive Blood From: B or O
Blood Type AB
Genotype: AB
Antigen Type: A and B
Antibodies Made: None
Can Receive Blood From: A, B, AB, or O
Universal Recipients
Blood Type O
Genotype: OO
Antigen Type: None
Antibodies Made: Anti-A and Anti-B
Can Receive Blood From: O
Universal Donors
