Mendelian Inheritance III Flashcards
Phenotype
overall genotype and unique environmental history
Ex: hydrangeas are pink in basic soil and blue in acidic soil
Norm of reaction
the way in which the environmental distribution is transformed into the phenotypic distribution for a given phenotype
Is it possible to predict the phenotypes of different genotypes in new environments?
No because norm of reaction curves of different genotypes in new environments
Pedigree
a family tree that describes the interrelationships of parents and children across generations
Rare autosomal dominants
-Every affected person has an affected parent
-About 1/2 of offspring of an affected parent are also affected
-Usually occurs in both sexes
Rare autosomal recessives
-Affected people usually have two parents who are not affected
-In affected families, about 1/4 of children of unaffected parents are affected
-Usually occurs in both sexes
Dominantly Inherited Disorders
-homozygous or heterzygous
-Ex: achondroplasia, Huntington’s Disease
Achondroplasia
-dominantly inherited disorder
-a form of dwarfism
-homozygosity is lethal
Recessively Inherited Disorders
-ONLY homozygous
-Ex: albinism, CF, hemochromatosis, phenylketonuria, spinal muscular atrophy
Sickle Cell Disease
-caused by a substitution of a single amino acid in the hemoglobin protein in RBCs
-affects 1/400 African Americans
-reduction against malaria symptoms
Symptoms of Sickle Cell Disease
physical weakness, pain, organ damage, and even paralysis
Sickle Cell Disease alleles
-2 sickle-cell alleles: ONLY sickled RBCs
-1 sickle-cell and 1 normal allele: Sickled and normal RBCs (carrier)
Carrier
heterozygous individuals who carry the recessive allele for a disorder but are phenotypically normal
Why are recessively inherited disorders more common than dominantly inherited?
Because carriers of recessively inherited disorders are phenotypically normal
Why do inherited disorders show variable frequency in different human populations?
Because historical geographic isolation of different human populations
Theodor Boveri (1885)
First to propose that chromosomes are the physical basis of inheritance
Chromosomal Theory of Heredity
Mendel’s hereditary factors (genes) have specific loci (positions) on chromosomes, and it is chromosomes that undergo segregation and independent assortment
Thomas Hunt Morgan’s Chromosome Experiment
-First solid evidence associating a specific gene w/ a specific chromosome
-Used fruit flies to provide evidence that chromosomes are the location of Mendel’s heritable factors
Why did Thomas Hunt Morgan use fruit flies for his experiment?
- They breed at a high rate (a generation can be bred every 2 weeks)
- They only have 4 pairs of chromosomes
Wild type phenotype
normal phenotypes that are common in populations
Mutant phenotype
traits alternative to the wild type
Results of Thomas Hunt Morgan’s experiment
-Mated male flies w/ white eyes (mutant) w/ female flies w/ red eyes (wild type)
-F1 generation: ALL red eyes
-F2 generation: 3:1 red:white eye ratio, but ONLY MALES had white eyes
-White-eye mutant allele must be located on X chromosome
sex-linked gene
a gene located on either sex chromosome, follow specific patterns of inheritance
Recessive X-linked
- Female needs 2 copies of allele (homozygous)
- Male needs only one copy of allele (hemizygous)
-More common in males (only one X chromosome)
-Ex: color blindness, Duchenne muscular dystrophy, hemophilia
Diversity of Sex Determination Systems
Z-W system: 76 + ZW/SS
X-0 system: 22 + XX/X
Haplo-diploid system: 32 and 16
