Lecture 10 Flashcards
Essential genes
- required for survival
- mutations can be tolerated if heterozygous
- one wild-type allele sufficient for survival
- homozygous recessive will not survive
- mutations behaves as recessive lethal allele
Lethal allele
- has potential to cause death of organism
- alleles are result of mutation in essential genes
- inherited in recessive manner
Dominant lethal allele
- presence of one copy of allele results in dead
Mutant allele
- behaves dominantly to normal allele to control coat color
- behaves as homozygous recessive lethal allele
Different modes of inheritance combined…
results in many variants of modified ratios
- albinism and blood type
What influences phenotypic characters
many different genes and their products
Gene interaction
- several genes influences a particular characteristic
- cellular function of numerous gene products contributes to development of common phenotype
Epistasis
- expression of one gene masks/modifies effect of another gene pair
- gene masks phenotypic effects of another gene
- each step of development increase complexity of organ, under control and influences of many genes
- has effect one one or more of four phenotypic categories
Hereditary deafness
- ears form as result of many genes
- genes interact to produce common phenotype
- mutation interrupt development and lead to hereditary deafness
- Mutant phenotype: heterogeneous trait where many genes are involved
Bombay phenotype
- homozygous recessive condition
- first locus masks expression of second lous
- mutant FUT1 gene masks expression of Ia and Ib alleles
- A and B antigen forms only when individual has one wild-type allele
Gene interactions…
reveals inheritance patterns
Dominant epistasis
- dominant allele at one loci masks an allele at second loci
example: summer squash fruit color
if the genotype has A, the color will be white no matter what the other letters are, if the genotype is missing the A then it will be a different color depending on the genotype
Recessive epistasis example
B allele: black pigment
A allele: agouti phenotype
- aa genotype: all black
- bb genotype: no pigment, even if A or a alleles are present
bb genotype MASKS expression of A allele which explains recessive epistasis
AABB x aabb
9:3:3:1 genotype ratio
9:6:1 phenotype ratio
wild type eye color is due to the deposition and mixing of pigments
each step of each pathway is catalyzed by a separate enzyme and is thus under the control of a separate gene
pleiotropy
expression of single gene has multiple phenotypic effects
X-linkage
- genes present on X chromosome exhibit patterns of inheritance
- different from autosomal genes
Y chromosome
- relatively inert genetically
- male-specific genes on human Y chromosome
- lacks copies of genes found on X chromosome
when a gene is X linked…
reciprocal cross between the multiple groups of different phenotypes is not always the same
Color blindness is…
X-chromosome linked
- mother passes to all sons and no daughters
- however daughter can be a carrier
sex-limited inheritance
expression of specific phenotype is absolutely limited to one sex
sex-influences inheritance
- sex of individual influences expression of phenotype
- not limited to one sex or the other
