Top4-Ch5-P117-133 Flashcards
Explain Cytoplasmic Inheritance
- Some traits are encoded by mitochondrial DNA (mtDNA)
- Mitochondria only inherited from mother
- extensive phenotypic variation due to unequal distribution of cytoplasmic genes in daughtercells
See below illustration and also see how for the four o’clock plant the female variegated can produce all types of leaf inheritance.
True or False? A number of human diseases (mostly rare) that exhibit cytoplasmic inheritance have been identified
True
Genetic maternal effect is
- Phenotype of offspring is determined by genotype of mother
- Genes inherited from both parents
The mother produces a substance that passes to off spring so her genotype determines phenotype of offspring.
Looks like cytoplasmic inheritance but is different
Genomic imprinting
the expression of genes is affected by parental origin
Explain how Prader-Willi and Angelman syndrome are examples of Genomic imprinting.
Prader-Willi:
- small hands, short stature, mental retardation
- deletion of small region on long arm of chromosome 15 inherited from father
Angelman syndrome:
- unusual seizures, uncontrolled muscle movement
- deletion of small region on long arm of chromosome 15 inherited from mother
Depending on whether it is mother or father inheritance depends on how the disorder is expressed.
In Genomic imprinting explain about Igf2
Igf2 (insulin like growth factor II). Same effect in humans and mice. One allele is inherited from each parent but only the male allele is expressed which causes the fetus to grow.
What is the genetic conflict hypothesis?
In relation to genomic imprinting, genetic conflict hypothesis suggests that there are different and conflicting evolutionary pressures acting on paternal and maternal alleles for genes. For instance, paternal alleles that maximise offspring size are favoured because birth weight is strongly associated with infant mortality and adult health. While maternal alleles cause more limited fetal growth because giving birth to big babies is risky and difficult and giving all those nutrients to a fetus to make it big takes away from mum and might limit her ability to have babies in the future.
Sex influences on heredity chart to learn
epigenetics is
the study of changes in gene expression or cellular phenotype, caused by mechanisms other than changes in the underlying DNA sequence, some of which are heritable.
It refers to functionally relevant modifications to the genome that do not involve a change in the nucleotide sequence. Examples of such modifications are DNA methylation and histone modification, both of which serve to regulate gene expression without altering the underlying DNA sequence. These changes may remain through cell divisions for the remainder of the cell’s life and may also last for multiple generations.
An example is bees. A female bee fed royal jelly turns into a fertile female who becomes a queen, while other female bees fed just normal food become sterile workers.
Anticipation is when
- A trait gets more strongly expressed or more early expressed as it is passed from generation to generation
- An unstable region of DNA increases in size in successive generations
- Implicated in fragile X, Huntington disease, Myotonic dystrophy
Environment is when
a trait gets expressed differently in different environments.
For example, fruit flies develop reduced wings when raised at temperature below 29°C but the same genotype develops much longer wings when raised at 31°C. Called temperature sensitive allele.
Explain how environment affects a child with PKU
PKU (Phenylketonuria) is due to an autosomal recessive allele that causes mental retardation. Defect in gene that normally metabolises the amino acid phenylalanine. The defective enzyme cannot metabolize phenylalanine and its build up causes brain damage in the child. Putting child on low phenylalanine diet prevents retardation.
Genes and products are influenced by environment
What is phenocopy?
is when environmental factors alone produce a phenotype that is the same as the phenotype produced by a genotype.
For instance, in fruit flies the autosomal recessive mutation eyeless produces greatly reduced eyes. The eyeless phenotype can also be produced by exposing the larvae of normal flies to sodium metaborate.
Discontinuous characteristics exhibit a?
few distinct phenotypes
Continuous characteristics exhibit a
range of phenotypes. A continuous characteristic is frequently produced when genes at many loci and environmental factors combine to determine a phenotype.
Examples are height and intelligence.
More from the class slides:
- Display a continuum of different varieties
- Continuous or quantitative characteristics
- Continuous characteristics influenced by environment, multifactorial
