Uniparental Inheritance Flashcards
What is Uniparental Inheritance?
Uniparental Inheritance:
- A non-Mendelian form of inheritance that consists of the transmission of genotypes from ONE parental type to all progeny
(inheritance matters based on what you get from one parent (not from other) )
what is an example of parental inheritance ?
The Y chromosme can be an example of parental inheritance
-anything that a child inherits on Y chromosome will come from father.
(only affects sons, NOT daughters)
Compare and Contrast the Y chromosome to X chromosome
-The X and Y chromosomes pair during meiosis
-The X is much LARGER and carries MANY types of genes
-The Y chromosome is SMALL and has LESS than 100 genes
-Most Y genes control sex determination or Spermatogenesis (production of sperm)
Explain how Y-linked traits are passed down to children. Include What each child receives from Father
-Each son receives his Y from his father
-Each daughter receives an X from her father
-Thus, the Y chromosome is passed in an UNBROKEN chain father to son
Y-linked traits should be passed to ALL SONS and NO Daughters
What is an example of a rare Y-linked mutation that is passed on to children?
HEARING IMPAIRMENT (Y-linked mutation that causes hearing impairment)
-affected males pass on trait to all sons, Not to daughters
Explain the major Y genes that are required for male production. What happens when there is a mutation in one of these genes?
The major Y genes required for male reproduction;
-*The SRY gene (initiates Male DEVELOPMENT
(SRY: Sex determining region Y gene; aka TDF gene (test determining factor) )
-mutations in the SRY cause XY individuals to develop as females
-These SRY females have DEFECTIVE Gonads
-**Many genes in the AZF region control Spermatogenesis
-most mutations in these Y genes cause STERILITY
(SRY gene is reason why males are identified. mutation in this gene prevents Y from becoming male, and ends upping female. SRY mutant females do NOT reproduce; ovaries are messed up)
Further explain how SRY gene controls male development. Include examples and discuss method used to determine if there is a mutation in gene
The SRY gene controls male development
- A family with two daughters who are each XY^SRY
- Southern Blots were probed with DNA that binds the SRY gene
-No band NO Y
-Three band= NORMAL SRY
-Two bands= MUTANT SRY
The father must have had a SRY mutation in his testes
(this is a very rare case, where Dad is normal phenotype, but has mutations in Y gene that changed Y to decreased gene and passed on to children. End up having 1 normal daughters, two daughters with mutant alleles in SRY gene, and 1 normal son; germline mutation)
What are germline mutations?
Germline mutations: new mutations or changes in DNA that you inherit from sperm and egg during conception)
(parents are not affected, but children are from new mutation)
What kind of mutations are cause Y chromosome defects?
Y chromosome defects are almost always SPONTANEOUS MUTATIONS
The Y chromosome has FEWER genes than the X
-Most Y-linked genes are required for Fertility.
-Sex-determination genes like SRY
-Spermatogenesis genes
**Thus, most Y mutations are NOT passed on to future generations
What is Sex-specific imprinting? What genetic disorders are examples of this?
Sex-specific chromosome imprinting: epigenetic process that marks chromosome (hence only one copy of gene is expressed; whether father or mother, while the other gene is suppressed)
2 genetic disorders that use this imprinting:
-Angelman Syndrome
-Prader-Willi syndrome
What is Angolan Syndrome and what are its symptoms?
Angelman Syndrome: genetic disorder causing developmental disabilities.
Symptoms:
-Small head
-Intellectual disability
-Developmental disability
-Problems with speech, balance, movement, seizures, and sleep.
-Affected children are usually happy (mood happy) and interested in WATER
What are the clinical features of Prader-Willi Syndrome ?
Prader Wili-Syndrome:
-Weak muscles
-Slow development
-Constant hunger:
-Severe obesity
-Type 2 diabetes
-Short with small hands and feet and narrow forehead
What do Angelman Syndrome and Prader-willi syndrome have in common ? How are they differen
The same mutation causes both Angelman Syndrome and Prader-Willi syndrome
(they are both caused by same deletion of same part of chromomse)
- The SAME mutation deletion can cause both disorders
- In most cases, these very Different diseases are caused by a DELETION of the same part of chromosome 15.
-***The key difference is whether the maternal or paternal chromosome is affected.
Describe how maternal and paternal chromosomes are normally treated vs in rare cases.
To form offspring, you need sperm and egg to fuse together, and mother and father will each carry single copy of each chromosome and have child diploid for each chromosome
- In rare ceases, these chromosomes are treated differently
What are parts of the chromosomes are IMPRINTED in the egg or sperm?
Some parts of chromosomes are Imprinted in egg or sperm:
**The PWS region is marked for inactivation in the mother’s egg
-So in the child, only the Paternal copy is used.
-if the paternal copy is missing, the Child develops PRADER-WILLI SYNDROME
The AS region is marked for inactivation in the Father’s sperm
-so in the child, only the Maternal copy is used
- If the maternal copy is missing, the child develops ANGELMAN SYNDROME
Explain the molecular view of what causes Prader-Willi syndrome
Molecular view of the Prader-Willi cause
- if the father’s PWS-AS region is DELETED, a child Only expresses the mother’s AS gene
-The maternal PWS region is inactivated, resulting in Prader-Willi syndrome
Discuss the molecular view of what causes Angelman syndrome?
The molecular View of Angelman syndrome:
-If the mother’s PWS-AS region is DELETED, a child Only expresses the father’s PWS gene
-The paternal AS region is inactivated, resulting in Angelman syndrome.
How does Chromosome imprinting affect the genome? What are examples of imprinting that occur?
Chromosome imprinting:
-Parental imprinting affects only a SMALL part of the human genome
-The Prader-Willi and Angelman region was the first case described where it occurs
-In imprinting, regions of DNA are marked so they will remain turned off:
-Some marks involve DNA methylation
-Some marks change the histones that package DNA
How does DNA from nucleosomes?
DNA wraps around histone octamers to form nucleosomes
many types of histone marks can regulate DNA
(can affect whether DNA is likely or not likely to be used; and describe how DNA is used)
What are other examples of imprinting?
Othere examples of Imprinting:
-Beckwith-Wiedemann syndrome
-The DIRAS3 gene on chromosome 1
- Silver Russel Syndrome;
-half of cases have too little methylation of the H19 and IGF2 genes
-Rare form of dwarfism
-can be treated by diet and growth hormones
