Gene Inheritance, Meiosis, Cytogenetics Flashcards
what are alleles?
- are different forms of the same gene
- can be multiple, non-identical versions of the gene or only 2 versions depending not the specific gene
- can be dominant or recessive
Alleles and the human genome?
The human genome contains two versions of each gene (a paternal & a maternal copy)
-two copies don’t have to be identical, alleles are the variations in the two genes
Compound Heterozygotes
the presence of two mutant recessive alleles on the same gene locus in a pair of chromosomes
Phenotype of compound heterozygotes?
The symptoms/phenotype may be less severe because each mutant allele may partially complement the deficit of the other mutant allele
-can also be made more severe but this is rare
X-Linked Recessive
- No male–> male transmission since father gives a Y to the son
- Most cases boys
Why X-Linked Recessive Traits Uncommon in girls?
Because having the mutant recessive allele on both X chromosomes usually makes the disease too severe
-often times fatal
How X-Linked Recessive typically passed?
From unaffected carrier female to an affected son
Hypothesis if see only males affected by disease & male–> male transmission?
Autosomal dominant mutant allele but that is turned off/ doesn’t affect women
-due to changes in gene expression in men vs. women
Daughters of a male patient w/ X-linked inheritance and a +/+ female?
All daughters will be carriers
Mutation that causes Hemophilia A?
- X-linked dominant
- more than 2000 sequence variants within the affected gene have been catalogued
X-Linked Dominant Inheritance in females?
- Absence of male–> male transmission because males provide a Y to their sons
- Affected fathers have all affected daughters since donate their mutated dominant X chromosome to their daughter
- Look for affected father, all daughters and no sons affected
What marriage shows a direct difference between X-Linked Dominant and Autosomal Dominant?
Affected father x unaffected mother which gives a unique progeny ratio different than autosomal dominant
X-Linked Dominant Disorder in males?
- if have an affected mother
- some are more severe in males than females causes death during prenatal period
- this can affect the ratio of male:to female affected because all males die before birth
How is mitochondrial genome (mtDNA) inherited?
- Maternally inherited
- Disorders caused by mutations in mtDNA are transmitted from females to all children
Mitochondria & cell division? How does this affect pathogenic nature of mtDNA inheritance?
- each cell has thousands of mitochondria each w/ own mtDNA
- mitochondria are unevenly distributed during cell division
- pathogenic mtDNA mutations can be heteroplasmic
- meaning that an infected women can pass variable amounts of pathogenic mtDNA to child
- meaning child can vary in severity of the disease depending on proportion of pathogenic to healthy mtDNA
Heteroplasmic
Meaning a mix of wild-type & mutated DNA within the same individual
-ex: because each cell has thousands of mitochondria each with own mtDNA, you can have a mix of healthy and pathogenic mtDNA in your body
What is locus heterogeneity? Phenotype of individuals affected?
- when the same disorder can be caused by mutations in different genes
- in some cases phenotype is indistinguishable even when mutation is on different genes
- in other cases phenotypes have clear differences based on the specific mutant gene
What is allelic heterogeneity?
-a disease caused by different mutations in the same gene
-is found in almost all loss of function diseases (ex: hemophilia)
-
Allelic heterogeneity and severity?
- Allelic heterogeneity is when one gene can have multiple mutant alleles
- Severity of the disease phenotype is dependent on which specific mutant alleles the patient has
What is genomic imprinting?
- is when an autosomal gene has only maternally or paternally derived allele active
- the other allele is silenced
Genomic imprinting and diseased offspring?
- If the maternal allele is deactivated in on a specific gene, regardless of whether the allele is mutant or not, the child will be unaffected since that allele is silenced anyway.
- person only affected if the mutant allele is the active allele
