Mendelian Genetics Flashcards
What is an allele?
Variant of the same gene
What are Mendels 2 laws?
1) each trait has 2 hereditary determinants
1 allele per parent. Both alleles passed in equal proportions
2) traits segregate independently of each other
Why can you only infer a genotype from a recessive trait?
Recessive phenotypes can only have one genotype - homozygous recessive.
Whereas a dominant phenotype can either be homozygous or heterozygous
What is the F2 ratio for a dihybrid cross?
9:3:31
Independent assortment of two genes predicts a __:__:__:__ phenotype ratio from a __:__:__ genotype ratio
9: 3:3:1
1: 2:1
Why does Mendels 2nd law only work for unlinked genes?
Genes very close on a chromosome tend to be inherited as a haplotype
The trait that persists in the F1 generation is the _______ trait
Dominant
What is a backcross?
What is a testcross?
What is a monohybrid cross?
- From a F1 hybrid to one of the homozygous parents
- from an individual to a homozygous recessive parent to determine if individual is homozygous or heterozygous
- cross between parents that differ at a single gene pair
What is penetrance?
Probability that A carrier of a dominant mutation will actually show signs of the disorder
Incomplete penetrance is where a person with the mutation does not get the disease. Could be age linked. Explains skipping of generations
What is a de novo mutation?
Are males or females more likely to pass on a de novo mutation?
Healthy parents have an effected child. Many are lethal. Healthy parent could be a pre mutation carrier, harbouring an unstable repeat which could cause de novo in later generations
- males more likely, due to the pathophysiology of spermatogenesis
What is an obligate daughter? What % of her sons or daughters are affected?
Daughter of an x disorder male. Always a carrier.
50% of sons and 25% of daughters
What is allelic heterogeneity
And locus heterogeneity
Allelic - same gene but different allele mutation= same disorder
Locus - different gene mutation = same disorder
Monohybrid cross = W/W x __/__ = W/__
WW + ww = Ww
Dihybrid cross = Wg x __\_ = __\_
Wg x wG = WG/gw
What’s an easy calculation to work out the number of offspring with a trait for F2?
Number of Offspring/16 x selected trait (9 or 3 or 3 or 1)
Give the stages of spermatogenesis
Spermatogonium Primary spermocyte Secondary spermatocytes Spermatids Spermatozoa
Give the stages if egg gamete formation
Oogonium
Primary oocyte
Secondary oocyte OR polar bodies
Egg
What are the two main reasons that linked genes may not give an expected genotype
- close genes inherited as a haplotype
- physically linked genes undergo independent assortment
What are the main modes of inheritance? (Inheritance patterns)
Single gene/Mendelian
- autosomal dominant/recessive
- x linked dominant/ recessive
Multifactorial
Mitochondrial
