Test Cross and Pedigrees Flashcards
What phenotype are alleles named after in test crosses
Alleles are named after recessive phenotypes
Which phenotype is denoted by a capital or lowercase letter for test crosses
Dominant still capital, recessive still case
Can you have 2 different letter denotions for one trait in test crosses
NEVER have two different letter denotations for one trait
Which probability rule do you use if you see “and”
AND = x
Which probability rule do you use if you see “or”
OR = +
What are test crosses
A cross performed to determine the genotype of an organism showing the dominant trait.
Why are test crosses used
Since a heterozygote may have the same phenotype as the homozygous dominant
- To determine the genetic makeup of an individual
How are test crosses preformed
Individual with unknown genotype must be crossed with a homozygous recessive individual
If the unknown genotype is D_G_ and the tester genotype is ddgg, what will the results be if the unknown is homozygous dominant
If the unknown is DD, then the cross will result in Dd with 100% tall
If the unknown genotype is D_G_ and the tester genotype is ddgg, what will the results be if the unknown is heterozygous
If unknown is Dd, then cross will result in 50% being tall (Dd), 50% being dwarf (dd)
Define: obligate carrier
Obligate carrier- carries gene but does not have the trait
- hetrozygous
Define: asymptomatic carrier
Asymptomatic carrier - unaffected at this time but may latter exhibit trait
Define: proband
Proband - first affected family member coming to the attention of geneticist
What are pedigrees
A family tree focusing on genetics and family history
What do the roman numerals represent in standard pedigrees
Roman numerals refer to generations
How are order of offspring denoted in standard pedigrees
Order of offspring goes L to R with oldest to youngest
How is male vs female shown in standard pedigrees
If assigned male at birth: square
If assigned female at birth: circle
Def: autosomal trait
Autosomal = non-sex trait
How are affected conditions shown in standard pedigrees
Shaded symbols mean an individual is affected by a condition, while an unshaded symbol means they are unaffected
Explain characteristics of autosomal dominant traits
- In every generation, someone has phenotype
- Appears equally in males and females
- Unaffected people do not reflect trait
- Affected people have at least one affected parent (unless they have a new mutation)
Explain characteristics of autosomal recessive traits
- Tends to skip generations in phenotypes
- More likely to appear among progeny of related parents
- Appear equally in males and females
- Affected offspring usually born to unaffected parents
If you are affected by a condition are you a carrier?
If you are affected you are not a carrier
— These are 2 distinct categories
