Test Cross and Pedigrees

Question 1

What phenotype are alleles named after in test crosses

Answer 1

Alleles are named after recessive phenotypes

Question 2

Which phenotype is denoted by a capital or lowercase letter for test crosses

Answer 2

Dominant still capital, recessive still case

Question 3

Can you have 2 different letter denotions for one trait in test crosses

Answer 3

NEVER have two different letter denotations for one trait

Question 4

Which probability rule do you use if you see “and”

Answer 4

AND = x

Question 5

Which probability rule do you use if you see “or”

Answer 5

OR = +

Question 6

What are test crosses

Answer 6

A cross performed to determine the genotype of an organism showing the dominant trait.

Question 7

Why are test crosses used

Answer 7

Since a heterozygote may have the same phenotype as the homozygous dominant

• To determine the genetic makeup of an individual

Question 8

How are test crosses preformed

Answer 8

Individual with unknown genotype must be crossed with a homozygous recessive individual

Question 9

If the unknown genotype is D_G_ and the tester genotype is ddgg, what will the results be if the unknown is homozygous dominant

Answer 9

If the unknown is DD, then the cross will result in Dd with 100% tall

Question 10

If the unknown genotype is D_G_ and the tester genotype is ddgg, what will the results be if the unknown is heterozygous

Answer 10

If unknown is Dd, then cross will result in 50% being tall (Dd), 50% being dwarf (dd)

Question 11

Define: obligate carrier

Answer 11

Obligate carrier- carries gene but does not have the trait

• hetrozygous

Question 12

Define: asymptomatic carrier

Answer 12

Asymptomatic carrier - unaffected at this time but may latter exhibit trait

Question 13

Define: proband

Answer 13

Proband - first affected family member coming to the attention of geneticist

Question 14

What are pedigrees

Answer 14

A family tree focusing on genetics and family history

Question 15

What do the roman numerals represent in standard pedigrees

Answer 15

Roman numerals refer to generations

Question 16

How are order of offspring denoted in standard pedigrees

Answer 16

Order of offspring goes L to R with oldest to youngest

Question 17

How is male vs female shown in standard pedigrees

Answer 17

If assigned male at birth: square

If assigned female at birth: circle

Question 18

Def: autosomal trait

Answer 18

Autosomal = non-sex trait

Question 19

How are affected conditions shown in standard pedigrees

Answer 19

Shaded symbols mean an individual is affected by a condition, while an unshaded symbol means they are unaffected

Question 20

Explain characteristics of autosomal dominant traits

Answer 20

• 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)

Question 21

Explain characteristics of autosomal recessive traits

Answer 21

• 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

Question 22

If you are affected by a condition are you a carrier?

Answer 22

If you are affected you are not a carrier

— These are 2 distinct categories