Mendel and the Gene Idea

Question 1

Law of Segregation

Answer 1

Each parent passes one allele at random to their offspring

Question 2

Locus

Answer 2

fixed position on a chromosome where a particular gene or genetic marker is located

Question 3

Alternative versions of genes (aka alleles) account for variations in inherited characters (aka traits)

Answer 3

Different alleles have different DNA sequences at the same locus on a pair of homologous chromosomes

Question 4

Alleles

Answer 4

alternative versions of a gene

Question 5

Testcross

Answer 5

Breeding individual of unknown genotype with a known homozygous recessive individual

Using two punnet squares to test an unknown with a homozygous recessive

If any offspring display recessive phenotype, unknown parent must be heterozygous

Question 6

Heterozygote / Heterozygous

Answer 6

an individual having two different alleles

Question 7

Homozygote / Homozygous

Answer 7

an individual having two identical alleles

True Breeding

Question 8

Monohybrid Cross

Answer 8

a cross between monohybrids (one trait)

Ex: Pp

Question 9

Dihybrid Cross

Answer 9

a cross between dihybrids (two traits)

Ex: YyRr

Question 10

Complete Dominance

Answer 10

Occurs when phenotypes of heterozygote (Pp) and dominant homozygote (PP) are identical

Ex: Red + White alleles make a red flower (because red is dominant)

Question 11

Incomplete Dominance

Answer 11

Phenotype of F₁ hybrids is somewhere between phenotypes of the 2 parental varieties

phenotypes mix together

Ex: Red + White alleles make a pink flower

Question 12

Codominance

Answer 12

2 dominant alleles affect phenotype in separate, distinguishable ways

Ex: Red + White alleles make a red AND white colored flower

Question 13

Tay-Sachs Disease

Fatal inherited disorder

Answer 13

Dysfunctional enzyme causes an accumulation of lipids in brain

At biochemical lvl phenotype enzyme activity lvl is incomplete dominant

Heterozygous “carriers” will have half of the normal activity level. This means they have an intermediate phenotype arising from each allele’s contribution (or lack thereof)
-At molecular level, alleles are codominant

Question 14

Pleiotropy

Answer 14

genes have multiple phenotypic effects

one gene affects multiple characteristics

Question 15

Epistasis

Answer 15

The phenotypic expression of one gene affects the expression of another gene

outcome of one gene affects the outcome of another gene

Question 16

Polygenic Inheritance

Answer 16

A single phenotypic character is affected by two or more genes

two genes affect one characteristic together