Mendelian genetics I

Question 1

importance of Mendel:

Answer 1

• first to apply scientific approach to understanding inheritance
• before Mendel, blended inheritance and no understanding of equal role of parents

Question 2

quick facts about Mendel:

Answer 2

• Augustinian monastery in Brno
• applied scientific approach:
• design of experiments
• collection of data
• mathematical analysis
• tested predictions of hypothesis

Question 3

Mendels experiments: overview

Answer 3

garden peas:

• grew fast
• traits observable by eye
• self/ cross pollinate
• short generation time and many offspring

heritable feature: character
- variant: trait

Question 4

Mendels experiments: detailed

Answer 4

• established true breeding lines differing individual traits (phenotype)
• crossed pure bred purple w pure bred white flowers in P (parental) generation
• only purple flowers in F1 (filial) generation
• crosses through F2 as well-> white flower appeared
• refute blending hypothesis
• purple: dominant
• white: recessive trait
• 3:1 ratio in F2 gen

Question 5

heritable factors:

Answer 5

• traits encoded by heritable factors
• passes to next gen in defined ratios
• later called genes
• heredity is the ability to pass of factors

Question 6

gene:

Answer 6

determines trait (flower colour)

Question 7

locus:

Answer 7

place chromosome where gene is located

Question 8

allele:

Answer 8

alternative variant of gene producing specific form of trait

Question 9

dominant allele:

Answer 9

• expressed as phenotype when only 1 copy is present

Question 10

recessive allele:

Answer 10

• only expressed if have two copies present

Question 11

Mendel’s model:

Answer 11

• genes in pairs, different forms (alleles)
• gamete carries 1 member of each gene pair, organism inherits two alleles
• alleles separate equally into gametes (law of segregation)
• dominant/ recessive alleles

Question 12

testcross:

Answer 12

• determine genotype based on frequency of traits in offspring

Question 13

law of independent assortment:

Answer 13

• crossing plants differing in 2 characters produced 1 phenotype (F1) and 4 phenotypes (F2)
• 9:3:3:1 ratio
• different gene pairs assort independently in gamete formation

Question 14

Mendel was lucky:

Answer 14

• traits only dom/rec
• one gene controlled one trait
• trait had 2 alleles
• genes studied all different chromosomes
• none sex chromosomes

Question 15

incomplete dominance:

Answer 15

• cannot completely mask another allele
• pure bred: red and white = pink snapdragon
• reduced amount of protein product

Question 16

codominance:

Answer 16

• both alleles expressed in heterozygote

- ABO blood groups (AB codominant, dominant to O)

Question 17

pleiotropy:

Answer 17

• single gene regulates multiple traits

- frizzle gene: frizzled feathers also defect in metabolism

Question 18

epistasis:

Answer 18

effect of one gene dependent on presence of 1 or more ‘modifier genes’
- may be masked/ modified

Question 19

quantitative characters:

Answer 19

• vary along continuum
• rather than having 1 of 2 discrete characters
• polygenic inheritance: phenotype determined by multiple genes (height- 180 genes involved)

Question 20

pedigree:

Answer 20

• looks into fam tree
• traits across generations
• investigate genotype (Widow’s peak, dominant)

Question 21

autosomal dominant pedigree:

Answer 21

• affected individuals have affected parents
• nearly every gen
• both males and females
• heterozygous most likely

Question 22

autosomal recessive pedigree:

Answer 22

• affected individuals generally NOT affected parents

- small fam: single gen of affected people