Lecture 6- Mendelian genetics 1

Question 1

Genetic beliefs before Mendel

Answer 1

Belived to be blending process/ dilution

Question 2

Why did Mendel use pea plants?

Answer 2

Ideal for genetics
Strict control over breeding
Each plant has both male (stamens) and female (pistil) reproductive organs
Can be self fertilised

Question 3

Character definition

Answer 3

Heritable feature (physical feature)

Question 4

Trait definition

Answer 4

Each variant of character

Question 5

Mendel pea plant experiment steps

Answer 5

1. Grow true breeding plants- always produce offspring with the same traits (P/parent generation)
2. Monohybrid crossed- true bred purple x true bred white, produces F1 generation
3. Self fertilise F1 generation -> F2 generation with 3:1 ratio

Question 6

Pea plant s dominant and recessive colours?

Answer 6

Dominant: purple
Recessive: white

Question 7

2 facts an organism inherits?

Answer 7

Hereditary particles- genes
Alternative forms- alleles

Question 8

2 facts an organism inherits?

Answer 8

Hereditary particles- genes
Alternative forms- alleles

Question 9

Mendel’s Law of Segregation

Answer 9

Each gamete gives one factor (allele)
Each offspring gets one factor (allele) from each parent
Random fusion during fertilisation

Question 10

Dominant

Answer 10

The observed trait
Produces an effect when either one or two copies present

Question 11

Recessive

Answer 11

The masked trait
Produces an effect when no dominant allele present

Question 12

Rules of dominance

Answer 12

Dominant trait expressed when PP or Pp
Recessive trait expressed when pp

Question 13

Phenotype

Answer 13

Physical description of trait

Question 14

Genotype

Answer 14

Genetic makeup

Question 15

What are different alleles

Answer 15

Different versions of a gene
Sequence of nucleotide bases varies at specific locus

Question 16

Mendel’s Law of Independent Assortment

Answer 16

Different gene segregate independently from one another during formation of gametes

Question 17

Dihybrid cross

Answer 17

Cross true breeding dominant with true breeding recessive
eg. YYRR x eyry

Question 18

Pedigree analysis

Answer 18

Maps trait onto family tree

Question 19

Recessively inherited disorders

Answer 19

Disease only shows in homozygous recessive individuals
eg cystic fibrosis, Tay Sachs, sickle cell anaemia
Heterozygotes are phenotypically normal but act as carriers

Question 20

Dominantly inherited disorders examples

Answer 20

eg. Huntington’s disease
Achondroplasia (dwarfism)

Question 21

Dominantly inherited disorders- lethal dominant alleles

Answer 21

Less common than lethal recessives as effects not masked in heterozygotes so no carriers
Lethal dominant alleles escape elimination of late acting

Question 22

Huntington’s disease

Answer 22

Degenerative disease of nervous system
No obvious effect until age 35-45
Allele passed onto next generation as it doesn’t effect reproduction