Mendelian genetics pt1

Question 1

What did Gregor Mendel do?

Answer 1

The inheritance pea plant experiment

Used plant hybridisation - he developed 3 principles

Question 2

What were the 7 characteristics in pea plants that were looked at in the pea plant experiments?

Answer 2

• Flower colour
• Seed colour
• Seed shape
• Pod colour
• Pod shape
• Flower position
• Plant height

Question 3

What are the steps of monohybrid crosses in peas?

Answer 3

1 - Grew true breeding plants, plants that always produce offspring with the same traits

2 - Set up a monohybrid cross (crossed true bred purple & true bred white), produced an F1 generation, all offspring had purple flowers

3 - F1 generation self fertilised, plants w white flowers reappear in F2 (3:1 ratio)

Question 4

What did Mendel conclude from his monohybrid crosses?

Answer 4

• An organism inherits 2 factors (alleles) for a characteristic
• When the plant reproduces the alleles split
• Some alleles are dominant over others (dominant = observe, recessive = masked)
• PP = dominant, Pp = dominant, pp = recessive

Question 5

What is a phenotype?

Answer 5

Physical description of trait e.g. purple or white

Question 6

What is a genotype?

Answer 6

Genetic makeup e.g. PP or Pp

Question 7

What is a 3:1 phenotype ratio in genotypes

Answer 7

It’s actually a 1:2:1 ratio

Question 8

What is an allele?

Answer 8

Trait found on a specific locus on a gene

Purple & white gene are different versions of a gene found at the same locus on a gene

Question 9

What is a dihybrid cross?

Answer 9

Involves Mendel’s law of independent assortment

Genes get shuffled, gives many different combintations

Question 10

What were the results of Mendel’s dihybrid cross between:

• True breeding yellow round peas (dominant)
• Green winkled peas

Answer 10

F1 generation = 100% yellow round

F2 generation = 9:3:3:1
(Yellow round:Green round:Yellow wrinkled:Green wrinkled)

Question 11

What is the general ratio produced from a dihybrid cross in the F2 generation?

Answer 11

9:3:3:1

Question 12

Name some human traits that are inherited via Mendilian fashion?

Answer 12

• Tongue rolling
• Widow’s peak
• Hitchhikers thumb

All dominant

Question 13

Name some recessively inherited disorders

Answer 13

Cystic fibrosis and sickle cell anaemia

Question 14

How are recessive disorders like sickle cell anaemia and cystic fibrosis inherited/carried?

Answer 14

They’re only shown in homozygous recessive individuals

Heterozygotes are phenotypically normal but act as carriers

Question 15

Name a non-lethal dominantly inherited diseases

Answer 15

Achondroplasia (dwarfism)

• Most harmful alleles are recessive

Question 16

How does Achondroplasia display in most people?

Answer 16

99.9% of population are homozygous for recessive allele

Homozygous dominant and heterozygotes shoe the dwarf phenotype

Question 17

Name a lethal dominantly inherited diseases?

Answer 17

Huntington’s disease

• Much less common
• Lethal dominant alleles can escape elimination if late acting