After mendel

Question 1

Deviations from complete dominance

Multifactorial traits
…..the genotype and phenotype relationship is sometimes complex
….but throughout it all Mendels basic conclusions remain valid

Answer 1

.

Question 2

Codominance

Answer 2

1. Phenotype of heterozygote is a mixture of both homozygous phenotypes - both alleles expressed

Question 3

examples of co-dominance

Answer 3

1. ABO blood type gene 
possible genotypes
A
B
AB 
O (recessive) 

2. Shorthorn coat colour
   homozygotes red or white
   heterozygotes roan

Question 4

incomplete dominance 
(can also be called partial or semi)

Answer 4

1. heterozygous phenotype somewhere in between 2 homozygous phenotypes
   e. g. homozygous parents red and white heterozygous F1s all pink

Question 5

incomplete dominance examples

Answer 5

1. snapdragons
   homozygous white or red
   heterozygous pink
2. Belgian blue cattle
   gene for extreme muscularity

Question 6

type of dominance

Answer 6

1. often depends on phenotypic level observed (many alleles codominant at molecular level)
2. sickle cell gene in humans illustrates various types of dominance

Question 7

Pleiotropy

Answer 7

1. multiple effects of a single gene

Question 8

Lethal alleles
horse example
3 points

Answer 8

1. Overo allele in horses
2. homozygous foals die within days
3. LWFS lethal white foal syndrome

Question 9

lethal alleles
cats
4 points

Answer 9

1. manx allele (ML)
2. homozygotes die in utero
3. heterozygotes (ML M) lack a tail
4. F2 segregation ratio in a monohybrid cross (ML M x ML M) 2:1 instead of 3:1

Question 10

multiple alleles example

Answer 10

1. many genes have multiple alleles

2. coat colour in rabbits - 1 gene has 4 alleles

Question 11

multiple genes - interactions between genes

Answer 11

1. most traits controlled by 2 or more genes and influenced by environment (multifactorial or polygenic traits)
2. some gene interactions further modify phenotypic ratios

Question 12

Epistasis

Answer 12

1. occurs when a gene at one locus influences expression of a gene at another locus
2. common in control of fur and petal colour

Question 13

Epistasis example

Answer 13

1. labrador coat colour
2. 2 genes:
   B or b alleles for enzyme in melanin synthesis
   E or e alleles for melanin deposition in hairs
3. Black B-E-
   Chocolate bbE-
   Yellow –ee

Question 14

gene interactions and new combinations can generate

Answer 14

hybrid vigour (heterosis)
offspring perform better than both pure-bred parents

Question 15

environmental effects/variables

Answer 15

1. influence translation of genotype into phenotype
2. seen in polygenic and single gene traits
3. e.g. siamese coat colour.
   heat sensitive version of C gene (C superscript h)