7.1 - Inheritance

Question 1

Monohybrid

Answer 1

• 1 gene
• 3:1 ratio

Question 2

Dihybrid

Answer 2

• 2 genes
• 2 heterozygous = 2:3:3:1 ratio
  common examples: pea plants, drosophila

Question 3

Autosomal linkage

Answer 3

• chromosome not sex-linked
• 2 heterozygous = 2:3:3:1 ratio
• stay together during independent segregation unless crossing over occurs

Question 4

Define autosome

Answer 4

chromosome that is not sex-linked

Question 5

Sex linkage

Answer 5

alleles specific to sex (X and Y) chromosomes
female = XX, male = XY
written with X/Y then small letter to represent allele
common examples: colourblindness, haemophilia, family trees/pedigree charts

Question 6

Define allelomorphic

Answer 6

when a gene has more than 2 potential alleles

Question 7

Epistasis

Answer 7

allele of one gene masks expression of another in the phenotype
- recessive epistasis has ratio of 9:3:4
dominant epistasis has 12:3:1 ratio
common examples: enzymes, colour, flow chart

Question 8

Codominance/multiple alleles

Answer 8

written with capital letter then small letter (sometimes with a dash e.g Bbb’)
common examples: colour, shape/structural/physical feature, blood group

Question 9

Why use chi-squared?

Answer 9

categorical data

Question 10

Suggest 2 causes of genetic variation

Answer 10

crossing over, independent segregation

Question 11

Why are phenotypic ratios often not the same as the expected ratios?

Answer 11

crossing over, linked genes
(monohybrid) = random fertilisation, small population size

Question 12

Define phenotype

Answer 12

characteristic due to genetic constitution due to environment

Question 13

What does it mean when genes are linked?

Answer 13

they are located on the same chromosome

Question 14

Define dominant

Answer 14

allele which is always expressed in phenotype

Question 15

Define recessive

Answer 15

only expressed in phenotype when homozygous

Question 16

Define genotype

Answer 16

genetic constitution of an organism

Question 17

Define codominant

Answer 17

both alleles expressed equally and contribute to phenotype
(either characteristics blended or being seen together)

Question 18

What does ‘pure breeding’ mean?

Answer 18

homozygous pair of alleles

Question 19

Define allele

Answer 19

alternative form of a gene

Question 20

Where are 2 of the same alleles found on different chromosomes of a homologous pair?

Answer 20

at the same loci

Question 21

What does it mean if genes are linked?

Answer 21

genes on same chromosome