Topic 6: Heredity

Question 1

Inheritance

Answer 1

transfer of genetically determined characteristics from one generation to the next

Question 2

genetics

Answer 2

study of inheritance

Question 3

Recall – 23 chromosome pairs:

Answer 3

1) 22 homologous pairs autosomal - somatic characteristics

2) 1 pair sex chromosomes: male (♂) = XY and female (♀) = XX

Question 4

Alleles

Answer 4

genes occupying the same locus on homologous chromosomes

Question 5

homozygous

Answer 5

¦ same allele of a particular gene on homologous chromosomes

¦ i.e. both alleles express the same version of a trait

¦ e.g. blond hair (bb), black hair (BB)

Question 6

heterozygous

Answer 6

¦ different alleles of the same gene

¦ i.e. alleles code for different expressions of the same trait

¦ e.g. Bb

Question 7

Genotype

Answer 7

o catalogue of a person’s genes (genetic makeup)

o e.g. Bb

Question 8

Phenotype

Answer 8

o expression of genotype (genes) to give observable characteristics

o e.g. black hair

Question 9

Dominant allele

Answer 9

o expressed in phenotype regardless of other allele
o BB or Bb: dominant allele expressed
o e.g. black hai

Question 10

Recessive allele

Answer 10

o expressed in phenotype only if present on both alleles
o bb
o e.g. blonde ha

Answer 11

— non-sexual inheritance determined by gene on the X chromosome
o e.g. hemophilia, colour blindness, Duchenne’s muscular dystrophy – all due to
recessive alleles on the X chromosome
— XY = not truly homologous
o if gene is X-linked its expression is not masked because there is no corresponding
allele on Y chromosome
o XX = homologous