Heredity (Inheritance)

Question 1

What is Inheritance/Heredity?

Answer 1

Transfer of genetically determined characteristics (encoded by genes) from one generation to the next

Question 2

What is Genetics ?

Answer 2

Study of Inheritance

Question 3

How Many Chromosomes Pairs?

Answer 3

• 23 chromosomes pairs
  
  • 22 homologous pairs = autosomal
  • 1 pair sex chromosomes = XY or XX

Question 4

What is Alleles?

Answer 4

• genes occupying the same location (=locus) on homologous chromosomes
• Alleles may be:
  
  1. Homozygous
  2. Heterozygous

Question 5

What is Homozygous?

Answer 5

• Same allele of a particular gene on homozygous chromosomes
• i.e. both alleles express the same version of a trait
• e.g. blond hair (bb), black hair (BB)

Question 6

What is 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

What is Genotype?

Answer 7

• genetic makeup of an organism
• i.e. which alleles are homozygous and which are heterozygous
• e.g. BB, Bb, bb

Question 8

What is Phenotype?

Answer 8

• Expression of genotype (genes) to give observable characteristics
• e.g. black hair

Question 9

What is Dominant Allele (B)?

Answer 9

• Expressed in phenotype regardless of other allele
• BB or Bb
• e.g. Black hair

Question 10

What is Recessive Allele (b)?

Answer 10

• Expressed in phenotype only if present on both alleles
• bb
• e.g. blonde hair

Question 11

What Is The Way To Predict inheritance?

Answer 11

Punnet Square

Question 12

What is Punnet Square?

Answer 12

• determines probability of inheritance
• Predicts offspring genotype and phenotype
• e.g. hair colour

Question 13

If the parents are BB x Bb, what would be the genotype and phenotype?

Answer 13

• Bb, Bb, Bb, Bb
• Genotypes: 100% Bb (Heterozygous)
• Phenotype: 100% black hair

Question 14

If the parents are Bb x Bb, what would be the genotype and phenotype?

Answer 14

• BB, Bb, Bb, bb
• Genotypes: 25% BB (Homozygous Dominant), 50% Bb (Heterozygous), and 25% bb (Homozygous Recessive)
• Phenotype: 75% black hair and 25% blonde hair

Question 15

What is X-linked Inheritance?

Answer 15

• Inheritance of somatic characteristics determined solely by genes on the X chromosome
  
  • e.g. hemophilia, colour blindness, Duchenne’s muscular dystrophy - all due to recessive alleles on the X chromosome
• XY = not homologous
  
  • If gene is x-linked its expression is not masked because there is no corresponding allele on Y chromosomes
• XX = homologous

Question 16

What would be an example of X-linked Inheritance?

Answer 16

• Colour Blindness
  
  • N = not colour blind (Dominant)
  • n = colour blind (recessive)

Question 17

What would be the possible parental genotypes?

Answer 17

1. X^N X^N
2. X^N X^n
3. X^n X^n
4. X^N Y
5. X^n Y

Question 18

What would be the possible parental phenotypes and description?

Answer 18

1. Not colour blind - Homozygous dominant
2. not colour blind - heterozygous (carrier)
3. colour blind - homozygous recessive
4. not colour blind - one copy of dominant allele
5. one copy of recessive allele (no gene on Y to mask recessive gene on X)