Inheritance

Question 1

What is genetics?

Answer 1

Study of inheritance and variation.

Question 2

What are the sources of variation in genetics?

Answer 2

1. Mutation

2. Meiosis - cross-over and random assortment

Question 3

What are genotype and phenotype?

Answer 3

• Genotype = set of genes responsible for a particular trait (DNA).
• Phenotype = physical expression of a particular trait (protein).

Question 4

What do the terms homozygous, heterozygous and hemizygous mean?

Answer 4

• Homozygous = 2 alleles of a gene are the same
• Heterozygous = 2 alleles of a gene are different
• Hemizygous = only 1 allele of a gene on the X chromosome, i.e. Males only

Question 5

What do the terms dominant and recessive mean?

Answer 5

• Dominant = allele determining the phenotype in a heterozygote
• Recessive = non-dominant allele in a heterozygote

Question 6

What is co-dominance?

Answer 6

2 alleles are expressed equally, creating a new phenotype.

Question 7

Give an example of a gene that can show co-dominance of alleles.

Answer 7

• Human isoglutamin gene codes for glycoproteins on RBC surface - determines ABO blood types.
• Gene I has 3 alleles: A, B and O:
  
  • allele A is dominant over allele O
  • allele B is dominant over allele O
  • alleles A and B are co-dominant
• 4 possible genotypes: blood group A, B, AB and O.

Question 8

What is polygenic inheritance?

Answer 8

More than 1 gene involved in producing a phenotype (e.g. Multiple genes coding for multiple enzymes required for a single product).

Question 9

Give an example of a polygenic trait that may result in disease.

Answer 9

Albinism is inherited in a recessive manner but is polygenic - even if 2 parents are inherited, offspring may not be is parents are affected in different genes.

Question 10

What is genome complementation?

Answer 10

2 genomes complement each other if heterozygous for each allele.

Question 11

What is the difference between linked and unlinked genes?

Answer 11

• Linked: genes are on the same chromosomes - do not show independent assortment at meiosis
• Unlinked: genes are on different chromosomes

Question 12

What does recombination frequency between 2 linked genes depend on?

Answer 12

The distance between genes:

• genes close together are tightly linked.
• genes that are apart on the same chromosome almost behave as unlinked genes due to crossing over.

Question 13

What is the ration of linked and unlinked genes in gametes?

Answer 13

• Unlinked genes: 1:1:1:1
• Linked genes not 1:1:1:1 as rate dependent on how often cross-over occurs, itself dependent on distance between genes on chromosomes.