Lecture 10 Mendelian Genetics and beyond

Question 1

State and explain Mendel’s 1st Law

Answer 1

Law of seggregation. This states that for a given trait with two alleles, the alleles are separated into seperate gametes. Each gamete only carries one allele of each allel pair.

Question 2

State and explain Mendel’s 2nd Law

Answer 2

Law of Independant assortment. In Meiosis Metaphase I, the homologous pairs of chromosomes allign along the equator, (random). Genes on separate chromosomes are inherited independantly of eachother.

Question 3

Define Incomplete dominance

Answer 3

Where both alleles for a trait influence the phenotype of the progeny. There is blending of the phenotypes, producing an intermediete heterozygote phenotype. Eg Red x White prodces pink.

Question 4

Define Co-dominance

Answer 4

Where both alleles are equally and simeltaneously expressed in the phenotypes, but there is no blending. An example includes the ABO blood groups. AB are both expressed equally , and the progeny has both A and B antigen, not an intermediete.

Question 5

What are Multiple Alleles

Answer 5

Where one trait has more than 2 allelic variants. This is contrary to mendel’s initial postulates. Eg the ABO blood groups have 3 alleles in the population.

Thus simply, where there are more than 2 allelese that exist in the population.

Question 6

What are Lethal alleles

Answer 6

Lethal alleles are typically recessive. This allele will cause death of the organism that carries is.

Question 7

Define Pleiotropy

Answer 7

Where one gene controls the phenotype ofs multiple different and unrelated traits. PKU is an example

Question 8

Give an example of a disease caused due to Pleiotropy

Answer 8

PKU

Question 9

Give the F2 ratio for the Monohybrid cross

Answer 9

3:1

Question 10

Give the f2 ratio for the Dyhybrid cross

Answer 10

9:3:3:1

Question 11

Give the F2 ratio for a trait showing Incomplete dominance

Answer 11

1: 2 intermediete:1 recessive
1: 2:1

Question 12

Give the F2 ratio for a trait showing co-dominance

Answer 12

1:2:1

Question 13

What is the difference between incomplete dominance and Co-dominance

Answer 13

Incomplete dominance results when both alleles are expressed in th phenotype and there is blending of the resultant phenotype as no allele is completely cominant over the other. But co-dominance occurs when both alleles are equally expressed, resulting in offspring having both traits. Eg AB blood group.

Question 14

State the ratio for Lethal alleles

Answer 14

2:1 ratio

Question 15

Give an example of pleiotropy

Answer 15

Primary Ciliary dyskinesia. Here, a mutation in the cilia results in

Question 16

Define pleiotropy

Answer 16

This is a situation where one gene affects multiple traits.