Lecture 24: Mendelian Genetics

Question 1

What question is asked in transmission genetics?

Answer 1

Can we identify genes and phenotypes, mapping genes?

Question 2

What question is asked in molecular genetics?

Answer 2

What is the molecular basis to heredity - information flow?

Question 3

What question is asked in population genetics?

Answer 3

What can we say about the genetic makeup of populations in their natural state?

Question 4

Which phenotype pairs in peas did Mendel study?

Answer 4

1) Round/wrinkled seeds
2) Yellow or green seeds
3) Purple or white petals
4) Inflated or pinched ripe pods
5) Green or yellow unripe pods
6) Axial or terminal flowers
7) Long or short stems

Question 5

What is Mendel’s first law?

Answer 5

The principle of segregation:

• Characters are determined by particulate factors (genes) existing in pairs in each organism
• Each reproductive cell (gamete) contains only one of each pair - which one is entirely random - thus these factors segregate
• The union of male and female reproductive cells is a random process that reunites pairs of factors (genes)

Question 6

What are the key features of meiosis?

Answer 6

• Homologues synapse
• Chiasma form between homologues
• Homologues segregate at meiosis I
• No replication preceding meiosis II
• Gives 4 cells with haploid complement of chromosomes

Note:
How chromosomes behave is identical to how genes behave to account for pattern of inheritance:
1. Present in pairs	 				
2. Segregate 
3. One member of each pair inherited 		
4. One received from each parent

Question 7

What is genetics like in haploid organisms?

Answer 7

• Haploid organisms, such as fungi (like yeast), go through a transitory diploid stage briefly before meiosis.
• No dominant/recessive alleles (only one copy of gene so everything is expressed)