6.1: Mendelian genetics; the monohybrid cross

Question 1

What’s in the human genome?

Answer 1

The human genone is made up of 2.9 BILLION bases (~20,000 genes)

Only 2-3% of this codes for “proper” genes
The other 97% is “junk” DNA

Question 2

What’s junk DNA? What are some common types? Is any of it useful? Why?

Answer 2

Common types of junk DNA include…

RUBBISH:
- Psuedogenes, retropseudogenes, satellites, minisatellites, microsatellites, transposons, retrotransposons

Reverse transcriptase
– Commonest protein recipe in the human body
– Serves NO useful purpose
– Enables the AIDS virus to copy its own genome and insert it into human DNA

HERVs (human endogenous retroviruses)
– Thousands of near complete viral genomes
– 1.3% of the human genome

“Parasitic” DNA – 35% – LINE-1s (17%), Alus (10%)

NON RUBBISH:
Crucial non-coding areas (e.g. centromeres)
- e.g. telomeres to protect the ends

500 regions of junk DNA are highly conserved between species

• pseudo genes
– fossil genes
– Vr1 family of genes
- mice have 160 functional genes
- humans have 5

• Alternative splicing of RNA transcripts
– 10 exons per gene in different combinations
– multiple proteins per gene
– introns = 20% of the genome

• Regulatory role of gene expression
– regulatory sequences
– miRNAs & small RNAs

Question 3

What’s Mendel’s 1st Law?

Answer 3

The Law of Segregation (Mendels 1st Law) says…
“The two members of a gene pair segregate from each other into the gametes, so that half the gametes carry one member of the pair and the other half of gametes carry the other pair.”

Question 4

What was the product of Mendel’s monohybrid cross?

Answer 4

Mendel found that by crossing two heterozygous individuals a phenotypic ratio of 3:1 resulted.

We know this now to be a 1:2:1 ratio of homo dom, het, and homo rec.