Mendel's laws, genetics vs environment, PKU

Question 1

Name Mendel’s 3 laws of inheritance

Answer 1

law of segregation,
… independent assortment,
… dominance

Question 2

Define the law of segregation

Answer 2

when gametes form, alleles are separated so that each gamete only carries 1 allele for each gene

Question 3

Relate the law of segregation to what is happening in the cell

Answer 3

○ During meiosis, alleles are separated
○ 1 copy of each chromosome in a gamete
= 2 copies of each chromosome in a somatic cell
- Always 1 from mum, 1 from dad

Question 4

define the law of independent assortment

Answer 4

the segregation of alleles for one gene occurs independently to that of any other gene

Question 5

Relate the law of independent assortment to what is happening in the cell

Answer 5

In meiotic recombination, gametes each have 1 copy of each chromosome, each with a unique combo of alleles

Question 6

What is the exception to the law of independent assortment

Answer 6

When 2 genes are close together on chromosome = GENETIC LINKAGE
- The closer together 2 genes are, the less likely they are to be independently assorted

Question 7

Define the law of dominance

Answer 7

Some alleles are dominant while others are recessive. An organism with at least 1 dominant allele will display the effect of that dominant allele

Question 8

Relate the law of dominance to what is happening in the cell

Answer 8

○ Most recessive alleles do not code for a functional protein

Heterozygous: still receive the functional copy of the enzyme from one parent = can still make the product (i.e. lego house)
- May have less of product if this step is rate limiting

Homozygous recessive: do not receive a copy of the functional enzyme from either parent
- Build up of precursor
- Pathway to final product is incomplete = product not produced

Question 9

What are symptoms of PKU? (4)

Answer 9

intellectual disability, seizures, behavioural problems, and mental disorders

Question 10

When does PKU arise?

Answer 10

When missing the first enzyme of pathway for breaking down phenylalanine, resulting in Phe build up and not enough Tyr

Question 11

How can the effects of PKU be mitigated? What does this show?

Answer 11

with a low phenylalanine diet + (tyr) protein substitute
→ Shows genes interacting with environment
→ Environment determines phenotype

Question 12

What else affects the phenotype/severity of PKU? How/why?

Answer 12

genetics!
→ Phe transported to brain across blood-brain barrier
→ Genetic variation = difference in the efficiency of the transporter between different individuals
→ Individuals with less efficient transporters have lower levels of Phe in the brain and less damage (higher IQ).

Question 13

The severity of PKU can vary between individuals because of… (5)

Answer 13

• MUTATIONS in the genes coding for enzymes in the Phe breakdown pathway
• different TYPES/LOCATIONS of mutations within the enzymes for Phe breakdown pathway (i.e. sub vs del)
• mutations in the PROMOTOR REGION of enzymes in the Phe breakdown pathway changing the level of gene expression (too much or too little of the enzyme)
• genetic variation/mutations that effect presence/transport of Phe
• binding of transcription activators/repressors to the promotor region in response to environmental factors, resulting in changes to level of gene expression