L16: Core Genetic Concepts

Question 1

What are the 3 Mendelian laws of inheritance? Briefly explain what they are about.

Answer 1

Law of segregation - during meiosis, the alleles are separated so each gamete only carries one allele for each gene.

Law of independent assortment - segregation of alleles for one gene occurs independently to that of any other gene

Law of dominance - some alleles are dominant while others are recessive. An organism with at least one dominant allele will display the effect of the dominant allele.

Question 2

This is an alternate form of a gene and is located at the same place on a chromosome.

Answer 2

Allele

Question 3

These chromosomes have the same genes but have different DNA sequences.

Answer 3

Homologous chromosomes

Question 4

During independent assortment, each gamete gets how many copies of the chromosome? And are the gametes identical to each other?

Answer 4

Each gamete gets 1 copy of the chromosome. The gametes are non-identical and have unique allele combinations.

Question 5

What is meiosis recombination?

Answer 5

• it adds another layer of genetic diversity
• but it’s basically inheriting a unique combination of DNA from not only your parents but grandparents and siblings as well. (it’s like genetic shuffling)

Question 6

Segregation of alleles for one gene occurs independently to that of any other gene, except for one specific circumstance- what is the exception?

Answer 6

Linked genes/genetic linkage.

When two genes are close together on a chromosome, the alleles are more likely to be inherited together. They are less likely to be recombinated

Question 7

A dominant allele is always expressed, therefore it is also known as a?

Answer 7

Functional allele which will therefore form functional enzymes.

Recessive alleles do not form functional enzymes because the pathway to activate or even make those enzymes do not work.

Question 8

Defect in this enzyme leads to PKU.

Answer 8

phenylhydroxylase (PAH)

Question 9

This disorder can lead to intellectual disability, seizures, behavioural problems and mental disorders.

Answer 9

Phenylketonuria (PKU)

Question 10

How does failure of phenylalanine breakdown affect the development of the brain? (as it commonly leads to seizures, mental disorders and intellectual disability)

Answer 10

Two reasons:

• accumulation of phenylalanine means our metabolism will convert it into random compounds as a way to get rid of it (thus, we get random stuff in our body that we probably don’t want
• the accumulation of now random stuff, will inhibit the precursors that are important for brain development including behavioural and mental development.

Question 11

What are the two factors that can influence phenotype?

Answer 11

Environment (like diet) and genetics (efficiency of the transportation of phenylalanine across blood-brain barrier)

Question 12

Why do individuals with less efficient transporters are known to have higher IQ?

Answer 12

Because having less efficient transporters means having less phenylalanine transported into the brain and therefore less damage.