Non-Mendelian Genetics

Question 1

Codominance – define, solve word problems.

Answer 1

• Codominance: a pattern of inheritance where both alleles are expressed at the same time.
• Codominance is when both versions of a gene show up in an organism’s traits. It’s like if you mixed red and white paint and got both colors, instead of just a mix of pink. A classic example is the AB blood type, where both A and B traits are fully expressed.

Question 1

Incomplete dominance – define, solve word problems.

Answer 1

• Incomplete dominance: Think of incomplete dominance as “blending genes.” When two different alleles mix together to create a third, intermediate phenotype, that’s incomplete dominance. It’s like blending paint colors—red and white make pink, showing neither color dominates the other.

Question 2

Multiple alleles – e.g., rabbits and blood typing, solve word problems.

Answer 2

Remember:
- Multiple alleles mean there are more than two versions of a gene.
- Dominance relationships determine how these alleles interact.
- Imagine you have a pair of shoes, and you can only wear one shoe from each pair at a time. Similarly, an organism can only “wear” one allele from each pair of alleles for a gene because they have pairs of homologous chromosomes. So, even though there may be many alleles in a population, each organism can only have two alleles for a specific gene—one from each parent.
For rabbits:
- Coat color has multiple alleles: Chinchilla (C^ch), Himalayan (C^h), and albino (c).
- Chinchilla (C^ch) is dominant to Himalayan (C^h) and albino (c).
- Himalayan (C^h) is dominant to albino (c).
To solve problems:
1. List the alleles involved.
2. Determine dominance relationships.
3. Use Punnett squares or allele combinations to find genotypes and phenotypes.
4. For genotypic and phenotypic ratios, count the different combinations of alleles or traits.
- For example, in a cross between a chinchilla (C^ch) and Himalayan (C^h) rabbit, you can predict the possible offspring genotypes and phenotypes using the dominance relationships. Similarly, when crossing two Himalayan rabbits (C^hC^h), you can determine the genotypic and phenotypic ratios based on allele combinations.

Question 3

Blood typing – antigens, antibodies, universal donor, universal recipient.

Answer 3

1. Antigens:
   
   • What they are: Tags on cells that say “This is me!”
   • Job: Helps your body recognize its own cells and spot invaders.
   • In blood: A, B, and Rh (D) are types of these tags.
2. Antibodies:
   
   • What they are: Like bodyguards in your blood.
   • Job: They attack anything with the wrong tags (foreign invaders).
   • In blood typing: If your blood has a tag for A, it has guards to fight B tags. If it has B tags, it fights A tags. AB blood has no fighting guards, and O blood fights both A and B tags.
3. Universal Donor:
   
   • O-: No tags, safe for anyone.
4. Universal Recipient:
   
   • AB+: Tags match all, no guards to attack.

Question 4

X-linked genes – define, solve word problems.

Answer 4

X-linked genes:
- Found on the X chromosome.
- Different inheritance patterns in males (XY) and females (XX).
For word problems:
1. Know the pattern:
- In females, both X chromosomes are usually expressed.
- In males, traits on the X chromosome are expressed because they have only one X chromosome.
2. Alleles and expression:
- Recessive X-linked traits are more common in males.
- Dominant X-linked traits can be expressed by both males and females.
3. Use Punnett squares:
- For recessive traits, males need only one copy of the allele to express the trait, while females need two copies.
- For dominant traits, both males and females can express the trait.
Example:
- If there’s an X-linked recessive trait, like color blindness, males (XY) are more likely to express it because they have one X chromosome. Females (XX) need two copies of the recessive allele to express the trait.

Question 5

What are polygenic traits? Give an example.

Answer 5

• A polygenic trait is a characteristic, such as height or skin color, that is influenced by two or more genes
• Polygenic traits are like a team effort of many genes working together, kind of like how a team of players contributes to winning a game. Each gene adds a little bit to the trait, just like each player adds a bit to the team’s success. Think of human height as an example: it’s determined by a bunch of genes working together, making some people tall, some short, and most somewhere in between.