Unit 4 - Topic 1 (Inheritance)

Question 1

What is a gene?

Answer 1

Region/s of DNA that are made up of nucleotides; the molecular unit of heredity

Question 2

What is an allele?

Answer 2

An allele is a different form or version of a gene that occurs at the same place (locus) on a chromosome.

Question 3

What is Mendel’s Rules?

Answer 3

1. Law of Segregation – Alleles split apart when making gametes.
2. Law of Independent Assortment – Different traits mix and match freely.
3. Law of Dominance – The stronger (dominant) allele hides the weaker (recessive) one.

Question 4

What is a genotype?

Answer 4

The genetic makeup of an organism

Question 5

What is a phenotype?

Answer 5

The physical traits the organisms shows

Question 6

How is a phenotype determined?

Answer 6

Genotype: the combination of alleles an organism has for a particular gene
- Dominant:
- the phenotype expressed when at least one copy if its allele occurs in a genotype
- Recessive:
- the phenotype only expressed if both copies of its recessive allele occur in the genotype

Environment: external conditions can influence how genes are expressed

Question 7

What is incomplete dominance?

Answer 7

Alleles aren’t completely dominant, so they BLEND

Question 8

What is codominance?

Answer 8

Codominance is when both alleles are equally expressed in the phenotype — neither one is dominant nor recessive.

Question 9

What are sex-linked genes?

Answer 9

Sex-linked genes are genes that are found on the sex chromosomes — usually the X chromosome (since the Y chromosome is much smaller and has fewer genes).
- red–green colour blindness and haemophilia are X-linked disorders.
- males are more likely to show these traits because they only have one X chromosome, so if that gene is faulty, there’s no backup copy.

Question 10

What is polygenic inheritance?

Answer 10

• polygenic inheritance is when many genes are influencing one trait, producing continuous variation in the population.
• each gene adds a small amount to the overall effect, so the trait shows a wide range of variations instead of clear categories.

🧬 Examples:
-human height, skin colour, and eye colour

Question 11

What is complete dominance?

Answer 11

Complete dominance is a pattern of inheritance where one allele completely masks the effect of another at the same gene locus, so the dominant trait is fully expressed in the phenotype.

Question 12

What is heterozygous?

Answer 12

Heterozygous describes an organism that has two different alleles for a particular gene, often resulting in the dominant allele being expressed in the phenotype while the recessive allele is hidden.

Question 13

What is homozygous dominant?

Answer 13

Homozygous dominant describes an organism that has two identical dominant alleles for a particular gene, resulting in the dominant trait being expressed in the phenotype.

Question 14

What is homozygous recessive?

Answer 14

Homozygous recessive describes an organism that has two identical recessive alleles for a particular gene, causing the recessive trait to be expressed in the phenotype.

Question 15

Explain the difference between x-linked recessive and x-linked dominant?

Answer 15

X-linked recessive traits require two copies in females (one in males) to be expressed, often affecting males more. X-linked dominant traits are expressed with just one copy in either sex.