Module 15 Genetics and Heredity

What is the structural difference between DNA and RNA sugars?

One contains deoxyribose sugar, while the other contains ribose sugar.

What bases pair in DNA and RNA?

A-T and C-G; A-U and C-G.

What is the difference in structure between DNA and RNA molecules?

One is a double helix; The other is usually single-stranded.

What are the two main steps of protein synthesis?

Transcription (DNA → mRNA) and translation (mRNA → protein).

How do genes and alleles affect protein synthesis?

Differences in base sequences alter protein products, influencing traits.

How many chromosomes are in human somatic cells vs gametes?

46 (23 pairs, diploid). vs 23 (haploid).

Q: What are homologous chromosomes?

A: Pairs of chromosomes (one maternal, one paternal) carrying genes for the same traits.

What is the difference between autosomes and sex chromosomes?

22 pairs not related to sex. 1 pair (XX or XY) determining sex.

Define genotype and phenotype.

= genetic makeup (alleles). = observable traits expressed.

What are the three main processes that create genetic variation?

Independent assortment, crossing over, and random fertilisation.

Why is genetic variation important?

It ensures uniqueness and increases survival of a species.

What is dominant-recessive inheritance?

Dominant alleles mask recessive ones; recessive traits appear only if homozygous recessive.

What is a Punnett square used for?

To predict probabilities of specific genotypes and phenotypes in offspring.

What does it mean to be a carrier of a recessive condition?

A heterozygous individual carries one recessive allele but does not express the condition.

What is incomplete dominance?

A heterozygous phenotype intermediate between homozygous dominant and recessive (e.g., sickle-cell trait).

What is co-dominance?

Both alleles are expressed equally (e.g., AB blood group).

What is multiple allele inheritance?

A gene with more than two possible alleles (e.g., ABO blood types).

What is sex-linked inheritance?

Traits controlled by genes on sex chromosomes, often X-linked, more common in males (e.g., colour blindness).

What is polygenic inheritance?

Traits controlled by multiple genes, producing a spectrum of phenotypes (e.g., height, skin colour).

Why is polygenic inheritance the most common form?

Most traits depend on additive effects of several genes.

What factors influence gene expression?

Internal factors (hormones, regulatory proteins), external factors (nutrition, environment), and epigenetic changes.

Give an example of environment influencing phenotype.

Skin colour changes with sun exposure, despite genotype.

What is epigenetics?

The study of how gene expression is regulated by internal and external factors without changing the DNA sequence.

What is a gene?

A segment of DNA that codes for proteins and determines traits.

What is a chromosome?

A DNA molecule packaged with proteins, carrying many genes.

What is an allele?

Alternative versions of a gene at the same locus on homologous chromosomes.

What does homozygous mean?

Having two identical alleles for a trait (e.g., FF or ff).

What does heterozygous mean?

Having two different alleles for a trait (e.g., Ff).

What is a dominant allele?

An allele that is expressed in the phenotype and masks the recessive allele.

What is a recessive allele?

An allele masked by a dominant allele; expressed only when homozygous.