CH 19 Genetics and Inheritance

What is Genetics?

Genetics is the study of genes and how they are passed from one generation to the next.

• Genes are DNA sequences with instructions for building proteins.

What is the genome?

The genome is the total sum of an organism’s DNA.

How do we inherit DNA?

• One set of DNA comes from each parent.

• Siblings are genetically unique due to shuffled genes during meiosis (except identical twins).

What are chromosomes?

• DNA structures in the nucleus.

• Each has a single DNA molecule with proteins.

• Found in 23 pairs (46 total).

What is the difference between autosomes and sex chromosomes?

• Autosomes: 22 pairs of non-sex chromosomes.

• Sex chromosomes: 1 pair determines biological sex (XX for females, XY for males).

What are homologous chromosomes?

• One from each parent, similar but not identical.

• May carry different alleles (versions of a gene).

What are alleles?

• Alternative forms of a gene caused by mutations.

• Homozygous: Same alleles (AA or aa).

• Heterozygous: Different alleles (Aa).

What is a karyotype?

A visual of chromosomes, showing their number, size, and banding patterns.

What is the difference between genotype and phenotype?

• Genotype: Genetic makeup (set of alleles).

• Phenotype: Observable traits influenced by genotype and environment.

What tool predicts inheritance patterns?

The Punnett square, which combines parent alleles to show possible offspring traits.

What are Mendel’s two laws of inheritance?

• Law of Segregation: Each parent’s alleles separate into different gametes.

• Law of Independent Assortment: Genes for different traits are inherited separately.

How do dominant and recessive alleles work?

• Dominant: Always expressed (AA or Aa).

• Recessive: Only expressed if homozygous (aa).

What is an example of harmful recessive alleles?

• Cystic fibrosis: Caused by inheriting two recessive CFTR alleles.

• Thick lung mucus, breathing issues.

• Heterozygotes (Aa) are healthy.

What is incomplete dominance?

• Neither allele is fully dominant.

• Heterozygotes show a blended trait (e.g., wavy hair).

What is codominance?

• Both alleles are fully expressed together.

• Example: Blood type AB (A and B alleles are codominant).

What is polygenic inheritance?

• Traits influenced by multiple genes.

• Examples: Eye color, skin color, height.

How do genotype and environment affect phenotype?

Phenotype = genes + environment. Examples:

• Nutrition impacts height.

• Sun exposure impacts skin color.

How does sex-linked inheritance work?

• X-linked traits: Genes on the X chromosome.

• Males need 1 recessive allele to express it.

• Females need 2 recessive alleles to express it.

Examples of X-linked recessive disorders?

Red-green color blindness, hemophilia, Duchenne muscular dystrophy.

What causes Down syndrome?

• Trisomy 21: Three copies of chromosome 21.

• Causes developmental disabilities and distinct physical traits.

• Risk increases with maternal age.