Chapter 8: Genetics & Human Inheritance

Human karyotype

A visual display of all 46 human chromosomes arranged in homologous pairs.

Sex chromosomes

The X and Y chromosomes that determine biological sex (XX = female, XY = male).

Autosomes

The 22 pairs of non-sex chromosomes that carry genes for most body traits.

Abnormal chromosome number

A condition where an individual has too many or too few chromosomes (e.g., trisomy 21 = Down syndrome).

Chromosome diagram

A chromosome is a DNA molecule coiled around proteins; it contains many genes along its length.

Gene

A segment of DNA that codes for a specific protein or trait.

Allele

A version or form of a gene (e.g., dominant or recessive).

Locus (plural loci)

The physical location of a gene on a chromosome.

Genetic carrier

An individual who carries one recessive allele for a disorder but does not show symptoms.

Carrier genotype example

Heterozygous (Aa), with one normal allele and one recessive disease allele.

Carrier phenotype

Typically normal, because the dominant allele masks the effects of the recessive allele.

Sex determination in humans

Determined by the presence or absence of the Y chromosome (XX = female, XY = male).

Inheritance of sex-linked traits

Traits controlled by genes on the X or Y chromosome, usually the X; males are more affected because they have only one X.

Example of X-linked trait

Color blindness or hemophilia, which occur more often in males.

Recessive disorder inheritance

Affects individuals with two recessive alleles (aa); carriers (Aa) are unaffected.

Dominant disorder inheritance

Affects individuals with at least one dominant allele (A_); no carriers because one copy is enough to cause the trait.

Sex-linked disorder inheritance

Caused by genes on sex chromosomes; males (XY) more likely to express X-linked recessive traits.

Punnett square use

A diagram used to calculate the probability of inheriting specific genotypes or disorders.

Pedigree chart

A family tree diagram that tracks the inheritance of traits through generations.

Pedigree interpretation

Helps determine whether a condition is recessive, dominant, or sex-linked.

Recessive pedigree pattern

Trait often skips generations; affected individuals usually have unaffected carrier parents.

Dominant pedigree pattern

Trait appears in every generation; affected individuals have at least one affected parent.

Sex-linked pedigree pattern

More males than females affected; trait passes from carrier mothers to sons.