Unit 6: Heredity - Terminology & Introduction to Genetics

A set of vocabulary flashcards covering the fundamentals of human genetics, meiosis, inheritance patterns, and chromosomal anomalies.

Meiosis

A process involving DNA replication followed by two cell divisions that ensures the correct chromosome number in the zygote and only occurs in the gonads to produce gametes.

Zygote

A diploid ($2n = 46$) cell resulting from the fusion of a haploid sperm ($n = 23$) and a haploid oocyte ($n = 23$).

Gonads

Mixed glands that produce sex hormones and gametes; these are the testes in males and the ovaries in females.

Gametes

Haploid cells produced by meiosis, specifically spermatozoa in males and the ovum in females.

Somatic Cells

Diploid cells produced by mitosis that are responsible for the growth, repair, and regeneration of tissues; includes all cells except gametes.

Gametogenesis

The processes that result in a fully functional gamete, known as spermatogenesis in males and oogenesis in females.

Diploid ($2n$)

The normal chromosome number in somatic cells, which contains $46$ chromosomes.

Haploid ($n$)

The normal chromosome number in gametes, which contains $23$ chromosomes.

Homologous Chromosomes

The $23$ pairs of chromosomes in humans where each chromosome in a pair codes for the same genes, with one from the father and one from the mother.

Autosomes

The chromosomes numbered $1-22$ that code for everything except for genetic sex.

Sex chromosomes

Chromosome pair $23$ which codes for genetic sex and other traits.

Gene

A segment of DNA that codes for a trait.

Locus

The specific part of the chromosome where a gene is located.

Alleles

Different forms of a gene at a specific locus.

Homozygous

A condition where the alleles for a specific trait are the same on both homologs.

Heterozygous

A condition where the alleles for a specific trait are different on each homolog.

Dominant allele

An allele that masks or suppresses the expression of the recessive allele if present and determines the phenotype.

Genotype

The genetic makeup a person has for a specific trait.

Phenotype

The physical expression of a trait.

Segregation

A process occurring during anaphase I of meiosis where two alleles of one particular trait are separated and distributed to two different daughter cells.

Nondisjunction

An anomaly where homologous chromosomes fail to separate correctly during meiosis I or II, resulting in an abnormal number of chromosomes.

Aneuploidy

An abnormal number of chromosomes in a cell, which is responsible for about $80\%$ of miscarriages in the first trimester.

Independent Assortment

The principle that alleles of two different traits on two different chromosomes are distributed independently of one another, resulting in $8.5 \times 10^6$ possible combinations.

Punnett square

A grid used to make predictions regarding the possible genotypes and phenotypes of potential offspring.

Monohybrid crosses

A genetic cross that shows the combinations of a single trait.

Crossover

A process during meiosis where homologous chromosomes break and exchange gene segments, resulting in recombinant chromosomes.

Random Fertilization

The random manner in which a single egg is fertilized by a single sperm, resulting in approximately $72 \times 10^{12}$ possible zygote combinations.

Syndactyly

A dominant disorder characterized by webbed digits.

Achondroplasia

A dominant disorder where heterozygous individuals exhibit dwarfism and the homozygous dominant genotype is lethal.

Huntington’s disease

A dominant disorder caused by a delayed-action gene that is typically not activated until approximately age $40$.

Incomplete Dominance

A pattern of inheritance where heterozygous individuals have an intermediate phenotype, such as in the sickling gene ($Ss$).

Codominance

A pattern of inheritance where both phenotypes are expressed in a heterozygous individual, as seen in human Type AB blood group ($I^A I^B$).

Multiple Alleles

A single trait controlled by three or more alleles, such as the $I^A$, $I^B$, and $i$ alleles that control human blood types.

X-linked genes

Genes found only on the X chromosome, which bears over $1400$ genes.