Chromosomes, Meiosis, and Heredity

Flashcards covering the fundamentals of somatic and germ cells, the phases of meiosis, gametogenesis, and Mendelian genetics including laws of inheritance and complex dominance patterns.

What are somatic cells?

Body cells that make up most of your body tissues and organs; their DNA is not passed on to offspring.

What are germ cells?

Cells in reproductive organs that develop into gametes (sex cells) like eggs and spermatozoa.

Define homologous chromosomes.

Two chromosomes, one from the mother and one from the father, that have the same length and general appearance and carry copies of the same genes.

What are autosomes?

Chromosomes that contain genes for characteristics not directly related to the sex of an organism, comprising pairs $1$ to $22$ in humans.

Describe the Y chromosome.

The smallest sex chromosome that carries the fewest genes, including those that direct the development of testes and male traits.

What occurs during fertilization?

The fusion of an egg and a sperm cell where the nuclei fuse to form one nucleus.

What is the chromosome count for human diploid and haploid cells?

Diploid ($2n$) cells have $46$ chromosomes; haploid cells have only one copy of each chromosome ($22$ autosomes and $1$ sex chromosome).

How does meiosis differ from mitosis regarding cell production?

Meiosis produces genetically unique haploid cells and involves two cell divisions; mitosis produces genetically identical diploid cells and involves one cell division.

What separates during Anaphase I of meiosis?

Paired homologous chromosomes separate and move toward opposite sides of the cell, while sister chromatids remain attached.

What is the end result of Meiosis II?

$4$ haploid cells with a combination of chromosomes from both the mother and father.

Define gametogenesis.

The production of gametes; in males, it includes sperm formation, and in females, it results in an egg and polar bodies.

What are polar bodies?

Cells produced by meiosis in females with little more than DNA that are eventually broken down and do not typically undergo meiosis II.

What is Mendel's Law of Segregation?

Organisms inherit two copies of each gene (one from each parent) and donate only one copy in their gametes because the two copies segregate during gamete formation.

Define an allele.

Any of the alternative forms of a gene that may occur at a specific locus.

What is the difference between genotype and phenotype?

Genotype is the genetic makeup of a specific set of genes, while phenotype is the physical characteristics or traits of an individual organism.

What is a testcross?

A cross between an organism with an unknown genotype and an organism with the recessive phenotype.

What is the Law of Independent Assortment?

Mendel's second law stating that allele pairs separate independently of each other during gamete formation (meiosis).

What is the formula for probability?

$$\text{Probability} = \frac{\text{number of ways a specific event can occur}}{\text{number of total possible outcomes}}$$

Contrast incomplete dominance and codominance.

Incomplete dominance results in a phenotype in between the two parental varieties (no true dominance), while codominance results in both alleles being expressed without blending.