Genetics (DMD) Lessons 6-7 Sexual Reproduction and Inheritance

phenotype

A physical trait expressed by an organism. For example...brown eyes.

allele

An alternate form of a gene, for example brown eye color or blue eye color.

haploid

Half the normal number (n) of chromosomes. Only sex cells are haploid.

dominant allele

Represented by a capital letter ("B"). Only one allele is needed to express the phenotype. (BB or Bb)

recessive allele

Represented by a lowercase letter ("b"). Need to inherit two copies of an allele to express the phenotype. (bb)

genotype

The combination of alleles for a trait inherited on a pair of homologous chromosomes from each parent. (BB, Bb, bb)

autosomes

The first 22 pairs of human chromosomes.

diploid

The normal number of chromosomes (2n) in a body cell.

fertilization

The union of sperm and egg to make a zygote.

homozygous

Two identical alleles for a trait. (BB or bb)

heterozygous

Two non-identical alleles for a trait (Bb)

sex chromosomes

X and Y. The interaction of the genes on these two chromosomes determine the sex of an individual. Women are XX and men are XY.

genome

a complete set of chromosomes in an organism's cells.

chromosome

a long, coiled piece of DNA found in the nucleus of most cells.

gene

a section of a DNA molecule that provides a cell instructions to make proteins.

meiosis

cell division that produces haploid gametes

Punnett Square

diagram showing the probabilities of gene combinations that might result from a genetic cross

Deoxyribonucleic Acid (DNA)

genetic instructions to build proteins

genetic variation

members of the same species exhibit different traits due to the inheritance of different alleles

genetic recombination

new combination of genes produced by crossing over and independent assortment

mitosis

part of the cell cycle that ensures each new body cell receives the same genetic information.

independent assortment

random distribution of homologous chromosomes into sex cells during meiosis. Causes variation in offspring.

crossing over

random process during meiosis where pieces of a chromosome are broken off and reattached to another chromosome.

gamete

sex cell (sperm or egg) that have one of each pair of chromosomes

homologous pair of chromosomes

similar but not identical sets of chromosomes inherited from biological mother and father.