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.