biology - genetic variation

chromosome

long, coiled DNA molecule carrying many genes

DNA

molecule that stores genetic information. polymer made of repeating units called nucleotides

nucleotides have a phosphate group, a deoxyribose sugar and one of four nitrogenous bases

gene

a section of DNA that influences a specific characteristic. order of base sequences determines the gene

allele

an alternative version of a gene. you get one allele from each parent.

genotype

heterozygous (Aa) = dominant trait

homozygous dominant (AA) = dominant trait

homozygous recessive (aa) = recessive trait

gamete

mature haploid cell that unites during reproduction to form a zygote

haploid (n) vs diploid (2n)

cell containing a single set of unpaired chromosomes

cell containing two chromosome sets, one from each parent

meiosis process

interphase - DNA is copied

prophase 1 - chromosomes pair up with matching partners and swapping over happens

metaphase 1 - chromosome pairs line up in the middle of the cell

anaphase 1 - pairs are pulled apart to opposite sides of the cell

telophase 1 and cytokinesis - cell splits into two new daughter cells

prophase 2 - chromosomes get ready to split

metaphase 2 - chromosomes line up in a single line down the cell

anaphase 2 - the sides of each chromosomes (sister chromatids) are pulled apart to opposite ends

telophase 2 and cytokinesis - cells divide again, resulting in four haploid cells

in meiosis 1, sister chromatids stay together. in meiosis 2, they separate

crossing over (FOUR SOURCES OF VARIATION)

prophase 1, non sister chromatids exchange DNA segments, forming recombinant chromatids with new allele combinations

independent assortment (FOUR SOURCES OF VARIATION)

at metaphase 1, each homologous pair aligns independently and randomly. this creates 2ⁿ possible chromosome combinations (n = number of pairs)

random fertilization (FOUR SOURCES OF VARIATION)

any sperm can fuse with any egg, so two genetically different gametes combine to form a unique zygote

mutation (FOUR SOURCES OF VARIATION)

a change in the DNA base sequence can create a new allele. mutations are the original source of new genetic information