one parent cell gives rise to 2 identical daughter cells
asexual reproduction
maintains chromosomes (diploid) number
mitosis is the nuclear division
cytokinesis is a cytoplasmic division
occurs in billions of somatic cells each day
needed for tissue repair, maintenance, and growth
Meiosis (reproductive cell division):
one parent cell gives rise to 4identical/non-identical daughter cells
sexual reproduction
reduces chromosome number in half =(haploid #)
egg and sperm cell production = gametes
fusion of egg and sperm results in a zygote. When this single-celled zygote divides mitotically it becomes an embryo
Sexual Reproduction- produces genetic diversity among offspring, increasing the chances that some offspring survive in changing environments
chromosome: a long, coiled DNA molecule that carries genetic information
autosome: a chromosome that is not a sex chromosome
sex chromosome: a pair of chromosomes that determine the sex of an individual
homologous pair: two chromosomes that are identical in length and have the same number of chromosomes
sister chromatids: two identical chromosomes that are joined by a centromere
genes: the basic unit of heredity, consisting of a segment of DNA that codes for a particular protein
alleles: different versions of a gene that are inherited from parents and are passed on to offspring
Artificial Selection: The process by which humans selectively breed organisms to produce desired characteristics.
Allele Frequency:
# of copies of an allele
Total # of alleles for the same gene in the population
Adaptations: A feature of an organism that helps it survive and reproduce in its environment.
Gene Pool: The total number of alleles in a population of a species.
Fitness: The ability of an organism to survive and reproduce in its environment.
Hardy-Winberg Equilibrium: unlikely situation in which allele frequencies do not change between generations
Allele Frequencies:
p+q=1p2+2pq+q2=1
p is the frequency of the dominant allele and q is the frequency of the recessive allele
Genetic Drift: occurs purely by chance. It is most common in small populations
Founder Effect: when only a few individuals establish a new population, the allele frequency might change.
Population Bottleneck Effect: occurs if a disaster drastically reduces the size of a population
gene flow: moves alleles between populations
Directional Selection: a mode of natural selection in which a single phenotype is favored, causing the allele frequency to shift in one direction continuously
disruptive selection: extreme phenotypes are favored over an intermediate phenotype
Stabilizing selection: an intermediate phenotype is favored over the extreme phenotypes
Immigration: the movement of individuals into a population
Emigration: the movement of individuals out of a population
Survivorship curves: show the proportion of surviving individuals at each age
Type1 Survivorship Curve: A species that invests much energy in caring for young, has low death rates early in life. Most individuals survive to reproduce
Type II survivorship curve: have an approximately equal probability of dying at any age
Type III Survivorship Curve: a species that invests little energy into raising their young, resulting in a high death rate among offspring. Few individuals survive to reproductive age