Biology Chapter on Evolution and Genetics

Evolution

• Descent with modification is a key concept in evolutionary theory, meaning organisms change over time.
• Evolution is supported by scientific evidence and it's not merely a theory.

Meiosis

• Nondisjunction occurs when homologous chromosomes fail to separate during meiosis I.
• Meiosis I results in two genetically unique daughter cells, each with half the number of chromosomes as the parent cell.

Hardy-Weinberg Equilibrium

• The frequency of the recessive phenotype (q²) in a population is calculated using the Hardy-Weinberg equation.
• When the dominant allele frequency (p) is 0.6, the recessive allele frequency (q) is 0.4, and the recessive phenotype frequency (q²) is 0.16.

Genetics

• Heterozygous means having two different alleles for a trait.
• Mendel's Law of Independent Assortment states that alleles for different traits segregate independently of each other during gamete formation.
• Mutation is a primary source of genetic variation in both asexual and sexual reproduction.
• Crossing over is a process that occurs during prophase I of meiosis and involves the exchange of genetic material between homologous chromosomes.
• Divergent evolution occurs when species with similar characteristics evolve from a shared common ancestor.

Inheritance

• A cross between a BbTt (black fur, short tail) and BBtt (black fur, long tail) mouse would result in 50% of the offspring having black fur and long tails.
• Genetic drift happens when random events cause changes in allele frequencies within a population.
• Bottleneck effect is a type of genetic drift where a population drastically reduces in size, causing a loss of genetic diversity.
• Natural selection acts on heritable variation within a population, leading to adaptations.
• Fertilization combines two haploid gametes to form a diploid zygote, increasing ploidy.

Analogous Traits

• Wings in bats and birds are analogous traits, meaning they serve a similar function but evolved independently.

Karyotype

• A karyotype is a visual representation of an individual's chromosomes.
• A somatic cell is a non-reproductive cell.
• A diploid organism has two sets of chromosomes.
• A gamete, or sex cell, is haploid with one set of chromosomes.

Chromosomal Alterations

• Inversions occur when a segment of a chromosome detaches, rotates 180 degrees, and reattaches.

Mitosis vs Meiosis

• Both mitosis and meiosis involve the separation of sister chromatids.
• Meiosis results in increased genetic diversity, while mitosis produces genetically identical daughter cells.

Punnett Square

• A Punnett square is a diagram used to predict the genotype and phenotype of offspring from a cross.
• For a cross between Aa and Aa, the box labeled 4 would contain the genotype aa.

Modes of Inheritance

• Incomplete dominance occurs when the heterozygous phenotype is a blend of the two homozygous phenotypes.
• Codominance occurs when both alleles are equally expressed in the heterozygous phenotype.
• Polygenic inheritance involves multiple genes contributing to a single trait.
• Complete dominance occurs when one allele completely masks the other allele.

Gametes

• A canine gamete will have 19 chromosomes (38 autosomes + 1 sex chromosome).

Hardy-Weinberg Equilibrium in Populations

• If the frequency of homozygous dominant individuals (p²) is 0.49, the frequency of carriers (2pq) is 42%.
• In a population of 1000 individuals with 250 exhibiting the recessive phenotype, the frequency of the recessive allele (q) is 0.5.

Asexual Reproduction

• Asexual reproduction doesn't produce genetic diversity, unlike sexual reproduction.

Karyotype Analysis

• A karyotype with only one sex chromosome indicates a monosomy.

Probability of Offspring

• The probability of an offspring being heterozygous for all four loci from the cross AaBBccDd x aaBbCcDd is 1/16.

Lamarck's Theory

• Lamarck's theory of acquired inheritance proposed that traits acquired during an individual's lifetime were passed on to offspring, which has been disproven.

Mendel's Experiments

• Mendel's experiments involved studying the inheritance of traits in pea plants by crossing plants with different traits and observing the offspring over multiple generations.

Epistasis

• Epistasis is a genetic interaction where one gene masks the expression of another gene, as seen in albinism.