Need to Know

Sexual Reproduction

A type of reproduction involving the fusion of male and female gametes, resulting in offspring with genetic contributions from both parents.

Asexual Reproduction

A type of reproduction that does not involve the fusion of gametes, producing offspring genetically identical to the parent.

Haploid

A cell or organism having a single set of chromosomes (n).

Diploid

A cell or organism having two sets of chromosomes (2n), one from each parent.

Homologous Chromosomes

Pairs of chromosomes in a diploid organism that have the same structure and gene sequence, one from each parent.

Sister chromatids

Identical copies of a chromosome connected by a centromere, formed during DNA replication.

Non-sister chromatids

Chromatids belonging to homologous chromosomes, not identical but similar in gene sequence.

Gene

A segment of DNA that encodes a specific protein or functional RNA.

Allele

Different versions of a gene that may produce distinguishable phenotypic effects.

Locus

The specific physical location of a gene or other significant sequence on a chromosome.

Humans have how many chromosomes in somatic cells

46 (Diploid)

Humans have how many chromosomes in gametes

23 (Haploid)

What is the G1 phase

The first phase of the cell cycle, during which the cell grows and prepares for DNA replication.

What is the S phase

The replication/synthesis Phase

What is the G2 phase

The second growth phase of the cell cycle, where the cell prepares for mitosis by producing proteins and organelles.

What is Mitosis

The process of cell division where a single cell divides into two identical daughter cells, ensuring equal distribution of genetic material.

Males have how many pairs of homologous chromosomes

22

Females have how many pairs of homologous chromosomes

23

Condition to be considered one chromosome

Sister chromatids must be attached to the centromere

Interphase

• The cell prepares for division by replicating its DNA and organelles.

• Key Points:

  • DNA is in the form of chromatin.

  • The nucleus is intact.

  • The cell grows and performs normal functions.

  • This phase includes G1, S, and G2 phases, where the cell undergoes growth, DNA synthesis, and preparation for mitosis.

Prophase

• Chromosomes condense and become visible, the nuclear envelope breaks down, and spindle fibers form.

• Key Points:

  • Chromosomes consist of two sister chromatids joined at the centromere.

  • The nuclear membrane dissolves.

  • Spindle fibers begin to form from the centrosomes.

Metaphase

• Chromosomes line up at the metaphase plate (center of the cell).

• Key Points:

  • Chromosomes are aligned at the cell's equator.

  • Spindle fibers attach to the centromeres of the chromosomes.

Anaphase

• Sister chromatids are pulled apart to opposite poles of the cell.

• Key Points:

  • Spindle fibers shorten, pulling sister chromatids apart.

  • Chromatids move to opposite ends of the cell.

Telophase

• Chromatids reach the poles, nuclear membranes re-form around each set of chromosomes, and the cell begins to split.

• Key Points:

  • Chromosomes de-condense back into chromatin.

  • Nuclear envelopes re-form around each set of chromosomes.

  • The cell begins to divide through cytokinesis.

Cytokinesis

• The cytoplasm divides, resulting in two daughter cells.

• Key Points:

  • The cell membrane pinches in to divide the cytoplasm.

  • Two genetically identical daughter cells are formed.

Where/ when is mitosis used?

○Body cells: Normal growth, development, maintenance

○Asexual reproduction: One single individual passes all of its genes to its offspring

Prophase I

• Homologous chromosomes pair up and exchange segments.

• Key Points:

  • Chromosomes condense and become visible.

  • Homologous chromosomes undergo crossing over (exchange genetic material).

Metaphase I

• Homologous chromosomes align at the metaphase plate.

• Key Points:

  • Pairs of homologous chromosomes align in the middle of the cell.

Anaphase I

• Homologous chromosomes separate and move to opposite poles.

• Key Points:

  • Homologous chromosomes are pulled apart by spindle fibers.

Telophase I and Cytokinesis

• Two cells form, each with half the number of chromosomes.

• Key Points:

  • Nuclear membranes reform around chromosomes.

  • The cytoplasm divides, creating two haploid cells.

Prophase II

• Chromosomes condense again.

• Key Points:

  • Chromosomes recondense.

  • The nuclear envelope dissolves if it reformed.

Metaphase II

• Chromosomes align at the metaphase plate.

• Key Points:

  • Chromosomes line up individually at the center of the cell.

Anaphase II

• Sister chromatids separate and move to opposite poles.

• Key Points:

  • Sister chromatids are pulled apart by spindle fibers.

  • Chromatids move toward opposite poles.

Telophase II and Cytokinesis

• Four haploid daughter cells form.

• Key Points:

  • Nuclear membranes reform around each set of chromatids.

  • The cytoplasm divides, resulting in four non-identical haploid cells.

Meiosis reduces the number of chromosome sets from

diploid to haploid

meiosis is preceded by the duplication of chromosomes, so

each chromosome consists of two sister chromatids before meiosis.

What is responsible for genetic diversity/variation in Meiosis

Independent assortment and crossing over

Sexual Reproduction is better in

Changing Environments due to Genetic Variation

Asexual Reproduction is better in

Non changing environments, when clones are favored

Accumulation of Mutations is a

Slow Process

Independent Assortment

• The random distribution of homologous chromosome pairs to daughter cells during metaphase I of meiosis.

• Key Points:

  • Homologous chromosomes line up randomly along the metaphase plate.

  • Each gamete receives a different mix of maternal and paternal chromosomes.

  • This process generates diverse genetic combinations in gametes.

Recombination

• The exchange of genetic material between homologous chromosomes during prophase I of meiosis.

• Key Points:

  • Homologous chromosomes pair up and exchange segments of DNA.

  • Creates new combinations of alleles on each chromosome.

  • Increases genetic diversity by introducing novel gene combinations.

Homologs or Homologous Chromosomes have the

Same length and carry the same genes for the same inherited characters (Alleles may differ)

22 of the 23 for male and 24 for female chromosome pairs are

Autosomes, which are not sex chromosomes.

Chromatin is

A complex of protein/DNA (spaghetti-like fibers) that forms condensed, movable chromosomes in cell division.

PPMAT

Prophase, Prometaphase, Metaphase, Anaphase, Telophase and Cytokinesis

A new nucleus forms around the cells in

Cytokinesis

When the Nucleolus disapear

Prophase

When does the nuclear membrane completely dissolve

Prometaphase

What is the line where cells divide in animals called

Cleavage Furrow

Differences between Mitosis and Meiosis

For Meiosis is chromosome number cut in half in both Meiosis I and Meiosis II

No only Meiosis I

(In Meiosis I, homologous chromosomes are separated, reducing the chromosome number by half, while in Meiosis II, sister chromatids are separated without further reducing the chromosome number.)

Chiasmata

The points where homologous chromosomes exchange genetic material during recombination.

Synapsis

The process during meiosis (prophase I) where homologous chromosomes pair up and align closely together for recombination.

What three mechanisms contribute to genetic variation in Sexual Reproduction

Independent assortment, Recombination (crossing over), and Random Fertilization

Independent Assortment

Each pair of chromosomes orient randomly in metaphase I of Meiosis (2ⁿ where n is the haploid number can be used to determine all possible combinations of chromosomes in gametes)

Somatic Cell

body cells (diploid, 2n)

Gamete

sex cells (haploid, n), such as sperm and eggs

Homozygous

refers to having two identical alleles for a gene (e.g., AA or aa)

Heterozygous

refers to having two different alleles for a gene (e.g., Aa).

Pure-Breeding (True-Breeding)

An organism that always passes down certain phenotypic traits to its offspring; homozygous for the traits in question. These organisms are genetically uniform and produce progeny with the same traits.

Dominant

An allele that expresses its phenotype even in the presence of a recessive allele; represented by a capital letter (e.g., A).

Recessive

An allele that only expresses its phenotype when two copies are present; represented by a lowercase letter (e.g., a).

Gene

a segment of DNA that encodes a trait

Allele

variant form of a gene

Monohybrid

A cross between individuals focusing on one trait

Dihybrid Cross

A cross between individuals focusing on two traits

Test Cross

A cross between an organism with an unknown genotype but known phenotype and a homozygous recessive (Known Genotype) individual to determine the unknown genotype

Genotypic Ratio

The ratio of different allele combinations in the offspring

Phenotypic Ratio

The ratio of different observable traits in the offspring

Mendel’s 1st Law of Segregation

The principle stating that during the formation of gametes, the two alleles for a trait segregate from each other so that each gamete carries only one allele for each gene. This law explains how offspring inherit one allele from each parent, ensuring genetic variation.

Mendel’s 2nd Law

States that alleles for different traits segregate independently of one another during gamete formation, leading to genetic variation in offspring. (Independent Assortment)

Complex Inheritance

Refers to the inheritance patterns of traits that are influenced by multiple genes and environmental factors, resulting in a range of phenotypes.

1.Degrees of Dominance: incomplete dominance (flowers) and codominance (Blood type)

2.Multiple alleles: more than two alleles (blood type)

3.Pleiotropy (sickle cell)

4.Polygenic inheritance (skin color)

5.Gene Interactions (Golden Retrievers)

6.Sex-linked traits (x-linkage)These patterns demonstrate how traits can be influenced by various genetic and environmental factors, leading to diverse phenotypic expressions.

Codominance

A genetic scenario where two different alleles are both expressed in the phenotype of a heterozygote, resulting in a distinct phenotype that shows characteristics of both alleles, such as AB blood type in humans.

Incomplete Dominance

A genetic scenario where the phenotype of a heterozygote is intermediate between the phenotypes of the two homozygotes, such as pink flowers resulting from red and white parents.

Complete Dominance

A genetic scenario where one allele completely masks the effect of another allele in a heterozygote, resulting in a phenotype that reflects only the dominant allele.

Conditions for a male to express X linked trait

Only needs one affected X chromosome

Conditions for a female to express X linked trait

Requires two affected X chromosomes

Punnett Squares

A diagram used to predict the genotypes and phenotypes of offspring based on parental genotypes.

Probability Calculation

Use a Punnett square to determine the likelihood of specific genotypes and phenotypes in offspring.

Fertilization

Fusion of two haploid gametes (sperm and egg) to form a diploid zygote.This process initiates the development of a new organism.

Phenotype

Observable characteristics of an individual

Genotype

Genetic makeup of an individual, consisting of alleles inherited from parents

P generation

Parents

F1 Generation

Offspring

F2 Generation

Offspring of Offspring

What does the term “Perfect Flowers” mean

Flowers that have both male and female reproductive structures, allowing for self-pollination.

Self-Fertilization

Sperm and eggs are from the same flower

Cross-Fertilization

Sperm and egg are from different flowers

Dominance does not = ?

Prevalence

Dominance at the Molecular Level

Dominant alleles usually code for functional proteins that contribute to the phenotype. Recessive alleles may code for non-functional proteins or no protein at all.

Polygenic Inheritance

A type of inheritance where multiple genes influence a trait, resulting in a continuous range of phenotypes.

Microevolution

The small-scale evolutionary changes that occur within a species or population over time, often driven by mechanisms such as natural selection, genetic drift, and gene flow. (Generation to Generation Changes)

Organisms do not evolve

During their lifetime

Natural Selection does not act on

Individuals but instead on populations over generations

The source (origin) of genetic variation/diversity is

Mutation

Variation can be

Harmful, Beneficial, or Neutral

Gene Pool

All alleles for all genes for all individuals in a population

Hardy-Weinberg Equilibrium

When gametes contribute to the next generation randomly and Mendelian inheritance occurs, allele and genotype frequencies remain constant from generation to generation

Hardy-Weinberg Equations

p + q = 1

p² + 2pq + q² = 1