Biology 121 Exam 2

Genetics, etc

Somatic Cells

Whole Body Cells

Germ Cells

Reproductive Cells (what gametes develop from)

Interphase of Mitosis

Sister chromatids are created and wound around small proteins (histones)

Prophase of Mitosis

Mitotic spindle is formed in prophase (connects to chromosomes and pull them towards different poles), nucleus starts breaking apart, chromosomes get shorter and thicker

Metaphase of Mitosis

Chromosomes lined up in middle, nuclei are on different poles, mitotic spindle surround chromosomes

Anaphase of Mitosis

Sister chromatids pull apart from each other, move toward different poles

Telophase of Mitosis

New nuclear envelopes form, chromosomes are no longer connected to a spindle.

G1 of Interphase

Cell grows, acquires nutrients, synthesizes proteins.

S Phase of Interphase

DNA is Replicated (Daughter cells all have an identical set of chromosomes)

G2 of Interphase

Cell produces organelles and proteins needed for cell division.

Independent Assortment

A genetic principle stating that alleles for different traits segregate independently during the formation of gametes.

Crossing Over

The process in which homologous chromosomes trade parts.

DNA is broken at the same spot on each homologue and reconnected in a crisscross pattern so that the homologues exchange part of their DNA (ABc and aBC are homologous chromosomes. When they cross over they become ABC and aBc).

Random Fertilization

The selection of each egg and sperm is completely random.

What happens to chromosomes before meiosis begins?

Sister chromatids are formed and DNA replicates (interphase)

Prophase I of Meiosis

Chromosomes begin to condense and homologous chromosomes pair up along with the sister chromatids

Metaphase I of Meiosis

Homologous pairs are lined up in the middle, mitotic spindles are connected to sister chromatids.

Anaphase I of Meiosis

Homologues are pulled apart and move to opposite ends of the cell. Sister chromatids remain attached to one another and won’t come apart.

Telophase I of Meiosis

Homologous Chromosomes are fully separated in different cells, sister chromatids are still together. The nuclear membrane doesn’t reform and the chromosomes don’t decondense in every case because the cells will go through Meiosis II.

Meiosis II

DNA is not copied between telophase I and prophase II. It’s basically mitosis for haploid cells. Cells are haploid with a diploid amount of DNA— One chromosome from each homologous pair, but two sister chromatids. Sister Chromatids will separate during this phase.

Prophase II

Starting cells are haploid cells made in meiosis I, chromosomes condense and, if the nuclear envelope was developed, it breaks down. Centrosomes move apart, spindle forms between them, spindle microtubules begin to capture chromosomes.

Metaphase II

Chromosomes line up individually along the metaphase place.

Anaphase II

Sister chromatids separate and are pulled towards opposite pole of the cell.

Telophase II & Cytokinesis

Nuclear membranes form around each set of chromosomes, chromosomes decondense. Cytokinesis splits chromosome sets into new cells.

Final product: four haploid cells in which each chromosome has just one chromosome. (GAMETES)

How is Mitosis and Meiosis Different?

Mitosis produces daughter cells that are genetically identical to the parent cell.

Meiosis produces gametes that are genetically unique.

Phenotypic Plasticity

When a single genotype produces multiple phenotypes under different  environmental conditions.

How many Homologous pairs —> How many Total Chromatids

A diploid cell has 2 complete sets of chromosomes. So a germ cell containing X amount of chromosomes would have X/2 homologous pairs. Each of the chromosomes consists of 2 sister chromatids after DNA replication, so the X/2 pairs of chromosomes contain X*2 chromatids total at the beginning of Meiosis I

Chromosomal Deletion

The deletion of parts of chromosomes.

Law of Segregation

Only one of the two alleles present in an organism is distributed to each gamete that it makes, and the allocation of the gene copies is random.

What fuels evolution?

Variation

Epistasis

Where a gene at one locus alters the phenotypic expression of another gene. Multiple genes affect one trait (hair color, etc)

Polygene Inheritance

Multiple gene inheritance and the environment’s influence.

How are maternal lines traced in females?

Mitochondrial DNA

T.H. Morgan

Exponentially increased knowledge of genetics through the fruit fly experiment.

Rules for Crossing Over

• Recombination Frequency is NEVER OVER 50% UNLESS THE ALLELES ARE ON DIFFERENT GENES (Analogous chromosomes put together by the chiasmata can recombine but the sister chromatids on the outside never cross over)

• The closer together genes are, the less likely that are to recombine.

Map Unit

1% recombination frequency (centermorgans)

X-0 Sex

Many insects don’t have a Y-chromosome, males have X-0 Chromosomes.

ZW Sex

Birds and Butterflies have the opposite dynamic of mammals— males have the homogametic sex chromosomes (ZZ) while females are heterogametic (ZW).

Haploid Sex

Male Bees don’t have fathers, as they are from unfertilized eggs and are therefore haploid.

Female Bees are from fertilized eggs which are diploid.

Barr Body

Early in development— embryo is ~16 cells big— every cell is an identical daughter cell until on of the two X’s in a female cell shrivels up and is moved to right outside of the nucleus.

The same specific X chromosome does not shrivel in every cell, so females can present different genetics throughout their body.

Shriveled X’s — the Barr Body— appears as a smudge.

Nondisjuntion

When pairs of homologous chromosomes do not separare normally during meiosis I.

• One gamete gets two of the same type of chromosome and another gamete receives no copy.

• Two ways this could occur: in Meiosis I with homologous chromosomes or Meiosis II with Sister Chromatids.

  • Occurs in Meiosis I: all 4 resulting haploids are affected (½ are n+1, ½ are n-1)

  • Occurs in Meiosis II: only 2 of 4 resulting haploids are affected (¼ is n+1, ¼ is n-1, ½ are n)

Aneuploidy

Results from the fertilization of gametes in which nondisjunction occurred.

• most aneuploids die by miscarriage

• Monosomy (one of a chromosome in a fertilized diploid gamete), some trisomy (3 of a chromosome in a fertilized diploid gamete) survive like with Klinefelter Syndrome, Turner Syndrome.

• XXX can survive while I-I-I can’t survive.

When does sex cell development occur in male vs females?

Males are constantly creating sperm through meiosis in the testes while females start developing eggs through meiosis until the beginning of meiosis I during fetus development and then stops until puberty.