Unit 5 Heredity and Genetics

A set of vocabulary flashcards covering key terms and definitions related to heredity and genetics as discussed in the lecture notes.

Heredity

The transmission of traits from one generation to the next.

Genetics

The study of heredity and the variation that exists within heredity.

mRNA

genes- segments of DNA that code for basic units of heredity. They will be transcribed to and translated to protein.

Asexual Reproduction

• Single individual

• No fusion of gametes

• Clones: offspring are exact copies of parent

• Mutations are the only source of variation

• Can produce asexually through mitosis

Sexual Reproduction

• Two parents (male/female)

• Offspring are unique combinations of genes from parents

• Genetically varied from parents and siblings

• Genetic variation confers a survival advantage

Meiosis

A two-part process that ensures the formation of haploid gamete cells in sexually reproducing diploid organisms.

Process that is just forming gametes

Haploid

A cell that has one complete set of chromosomes (1n), found in gametes like sperm and eggs

Diploid

A cell that has two complete sets of chromosomes (2n), one set from each parent, found in most body cells

Somatic (body) cells

• Body Cells

• Diploid (2n) two complete sets of each chromosome

• Humans: 2n = 46

Sexual Reproduction

Haploid gametes fuse and produce a diploid zygote. 

Gametes (sex) cells

Haploid forms of cells produced through meiosis. 

• Egg and sperm

• Haploid (n) one set of each chromosome

• Humans (sperm and eggs): n = 23

Zygote

A diploid cell formed by the fertilization of an egg.

• After the zygote has formed, it begins dividing by mitosis. (not meiosis→ that process is just for forming gametes)

Autosomes and Sex chromosomes

Two types of chromosomes

Chromosomes

Eukaryotic DNA is packaged into

Homologous Chromosome

A  pair of chromosomes (same size, length, centromere position) that carry the same genetic information

• One homologous chromosome is inherited from mom and one is inherited from dad

Autosomes

Chromosomes that do not determine sex, humans have 22 pairs.

Sex Chromosomes

Chromosomes that determine sex, X and Y in humans.

• Eggs: X (humans: 22 + X)

• Sperm: X or Y (humans: 22 + X OR 22 + Y)

Fertilization

The process in which a haploid sperm and haploid egg combine to create a diploid cell called a zygote

• Sperm have enzymes on head of body that breaks down the outer membrane of egg. 

• Once egg is fertilized by one sperm, egg will release chemicals that inhibit other sperm from penetrating. 

Reduction Division

Meiosis 1 is also called

Meiosis 1: Interphase

The cell grows, each of the chromosomes makes a copy of itself, centrosome also divides.

G1: Meiosis 1

• The cell increase in size and prepares for DNA replication

• 46 chromosomes per cell

• 46 chromatids per cell

S Phase: Meiosis 1

Each chromosome duplicates to become two identical sister chromatids attached at the centromere. The centrioles get duplicated as well

G2 Phase: Meiosis 1

• Cell continues to increase in size with the synthesis of RNA and proteins. Prepares for division

• 46 chromosomes per cell

• 92 chromatids per cell (because duplication in S phase)

Prophase 1

Homologous chromosomes pair up and condense, synapsis occurs and then chiasmata may form, meiotic spindle begins to form, centrosomes move to opposite poles of the cell, and the nuclear envelope breaks down.

CROSSING OVER OCCURS

Synapsis

Joining of homologous chromosomes along their length that forms a tetrad

Recombincation

Occurs during prophase I when homologous chromosomes pair up and exchange segments of DNA. This swapping of genetic material between non-sister chromatids creates new allele combinations in the gametes, increasing genetic diversity in offspring.

Metaphase 1

Meiotic spindle fibers align homologous pairs of chromosomes along the equator of the cell at the metaphase plate. 

• Independent Assortment of Chromosomes

Anaphase 1

Homologous chromosomes separate, while sister chromatids remain attached,as meiotic spindle fibers pull chromosomes toward poles. 

Separation occurs as a result of depolymerization of the spindle fibers attached to the chromosomes

Telophase 1

• Meiotic spindle breaks down, chromosomes decondense (expand), a new nuclear envelope develops, a cleavage furrow (animal cell) or cell plate (plant cell) forms, and cytokinesis occurs.

• 23 chromosomes per cell

• 46 chromatids per cell

Cytokinesis 1

• Division of the cytoplasm occurs, producing two individual daughter cells.

• Forms 2 haploid daughter cells, duplicated but haploid

Interkinesis of Meiosis 2

• A period of rest that cells of some species enter during meiosis between meiosis I and meiosis II. 

• Not a true interphase since DNA replication doesn’t occur. 

• Brief pause allows the cell to replenish necessary proteins and RNAs.

• Occurs in humans

Prophase 2

Nuclear membrane breaks down, Meiotic spindle forms; sister chromatids connected at the centromere attach to meiotic spindle.  

NO CROSSING OVER

Metaphase 2

Chromosomes align along the metaphase plate; the kinetochore of each chromatid is attached to a microtubule extending from the poles. 

Anaphase 2

Proteins at the centromeres break down, and sister chromatids are pulled apart and toward opposite poles in the cell. 

Telophase 2

• Meiotic spindle breaks down, a new nuclear envelope develops, a cleavage furrow (animal cell) or a cell plate (plant cell) forms, chromatids begin to decondense, and cytokinesis occurs.

• 23 chromosomes per cell

• 23 chromaids per cell

Cytokinesis 2

• Cytoplasm splits

• 4 genetically distinct haploid daughter cells result

Meiosis Only Events

1. Synapsis and crossing over

2. At metaphase I, paired homologous chromosomes (tetrads) are lined up at the metaphase plate. 

→ in mitosis, it was individual replicated chromosomes

3. At anaphase I, duplicates of each homologous pair separate but the sister chromatids of each duplicated chromosome stay attached. 

                 → in mitosis, chromatids separate

2

haploid daughter cells are formed (at the end of meiosis I)

Meiosis in Males

In , meiosis divides the cytoplasm evenly, producing four functional sperm from each diploid germ cell.

Meiosis in Females

• Produce haploid cells of unequal sizes because the cytoplasm divides unequally → so one cell receives almost all of the cytoplasm and becomes the oocyte (egg), while the other three cells receive very little and form nonfunctional polar bodies.

• Ensures that the egg has enough nutrients and organelles to support early development after fertilization

Meiosis 1 and Meiosis (egg)

The primary occyte is arrested in and doesn’t resume until puberty

Independent Assortment

The random orientation or pairing up in any combination, with any of the pairs facing either pole when homologous chromosomes line up in the middle during metaphase I, leading to genetic variation.

Crossing Over

The exchange of genetic material between homologous chromosomes during prophase 1 when nonsister chromatids of homologous chromosomes exchange segments of DNA, creating new combinations of alleles on a single chromosome. 

Non-Mendelian Genetics

Patterns of inheritance that do not follow Mendel's laws.

Nondisjunction

Failure of chromosomes to separate properly during cell division, leading to an abnormal number of chromosomes.

Meiosis 1 affects all

Meiosis 2 affect only half

ex. Down syndrome (Trisomy 21), Trisomy 18, and Turner syndrome (XO)

Crossing over during Prophase I, Independent assortment of chromosomes during Metaphase I, Random Fertilization

Sexual reproduction in eukaryotes increases genetic variation through

Chiasmata

The points of contact where homologous chromosomes exchange parts of DNA during crossing over.

Intracytoplasmic Sperm Injections (ICSI)

• An infertilty treatment

• Injecting live sperm into a person’s eggs in a laboratory. 

• Creates an embryo 

• Improves the success rate of of in vitro fertilization (IVF).

Genetic Variation: Possibilities

Independent assortment of each tetrad creates, 2²³ combinations for one person

Locus

Location of a gene on a chromosome

2²³

Know that possibilites arise from independent assortment in humans