Genetic Processes: DNA and meiosis

SBI3U Lesson #1 (Secours)

what does DNA stand for?

Deoxyribo Nucleic Acid

DNA is coded to create ______

proteins

3 components of DNA

1. Sugar (pentose)

2. Phosphate Group (phosphoric acid)

3. Nitrogenous base (four types)

Purine nitrogenous bases

Adenine and Guanine

Pyrimidine nitrogenous bases

Thymine and Cytosine

Purines vs Pyrimidines

Purines are double ring, while pyrimidines are single ring

Complementary Bases + their # of Hydrogen Bonds

A = T (two hydrogen bonds)

C ≡ G (3 hydrogen bonds)

Hershey & Chase

discovered that genetic info was carried in the DNA, not the proteins (radioactive dye)

Chargaff

Chargaff’s Ratios: unviersal rule stating that regardless of species, the ratio of A and T is equal, as is the ratio of C and G

Rosalind Franklin

used x-ray crystallography to take Photo 51 and determine the double helix structure

Watson & Crick

Used Franklin’s photo to determine that strands align in opposite direction, creating a double helix

Identify the Complementary Bases

Mitosis takes place in ______ cells

Somatic

Meiosis takes place in ______ cells to create ______ cells

Somatic, sex/germ

Human somatic cells contain

46 chromosomes

Gametes (sex cells) contain

23 chromosomes

Diploids

• Somatic cell

• Formed by mitosis

• 2 sets of chromosomes (2n)

Haploids

• germ/sex cells

• formed by meiosis

• single set of chromosomes (n)

Each sperm or egg cell contains

22 autosomes and 1 sex chromosome (X or Y)

Autosomes

chromosomes unrelated to determining offspring’s sex

Genome

complete set of DNA in an organism

Gene

basic unit of heredity, a segment of DNA

Sex of offspring is determined by

the sex chromosome provided by the father

Karyotype

visual representation of homologous pairs

Purpose of meiosis

1. Reduce the number of chromosomes (fertilization will regenerate a regular number)

2. Genetic variation (ensures variation among population and increases survival chances for the species)

Homologous Pairs

chromosomes that are similar in shape, length, and arrangement of genes

Synapsis

physical pairing of the homologuous pairs, occurs during prophase I

Prophase I

• CROSSING OVER: maternal and paternal chromosomes exchange genetic material

• plus usual steps (spindle fibers form, nuclear membrane dissolves…)

Metaphase I

• chromosomes line up as TETRADS in the center

• the tetrads are oriented randomly, RANDOM ASSORTMENT

Anaphase I

• chromosomes pulled to opposite ends of the cell by spindle fibers (homologous pairs are separated)

Telophase I + Cytokinesis

• nuclear membranes reform

• cleavage furrow, cytoplasm splits, two new cells are formed

Meiosis II

• essentially mitosis

⤷ in metaphase II, chromosomes line up single file, and the chromatids are pulled apart

fill in the table:

What causes genetic variation?

1. Crossing Over: prophase I

2. Random Assortment: metaphase I

3. Fertilization: random encounter btn sperm and egg

Non-disjunction

• poor separation of chromosomes

• takes place during meiosis

• causes addition of deletrion of one or more chromosomes from a gamete

Trisomy

• occurs when a gamete with an extra chromosome is fertilized

• all cells that develop from the zygote will have an extra chromosome

Trisomy-21

Down Syndrome (extra chromosome 21)

Monosomy

Occurs when there is a chromosome missing (lethal)

Turner's syndrome

monosomy XO

Klinefelter's syndrome

trisomy XXY

Super female syndrome

trisomy XXX

Triploid

• occurs when chromosomes don’t separate during meiosis 1

• the resulting gamete is diploid

• if fertilized with a normal haploid, the zygote will contain 3 SETS of chromosomes (3n)

Polyploid

organisms that have more than two sets of chromosomes

Zygote

The fertilized egg; this cell has a comination of DNA from the parents

Fertilization

formation of a zygote

Spermatogenesis

• production of sperm cells (same size) in the testes

• starts at puberty and continues for life

Oogenesis

• production of the large egg cell (ovum) and polar bodies in the ovaries

• begins before birth and is properly completed at puberty (when ovulation starts)

Gametogenesis

Production of gametes