SBI3U Bio - Unit 2: Genetics

DNA (dioxyribonucleic acid)

a huge molecule in a double helix shape with 2 nucleic acid strands twisted around each other (antiparallel) and nitrogen bases that makes organisms unique

1953

James Watson and Francis Crick developed the double helix model

Rosalind Franklin

concluded there were 2 antiparallel sugar phosphate backbones

Nucleotide

a basic unit of nucleic acid made up of a phosphate group, sugar, and a nitrogen base

Nitrogen base pairing

adenine to thymine, cytosine to guanine

Basic replication stages

1. DNA unzips to form a “fork” 2. Complementary base pairing occurs 3. DNA winds back into a double helix resulting in 2 new double helixes made of one new strand and one old

Chromosomes

coiled DNA inside the nucleus of the cell that contains genetic information for a set of traits in genes

Gene

a segment of DNA that controls the expression of a trait with instructions to make 1 protein

Allele

variation of genes e.g. hair colour alleles like black, brown, blond, etc.

Homologous chromosomes

pairs of chromosomes with the same centromere location, banding pattern (alleles found on the same gene), and length

Protein functions

transport materials between membranes, form structures and enzymes, and many hormones are proteins

Diploid cells

contain two complete sets of chromosomes (one from each parent) represented as 2n

Haploid cells

contains only one set of chromosomes (half the typical amount) represented as n

n

the number of haploid chromosomes

Somatic cells

46 chromosomes (diploid) in a human body

Gametes

a haploid reproductive cell in an organism eg) sperm in testes or eggs in ovaries

3 reasons for asexual reproduction

growth, repair, replacement

Interphase

double cytoplasmic components, make structural proteins to repair & prepare for mitosis, transport nutrients, and eliminate waste

Chromatin

genetic material in long thin strands (will thicken to form chromosomes)

G1

growth & metabolic roles

S

DNA synthesis / replication

G2

growth & prepare for mitosis

Prophase

chromosomes thicken by condensing and form, 1 chromosome = 2 sister chromatids attached together by the centromere , nuclear membrane dissolves, centrioles move to poles

Metaphase

chromosomes line up on the equatorial plate in the middle of the cell, spindle fibers attach at the centromere

Anaphase

spindle fibers pull apart sister chromatids and centromere splits

Telophase

chromosomes unravel/ lengthen, spindle fiber dissolves, nuclear membrane BEGINS to form again

Cytokinesis

cytoplasm divides, animal cells cell membrane pinches between the 2 cells (cleavage furrow), plant cell forms a cell plate that turns into the cell wall

Prophase 1

nuclear membrane dissolves, centrioles move to opposite poles, homologous chromosomes pair and form tetrads with each other (4 chromatids in a tetrad), crossing over occurs

Metaphase 1

tetrads line up in a double line on the equatorial plate, spindle fibers attach to centromeres

Cytokinesis

cytoplasm divides, animal cells cell membrane pinches between the 2 cells (cleavage furrow), plant cell forms a cell plate that turns into the cell wall

Anaphase 1

spindle fibers pull homologous chromosomes apart

Fertilization

the sperm and egg cells connect to form a diploid zygote

Cancer

uncontrolled mitosis (normal cells stop dividing because of contact inhibition but not cancer cells)

Cancer drugs

usually damage RNA/DNA with instructions preventing division (cell

Chemotherapy may affect

blood cells, cells in mouth, stomach, bowel, and hair follicles

Karyotype

a snapshot of an individual’s set of chromosomes (organized largest to smallest usually). Notation eg) 47, XX, +21

Human karyotypes

22 pairs of autosomes and 1 sex chromosome pair (female XX, male XY)

Klinefelter’s Syndrome

extra X chromosome in males (non disjunction in formation of gametes)

Klinefelter’s Syndrome Attributes

breast tissue, less body hair, tall, small testicles, sterile, more likely to get breast cancer, diabetes, lung disease, and depression

Down syndrome/trisomy 21

extra chromosome 21 (non disjunction during formation of the egg)

Down syndrome/trisomy 21 Attributes

short, broad hands with single fold, large protruding tongue, intellectually challenged, higher chance of leukemia, respiratory infections, heart defects, and shortened lifespan

Patau’s Syndrome

extra chromosome 13 (non disjunction during formation of gametes)

Patau’s Syndrome Attributes

abnormal cerebral function, death at infancy, cleft on lips & palate, broad nose, small cranium, non functional eyes, heart defects, and severe intellectual impairment

Spermatogenesis

male testes germ cells undergo meiosis to form sperm cells. Diploid primary spermatogonium forms 2 secondary haploid secondary spermatocytes, which divide to become 4 haploid sperm cells

Oogenesis

diploid oogonium cells in the ovaries undergo meiosis to form ovum. Three polar bodies and one viable egg will be produced.

Four methods to increase genetic variation

independent assortment, crossing over, non disjunction chromosomal mutations, structural chromosomal mutations

Independent assortment

Chromosomes separate independently when gametes are formed during meiosis

Crossing over

homologous chromosomes overlap and exchange parts of their chromatids

Non disjunctional mutations

a pair of homologous chromosomes fails to separate properly during anaphase 1 or sister chromatids fail to separate properly in anaphase 2 resulting in either: monosomy (missing one), trisomy (one extra), or polyploidy ( extra set, usually in plants)

Structural chromosomal mutations

something wrong during crossing over. Either deletion (removal of a chromosomal segment), duplication (repeats a chromosomal segment), inversion(reverse of a chromosomal segment), or translocation (movement of a chromosomal segment to a non