Scientific Basis of Genetics

Janice S. Dorman, PhDUniversity of Pittsburgh

School of Nursing

Lessons

Cell cycle Chromosomes DNA and RNA Structure of a

gene

Transcription Translation Mutations

Lesson One

Cell Cycle

Mitosis Somatic cells divide by mitosis

– Involves 1 cell cycle / division

Parental and 2 daughter cells are genetically identical

Parental cells are diploid (46 chromosomes)

2 daughter cells are diploid (46 chromosomes)

Meiosis Germ cell precursors (parental cells) divide

by meiosis– Involves 2 cell cycles / divisions instead of 1

Germ cells precursors and 4 gametes (daughter cells – either egg or sperm) are NOT genetically identical

Germ cell precursors are diploid (46 chromosomes)

4 gametes are haploid (23 chromosomes)

The stages of meiosis in an animal cell

The stages of meiosis in an animal cell

Recombination occurs here

The stages of meiosis in an animal cell

Lesson Two

Chromosomes

Chromosome Structure

Chromosomes have 2 arms that are separated by the centromere:

– p arm – for petite– q arm – long arm

Ends of chromosomes are called telomeres

Chromosome Types Autosomes: the numbered chromosomes

– All individuals have 2 copies of each type of autosome (homologous chromosomes – 1 maternal, 1 paternal)

Sex chromosomes: the X and Y chromosomes

– All individuals have 2 sex chromosomes•XX = female•XY = male

Karyotype An organized picture of the chromosomes

found in a cell– Captured during mitosis, just before cell divides

Generally demonstrates the normal complement of chromosomes – 46,XX for females and 46,XY for males

Can point out gross chromosomal abnormalities (such as extra or missing chromosomes)

Lesson Three

DNA (Deoxyribonucleic Acid) and

RNA (Ribonucleic Acid)

Components of DNA / RNA

Phosphate group

Sugar group – Deoxyribose in DNA– Ribose in RNA

Bases – Adenine, guanine, cytosine, thymine in

DNA– Adenine, guanine, cytosine, uracil in RNA

RNA Structure RNA is generally single stranded

– Can fold and create complicated structure

– Multiple types of RNA, each with a different function

Sugar-phosphate groups form the backbone of the molecule– Nucleotides are organized 5’ to 3’

Bases form the center of the molecule

3’ end

5’ end

Double stranded RNA: Possible secondary structures of RNA molecules. The double-stranded regions are depicted by connecting hydrogen bonds. Loops are noncomplementary regions that are not hydrogen bonded with complementary bases. Double-stranded RNA structures can form within a single RNA molecule or between two separate RNA molecules

DNA Structure DNA is a double helix

Sugar-phosphate groups form the backbone

Two DNA strands are anti-parallel– One strand, nucleotides are organized 5’ to 3’– Other strand, nucleotides are organized 3’ to 5’

Bases are held together by hydrogen bonds and are complementary– A is complementary to T – C is complementary to G

3’ end 5’ end

DNA ReplicationUncoil DNA

 Strand Separation 

 Templates are Single Stranded 

 RNA Primers Needed For New Strands 

 Both DNA Strands Extended From the

RNA Primer (5’ to 3’) 

One Strand is the Leading StrandOther Strand is the Lagging Strand