GENETICS 1

What does a gene determine?

• chemical structure of structural proteins of a cell which determines cell structure, which determines cell function

• chemical structure of enzymes (functional) which determines cell function

What allows a gene to determine structure or function?

• genetic code

• transcription and translation

• triplets of nucleotides code for certain amino acids

• nucleotide order determines structure + function of protein

What is a gene?

• dna sequence in a specific location in the genome that results in a protein production related to a particular character in an organism

• genes are linearly arranged on chromosomes

• genes are passed from generation to generation; biological unit of hereditary

What is a genome?

• total genetic information carried in a cell or organism

What is chromatin?

• complex containing dna and proteins

• chromatin appears as a diffuse, granular mass in non dividing cells

• chromatin is duplicated, forming a pair of chromatids when cells are ready to divide

• chromatin can condense into chromosomes

How many chromosomes exist in a human?

• somatic (body) cells have 46 chromosomes; 23 pairs, half from mom half from dad

• 22 pairs are autosomes

• 1 pair is sex chromosomes (females XX, males XY)

What is an autosome?

• homologous chromosomes that look alike

• hold the same sequence of genes but not the same version / allele of each gene

What is the cellular division process of mitosis?

• somatic cell division that produces daughter cells with the same chromosome complement as the parent cell

• used for tissue growth or to replace dead / injured cells

What is the cellular division process of meiosis?

• reproductive cell division

• produces genetically unique daughter cells used to form the next generation

What is the cell cycle?

• each somatic cell goes through a cell cycle with two main phases:

  • interphase where cell growth and DNA replication occurs

  • mitosis

  • can include cytokinesis (cytoplasm division)

What phases are included in the cell cycle?

• G0 = resting

• G1 is where the cell duplicates organelles and cytosol centrosome replication begins; 8-10 hours

• S is DNA replication; 8 hours

• G2 is cell growth where enzymes / proteins are synthesized + centrosomes are replicated; 4-6 hours

• M phase which includes prophase, metaphase, anaphase, and telophase (PMAT)

What is DNA replication?

• during S phase

• highly regulated process that doubles DNA in a cell

• DNA is replicated so that each new daughter cell gets a complete + identical set of DNA after cell division

• duplicated chromatids are held tgt by a centromere

What are the key stages and differences in mitosis and meiosis?

• each process has four stages: prophase, metaphase, anaphase, and telophase (cytokinesis)

• both occur after chromosome duplication

• mitosis has 1 round, meiosis has 2 rounds

What occurs in meiosis 1?

1. in prophase, chromosomes condense + nuclear envelop breaks down; crossing over occurs

2. in metaphase, pairs of homologous chromosomes move to cell equator

3. in anaphase, homologous chromosomes move to opposite poles of cell

4. in telephase / cytokinesis, chromosomes gather at each pole + cytoplasm divides

What occurs in meiosis 2?

1. in prophase, a new spindle forms around chromosomes

2. in metaphase, the metaphase 2 chromosomes line up at the equator

3. in anaphase, the centromeres divide + chromatids move to opposite poles of cell

4. in telephase / cytokinesis, a nuclear envelope forms around each set of chromosomes + cytoplasm divides

What happens in the first way of genetic variation in the gametes?

• occurs during prophase 1

• homologous chromosomes will pair off

• when that happens, crossing over occurs where there is gene exchange

What happens in the second way of genetic variation in the gametes?

• occurs during metaphase 1

• independent assortment occurs which is where homologous chromosomes can line up on either side of the metaphase plate, independent of each other

• genetic vvariation is also introduced during fertilization