BISC 120: Genetic Variation and Inheritance

Gene

section of DNA that codes for specific traits

heredity

transmission of genes across generations

Genetics

study of heredity

Genes are passed down to the next generation via …

gametes

How many total chromosomes do humans have?

46; 23 pairs

Locus

specific location of a gene on a chromosome

How many copies of a gene do we have?

2

Autosomes

non-sex chromosomes

sex chromsomes

X and Y

Fertilization

union of sperm and egg to make a zygote (2n=46)

Somatic cells

any cell other than a reproductive cell

What are the stages of Mitosis

1) Interphase 2) Meiosis 1 (PMAT) 2 Meiosis 2

Meiosis

cell division that produces four haploid daughter cells (gametes)

Meiosis 1 separates ….

homologous chromosomes

Meiosis II separates …

sister chromatids

Prophase 1

1) centrosome movement to poles 2) formation of microtubules/spindle fibers 3) nuclear envelope breaks down 4) chromosomes condense 5) crossing over 6) synapsis

Centromere

connects sister chromatids

Centrosome

microtubule organizing center (contains a pair of centrioles)

Centriole

barrel shaped organelle that organize microtubules

Synaptomenal complex

protein that holds the homologous chromosomes together along their lengths

Chiasmata

site at which homologous chromosomes/tetrads cross over

Crossing over

pairing of homologous chromosomes and exchange of genetic material;leads to non-identical chromatids/gametes

Synapsis

fusion of homologous chromosome pairs into tetrads

Metaphase 1

Spindle fibers attach to kinetochores of the pairs and line them up at the metaphase plate

Anaphase 1

motor proteins in kinetochores “eat” away at the microtubules, pulling the homologous pairs apart to either pole

Telophase 1 and Cytokinesis

1) each half of cell has a haploid set of duplicated chromosomes (2 sister chromatids) 2) nuclear envelope reforms 3) necessary cell structures are built 4) spindle fibers disassemble 4) cytoplasm divides

Prophase II

1) centrosomes move to poles and spindle fibers form 2) nuclear envelope breaks down 3) chromosomes condense 4) NO CROSSING OVER

Metaphase II

chromosomes line up at metaphase plate

Anaphase II

sister chromatids are pulled to opposite poles (each chromatid is now called a chromosome)

Telophase II and Cytokinesis

1) spindle fibers disassemble 2) nuclear envelope reforms 3) chromosomes decondense 4) cytoplasm divides RESULT: 4 genetically unique daughter cells (gametes)

Alleles

different versions of genes

What three things lead to genetic diversity?

1) Independent assortment 2) Random fertilization 3) Crossing over

Independent Assortment

alleles for different genes segregate independently of each other during gamete formation;random pairing and arrangement at metaphase plate

What is the equation of find the number of possible combinations of independent assortment?

2^n (n=haploid number)

Recombinant chromosomes

chromosomes with DNA from both parents