Genetics ch. 4: the chromosome theory of inheritance

what makes diploid cells?

Mitosis

what makes haploid cells?

meiosis

Sister chromatids

identical copies of a replicated chromosome

Homologs

contain same set of genes but can have different alleles for some genes

nonhomologs

carry completely unrelated genes

karyotype

micrograph of stained chromosomes arranged in homologous pairs

autosome

all chromosomes except x and y

sex chromosomes

unpaired x and y or paired x and x

SRY

sex-determining region of the y chromosome of males. it is always present of xx males and nonfunctional in xy females

The cell cycle

• G1 (growth 1)

• The S phase (genetic duplication)

• G2 (growth 2)

• G0 (if the cell needs rest or is holding off replication)

• M phase (Mitosis)

Mitosis

• Prophase (chromosome becomes visible)

• Prometaphase (spindle forms and sister chromatids attach to microtubules from opposite centrosomes)

• Metaphase (chromosomes align at equator)

• Anaphase (sister chromatids separate and move to opposite poles)

• Telophase (chromosomes recondense and are enclosed in two nuclei)

somatic cells

non-reproductive cells

Meiosis

• Two rounds of cell division

• Chromosomes duplicate once, nuclei divides twice

• Meiosis II reduces chromatids from 2n to n

Meiosis prophase 1

• Leptotene (chromosomes thicken and become visible and centrosomes move towards opposite poles)

• Zygotene (synaptonemal complex forms)

• Pachytene (when synapsis is complete and crossing over occurs)