3. Meiosis and nondisjunction: terms

Somatic cell

all cells of an organism excluding reproductive (germ) cells

• every somatic cell in your body with a nucleus has 46 chromosomes (23 from sperm and 23 from ovum

• each parent (sperm and ovum) has 22 autosomes and 1 allosome

Autosomes and Allosomes

• Autosomes are the non sex determining chromosomes (1-22)

• Allosomes are the sex determining chromosomes (X,Y)

Diploid and Haploid

• Diploids have 2 complete sets of chromosomes (46)

• Haploids have 1 complete set (23)

Gamete

Reproductive cell (sperm and ovum)

23 chromosomes (haploid)

Homologous chromosomes

Chromosome pairs that are the same size and have the same genes

Genome

All genetic information of an organism or cell

Alleles

alleles are different versions of the same gene

any given gene has 2 alleles one from each parent

What is Meiosis and whats the most important phase

Meiosis is the name of the steps when a germ cell in reproductive organs form gametes

the most important step is prophase 1 because it is the step in which “crossing over” occurs

What is “crossing over”

Crossing over is the action where two homologous chromosomes (one from each parent) pair up side by side in a process that’s called synapsis

the point where they touch is called the chiasma and that’s where the chromatids in each chromosome exchange information

why is crossing over so important

• It ensure genetic variation creating new combinations of alleles and increasing diversity in offspring

• helps homologous chromosomes stay pared until anaphase 1

Tetrad

When the chromosomes cross over during synapsis they become a tetrad

difference between sexual and asexual

Asexual = identical copies, one parent. Sexual = unique offspring, two parents.

difference between mitosis and meiosis

• Mitosis is Asexual reproduction in which one diploid cell divides into another identical diploid cell

• Meiosis is sexual process in which one diploid germ cell divides into 4 unique haploid gametes