Meiosis
Males – only occurs in the testicles.
Females – only occurs in the ovaries.
Formation of four cells that are NOT genetically identical
with only half the chromosome number as the parent cell.
Vocabulary
Haploid – half the regular number of chromosomes
Diploid – Regular number of chromosomes
Tetrads – Homologous pairs side by side
Homologous pairs – Same size chromosomes that contain
genes for the same trait. Humans have 23 homologous pairs.
Crossing over – Occurs between homologous chromosomes.
Pieces of the homologous chromosomes sometimes cross
over and exchange segments.
Law of Segregation (1st law) – Pairs of alleles separate in
meiosis and each gamete receives one allele of a pair.
Law of Independent Assortment (2nd law)– Homologous
chromosomes line up independently from other homologous
chromosomes during metaphase 1.
Meiosis 1
Prophase 1 – Duplicated chromatin condenses. Each
chromosome consists of sister chromatids. Crossing over can
occur in the latter part of this stage.
Metaphase 1 – Homologous chromosomes align in the
middle of the cell
Anaphase 1 – Homologous pairs separate with sister
chromatids remaining together.
Telophase 1 – Two daughter cells are formed with each
daughter cell containing only one chromosome of the
homologous pair.
Meiosis 2
Prophase 2 – DNA does not replicate.
Metaphase 2 – Chromosomes align in the middle of the cell
Anaphase 2 – Sister chromatids are pulled apart at the
centromere by the centrioles.
Telophase 2 – Cell division is complete. Four haploid
daughter cells are obtained.
Meiosis
https://www.youtube.com/watch?v=CMXjBgLjjxo
Comparison of Meiosis and Mitosis
https://www.youtube.com/watch?v=i9WDSfaPW00
Connect the words
Phenotype
Recessive
Gene
Dominant
Heterozygous
Allele
Homozygous
Genotype
Fundamentals of Genetics
Gene – Segment of DNA that codes for a particular trait.
Ex: eye color
Allele – One of the number of different forms of the same
gene for a specific trait. Ex: blue eyes and brown eyes. In
general, for every one gene there are two alleles.
Dominant – Referring to an allele that masks the presence of
the recessive allele for the same gene. Usually noted with a
capital letter. Ex: B.
Recessive – Referring to an allele that is masked by the
presence of the dominant allele. Usually noted with a lower
case letter. Ex. b.
Homozygous – Referring to an allele pair in which the two
alleles code for the same thing. Ex: BB or bb.
Heterozygous – Referring to an allele pair in which the two
alleles do not code for the same thing. Ex: Bb.
Genotype – The genetic makeup of an organism. Ex: BB, Bb
or bb.
Phenotype – The physical appearance of an organism that is
determined by the individual’s genotype. Ex: blue eyes,
brown hair, dimples, etc.
Punnett square – a model used to establish the probabilities
of the results (offspring) of a genetic cross.
Genotypic ratio – The probable ratio of genotypes for the
offspring.
Phenotype ratio – The probable ratio of phenotypes for the
offspring.