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.

VocabularyHaploid – 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.