Meiosis and Mendelian Inheritance

Heredity - transmission of trait from one generation to the next

Locus - specific location of a gene on a chromosome

  • max of only 2 alleles

Alleles - variation of DNA sequence at a locus

  • only inherit 2 and pass on 1

Sexual reporduction increases gentic variation

  • only way for variation to happen in asexual reporduction is throuhg environemtn

Meiosis -

  • a diploid cell is created by fusion of egg and sperm (a zygote)

  • meiosis splits that diploid cell to a single haploid set of chromosomes

  • each gamete provides half of its genetic material to offspring

  • males determine sex of offspring

  • from a single cell in meiosis, you get 4 in the end

Comparing mitosis and meiosis:

second half of meiosis is just mitosis in the second half (kind of)

mitosis splits into 2 identical cells

Meiosis I:

1st step of meiosis: Prophase I:

  • diploid set happens after inter[hase because they gt duplicated

  • chromosomes become visible

  • centrosomes migrate to the poles

  • homologous chromosomes that came from each parent are going to line up side by side (does not happen in mitosis)

  • tetrads - term for the 4 chromatids at this point

  • bivalent - structure formed during prophase I of meiosis, when two homologous chromosomes pair up and align closely

  • the chromosomes inherited from mom and dad then cross over and exchange dna

  • recombination/crossing over - process in which genetic material is exchanged between different chromosomes or different regions of the same chromosome

    • contributes to genetic variation

    • results in a recombinant chromosome

  • chiasma/chiasmata (plural) - positions where the two chromosomes exchanged DNA

  • synaptonemal complex - protein-based structure that forms between homologous chromosomes; ensures precise alignment of homologous chromosomes

    Prometaphase:

  • spindles form and microtubules bind to kinetochores

  • Metaphase I:

  • chromosomes line up in the middle, but each spindle can randomly be pulled to either size

    Anaphase:

  • separates homologs from each other into separate daughter cells

    Telophase I:

  • nuclear envelope forms

  • results in haploid daughter cells with only one chromosome each

    Cytokinesis - cytoplasm splits to distribute and equal amount of organelles and resources to each new daughter cell so it can survive

Meiosis II:

No dna synthesis occurs in Meiosis II

follows the same process, but splits using the recombinant types of chromosomes from Emiosis I

Mechanisms of genetic variation: crossing over, independent assortment, and random fertilization (idea that any sperm can fuse with any egg)

Modern Genetics:

True-breeding - when plants or something cn ferrtlize themselves and will create only offspring that are the same thing they are

hybridization - offpsring of gentically different parents

Pedigree analyisis - diagram that studies inheritance of certain traits

monohybrid corss- studying inheritance of a single trait

In f1, dominant trait was present in all of them, but in F2 it was 3:1 dominant and recessive

  • therefore, there are 2 alleles for each trait (in this case)

Law of Segregation - alleles for a particular gene are separated during the formation of gametes in sexual reproduction; you inhereit 2 alleles for a trait from each parent, but you end up with one of each