Unit 5 Heredity

• Zygote


  A fertilized egg, it is the cell we started as
• Meiosis


  The formation of gametes

  
• 3 Ways to Increase genetic diversity

  1. Prophase 1 during meiosis through Synapsis (crossing over)

  2. During independent assortment in Metaphase 1: The ways genes sort do not depend on another gene

  3. Fertilization: Genes are randomly combined creating unique combinations

  
• Meiosis Steps


  1. Two rounds of division in meiosis

  2. The only cells that divide by meiosis are sex cells

  3. Cells go through the cell cycle (G1, S, G2) for both Meiosis and Mitosis

  
• Meiosis 1


  1. Interphase: G1, S, G2

  2. Prophase 1: Supercoils DNA, Nuclear membrane disintegrates, Spindle fibers form, Homologous chromosomes pair themselves, Crossing over occurs, Form recombinant DNA

  3. Metaphase 1: Homologous chromosomes line up in the middle, Independent assortment may occur

  4. Anaphase 1: Chromosomes are separated

  5. Telophase 1: Pinches in the middle of cell, Chromosomes decondense into chromatin, Spindle fibers disappear

  6. Cytokinesis 1: Cell divides and splits into two

  
• Meiosis 2


  1. Prophase 2: No pairing of chromosomes

  2. Metaphase 2: Single chromosomes line up in the middle, Spindle fibers attach to centromeres

  3. Anaphase 2: Sister chromatids are pulled apart

  4. Telophase 2: Sister chromatids supercoil back into chromatin, Nuclear envelope redevelops

  5. Cytokinesis 2: Cells finishes dividing

  
• Results in 4 genetically not identical daughter cells
• DNA


  Found in the nucleus and carries genetic information
• Chromatin


  Undivided/organized DNA, is super coiled into chromosomes during prophase
• Chromosomes


  Supercoiled DNA, made up of two chromatids (sister chromatids)
• Somatic Cell


  They are diploid body cells, all cells except gametes
• Gametes


  Haploid sex cells including egg, sperm and pollen
• Diploid cell


  Has full sets of chromosomes (2n)
• Haploid


  Half number of chromosomes (n)
• Spermatogenesis


  Process of sperm formation
• Oogenesis


  Process of egg formation
• Locus


  Positions of a gene on chromosomes
• Synapsis


  Nonsister chromatids cross over (Chiasmata) and exchange genes
• Chiasmata


  Point of contact between two chromatids of two homologous chromosomes
• Recombinant DNA


  DNA that has been exchanged, contains genes from more than one source
• Female - XX, Male - XY
• Y chromosome


  Only has a few genes, not biologically important except for determining the sex of the organisms
• Everyone starts as a woman with XX genes until the SRY gene is expressed for men
• The sex of a gamete is independent regardless of the genes of previous children, all probabilities of the sex of a child is 1/2
• Polar bodies


  Inactive cell that only has enough cytoplasm for one cell to divide, it is a way to dispose chromosomes

  
• Crossing over


  When nonsister homologous chromosomes exchange genes
• Homologous chromosomes


  Same size, same alleles of the same gene on the same locus, centromeres on the same positions
• SRY gene


  A gene that determines the sex of the offspring

  
• Law of Segregation


  Alleles can segregate independently, You can only inherit one copy of a gene, Punnett squares show F1 generations, Alleles are randomly assorted in Meiosis

  
• Law of independent assortment


  Two or more genes assort independently, one trait is not automatically inherited because of the other, Can be packaged in any possible combination, Not linked, can be without other gene
• Punnett Squares


  Monohybrid: inheriting 1 gene, Dihybrid: inheriting 2 genes
• When choosing allele letters, make sure they look different in capital and lowercase letters (don't choose Cc, Ss, Uu, Zz)
• Alleles are genetically unique as there are different variants
• Anytime you do a dihybrid cross with two heterozygous parents, the ratio will always be 9:3:3:1
• Crossing over occurs, so predicted alleles differ
• When genes are linked, there is a 3:1 phenotypic ratio instead, expect 2 phenotypes
• There also can be limited crossing over with autosomal linking which can result in 4 phenotypes
• Types of Inheritance


  • Autosomal recessive
  • Autosomal dominant
  • Sex linked dominant
  • Sex linked recessive
• Chi Square Analysis Steps

  1. Establish Research Question

  2. Null Hypothesis (Ho): Always consistent with the mode of inheritance

  3. Alternative hypothesis (HA): Opposite of Null hypothesis

  4. Determining expected values: Find the F1 Generation, Find the F2, Add all the observed, Look at the di/monohybrid cross of F2 generations to find ratios of each phenotype, Multiply the total of observed and each phenotypic ratio

  5. Chi Square Formula: Observed - Expected^2 divided by expected

  6. Calculate the degrees of freedom

  7. Find Critical value

  
• If Chi square value is higher than critical value, reject the null hypothesis