GENETICS OVERVIEW

REMINDER YOUR UNIT 6 TEST IS TOMORROW!! YOU NEED TO KNOW AND UNDERSTAND THE FOLLOWING!!

DNA Structure and DNA Replication

  • DNA = Deoxyribonucleic acid = the genetic code = nucleic acid
  • DNA made of a sugar (deoxyribose), a phosphate group and a base (Adenine, Thymine, Guanine or Cytosine)
  • DNA is made up of nucleotides
  • A nucleotide is a sugar, a phosphate and a base
  • The base pairs are “complimentary”, meaning Adenine always bonds with Thymine and Cytosine always bonds with Guanine.
  • The complimentary strand to TGA-GCC is ACT-CGG
  • DNA is double stranded and in the shape of a double helix
  • The bases (A,T, C and G) are held together by weak hydrogen bonds
  • The order of the bases (A,T,C and G) helps determine different characteristics/traits (eye color, fur thickness, height, etc) by coding for specific proteins (refer to protein synthesis) = GENETIC CODE!
  • In eukaryotes, DNA is found in the nucleus. Is prokaryotes, DNA is found “floating” in the cytoplasm
  • Before a cell can divide, the DNA must replicate.
  • Because DNA is ALWAYS in the nucleus, DNA replication takes place in the nucleus
  • Once there are two identical stands of DNA, the cell can divide into two new cells (each getting a strand of DNA)

Meiosis

  • Makes gametes (sex cells- sperm and egg)
  • Makes FOUR cells/gametes
  • These four gametes/cells are not identical to one another or the parents (this is why you and your siblings aren’t identical to one another or your mom/dad)
  • These four gametes/cells are not identical to the parents
  • Gametes have 23 chromosomes 23 for the sperm, 23 for the egg
  • Meiosis has two divisions of the nucleus: P1,M1,A1,T1, and then repeats P2,M2,A2,T2.. cytokinesis (refer to mitosis)
  • The gametes produced are HAPLOID
  • Sexual reproduction produces MORE genetic variation than asexual reproduction
  • Crossing over provides new combinations of genes that are different than the parents. Happens in prophase 1
  • Independent assortment is when homologous chromosomes are distributed randomly during meiosis

PROTEIN SYNTHESIS:

  • Protein Synthesis in a nutshell:
  • mRNA is made from the DNA found in the nucleus
  • making mRNA from DNA is called TRANSCIPTION and takes place in the nucleus
  • G bonds with C, and A bonds with U
  • If DNA read ACT-GCA the mRNA made would be UGA-CGU
  • Once the mRNA is made, it leaves the nucleus and travels through the cytoplasm
  • mRNA attaches to the ribosome (which is floating in the cytoplasm)
  • At the ribosome, mRNA provides the codon that “tells” tRNA what amino acid it needs to bring to the ribosome.
  • tRNA is floating in the cytoplasm attached to a specific amino acid
  • if mRNA read AUG-CGA the tRNA that would attach to it would be UAC-GCU
  • The amino acid that tRNA brings would be:
  • The process of tRNA bringing mRNA amino acids at the ribosome is called TRANSLATION
  • Translation takes place at the ribosome/cytoplasm
  • To determine what amino acid tRNA needs to bring you can use a codon table chart YOU USE THE mRNA TO READ THE CHART:
  • mRNA read AUG- CGA so the amino acids that tRNA needs to bring to the cytoplasm are Methionine/initiation codon and Arginine.
  • A chain of amino acids = 1 protein
  • If you changed the DNA template/code because of a mutation, it would most likely change the protein being made.

Chromosomes/Karyotypes

  • ChromaTIN is THIN threadlike DNA
  • When chromatin is coiled up it is called a ChromaTID
  • Two sister chromatids make up a chromosome
  • Sister chromatids are held together by a centromere
  • Chromosomes look like this -
  • They contain the DNA that make up genes that make us who we are
  • A GENE is a segment of a chromosome (or an allele = different form of a gene) genes can be affected by THE ENVIRONMENT!
  • Humans have 23 pairs of chromosomes for a TOTAL of 46.
  • So, humans have 46 total chromosomes
  • A karyotype is a picture of chromosomes arranged from largest to smallest

Genetics

  • Phenotype is what you see- purple, wrinkles, freckles, etc
  • Genotype are the letters, and code for phenotype BB, Bb, bb
  • Homozygous/Purebred- same sized letters- BB, bb, TT, tt, PP,pp
  • Heterozygous/Hybrid- different sized letters- Rr, Tt, Bb
  • Gregor Mendel is the father of genetics- he studied pea plants
  • Dominant Alleles are always seen and can mask recessive alleles!
  • Monohybrid cross:

A heterozygous blue flower is crossed with a homozygous white flower.

  • Dihybrid cross:

A heterozygous tall, green pea plant is crossed with a homozygous short, heterozygous green pea plant.

Parents:

Gametes:

Dihybrid Probability:

  1. In a rabbit, Brown fur (B) is dominant to white (b) and Long fur (L) is dominant to short fur (l). What percent of the offspring is expected to be heterozygous for both traits when crossing the following parents:

BbLlxbbll

  1. In a rabbit, Brown fur (B) is dominant to white (b) and Long fur (L) is dominant to short fur (l). What percent of the offspring is expected to be BBLl when crossing the following parents:

BbllxBBLl

  1. What is the expected phenotype when crossing: BBLlXbbll
  1. If given the following egg cell, what would its gametes look like?