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Heredity and Meiosis
 Gregor Mendel- Austrian monk that studied heredity. He
discovered that certain traits could be passed from
generation to generation.
 He studied pea plants to study traits
 Heredity- the passing of characteristics from parents to
offspring
 Trait- the characteristic that is inherited, can be seen or
unseen
 Genetics- the study of herdity
 Sex cells are called gametes
 Both male and female make them
 When the male and female gametes unite it is
called fertilization and a zygote is formed
 The zygote then undergoes mitosis and develops
into the organism
 Why mitosis?
Monohybrid cross
 Hybrid- a cross between parents that have
different forms of a trait
 Tall and short stems
 Red and white flowers
 Monohybrid cross- a cross of only 1 trait
 Tall and short
 Each gene has 2 alleles
 1 from mom and 1 from dad
 Dominant allele- the trait that expresses
itself
 Recessive allele- the trait that is not
expressed
 As long as 1 dominant allele is present that trait
will show
 Law of segregation- each organism has 2
alleles per gene and when gametes are
made, each gamete gets 1 of the alleles
 Phenotype- the way an organism looks or
behaves
 Genotype- the genetic make up of an
organism
 Homozygous- this organism contains the
same alleles for a trait
 Both tall alleles
 Heterozygous- this organism contains
different alleles for the same trait
 1 tall and 1 short
 So how does this affect phenotype and
genotype?
 2 organisms can look the same, but be very
different genetically
 Dihybrid cross- when you cross 2 alleles at
one time
 Height and color
 Color and shape
 Law of independent assortment- each trait
is inherited independently from each
other.
Punnett square
 Made by Reginald Punnett as a way to
quickly see the genotypes of a certain
cross.
 You can use the genotypes to see what
phenotypes may occur within a certain cross
 Practice punnett squares
Meiosis
 Meiosis- the division of chromosomes into
gametes with half the information as the
whole
 Cells contain thousands of pieces of genetic
material called genes on segments of DNA that
make up multiple chromosomes.
 The human body has 46 chromosomes
 23 from each parent
 Diploid cell- has 2 sets of chromosomes
 Haploid cell- has 1 set of chromosomes
 gamete
Meiosis
 Meiosis is used to divide the number of genes in half so
that only 1 allele is given to the offspring.
 Has 2 separate steps similar to mitosis
Meiosis 1
 Interphase- DNA replicates and sister chromatids
become attached by a centromere
 Prophase 1- chromosomes coil and create a tetradpairing of homologues chromosomes. Cross over
occurs between non-sister chromatids and genetic
information is split
 Metaphase 1- the tetrads line up and spindle fibers
attach
 Anaphase 1- the tetrads separate but do not split,
this makes sure that each new cell will receive only
1 chromosome per pair
 Telophase 1- 2 new cells are made, each contains
2 copies of a gene
Meiosis 2
 Prophase 2- spindle fibers form
 Metaphase 2-spindle fibers attach and they line up
across equator of cell
 Anaphase 2- sister chromatids split and move to
opposite ends
 Telophase 2- new membrane forms and 4 new
single chromosomal cells are made
Problems with meiosis
 Nondisjunction- when a homologous pair
do not split information
 Trisomy-extra chromosome could occur zygote has 47 instead of 46 causing Downs
syndrome
 Monosomy-missing chromosome
 usually causes death. In women a missing X
chromosome causes Turners syndrome
 Karyotype- a physical way of looking at
chromosomes in a specified order.
Trisomy
21st chromosome has 3 copies
Monosomy
22 chromosomes, missing X
 Polyploidy- most animals will die from
this, many plants thrive with it. Can
cause larger fruits and have huge
commercial benefits for farmers
DNA
 DNA controls the cells by determining a proteins
structure
 They are needed in muscle, bone, and enzymes
 DNA contains all information for making proteins
for a cell
 Even a virus, which is made of proteins, contains
DNA
Structure of DNA
 Nucleotide- a repeating unit that makes
up DNA
 Contains:

Deoxyribose sugar

phosphate group

Nitrogenous base( 4 possible)
 Nitrogenous bases
 Made of a nitrogen ring with other atoms
arranged in different orders
 Purine- a double nitrogen ring
 Adenine
 Guanine
 Pyrimidine- a single nitrogen base
 Thymine
 cytosine
 The DNA molecule is made by the ribose sugar of
one nucleotide binding to a phosphate group next
to it.
 Because of the structure of the nucleotide, DNA
twists so that the phosphate and ribose will match
up
 Nitrogen base bonding
 Because DNA is a double helix, made of 2
strands, the nitrogen bases will only bind with
the correct match through hydrogen bonding.
 Adenine with Thymine
 Cytosine with Guanine
 Notice it is one of each type of nitrogenous base
 DNA can store huge amounts of information
because it is very long.
 Since there are only 2 possible choices of how
nucleotides (A-T) (C-G) will match up, DNA
sequences the information in different orders to
code for different genes
 Can use these sequences to check for evolutionary
relationships
DNA Replication
 DNA makes a copy of the chromosome before
mitosis and meiosis
 Starts with an enzyme that breaks the hydrogen
bonds between nitrogenous bases and unzips the
molecule.
 Free nucleotides then bind to their matching base
and a new chain is formed for each side of the DNA
Making Proteins
 First DNA must be transcribed into RNA.
 RNA is a single strand of genetic material made
from one side of DNA
 RNA has 4 nucleotides just like DNA, but 1 is
different
 RNA Uracil binds with DNA adenine
 RNA Adenine binds with DNA thymine
 RNA Cytosine binds with DNA guanine
 DNA unzips and free nucleotides join together to
form RNA
 3 types of RNA
 Messenger RNA (mRNA)
 Brings the instructions to make proteins from the
nucleus to the cytoplasm
 Ribosomal RNA (rRNA)
 Makes ribosomes- where proteins are made
 Transfer RNA (tRNA)
 Transfers amino acids to the ribosome to make
amino acid chains (proteins)
 mRNA is the message from DNA, but
before proteins can be made the code
must be translated.
 Amino acids are the code used for proteins
 20 different amino acids that make up proteins
 But ONLY 4 nucleotide on RNA??????
 To code for a protein, 3 nucleotides are
used and are called a codon
 Each codon represents an amino acid
 Some codons are instructional
 Start codons at the front of mRNA
 Stop codons at the end of the protein section
 More than one codon can code for the
same amino acid
How to make a protein
 1. mRNA from the nucleus moving into the
cytoplasm and then attaching to a ribosome
 2. amino acids must be brought to the
ribosome by transfer RNA (tRNA)
 Each tRNA will attach to 1 type of amino acid
 Each tRNA has an anti codon that will match up
with the mRNA code
 This is how nitrogen bases are translated into
amino acids
 The ribosome will then allow the tRNA to bind to
the active site of the mRNA and start a protein,
one amino acid at a time.
 The process starts at a start codon and ends at a
stop codon, both are recognized by the ribosome
 As one tRNA adds its amino acid to the
chain, a peptide bond occurs between
amino acids to hold the chain together.
 When a bond has been made the ribosome will
then move on down the mRNA to the next
active site and continue the process.
 The used tRNA then returns to the cytoplasm
Mutations
 Mutation- a change in DNA sequence
 Mutations can be caused by errors in:
 Replication
 Transcription
 Cell division
 External factors
 Mutations in reproductive cells
 A change in sequence of DNA in a gamete
 If a zygote is made the mutated DNA would become part of
the organism
 This can cause:
 Problems with protein synthesis, the proteins do not work
 Death to a zygote because proteins are non functional
 A positive mutation to help an animal to survive
 Mutations to body cells
 Caused by radiation or other external factors
 Once damaged the cell will continue to replicate with the
damaged DNA as long as it can
 Loss of control because of DNA mutations can cause cancer or
other issues because of lack of proteins
 Point mutations to DNA
 A point mutation is when a single nitrogenous base is
switched with another.
 This could cause the entire structure of a protein to
be changed because the codons would be messed up
 RUN DOG RUN
 RUN DOC RUN
 Frame shift mutation to DNA
 The deletion or addition of a nitrogen base to a DNA
strand
 This could cause the entire structure of a protein to
be changed because the codons would be messed up
 RUN DOG RUN
 RUD OGR UN
 DNA repair
 There are enzymes that repair DNA as mistakes
are made. But even they can mess up.
 Chromosomal mutations- structural
changes to chromosome
 May break or get lost during division
 If the break and rejoin they might join
backwards
 Or on a different chromosome
 Often happens in plants
 Few chromosomal changes are passed to off
spring because zygote dies from missing or
wrong placed information