Transcript Chapter 5 - TeacherWeb

Chapter 5
GENETICS AND HEREDITY
Genetics and Heredity
 Heredity- the passing of traits from parents to
offspring
 Genetics- the study of how traits are passed from
parents to offspring
Gregor Mendel
 Considered the Father of Genetics
 Austrian Monk
 He studied pea plants because they have a wide
variety of traits
 Pea plants also are readily available and have a
relatively short life span
 He could also control pollination
Mendel Laws
 Law of Segregation- each allele separates from the
other allele independently
Dominant and Recessive
 Dominant- a genetic factor that blocks another
genetic factor
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Only one copy of the gene is necessary for expression of the
trait
“Stronger”
 Recessive- A genetic factor that is blocked by the
presence of a dominant factor
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Two copies of the trait are necessary for expression of the trait
Hidden, may appear to “skip generations”
Understanding inheritance
 Mendel concluded that one gene (factor) from each
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parent controlled each trait
We know these factors to genes.
Genes are located on chromosomes
Humans have 46 total or 23 pairs
22 pairs are the autosomal chromosomes
23 pair determines the sex of the individual
Male
XY
Female XX
Genes and alleles
 Gene- a section on a chromosome that has genetic
information for a trait
 Allele- the different forms of a gene are called the
alleles
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R- for round r- wrinkled
Genotype and Phenotype
 Genotype- the genetic makeup
 The two alleles that control the phenotype of the triat
 Phenotype- the physical appearance
 How the trait appears or is expressed
Homozygous and Heterozygous
 Homozygous- when the two alleles of the gene are
the same
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RR, rr
Purebred
 Heterozygous- If the two alleles are different
 Rr
 Hybrid
Modeling inheritance
 Punnett square- a model used to predict genotypes
and phenotypes of the offspring
 Pedigree- family tree showing the phenotype of the
family members. Can be used to infer genotypes
Complex patterns of inheritance
 Incomplete dominance- some traits appear to be a combination of
alleles
 A red flower camellia plant with a white flower camellia only produces
pink flowers
 Codominance- When both alleles can be observed in the
offspring
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Cows- both red and white traits
 Multiple Alleles- More than two alleles for a trait
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ABO blood groups
 Polygenic inheritance- a combination of many genes and
usually some environmental factor (can be unknown)
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Hair color, skin color, cleft lip, club foot
DNA and Genetics
 Genes provide the instruction or blueprint for
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making an organism
DNA- organisms genetic material
DNA codes for the genes
DNA is tightly coiled
It is a double helix structure or twisted ladder or
zipper
Discovered by Watson and Crick
DNA
 It is composed of three parts
 A sugar- deoxyribose
 A phosphate group
 A nitrogen base
 There are four common nitrogen bases
 Adenine- (A) pairs with Thymine (T)
 Cytosine (C) pairs with Guanine (G)
DNA replication
 Replication- process of copying a DNA molecule to
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make another DNA molecule
1. DNA strand separates and nitrogen bases are
exposed
2. Nucleotides move in and form new nitrogen bases
3. Two new identical strands are made
Almost like a zipper opening
Making proteins
 Made with the help of Ribonucleic acid (RNA)
 RNA is single stranded
 RNA has nitrogen base Uracil (U) rather than
Thymine (T)
 Sugar is ribose
 Transcription- making mRNA (messenger RNA)
from DNA
Translation
 The process of making proteins from RNA is called
translation
 There are 2 other types of RNA
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tRNA- transfer RNA
rRNA- ribosomal RNA
Translation
tRNA carries amino acids to the proteins
 mRNA helps form chemical bonds that attach one amino acid to
another
 The first tRNA separates from its amino acid and mRNA.
 The cycle continues.
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Translating the RNA code
 The order of the nitrogen bases in the mRNA
determines the order of the amino acids in the
protein
 Three nitrogen bases are read to pick up the correct
amino acid
 Three nitrogen bases= codon
 64 codons but only 20 amino acids
 Some code for the same amino acid, some code for a
stop, and some code for the beginning.
Mutations
 A mutation is a change in the nucleotide sequence of
a gene
 Most mutations are corrected during replication
 Mutations can be triggered by X-rays, UV light,
chemicals, and radioactive materials
Types of mutations
 Deletion- one or more nitrogen bases are left out of
the DNA sequence
 Insertion- one or more nitrogen bases are added to
the DNA
 Substitution- a nitrogen base is replaced by another
different nitrogen base.
Results of mutations
 Not all mutations are harmful, some help an
organism survive a change in environment
 Some will cause a genetic disease or disorder like
cystic fibrosis or PKU.