unit 6 - central bucks school district€¦ · unit 6 genetics. lesson 1 patterns of inheritance....

UNIT 6

Genetics

LESSON 1

Patterns of Inheritance

Objective

◦ Describe and/or predict observed patterns of inheritance (i.e.,

dominant, recessive, co-dominance, incomplete dominance,

sex-linked, polygenic, and multiple alleles)

Gregor Mendel

◦Bred different varieties of pea plants and recorded offspring types

◦Died before he was famousPublic Domain via Wikimedia Commons

Public Domain via Wikimedia Commons

Mendel’s Findings

◦ Individuals carry 2 copies of every trait (gene)

◦Different forms of genes occur (alleles)◦ Flower color gene; purple, white alleles

◦Different alleles can interact in dominant and recessive ways

◦When organisms pass on genes, one copy of each gene is randomly passed on

Predicting Inheritance Patterns◦Choose a letter for each gene◦ P/p = flower color

◦Assign capital letter to dominant trait◦ P = purple, p = white◦ Dominant alleles always show up if present

◦ Individuals always have 2 alleles◦ PP or pp = homozygous◦ Pp = heterozygous (dominant always listed first)

◦Genes vs. Traits◦ Genotypes = genes of an individual◦ Phenotypes = physical appearance of an individual

Punnett Squares

◦Visual way of predicting outcomes of a

cross using the principles of probability

◦Generally assume that each allele has a

50% chance of being passed on

◦WHY?

Punnett Squares

◦ Steps for Solving1. Read problem carefully2. Write down alleles and traits they represent3. Identify parent genotypes4. Determine possible gametes (sperm & eggs)5. Set up Punnett Square6. Interpret Punnett Square7. Answer question

Sample Question

◦ Question: In pea plants purple flowers are dominant to white

flowers. If a heterozygous purple flower is crossed with a

homozygous white flower plant, what are the possible

phenotypes of the resulting offspring?

This tells the alleles & no

letters are designated so

you can make up your

own.

F = purple flower

f = white flower

This describes the

parents:

Heterozygous purple = Ff

Homozygous white = ff

Phenotypes is what

the traits of the

offspring are, so it

should be described

as flower color

Punnett Square

Parents: Ff ff

Gametes: F f f f

f fFf = purple

ff = white

50% purple

50% white

F

f

Ff Ff

ff ff

Other Patterns of Inheritance

◦ Incomplete dominance

◦ The resulting trait is a blend of both allele

traits

◦ Co-dominance

◦ Both alleles are fully expressed

◦ Multiple alleles

◦ 3 or more alleles each with their own

interactions

Creative Commons , courtesy of Wildfeur via

Wikimedia Commons

Public Domain via Wikimedia

Commons

Other Patterns of Inheritance (continued)

◦ Polygenic inheritance

◦ Multiple genes affecting one

trait

◦ Alleles often have additive

affects

◦ Sex-linked traits

◦ Genes that occur on the sex

chromosomes (X & Y)

◦ Males often affected more then

females. WHY?


A model for skin color

Parents: aabbccdd X AABBCCDD

Offspring: AaBbCcDd

LESSON 2

Gene to Protein

Objective

◦ Describe how the processes of transcription and translation are

similar in all organisms

◦ Describe the role of ribosomes, endoplasmic reticulum, Golgi

apparatus, and the nucleus in the production of specific types of

proteins

Gene to Protein

◦DNA contain genes that code for the amino acid sequence of proteins◦Basic process◦DNA → mRNA → Protein◦Transcription – process of creating messenger RNA (mRNA) from gene◦Translation – mRNA translated to amino acid sequence using ribosomes

The Genetic Code

◦ Bases grouped in threes

(codons)

◦ Each codon codes for an

amino acid, a start, or a

stop

◦ 64 possible codons (only 20

amino acids)

◦ Starts and stops needed to

frame gene

◦ Genetic code is nearly

universal Public Domain via Wikimedia Commons

Transcription

◦ Initiation – RNA polymerase

attaches at the beginning

of a gene

◦ Elongation – One side of the

DNA is used to build a

matching RNA strand

◦ Termination – mRNA is

released and moves out of

the nucleus


Translation

◦ mRNA slides through ribosome

◦ tRNA match with each codon with the correct amino acid


Sample Problem

◦ DNA: A T A C C G T C G T A G C T A G A T T C G G A

◦ mRNA:

◦ AA:


◦ mRNA: U A U G G C A G C A U C G A U C U A A G C C U

◦ AA:

Sample Problem (continued)

Genetic Code

Solution


◦ mRNA: U A U G|G C A|G C A|U C G|A U C|U A A|G C C U

◦ AA: Start – Ala – Ala – Ser – Ile – STOP

LESSON 3

Mutations and Proteins

Objective

◦ Describe how genetic mutations alter the DNA sequence and

may or may not affect phenotype (e.g., silent, nonsense, frame-

shift)

Mutations and Proteins

◦ As much as 95% of human DNA does not code for proteins

◦ Any mutation in these noncoding areas will probably not affect the proteins

produces

◦ Only mutations that occur in sex cells will be passed on to the next

generation

◦ Any mutation that does alter a protein can have a range of impacts

on cell and body functions

Point Mutations

◦ One nitrogenous base is changed

◦ Silent mutations do not cause a change in amino acid

◦ Nonsense will stop the transcription before the end

◦ Missense will change the amino acid sequence of the protein

◦ Can vary in its affect on the protein from no affect to drastic affects

Creative Commons , courtesy of Jonsta247

via Wikimedia Commons

Frameshift Mutations

◦Word example

◦ Original message

◦ The Old Man and the

Sea

◦ Mutation

◦ The Oxl dMa nan dth eSe

a

◦ The DNA code is read in groups of 3

(codons)

◦ If a base is added or removed, it will

throw off every codon after that

◦ DNA example

◦ Original message

◦ GAC CAT TTA GGG CTA TAT

◦ Leu – Val – Asn – Pro – Asp – Ile

◦ Mutation

◦ GAC CTA TTT AGG GCT ATA T

◦ Leu – Asp – Lys – Ser – Arg – Tyr

LESSON 4

Chromosome Changes

Objective

◦ Describe the processes that can alter composition or number of

chromosomes (i.e., crossing over, nondisjunction, duplication,

translocation, deletion, insertion, and inversion)

Chromosome Changes

◦ Normal chromosome changes

◦ Genes recombine on a chromosome during

meiosis due to crossing over

◦ Mutations

◦ Any permanent alteration to the number of

chromosomes or the composition of a

chromosome


Types of Mutations

◦Nondisjunction

◦Deletion

◦Duplication

◦Inversion

◦Insertion

◦Translocation


Types of Mutations◦ Nondisjunction – extra or missing copies of whole chromosomes

◦ Caused by failure of chromosomes to separate properly during meiosis


Types of Mutations

◦ Deletion – section destroyed


Types of Mutations

◦ Duplication – section repeated


Types of Mutations

◦ Inversion – section flipped


Types of Mutations

◦ Insertion – section transferred from one nonhomologous

chromosome to another


Types of Mutations

◦ Translocation – sections exchanged between nonhomologous

chromosomes


LESSON 5

Genetic Engineering

Objective

◦ Explain how genetic engineering has impacted the fields of

medicine, forensics, and agriculture (e.g., selective breeding,

gene splicing, cloning, genetically modified organisms, gene

therapy)

Genetic Engineering

◦ Genes from one organism can express

themselves in other organisms even if they are

very distantly related

◦ Obstacles

◦ Cutting and sorting genes from whole genomes

◦ Replicating large amounts of DNA

◦ Inserting genes into new organisms

A tobacco plant genetically

engineered with a firefly gene.

Creative Commons , courtesy of Kieth Wood and Science Magazine


Cutting DNA

◦Restriction enzymes

– naturally

occurring proteins

that cut apart DNA

◦ Some leave sticky

and some leave

blunt ends


Sorting DNA

◦Gel Electrophoresis –

DNA fragments

pushed through a gel

with an electrical

current

◦ Smaller fragments go

further


Creative Commons , courtesy of Jeffery

Vinocour via Wikimedia Commons

Replicating DNA

◦ Polymerase Chain Reaction (PCR)

◦ One cycle takes 5 minutes (DNA doubles every time)

Creative Commons , courtesy of Madprime



Inserting Genes

◦ Very difficult to get new DNA in

lots of cells at the same time

◦ Solutions:

◦ Start with a single cell and grow it

into many

◦ stem cells can grow into many types

of cells

◦ Use a vector

◦ Viruses


Uses of Genetic Engineering

◦ Forensics◦ DNA fingerprinting

◦ Environmental ◦ Oil and toxin eating bacteria

◦ Agricultural uses◦ Pesticide resistance◦ Frost resistance◦ High yields

◦ Medicine◦ Gene therapy◦ ‘good’ genes are inserted in to human cells to take the

place of faulty ones◦ Protein supplements◦ Insulin◦ Human growth hormone

◦ Many other uses!!!!

unit 6 - central bucks school district€¦ · unit 6 genetics. lesson 1 patterns of inheritance....

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