Genetics

IB Biology II

Van Roekel

1/15/14

What can you tell me about this individual based on its Karyotype. When finished, read the article.

Topic 4.1 Notes

• 4.1.1 State that eukaryote chromosomes are made of DNA and proteins.

• 4.1.2 Define gene, allele and genome. • 4.1.3 Define gene mutation . • 4.1.4 Explain the consequence of a base

substitution mutation in relation to theprocesses of transcription and translation, using the example of sickle-cell anemia.

Background Info

• Somatic Cells – typical body cell (non-sex cell)

• Gamete – Egg and sperm cells

• Haploid – a cell containing a single set of chromosomes (N)

• Diploid – in an organism that reproduces sexually, a cell that contains 2 homologous sets of chromosomes.

Meiosis

• Meiosis is for the reproduction of sex cells. (sperm and egg)

• It makes 4 daughter cells

• They are Haploid (half the number of chromosomes as the parent cell)

• They are not identical

Chromosome Refresher

• Chromosomes are made of DNA and Protein.

• Unwinding DNA is similar to unwinding a ball of string…the proteins help keep it organized (histones).

Chromosome Refresher

• In eukaryotes, chromosomes always come in homologous pairs in somatic cells (one from mother, one from father)

• Humans have 23 pairs of chromosomes, or 46 total

What is a gene?

• A gene is a heritable factor that controls a specific characteristic (hair color, eyes, etc.)

• Humans have roughly 30,000 genes.

• Many genes have variations of forms called ALLELES.

Alleles cont.

• One specific form of a gene.

• Different alleles typically only differ by a few base pairs (nucleotides).

• Alleles of the same gene occupy the same LOCUS on each chromosome pair. Locus is a corresponding region on chromosome.

Genome

• The complete set of an organism’s base sequences is called it’s genome

Mutation

• A mutation, by definition, is a change in the genetic material. (typically rare)

• Types of mutations:– Insertion/DeletionFrameshift mutations– Base substitutionMissense mutations

Insertion/Deletion

• Additions or losses of nucleotide pairs in a gene

• Has disastrous effect on resulting protein

• Results in Frameshift mutation because reading frame (codon grouping) is altered, usually results in nonfunctional proteins

Base Substitution

• A single base substitution may or may not have an effect on the overall gene (and ultimately protein). Why?

• A base substitution would be like guanine changing to adenine in the parent sequence.

• Missense mutation: altered codon still codes for an amino acid, although it may not be planned amino acid

Base Substitutions-Sickle Cell Anemia

• DNA is mutated from CTC to CAC, so codon GAG converted to GUG

• Valine is added instead of Glutamic Acid to growing polypeptide.

• Ultimate mutation is a “sickle” shaped cell.

• Oxygen is ultimately not carried as efficiently throughout the body.

Define the following terms• Chromosome:

– Bundled packages of DNA and protein

• Gene:– Heritable factor that controls a specific

characteristic

• Allele:– Specific forms of a gene

• Mutation: – Random, rare change in the genetic material

Topic 4.3 Theoretical Genetics• 4.3.1 Define genotype , phenotype , dominant allele , recessive allele, codominant• alleles , locus, homozygous, heterozygous, carrier and test cross.• 4.3.2 Determine the genotypes and phenotypes of the offspring of a monohybrid• cross using a Punnett grid.• 4.3.3 State that some genes have more than two alleles (multiple alleles). • 4.3.4 Describe ABO blood groups as an example of codominance and multiple• alleles.• 4.3.5 Explain how the sex chromosomes control gender by referring to the• inheritance of X and Y chromosomes in humans.• 4.3.6 State that some genes are present on the X chromosome and absent from the• shorter Y chromosome in humans.• 4.3.7 Define sex linkage. • 4.3.8 Describe the inheritance of colour blindness and hemophilia as examples of• sex linkage.• 4.3.9 State that a human female can be homozygous or heterozygous with respect• to sex-linked genes.• 4.3.10 Explain that female carriers are heterozygous for X-linked recessive alleles. • 4.3.11 Predict the genotypic and phenotypic ratios of offspring of monohybrid• crosses involving any of the above patterns of inheritance.• 4.3.12 Deduce the genotypes and phenotypes of individuals in pedigree charts.

Gregor Mendel

• Father of Genetics.

• Used pea plants to construct crosses between different types of pea plants.

• Crossed tall with tall; tall with short; etc. for generations of pea plants

Genotype

• The symbolic pair of alleles possessed by an organism…represented by two letters.

• Bb, GG, tt

Phenotype

• The physical characteristic or trait of an organism.

• Hair color, shell color, eye color, etc.

• “PHysical characteristic”

Dominant vs. Recessive

• Dominant alleles are always expressed in phenotype when present in genotype.– BB, Bb

• Recessive are only expressed when they are homozygous.– bb

Codominance

• Pair of alleles that both affect the phenotype when present in a heterozygote.

Homozygous vs. Heterozygous

• Homozygous- having two identical alleles of a particular gene (ex. AA rather than Aa)

• Heterozygous – having two different alleles of a particular gene (ex. Aa rather than AA)

Carrier

• An individual with a recessive allele that does not effect phenotype of the individual.

• Ex. – Aa individual is a carrier for the albinism gene.

Test Cross

• Testing a suspected heterozygote plant with a known homozygous recessive (aa).

• It is very difficult to tell just by phenotype whether or not an individual is AA or Aa until a test cross is done.

Setting up a Punnett Grid for monohybrid crosses

Steps of setting up Punnett Square

• Choose and indicate a letter to show alleles.

• Determine the parents’ genotypes

• Determine possible gametes

• Draw and complete Punnett grid

• Determine percentages of genotypes and phenotypes

• In dogs, the gene for fur color has two alleles. The dominant allele (F) codes for grey fur and the recessive allele (f) codes for black fur.

• The female dog is heterozygous. The male dog is homozygous recessive. Figure out the phenotypes and genotypes of their

possible puppies by using a Punnett Square.

• The female dog has black fur. The male dog has black fur. Figure out the phenotypes and genotypes of their possible puppies by using a Punnett Square.

• In fruit flies, red eyes are dominant (E). White eyes are recessive (e).

• If both flies are heterozygous, then what are the possible phenotypes and genotypes of their offspring?

• If the female fly has white eyes and the male fly has homozygous dominant red eyes, what are the possible phenotypes and genotypes of their offspring?

• Using CR and CW as alleles for incomplete dominance in snapdragon flower color, show how two plants could have some white-flowered offspring, pink-flowered offspring, and red-flowered offspring within one generation?

• Having a widow’s peak is dominant to not having a widow’s peak. Look at the pictures of Jay Z and Beyonce. If these two have more children, could they have widow’s peak? Why or Why not? Use a Punnett Square to explain your answer.

Multiple Alleles

• Occurs when there are three of more alleles for one gene, which results in more than two possible phenotypes.

• Example: Blood Type in humans

• Type A, B, AB, or O

Blood Type

• Three alleles for gene– IA – Allele for type A – IB – Allele for type B – i – Allele for type O

• Crossing these together can create 6 possible genotypes and 4 phenotypes

Blood Type

• IAIA or IAi = Type A

• IBIB or IBi = Type B

• IAIB = Type AB

• ii = Type O

• Determine the possible blood types of a child whose mother has type A blood, and whose father has type O blood. The child’s maternal grandparents had type A blood and type O blood.

Sex chromosomes

• 23rd chromosomes are the sex chromosomes

• XX = Female

• XY = Male

• X chromosome is longer and contains more genes than Y chromosome

Sex Chromosomes

• Females - all gametes carry the X chromosome

• Males – 50 % of gametes carry X chromosomes, 50% carry Y chromosome

• Always a 50/50 chance of male or female

Sex-Linked Traits

• Any genetic trait whose allele has its locus (location) on the X or Y chromosome.

• Examples: – Color Blindness– Hemophilia

Sex-Linked Alleles

• Color Blindness– Xb = recessive allele for color blindness– XB = allele for ability to distinguish colors

• Hemophilia– Xh = allele for hemophilia– XH = allele for ability for blood to clot

Sex Linked Traits

• XBXB = phenotype for non-affected female • XBXb = phenotype for non-affected female• XbXb = phenotype for affected female• XBY = phenotype for non-affected male• XbY = phenotype for affected male

• Rare in females because require two recessive alleles, whereas males only require one

Sex-Linked Carriers

• Only females can be carriers of sex-linked traits

Autosomes vs Sex Chromosomes

• Autosomes: any chromosome that is not a sex chromosome. 22 pairs in humans

• Genes can be autosomal or sex-linked– Autosomal means they are found on any of

the 22 autosomes– Sex-linked means the genes loci are on the X

or Y chromosome.

Pedigree Charts

• Pedigree – refers to the record of an organism’s ancestry

• Constructed to show biological relationships, specifically how traits pass from generation to generation

Pedigree Charts – Is this trait dominant or recessive? Is it sex

linked? Explain your answer.

Topic 10 (Genetics Continued)

• 10.1.1 Describe the behavior of the chromosomes in the phases of meiosis.

• 10.1.2 Outline the formation of chiasmata in the process of crossing over.

• 10.1.3 Explain how meiosis results in an effectively infinite genetic variety in gametes through crossing over in prophase I and random orientation in metaphase I.

• 10.1.4 State Mendel’s law of independent assortment. • 10.1.5 Explain the relationship between Mendel’s law of

independent assortment and meiosis.

• 10.2 Dihybrid crosses and gene linkage Assessment statements

• 10.2.1 Calculate and predict the genotypic and phenotypic ratio of offspring of 3 dihybrid crosses involving unlinked autosomal genes.

• 10.2.2 Distinguish between autosomes and sex chromosomes. • 10.2.3 Explain how crossing over between non-sister chromatids of

a homologous• pair in prophase I can result in an exchange of alleles.• 10.2.4 Define linkage group . • 10.2.5 Explain an example of a cross between two linked genes.

• 10.2.6 Identify which of the offspring are recombinants in a dihybrid

cross involving linked genes.

Mendel’s Law of Independent Assortment

• What does it state?

• The separation of one pair of alleles is independent of the separation of another pair of alleles, provided that they are on separate chromosomes (unlinked)

Dihybrid crosses

• Consider two traits on separate chromosomes (unlinked genes)

• Example: Seed color (yellow-Y; green- y)

Seed shape (round-R; wrinkled-r)

Two parents each of which are heterozygous for each trait mate, what are the possible offspring’s

genotypes?

R Y R y r Y r y

R Y

R y

r Y

r y

RR YY RR Yy Rr YY Rr Yy

RR Yy

Rr YY

Rr Yy

Rr Yy

Rr Yy

RR yy Rr yy

Rr yy

rr YY rr Yy

rr Yy rr yy

Dihybrid Crosses

• When two heterozygous parents mate, the following phenotypic ratio is expected: – 9:3:3:1– 9 represents both dominant traits expressed– 3 represents one dominant one recessive trait– 1 represents both recessive traits

Dihybrid Practice

• A pea plant with round yellow seeds is crossed with a pea plant that has wrinkled green seeds, what are the possible genotypes of their offspring?

Dihybrid Cross

• In man, assume that spotted skin (S) is dominant over non-spotted skin (s) and that wooly hair (W) is dominant over non-wooly hair (w). Cross a marriage between a heterozygous spotted, non-wooly man with a heterozygous wooly-haired, non-spotted woman. Give genotypic and phenotypic ratios of offspring.

Dihybrid Cross

• In horses, black is dependent upon a dominant gene, B, and chestnut upon its recessive allele, b. The trotting gait is due to a dominant gene, T, the pacing gait to its recessive allele, t. If a homozygous black pacer is mated to a homozygous chestnut trotter, what will be the appearance of the F1 generation?

Autosomes vs Sex Chromosomes

• Autosomes: any chromosome that is not a sex chromosome. 22 pairs in humans

• Genes can be autosomal or sex-linked– Autosomal means they are found on any of

the 22 autosomes– Sex-linked means the genes loci are on the X

or Y chromosome.

Linked Genes

• Any two genes found on the same chromosome are said to be linked to each other.

• Linked genes usually pass from generation to generation together.

• Any set of genes inherited together because they are on the same chromosome are referred to as a linkage group.

Linked Genes

• Linked Genes are represented as

• Horizontal bars represent homologous chromosomes, with G & L being on the same chromosome

• Genotype is read by pairing vertical alleles, i.e. GGLL

G L

G L

• Crossing over still produces genetic variations of linked genes.

• Offspring can have different combinations of alleles of linked genes by crossing over, new forms of chromosomes are referred to as recombinants

Linked Genes

• 10.3 Polygenic inheritance Assessment statement

• 10.3.1 Define polygenic inheritance

• 10.3.2 Explain that polygenic inheritance can contribute to continuous variation using two examples, one of which must be human skin color.

Polygenetic inheritance

• Characteristics are influenced by two or more genes.

• Large number of possible genotypes and phenotypes

• Most human traits are considered polygenetic– eye color, skin color, height, susceptibility to

certain illnesses, etc…

Continuous Variation

• Occurs in traits with large number of possible genotypes, which leads to an array of possible phenotypes that transition from one to the next.

• Continuous variation results because of the interaction between multiple genes

• Affected by genetics, as well as the environment

• Results in a bell shaped distribution curve

Beak Depth in Finches

Skin Color

Discontinuous Variation

• Occurs when there are no transitions between phenotypes for specific traits.

• Distinct phenotypes that can be easily separated

BILL

• What is the difference between continuous and discontinuous variation?

• Continuous variation occurs in polygenetic genes and shows a transition between phenotype. Discontinuous variations occur in single gene traits, and the phenotype is either present or it is not.

Genetic Engineering & Biotechnology

• How can I use genetics in useful, real life applications?

• DNA Profiling

• The Human Genome Project

• Gene Transfer

• Genetically Modified Organisms

• Cloning

DNA Profiling

• Use polymerase chain reaction (PCR) to make millions of copies of DNA

• Often amounts of DNA collected are limited

• Using PCR, forensics experts can obtains millions of copies of DNA in order to have enough to analyze it.

DNA Profiling

• Gel electrophoresis separates fragments of DNA in order to identify its origin

• DNA is broken into pieces by enzymes and placed in the gel

• Gel is Introduced to an electrical current– Largest particles don’t move far– Smaller particles pass through gel

• Results in unique banded patterns for each individual based on DNA composition

What to do with DNA Profiling?

• Match unknown samples of DNA with known sample to see if they correspond to determine:– Paternity cases

– Analyze crime scenes

– Study ecosystems to see which individuals are related

The Human Genome Project

• Started in 1990, project set out to determine the order of all the bases A, T, C, & G in human DNA.

• Completed in 2003, now deciphering what sequences represent which genes

• Used to:– Determine which chromosomes carry specific genes– Produce beneficial medications– Compare ancestries

Gene Transfer

• Takes a gene out of one organisms and places it in another organism

• Possible because DNA is universal, meaning that A,T,C,& G are used in all organisms to code for protein

• Tomatoes resistant to cold– Proteins used by fish to resist icy temps are now produced in

modified tomatoes

• Bt-corn– Produces toxins that kill bugs which attack it, thanks to gene

from a soil bacterium that produces a protein fatal to certain larvae

Gene Transfer – Cutting and Pasting

• Cut specific sequences of DNA using enzyme endonuclease

• Paste sequences using DNA ligase

• Sequences can be copied using host cells such as E. coli– Splice sections of DNA into plasmids (small

circles of extra copies of DNA), place host cells in ideal conditions to grow and replicate

Genetically Modified Organisms

• Genetically modified organisms (GMO) is one that has had an artificial change using techniques of genetic engineering

• Transgenic plants: undesirable genes are removed or replaced with desired sequences of DNA– Tomatoes that can grow in high salinity soil– Rice plants that produce beta carotene

• Transgenic animals– Use animals to produce substances for medical

treatment, i.e. transgenic sheep produce Factor IX

Cloning

• Clone: genetically identical organism artificially derived from a single parent

• Usually done using an undifferentiated, but fertilized egg cell

• Dolly, sheep whose genetic material did not originate from egg cell

How Dolly was made

Therapeutic Cloning

• Interested in cloning only cells.

• Stem Cell research, aka culturing stem cells in order clone healthy cells to be used for medical treatment

Genetics Test

• Thursday, 1/30

• Covers:

• Chapter 4 & 10

• Meiosis

• Genetics

• Genetic Engineering & Biotechnology