Why is Gregor Mendel the GREATEST BIOLOGIST EVER ? Even though he wasn’t really a biologist
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Transcript of Why is Gregor Mendel the GREATEST BIOLOGIST EVER ? Even though he wasn’t really a biologist
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Who is theGREATEST BIOLOGIST
EVER?
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Why Gregor Mendel is theGREATEST BIOLOGIST
EVER…Even though he wasn’t really a biologist
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Ch 14
Mendelian Genetics
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Pre-Mendel Predominate belief in “blending”, child is a mix of
parents problem with this was traits skipping generations
Terms early genetic study Character = detectable, inherited feature, ex. color Trait = variant of an inheritable character, ex. green or
red color True-Breeding = always produce plants with same
traits as parents, self fertilization Cross-Breeding = cross parents with different traits to
create hybrids
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Generations are named
P = parental F1= results of PxP F2= results of F1 x F1
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Mendel’s experiment Mendel looked at 7 characteristics,
each had 1 alternate form that did not “blend” when cross-bred
His experiment– if a cross of purple & white P’s
gives all purple, then a cross between F1’s, self-pollinating, would produce white again in F2 generation
results – 3:1 ratio of purple to white flowers,
conclusions – ?
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Mendel’s experiment Mendel looked at 7 characteristics, each had 1 alternate
form that did not “blend” when cross-bred
His experiment– if a cross of purple & white P’s gives all purple, then a cross between F1’s, self-pollinating,
would produce white again in F2 generation results – 3:1 ratio of purple to white flowers,
conclusions Heritable trait for whiteness is masked Purple trait is dominant
Extension If 2 purple P’s were mated, what ratio of traits would you expect to
observe?
The ratio does not match the ideal. Create a plan to test if this difference is acceptable.
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So… there are alternate forms of the same gene = alleles,
p265
we inherit one allele from each parent if alleles are different, one is dominant (noted by capital
letter), one is recessive (lowercase letter) When do alleles segregate?
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So… there are alternate forms of the same gene = alleles,
p265
we inherit one allele from each parent if alleles are different, one is dominant (noted by capital
letter), one is recessive (lowercase letter) When do alleles segregate? Anaphase I
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More Terms homozygous – 2 identical alleles for a trait, ex. DD, dd
heterozygous – 2 different alleles for a trait, carrier, ex. Dd phenotype – organism’s expressed traits, ex. color, height genotype – organism’s genetic makeup, letters, ex. PP, Pp
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Testcross – a cross between a recessive and an unknown tells if it is homo or
heterozygous
monohybrid cross – dealing with 1 trait
dihybrid cross – 2 traits Trihybrid – 3 traits
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Mendel’s first postulate:Law of Segregation = allele pairs separate
randomly during meiosis, p. 266
There are 2 alleles for flower color, if 1 purple and 1 white: there is a 50% chance of getting either allele
Punnett square used to predict the results
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Mendel’s secondpostulate:Law of Independent Assortment when dealing with 2
or more traits, each allele of the different genes segregates independently of each other
WHY? If cross 2 dihybrid
heterozygotes, get 9:3:3:1 ratio
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Probability= mathematical chance of an event happening
Rule of multiplication- probability of 2 events occurring at the same time = product of their individual probabilities
Ex: 2 coins both coming up heads = ? Ex: If DdRr x DdRr what is probability of getting DDRR is ?
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Probability= mathematical chance of an event happening
Rule of multiplication- probability of 2 events occurring at the same time = product of their individual probabilities
Ex. 2 coins both coming up heads = ½ x ½ = ¼ Ex: If DdRr x DdRr what is probability of getting DDRR is ?
chance of DD = ¼, chance of RR = ¼ so ¼ x ¼ = 1/16
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Rule of addition –p.270, probability that either of two or more mutually exclusive events will occur is calculated by adding the individual probabilities.
What are the chances you will get heads or tails when you flip a coin?
Ex. cross of 2 heterozygotes, what are chances of result being hetero?
Use → trihybrid AaBbCc x AaBbCc ? chance of AabbCC?
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Rule of addition –p.270, probability that either of two or more mutually exclusive events will occur is calculated by adding the individual probabilities.
What are the chances you will get heads or tails when you flip a coin?
½ + ½ = 1Ex. cross of 2 heterozygotes, what are chances of result being hetero?
Chance of recessive egg + dominant sperm = ½ x ½ = ¼ Chance of dominant egg + recessive sperm = ½ x ½ = ¼ chance of hetero child is ¼ + ¼ = ½
Use → trihybrid AaBbCc x AaBbCc ? chance of AabbCC?
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Extensions: Mendel’s laws were not
perfect, in fact, he was lucky (or wise) that he choose peas which have simple inheritance (except pod shape)
Incomplete dominance = 1 allele is not completely dominant over the other thus, there is a 3rd phenotype, intermediate, ex.Carnations/snapdragonsp. 271
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Codominance= both alleles are expressedLevel of expression varies at different levels
ex: Tay-sachs at the molecular level – looks codominant – both alleles
transcribed at the biochemical level – looks like incomplete→ a partial
level of lipid-metabolizing activity at the organismal level – heterozygotes are symptom free,
homoygote recessives express disorder
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Multiple Alleles= genes that have more than 2 alleles
Ex. blood groups A, B, AB, O (surface carbohydrates)
blood type is the antigen present on the RBC, p. 273
also contains Rh factor, + or – with standard Mendelian rules
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Pleiotropy = a single gene has multiple effects ex: sickle-cell
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Epistasis = one gene affects the expression of another gene, Ex. pigments in mice
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Polygenic inheritance = many genes affect the same trait Ex: skin color, very dark to very light, p. 274
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Environment plays an important part in gene expression, how much is dependent on the gene, nature vs. nurture argument
Norm of Reaction = The phenotypic range for a genotype, p.275
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Humans Pedigree – family tree that shows inheritance over many
generations, shows patterns = male, O = female, ●= affected, ○= non-affected
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- usually caused by a defective protein - heterozygotes are carriers Why more common than dominant disorders?Examples Cystic Fibrosis – most common amongst Europeans (4%
carry), membrane protein that controls Cl⁻ traffic, causes increase mucus in lungs infections persist
Tay-Sachs – higher in Ashkenazic Jews, can’t break down a type of lipid. How can it be high in a particular pop?
Sickle cell – substitution in one hemoglobin, causes RBC to sickle and clog, carriers are immune to malaria, p. 278 In which pop. would sickle cell predominate?
Consanguinity – mating with relatives, increases expression of recessive disorders. Why?
Recessive human disorders
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– rarer than recessive. Why?Examples Achondroplasia – type of dwarfism Huntington's – late acting degeneration of nervous
system, due to single allele on tip of chromosme #4 Knowledge of this makes disease detectable.
many different factors affect onset, but genetic predisposure present
ex. Heart disease, diabetes, cancer
Dominant inherited disorders
Multifactorial disorders
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Genetic testing and counseling 1) carrier recognition - help make decisions about
whether or not to reproduce Can test for Tay-Sachs, sickle-cell, and cystic fibrosis, etc.
2) fetal tests amniocentesis – take amniotic fluid from around fetus, do karyotype chorionic villus sampling (CVS) – take villi, do karyoptype, fast,
earlier, more risk, p. 280 ultrasound – imagery using sound waves, look for physical
problems fetoscopy – fiber optics Culturing escaped fetal blood cells in mother’s blood
3) Newborn screening – ex. PKU
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Big Picture of Inheritance…
must be looked in integrated light…i.e. it is a product of genes working collectively and is influenced by environmental cues Must view emergent properties of organism as a
whole, not a reductionist view of single genes acting in isolation
So, why is Gregor Mendel the
GREATEST BIOLOGIST
EVER?Even though he wasn’t really a biologist
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Ch 15
Chromosomes and Inheritance
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Chromosome theory of inheritance: genes are located on chromosomes, they segregate and independently assort
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T.H.Morgan rediscovered Mendel’s work 1900’sQUESTION: specific genes on specific chromosomes?
work on fruit fly, why? fast repro., easy to handle, 4 pairs of chromosomes (1 pair
are sex chromosomes) gene symbol is based on the mutant or recessive
ex. curly is recessive = Cy, if normal then Cy+ “wild type” is the type seen in nature = +
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Experiment- p 289 white eyed male (♂)→ crossed with a red eyed female (♀)→ in F2 only males had white eyes ?
how is no independent assortment possible (sex and white eyes)?
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Experiment- p 289 white eyed male (♂)→
crossed with a red eyed female (♀)→ in F2 only males had white eyes ?
→ eye color and sex are linked
Linked genes = when genes are on the same chromosome, so they are inherited together
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Sex linked traits = located on a sex chromosome, p. 290, ex. Hemophilia few genes on the Y, thus
most sex-linked diseases are seen in males b/c on the X (not masked), females often carriers, p. 290
X-inactivation = females inactivate one of their X’s (see cat diagram) inactive X becomes a Barr body Typically both chromosomes’
genes are expressed
Why do X chromosomes get inactivated?
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Genetics in the lab
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Genetics in the lab: How could you determine if a two genes were “linked”?
How could you tell distance between two genes?
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How could you determine if a two genes were “linked”?
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Recombination = offspring with different combinations of traits than the parentsParental types – same phenotype as a parentRecombinants – differ from parents, *p. 293-294
What is % of recombination of the peas?
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Recombination = offspring with different combinations of traits than the parents, caused by crossing over or mutations
Parental types – same phenotype as a parentRecombinants – differ from parents, *p. 293-294
What is % of recombination of the peas?50% - one-half of the offspring are expected to inherit either of the two phenotypes
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Recombination What would a recombination of 25% tell
you about the chromosomal location of two given genes?
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Recombination What would a recombination of 25% tell you about the
chromosomal location of two given genes? The genes’ loci are on the same chromosome
Why is the recombination % not 0?
What would a recombination of 0.5% tell you about their respective locations?
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Recombination What would a recombination of 25% tell you about the
chromosomal location of two given genes? The genes’ loci are on the same chromosome
Why is the recombination % not 0? Crossing-over separates them
What would a recombination of 0.5% tell you about their respective locations? That their respective loci are in close proximity on the same chromosome
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Sturtevant and gene mapping use recombination frequency to determine distance of genes The farther apart two genes are, the higher the probability that
crossover will occur between them and ∴ the higher the recombination frequency
made chromosome maps find relative distance between farthest genes, find distance of an
end and a middle, fill in other genes Made distance unit: 1 map unit = 1% recombination double crossovers can occur too, throw # off a little
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Final product: a genetic (linkage) map
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HUMAN GENETIC DISORDERS
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Nondisjunction –two chromosomes stuck together or not present Why and when would this occur?
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Nondisjunction –two chromosomes stuck together or not present Why and when would this occur?
Aneuploidy = having an abnormal # of chromosomes Trisomy – 3 copies of 1 chromosome Monosomy – 1 copy of the chromosome
Polyploidy = more than normal chromosome set Triploidy – 3 chromosome sets (3N)
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Nondisjunction –two chromosomes stuck together or not present Why and when would this occur?
Aneuploidy = having an abnormal # of chromosomes Trisomy – 3 copies of 1 chromosome Monosomy – 1 copy of the chromosome
Polyploidy = more than normal chromosome set Triploidy – 3 chromosome sets (3N)
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Basic Mutations Deletion – chromosome loses a piece, p. 298 Duplication – double of gene Inversion – chromosome is in reverse Translocation – gene moves to another chromosome →caused by UV light, chemicals or random →effects can be silent, lethal or in between
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Down Syndrome – trisomy 21, female age makes more frequent?
Klinefelters – XXY, XXXY male, sterile, some female features
XYY – male, usually normal, XXX- female, usually normal Turner syndrome – X, female, sterile, few sexual features
Some effects of chromosomal abnormalities depend on what parent inherited by (genomic imprinting, p.300)- Prader–Willi disorder– deletion of part of #15 from dad- Angelman syndrome– deletion of same part of # 15 from mom,
motor issues
Human aneuploid conditions
Genomic Imprinting
is the activation or deactivation of a gene depending upon whether it was inherited from mom or dad Mechanism is typically methylation (adding of
methyl group, –CH3 ). Methyl group acts as an on/off switch. Key player in epigenetics
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Organelles and their genes
Do not follow Mendelian rules of inheritance.
Why?
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Organelles and their genes
Do not follow Mendelian rules of inheritance. Why? They do not undergo meiosis
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Study tip of the day: always be able to explain text chapter concepts Concept 15.1: Mendelian inheritance has its physical
basis in the behavior of chromosomes Concept 15.2: Sex-linked genes exhibit unique patterns
of inheritance Concept 15.3: Linked genes tend to be inherited together
because they are located near each other on the same chromosome
Concept 15.4: Alterations of chromosome number or structure cause some genetic disorders
Concept 15.5: Some inheritance patterns are exceptions to standard Mendelian inheritance
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Chapter 14 & 15 White-board challenge
pedigree charts
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Pedigree Practice Problems: Identify each pedigree as autosomal recessive, autosomal dominant, X-linked, or Y-linked (aka “patterns of inheritance”)
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Pedigree Practice Problems: Identify each pedigree as autosomal recessive, autosomal dominant, X-linked, or Y-linked (aka “patterns of inheritance”)
ANSWERS
a. autosomal recessive
b. autosomal dominant
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ANSWERS c.
autosomal dominant
d. autosomal recessive
e. x-linked recessive
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ANSWERS f.autosomal
dominantg.autosomal
recessive
1. If a plant with purple flowers produces only the same variety as the parent plant over many generations, what is the plant said to be?
2. What is Mendel’s law that states that the two alleles for a heritable character separate from each other during gamete formation?
Chapter 14
1. True-breeding plants
2. Law of Segregation
Chapter 14
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3. If two heterozygous purple flowers produce offspring, what are the odds that the offspring will have white flowers?
4. The child’s mother has blonde hair, and their father is heterozygous and has brown hair. If blonde hair is a recessive trait, what are the odds that the child would have blonde hair? 5. When red snapdragons are crossed with white snapdragons their offspring is pink. What type of dominance is this?
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3. 25%4. 50%
5. Incomplete
1. The law that states that alleles of genes on nonhomologous chromosomes assort independently during gamete formation is?
2. Who has a greater chance to receive X-linked recessive disorders? Males or females?
3. Genes located near each other on the same chromosome tend to be inherited together in genetic crosses are called ?
Chapter 15
1. Law of Independent Assortment
2. Males
3. Linked Genes
Chapter 15
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4. When the members of a pair of homologous chromosomes do not move apart properly during meiosis I they can alter the chromosome structure. What is this error called?
5. What are the four types of changes that can occur to chromosome structure?
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4. Nondisjunction
5. Deletion, duplication, inversion, translocation
Test your skills at…
practice pedigree problems
Or more on following pages
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Dominant or recessive?autosomal, x-, or y-linked?
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?
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A
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