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Who is the

GREATEST BIOLOGIST

EVER?

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Why Gregor Mendel is the

GREATEST 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’s, 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?

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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

Examining 2 genes: How could you determine if a two genes were “linked”?

How could you tell distance between two genes? 41

Examining 2 genes: How could you determine if a two genes were “linked”?

How could you tell distance between two genes?04/18/23 42

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Recombination = offspring with different combinations of traits than the parents, caused by crossing over or mutationsParental 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 mutationsParental 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 double crossovers can occur too, throw # off a little

Made distance unit: 1 map unit = 1% recombination

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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 Quiz

pedigree charts

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Pedigree Practice Problems: Identify each pedigree as

autosomal recessive, autosomal dominant, X-linked, or Y-linked

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Pedigree Practice Problems: Identify each pedigree as

autosomal recessive, autosomal dominant, X-linked, or Y-linked

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

Try your luck 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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