Unit 6: Genetics & HeredityCh 8: Heredity & Ch 11: Human Genetics

• What is genetics?– __________________ = the passing of traits

from parents to offspring

– Why is your combination of genes unique?

heredity

Gregor Mendel – the Father of Genetics

1822-1884

Mendel’s Experiments• Studied garden peas – _____ different traits

with clearly different forms– Tried to determine how these traits were transmitted

from parent to offspring

7

• Male & female parts in same flower–Normally

• Self pollinate–Produce pure

offspring» ______ parents

produce______ offspring

» ______ parents produce _________ offspring

Mendel’s Experiments

purplepurple

whitewhite

Mendel’s Experiments• Cross pollination of pure

purple parent & pure white parent (parent generation)• Purple offspring (________

____________ generation)• Hybrids (genes for both

purple & white in all offspring)

F1

or first filial

• Offspring allowed to self pollinate• New offspring (F2, second filial, generation) weren’t

all purple– _______– _______

Mendel’s Experiments

Parent

First filial

Second Filial

Crossed 2 F1 plants to get F2

3 purple

1 white

Mendel’s Principle of Dominance• Mendel noted that for each trait one form

dominates the other– In other words, the __________ trait prevents

the expression of the _______________ trait.• Ex. In peas, purple x white gives all purple

offspring– ____________________– ____________________

dominantrecessive

Purple = dominantwhite = recessive

Punnett Squares• Helps to predict the results of crosses

– all possible resulting offspring• & the probability of each offspring’s genes

• Ea. parent can contribute 1 of 2 genes for a trait (______)- found on homologous chromosomes– Represent with letters

• ________________ = dominant gene• ________________ = recessive gene• ________________ – alleles same

– ex. AA or aa

• ________________ – alleles different– ex. Aa

allele

CAPITALlowercase

homozygous

heterozygous

Genotype vs. Phenotype• ____________________ = actual

genetic make-up of individual– represented by letters

• __________ = outward (physical) expression of the genotype– (due to) the protein that is produced

• Ex. Let P = purple & p = white– Genotypes PP & Pp both have the

same phenotype (purple)• PP = ________________ dominant

• Pp = ________________________

– Genotype pp has (white) phenotype:• pp = ________________ recessive

genotype

phenotype

homozygousheterozygous

homozygous

Mendel’s Principle of Segregation• During gamete formation, the

pair of genes responsible for each trait separates so that each gamete receives only 1 gene for each trait.– happens during meiosis I when

homologous chromosomes line up (randomly) @ equator (metaphase 1) & separate (anaphase 1)

BA

b

Ba

b

Mendel’s Principle of Segregation

Mendel’s Principle of Segregation• tested segregation using

heterozygous purple flower & homozygous white flower– Predicted ______ purple &

______ white offspring b/c:

• P gene would combine w/ p gene _______ the time

– producing ___________ _____________ flowers

• p gene would combine w/ p gene _______ the time

– producing ___________ _____________ flowers

½ ½

½ heterozygous

purple

½ homozygous

white

Mendel’s Principle of Independent Assortment• Genes for different traits segregate independently

during gamete formation when they are located on different chromosomes…– What if they are on the same chromosome?

Genes on samechromosome

Genes on samechromosome

meiosis

Probability• The chance an event

will occur

• What is the chance of getting heads? Tails?– If you flip two coins, of

getting 2 heads? 2 tails?

– What is the chance of a couple having a boy? A girl? Of having four boys? Five girls?

Ratios• _______________________ = probable ratio of

genotypes in offspring of a cross– Ex. If cross Pp & Pp

• 1PP : 2Pp : 1 pp

• _______________________ = probable ratio of phenotypes resulting from the genotypic ratio

• Ex. If cross Pp & Pp• 3 purple : 1 white

• ________________________ = ratio expected based on probability (Punnett Square)

• ___________________ = what actually occurs– Why would these be different?

genotypic ratio

phenotypic ratio

expected ratio

observed ratio

Phenotypegenotype

Phenotypegenotype

Pp

Pp

Pp

Pp

P p

p P

Monohybrid Cross• a cross where __________________________

_______________________ (gene) is studied– ex. only height, flower color, eye color, etc...

T t

only onecharacteristic

Dihybrid Cross• involves study of inheritance patterns for

organisms differing in _____ (each w/ 2 forms).– Mendel determine if different traits of pea plants,

such as flower color & seed shape, were inherited independently.

Dihybrid Cross Animation

2 traits

Dihybrid Cross

2 traits with 2 forms

Test Cross• Used to determine

__________________

of dominant phenotype– Cross ______________

phenotype w/ ________ phenotype

• If any offspring show recessive trait, unknown parent heterozygous

• If all show dominant trait, then parent homozygous dominant

Show as P_

unknown genotype

dominantrecessive

Dominant/Recessive is Not Always the Mode of Inheritance

• Traits are not always as clearly defined as the 7 pea plant traits Mendel studied– Incomplete dominance– Codominance– Multiple alleles– Sex-linked inheritance– Polygenic inheritance

• Continuous variation

Incomplete Dominance• No allele is ________

__________________– results in _ phenotypes

– ________________, ___________ (mixed), __________________. • Genotypic & phenotypic

ratios same– ___________________– ___________________

– Ex. Pink four o’clock flowers

dominantover another

3“dominant” 1

intermediate“dominant” 2

1 CRCR : 2 CRCW : 1 CWCW

1 red : 2 pink : 1 white

Codominance• heterozygote

displays the protein products of both alleles __________

– Ex. Roan cow has a mixture of both red & white hairs.

equally

Multiple Alleles• More than ______ different forms of an allele

exist, but individual still has just 2.

• Ex. alleles that code for human blood types– A = ______– B = ______– O = ______– exhibit both codominance & multiple alleles

• (____ = ____) > _____•How many possible genotypes are there?

•How many phenotypes?

•Can you spot the blood type that is a product of codominance?

2

IA

IB

i

IA

IB i

antigen

antigen

antigens

No antigens

• Agouti rabbits– 4 alleles: C, cch, ch, c

– w/ dominance relationship to one another: _________________________________

• agouti rabbit (wild type)– Phenotype: brown, Genotype: CC, Ccch, Cch, or Cc

• “Chinchilla” (mutant)– Phenotype: silvery gray, Genotype: cchcch, cchch, or cchc

• “Himalayan” (mutant):– Phenotype: white w/ black points, Genotype: chch or chc

• “Albino” (mutant)– Phenotype: white, Genotype: cc

Multiple Alleles

C > cch > ch > c

Sex Determination• In humans chromosomes:

– Pairs 1 – 22 = _____________________________– 23rd pair determine gender = __________________

• ______________ = female• ______________ = male

What is the probability of having a son? A daughter?

autosomessex chromosomes

XX

XY

Sex-linked Inheritance• X & Y chromosomes not fully homologous

– X is bigger & carries more genes

• Males will have _____________________ for traits carried only on X– called _______________________________

• Ex.: – In Drosophila (fruit flies) eye color

– In humans ______________________________ &

___________________________________________

– X-linked traits more common in males• Why???

only 1 allele

X-linked or sex-linked

hemophilia

colorblindness

• Predictions made using Punnett square– Include sex of each parent– Consider the sex chromosomes & genes they

carry together as a unit…• ex. XG (= dominant gene), Xg (= recessive gene),

Y (= no gene)

Sex-linked Inheritance

XG female Xg

XG XG XG Xg

XG Y Xg Y

• Ex. In Drosophila (fruit flies) eye color– What are the sex, genotype, & phenotype of each

offspring?• Are there any female carriers for the white eye gene?

Sex-linked Inheritance

Heterozygous red-eyed

carrier for white eye allele

red-eyed

P generation genotypes were XRXR & XwY

Sex-linked Inheritance

– If mother is carrier & father has hemophilia:

• genotypic ratio?• phenotypic ratio?

– If mother is carrier & father is normal:

• Make a Punnett square– genotypic ratio?– phenotypic ratio?

•Hemophilia is X-linked recessive

• pedigree chart showing inheritance of hemophilia

– Does hemophilia affect one gender more often?

• Why?

Sex-linked Inheritance

• Colorblindness is X-linked recessive– In this Punnett square, what are

the genotypes & phenotypes of the parents?

Sex-linked Inheritance

Ishiharatest forred-greencolorblindness

Polygenic Inheritance• ______________

affect a single trait– shows range of

phenotypes from one extreme to another (_______ _____________)• Ex. in humans:

hair color, height, skin color

Many genes

continuousvariation

Expression of Genes• Genes can ________________________ to

control various other patterns of inheritance– Most characteristics that make up individual’s

phenotype not inherited in Mendelian patterns• Ex. Modifier genes affect eye color

– influence amount, intensity, & distribution of melanin (color pigment) in eye cells

interact w/ one another

• ______________ in which organism develops is another factor that affects expression– Probably due to how enzymes (proteins) operate at different

temperature• Higher temps may “deactivate” enzyme & prevent a reaction form

occurring (therefore, changing phenotype)

• Examples:– temp & size of fruit fly wings: Warmer temps = larger wings

& colder temps = smaller wings– __________: Low altitudes = taller & high altitudes = shorter– ____: Poor soil or drought may produce shorter (or no) ears– _______________: Green (dominant) & albino (recessive)…

• however green color is also affected by environment– No sunlight green color cannot be expressed due to lack of chlorophyll production– Put in light green will appear b/c chlorophyll being produced

Expression of GenesEnvironment

treescorntobacco seedlings

Human Genetic Disorders

Pedigree Charts• A family tree (chart) of genetic history

of family over several generations–Scientist or a genetic counselor would

find out about your family history & make this chart to analyze.• used to find out probability of a child having

a disorder in a particular family–To begin to interpret a pedigree, determine if

the disease or condition is autosomal or X-linked and dominant or recessive.

Pedigree Chart

Square = male

Circle = female

Shaded = studied trait

Marriage = horizontal line

Offspring = vertical line

• Due to DNA mutation (usually recessive) or chromosome abnormalities (# or structure)– Causes production of abnormal proteins

• Examples:– Autosomal recessive (***most genetic disorders)

» Cystic Fibrosis

» Sickle-cell Anemia

» Tay-Sachs Disease

– Autosomal dominant» Huntington’s Disease

– Sex-linked» Hemophilia

» Color Blindness

– Chromosomal abnormality» Down Syndrome (trisomy 21)

» Klinefelter’s Syndrome

Human Genetic Disorders

Autosomal Recessive• Must be homozygous b/c allele

needed to produce trait is recessive– Cystic Fibrosis

– Sickle-cell Anemia

– Tay-Sachs Disease

AA AS

AS SS

A female S

Autosomal Dominant• Can be homozygous or heterozygous b/c allele

needed to produce trait is dominant– Huntington’s Disease

Sex-linked Disorders•Hemophilia•Color blindness

Chromosomal Abnormalities• Affects # or

structure of chromosomes– #:

• Down Syndrome (trisomy 21… 3 copies of chromosome # 21)

– Cause non-disjunction (failure of paired chromosomes to separate during meiosis 1 or meiosis 2)

• Klinefelter’s Syndrome– Sex chromosome disorder

» Males have extra copy of the X chromosome *XXY (or 47, XXY b/c 47

total chromosomes)

» Cause non-disjunction (failure of paired chromosomes to separate during meiosis 1 or meiosis 2)

Detecting Abnormalities

Chromosomal Abnormalities• Affects # or

structure of chromosomes– Structure:

• Added, deleted, inverted, or translocated pieces

Detecting Abnormalities• Karyotyping

– “picture of human chromosomes”• From blood

sample– Can detect extra

chromosomes or chromosomal abnormalities (additions, deletions, inversions, translocations)

• Amniocentesis– sample of fluid

surrounding fetus (karyotype then made)

• Can detect Down Syndrome

– 14th + week of preg.

• Chorionic villus biopsy– sample of cells from

chorion (part of structure by which fetus linked to mother)

– 9th + week of preg.

Detecting Abnormalities

Review & Animations• Vocab interactive

– http://nortonbooks.com/college/biology/animations/ch10a02.htm

• Crosses– http://www.sonefe.org/online-biyoloji-dersleri/grade-12/monohybrid-

cross/

• Drag & drop genetics– http://www.zerobio.com/drag_gr11/mono.htm

• Various– http://www.abpischools.org.uk/page/modules/genome/dna4.cfm?

coSiteNavigation_allTopic=1

• Pedigrees– http://www.learnerstv.com/animation/animation.php?ani=13&cat=biology

• Genetic disorders– http://www.humanillnesses.com/original/Gas-Hep/Genetic-Diseases.html