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Unit 6: Genetics & Heredity Ch 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. 7. - PowerPoint PPT Presentation
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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