Chapter 13 Alleles and Traits Blending inheritance Example Black and white horse will produce offspring Failed to explain how traits disappear over several generations and then unaltered ID: 526675
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Slide1
Patterns in Inherited Traits
Chapter 13Slide2
Alleles and Traits
Blending
inheritance
Example: Black and white horse will produce _________offspringFailed to explain how traits disappear over several generations and then _________________unaltered generations laterCharles Darwin did not accept this ideaGregor Mendel (____________________)Started breeding thousands of _______________________Kept detailed record of how traits passed from one ____________________to the nextBegan to formulate how _________________worksSlide3
Mendel’s Experiments
Garden
pea plant is
________-fertilizingThe flowers produce male and female _____________The experimentsControlled the pairings between individuals, by removing ___________________, with specific traits and observed traits of their _____________________________________fertilized plants and collected _____________Recorded traits of new pea plantsSlide4
Mendel’s Experiments
Started with garden pea plants that “
bred true
” for a particular trait _________________________________________________Cross-fertilized pea plants with different traits and offspring appeared in ___________________________________Concluded (correctly) that hereditary information is passed in discrete unitsSlide5
Inheritance in modern terms
Locus:
_______________________________________________
Homozygous: ____________________________________________Heterozygous: ___________________________________________Hybrids are _____________offspring of a cross between individuals that breed true for different forms of a traitDominant: Effect masks that of a recessive allele paired with itrepresented by italic _____________letters
Recessive: Effect is masked by a dominant allele paired with it
represented by italic
_____________________
letters
Genotype:
______________________________________________
Phenotype:
_________________________________Slide6Slide7Slide8
Allele distribution into gametes
A homozygous dominant pea plant with two alleles
(
____) has purple flowers, and a homozygous recessive pea plant with two alleles (___) has white flowersIf these ______________plants are crossed (PP × pp), all offspring will be _____________________All
____________________
(
F
1
) offspring will be heterozygous
Genotype =
_______
Phenotype =
__________________________Slide9
zygote (
Pp
)
gametes (
p
)
meiosis II
gametes (
P
)
DNA replication
meiosis I
1
2
3Slide10
Punnet square
A grid used to predict the
_____________ and _________________ outcome
of a cross
male gametes
female gametesSlide11
Testcross
__________________________________________________
An individual that has a dominant trait (but
an unknown genotype [PP/Pp]) is crossed with one that is homozygous recessive_________Results?Slide12
Monohybrid cross
Breeding experiment in which individuals identically
____________________for
_______gene are crossed (Pp×Pp)Frequency of traits among offspring in the ________________ offers information about the dominance relationship between the alleles First generation = _______Second generation = ________Results? (Ratio, %)Slide13
Mendel’s Seven Pea Plant TraitsSlide14
Monohybrid cross
https://
www.youtube.com/watch?v=EYYc7z4yX38Slide15
Law of segregation
The 3:1 phenotype ratios in F
2
offspring of monohybrid crosses became the basis of __________________________________cells carry pairs of genes on each pair of __________________________________The two genes of each pair are ______________from each other during meiosis so that they end up on ___________ gametesSlide16
Dihybrid cross
Individuals
___________________for
alleles of _______genes (dihybrids) are crossed, and the traits of the offspring are observedFrequency of traits among the _____________offers information about the ___________relationships between the paired allelesSlide17
Dihybrid cross
One parent plant that breeds true for purple flowers and tall stems
(
______) is crossed with one that breeds true for white flowers and short stems (________)Each plant makes only one type of gamete (________)All F1 offspring will be dihybrids (________) and have purple flowers and tall stems
Punnett square
PT×ptSlide18
Dihybrid cross
The result of two F
1
plants crossing: a dihybrid cross (PpTt × PpTt)Four types of gametes can combine in sixteen possible waysPunnett squareSlide19
Dihybrid cross
In F
2
plants, four phenotypes result in a ratio of ________________________________________________________________________________________________________________________________________________Go back and check results!Slide20
Law of Independent Assortment
Mendel discovered the 9:3:3:1 ratio in his dihybrid experiments
Each trait still kept its individual 3:1 ratio
Each trait sorted into gametes ______________of other traits During meiosis, members of a pair of genes on homologous chromosomes get distributed into gametes independently of other gene pairsSlide21
Contribution of Crossovers
How two genes get sorted into gametes depends on if they are found on same chromosome
Random assortment
Genes on one chromosome assort into gametes independent of genes on other chromosomesLinkage group – all genes on a chromosomeGenes that are far apart on a chromosome tend to assort into gametes independentlyGenes very close together on a chromosome are linked They do not assort independently because crossing over rarely happens between themSlide22
Patterns of Inheritance
Simple/Complete
dominance
A dominant allele fully masks the expression of a recessive oneOther patterns of inheritance are not so simple:CodominanceIncomplete dominanceEpistasisPleiotropySlide23
Codominance
Two alleles that are
both
fully expressed in heterozygous individualsMultiple allele systems – gene for which three or more alleles persist in a populationExample: an ABO gene for blood type, human hair/eye color. Slide24
Codominance
Which two of the three alleles of the
ABO
gene you have determines your blood typeThe A and the B allele are codominant when pairedGenotype AB = blood type ABThe O allele is recessive when paired with either A or B
Genotype
AA or AO
= blood type A
Genotype
BB or BO
= blood type B
Genotype
OO
= blood type OSlide25
Genotype:
Phenotype:
A
AB
B
O
AA
or
AO
AB
BB
or
BO
OOSlide26
Incomplete dominance
One allele is not fully dominant over
another
The heterozygous phenotype is between the two homozygous phenotypes (example: red×white=pink)In snapdragons, one allele (R) encodes an enzyme that makes a red pigment, and allele (r) makes no pigment RR = red; Rr = pink; rr = whiteA cross between two pink (Rr × Rr) yields red, pink, and white in a 1:2:1 ratio Slide27
Epistasis
T
he
effect in which a trait is influenced by the products of multiple genesExample: Fur color in dogsB=__________, b=___________E=colour in fur, e=reduced colour in fur Slide28
Pleiotropy
__________________________________________________
Mutations in pleiotropic genes are associated with complex genetic disorders
Sickle-cell anaemia: a severe hereditary form of anemia (deficiency of red blood cells) in which a mutated form of ________________distorts the red blood cells into a crescent shape at low oxygen levelsCystic fibrosis: a hereditary disorder affecting the _______________. It causes the production of abnormally thick __________, leading to the blockage of the pancreatic ducts, intestines, and bronchi and often resulting in ________________________.
Marfan
syndrome:
a hereditary disorder of
____________________,
resulting in abnormally long and thin digits and also frequently in optical and cardiovascular defectsSlide29
Environment and Phenotype
Epigenetic research is revealing that environment can influence
phenotype
Some examples of environmental effects____________________________________________________________________________________________________________________Slide30
Short tandem repeats
Some genes have regions of DNA in which a series of two to six nucleotides is repeated hundreds or thousands of times in a row
Example: 12 alleles of homeotic gene that influence face length in dogs
___________________________________________________Slide31
Continuous variation
Some traits appear in two or three
forms
Example: _________________________________________Others occur in a range of small differencesExample: __________________________________________The more genes and environmental factors that influence a trait, the more continuous the variationIf a trait varies continuously, it will have ________________ curveSlide32
Cystic fibrosis
Most common fatal genetic disorder in
the U.S
. Most CF patients live no more than _______________The CFTR gene encodes a protein Protein moves chloride ions out of ________________________Binds disease-causing bacteriaOccurs in people __________________for a mutated allele of CFTR gene (______________________) The allele of CF has a 3 base pair deletionCalled ΔF508 because protein is missing the normal 508th amino acid
People with CF inherit 2 copies of ΔF508
The deletion causes mucus to accumulate, making breathing difficultSlide33