AIII. Inheritance (Mendel’s Law of Inheritance) Flashcards
1
Q
The question of how hereditary material (?) itself was one of the most baffling problems of biology for many years. Generations of biologists attempted in vain to solve this problem and to answer the question “Why are the offspring of the species undeniably of the species?”.
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duplicates
2
Q
Many though that the chemical basis for heredity lay in the structure of (?). But no one was able to provide evidence showing how it could reproduce itself.
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proteins
3
Q
The answer to the heredity question was finally found in the structure of (?). The unit structure of all living things is the (?).
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nucleic acids
cell
4
Q
Suspended in the nuclei of the cells are (?), which consist largely of proteins and nucleic acids.
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chromosomes
5
Q
Since genes are carried on chromosomes, knowledge of (?) has far-reaching implications for basic genetics, human health, and evolution.
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chromosome number and structure
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Q
− Alternative forms of the same gene
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Alleles
7
Q
− Alleles for a trait are located at corresponding positions on
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homologous chromosomes
8
Q
– chromosomes that have the same genetic information (genes)
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• Homologous chromosomes
9
Q
• Homologous chromosomes Example:
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gene for hair texture exists as two alleles (e.g. one curly code, and one straight code)
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Q
− The genes present in the DNA of an organism
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Genotype
11
Q
− The combination of genes
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genotype
12
Q
− It designates the genetic or hereditary make-up of an organism
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genotype
13
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− Uses a pair of letters (example: Tt or YY or ss, etc.) to represent genotypes for one particular trait
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genotype
14
Q
− There are always two letters in the (?) as a result of sexual reproduction
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genotype
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− How the trait physically shows up in the organism
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Phenotype
16
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− It is the outward appearance of an organism as the result of gene action
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Phenotype
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− Examples: Blue eyes, brown fur, striped fruit, yellow flowers, curly hair, etc
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phenotypes
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Q
− A genetic condition where an individual inherits the same alleles for a particular gene from both parents
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Homozygous
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Q
− A pair of identical genes
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Homozygous
20
Q
− Represented by two capital or two lowercase letters in the genotype (example: TT or tt)
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Homozygous
21
Q
− Sometimes the word “pure” is used instead of homozygous
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Homozygous
22
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− Refers to a pair of genes where one is dominant and one is recessive
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Heterozygous
23
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− The paired genes are different or contrasting
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Heterozygous
24
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− Having the two alleles at corresponding loci on homologous chromosomes different for one or more loci
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Heterozygous
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− Represented by one capital letter and one lowercase letter (example: Tt)
Heterozygous
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− Can also be referred to as HYBRID
Heterozygous
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− One that is manifested, plainly shown and readily perceived by the senses
Morphological Trait
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− Example: Y – yellow; y – green
Morphological Trait
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Morphological Trait
• Dominant –
• Recessive –
upper case
lower case
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– one that can be perceived only by means of special methods that enable differences between molecules to be visualized
• Molecular trait
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GENOTYPE PHENOTYPE
Yy Yellow
yy Green
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A cross of only one trait
Monohybrid cross
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Can be used to show law of dominance and segregation
Monohybrid cross
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The character/s being studied in monohybrid cross are governed by two or multiple alleles
single locus
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a mating between two individuals with different alleles at one genetic locus of interest
Monohybrid cross
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A cross of two traits
Dihybrid cross
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Can be used to show law of independent assortment
Dihybrid cross
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describes a mating experiment between two organisms that are identically hybrid for two traits
Dihybrid cross
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one that is heterozygous, which means that it carries two different alleles at a particular genetic position or locus
hybrid
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The mating of two individuals, organisms or strains that have different gene pairs that determine three specific traits or in which three particular characteristics or gene loci are being followed.
Trihybrid cross
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Demonstrates that Mendel’s principles apply to inheritance of multiple traits.
Trihybrid cross
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− Transmitted on unbroken descent
Autosomal dominant
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• 50% mutant gene; Autosomal dominant
− Heterozygote and homozygous recessive
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− Between two heterozygotes • Severe conditions are unlikely to be passed on
Autosomal recessive
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− Transmitted by a long line of carriers
Autosomal recessive
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− ¼ chance
Autosomal recessive
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− Common in in-breeding
Autosomal recessive
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• Severe conditions are unlikely to be passed on
− Between two heterozygotes
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− The chance that both maternal and paternal alleles at one locus are identical by descent
Coefficient of In-breeding
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− The proportion of all the individual’s genes are homozygous because of identity by common descent
Coefficient of In-breeding
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Case example: F = ½ x ½ x ½ x ½ = 1/16
Coefficient of In-breeding
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The Independent Assortment
Mendel’s Postulate
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• Where two characteristics behave completely independently of each other
The Independent Assortment
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• Uses the dihybrid cross (aka: 2 factor cross)
The Independent Assortment
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• Produces a 9:3:3:1 ratio – applies the principle of probability
The Independent Assortment
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− The Mendel’s Law of Probability allows us to easily calculate probability, of genotypes and phenotypes among the offspring
Principle of Probability
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− The probability of an impossible event is
0
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− The probability of a certain event is
1
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− If the probability of event is x = (?) then the probability of ‘not x’ = (?)
p
1-p
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− The probability of two independent events occurring is the product of their two individual probabilities
Principle of Probability
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− “when two independent events occur simultaneously, the combined probability of the two outcomes is equal to the product of their individual probabilities of occurrence.”
Product Law
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− Example: Ex. (3/4)(3/4) = 9/16
Product Law
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− He is an Augustinian priest from Czechoslovakia (in some books, Gregor Mendel is an Austrian monk)
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− Studied varieties of peas (WV– self-fertilization and cross-fertilization
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− His study among plants lasted from 1856-1868; the result of his studies was later published in 1866
Gregor Mendel
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− is known as the Father of Genetics
Gregor Mendel
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− The study of inheritance from generation to generation is known as
“transmission genetics”
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transmission genetics is also called as
“Mendelian genetics”
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each of the parental factors remained unchanged and it was passed from one generation to the next
Factors in pairs
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Factors in modern times are the
Genes
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“true breeding” varieties in which the plants produced only progeny like themselves when allowed to selffertilize
Factors
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When 2 varieties that differ in one or more traits are cross ed, the progeny constitute a hybrid between the parental varieties
Factors
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Crosses in which parental varieties differ in one, two, or three traits of interest (e.g. monohybrid, dihybrid, trihybrid)
Factors
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Why did Gregor Mendel choose peas?
They grow quickly
They reproduce by self-pollination
They possess characteristics that are easily recognized
Their pollination can be controlled
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Tall = S
Short = s
Stem length
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Axial = T
Terminal = t
Flower position
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Round = R
Wrinkled = r
Seed shape
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Yellow = G
Green = g
Seed color
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Colored = W
White = w
Seed coat color
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Inflated = C
Constricted = c
Pod shape
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Green = Y
Yellow = y
Pod color
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He started by performing artificial pollination between pure tall plants and plants that were short – the result: all plants grew
tall
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He repeated using pure tall plants and pure short plants – the result: all plants grew
tall
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− the result from a cross between two pure breeding plants
F1 generation
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− The traits that appear in the F1 generation are
Dominant
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− The traits that are hidden were called
Recessive
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Mendel’s Experiment
He replanted the peas from the hybrids (results of a cross between parents differing in one or more traits)
Result: [?] tall and [?] short (ratio: 3 dominant is to 1 recessive; [?])
75%
25%
3:1
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− comprised of offspring(s) resulting from a cross of the members of F1 generation.
F2 generation
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− Recessive trait usually reappears
F2
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The [?] expresses only the dominant trait
F1 hybrid
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The [?] reappeared again in the F2 generation
F1 generation
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The [?] in some plants show the dominant and others the recessive trait
F2 generation
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In Mendel’s work, there are [?] as many plants with the dominant trait as plant with the recessive trait
3x
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Mendel’s Postulates:
Unit Factors in Pairs
Dominance and Recessiveness
Segregation
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− “Genetic characters are controlled by unit factors that exist in pairs in individual organisms”
Unit Factors in Pairs
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“When 2 unlike unit factors responsible for a single character are present in a single individual, one unit factor is dominant to the other and the other is recessive.”
Dominance and Recessiveness
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“During the formation of gametes, the paired unit factors separate or segregate randomly so that each gamete receives one or the other with equal likelihood.”
Segregation
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o During the formation of gametes (Meiosis or Gametogenesis), the two alleles responsible for a trait separate from each other.
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o Alleles for a trait are then "recombine" at fertilization, producing the genotype for the traits of the offspring.
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o For every given trait, an organism must inherit one factor from the sperm and one from the egg
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o Each sperm or egg cell contains one hereditary factor for each trait
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o Therefore, a new organism receives one factor for each trait from each parent
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o The combination of one factor is not altered by the presence of another factor or a pair.
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o Mendel noticed during all his work that the height of the plant and the shape of the seeds and the color of the pods had no impact on one another
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o In other words, being tall didn't automatically mean the plants had to have green pods, nor did green pods have to be filled only with wrinkled seeds
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o The different traits seem to be inherited INDEPENDENTLY or they are inherited as independent units
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o Alleles for different traits are distributed to sex cells (& offspring) independently of one another.
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o Alleles on different chromosomes are distributed randomly to individual gametes.
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o He claimed that each pea plant has a pair of hereditary factors for each trait
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o These factors are now called genes
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o The genes of one characteristic were not influenced by the genes for any other characteristics
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o The separation of gene pairs in a given pair of chromosomes and the distribution of the genes to gametes during meiosis are entirely independent of the distribution of other gene pairs in other pairs of chromosomes
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o When Mendel crossed plants that have pure traits with plants having seven other traits, all offspring showed only one form of the trait
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o It appeared that for each trait, one was stronger than the other (dominant)
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o Mendel also noted that the first hybrid generation always resembled only one of its parents
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The recessive trait showed in about ¼ of the second generation traits
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A dominant allele completely masks the expression of a recessive allele.
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A dominant allele produces the same phenotype in heterozygotes and in homozygotes.
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When pure parents with opposite traits are mated, the F1 generation shows only one trait (dominant) the other trait (recessive) is hidden
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Invented by Reginald Punnett
Punnett Square
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Can be used to determine the possible combination of genes in a cross
Punnett Square
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Importance of the Punnett Square:
They can be used as predictive tools when considering having children
They are used as standard tools by genetic counselors; the likelihood of inheriting many traits, including useful ones can be predicted using them
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Importance of the Punnett Square Examples:
-cystic fibrosis is genetically inherited disease which afflicts only those who are [?]
-Polydactyly, Huntington disease, achondroplastic dwarfism are disorders caused by [?]
-homozygous recessive
-dominant allele
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-Inheriting just one copy of such a [?] will cause the disorder
-[?] chance of inheriting the disorder and [?] of being entirely normal
dominant allele
50%
50%
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Mendel carried out his pathbreaking research in relative obscurity. He studied the inheritance of [?] in peas, which he grew in the [?] garden. His method involved [?] plants that showed different traits example, short plants were bred with tall plants to see how the traits were inherited by the offspring.
-different traits
-monastery
-interbreeding
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Mendel ’s careful analysis enabled him to discern patterns, which led him to postulate the existence of [?] responsible for the traits he studied. We now call these factors as [?].
-hereditary factors
-genes
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The type of analysis that [?] pioneered was applied to many kinds of organisms, and with notable success. Of course, not every result fit exactly with Mendel’s principles. Exceptions were encountered, and when they were investigated more fully, new insights into the behavior and properties of genes emerged.
Mendel
