Don't forget to check out the Videos/Websites section (Chapter 16 - Mendelian Genetics) for great review on the topics covered :)
unit_3_mendelian_genetics_ch_16.docx | |
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Objective Sheet in file above
Unit 3: Mendelian Genetics. Chapter 16. Starting on p. 524.
Objective 1
Heredity - the passing of genetic traits such as the color
of hair or eyes from one generation to the next, resulting in similarities
between members of one family or strain.
genetics - the branch of Biology dealing with the principles of variation and inheritance
in organisms; how traits are passed from generation to generation.
Objective 2
Unit characters - a term describing Mendel’s “factors” of inheritance (genes) which are inherited as independent units.
Unit theory of inheritance - a term describing Mendel’s laws of inheritance, from his discovery that genes (which he termed factors) are inherited as independent units.
Objective 3 - terminology
•allele - alternate form of a gene
•Different copies or forms of a gene controlling a certain trait are called alleles (B or b)
•If alleles for a certain trait in an organism are the same they are homozygous (BB or bb), if they are different they are heterozygous (Bb).
•dihybrid cross - cross of two heterozygous individuals that differ in two traits (AaBb X AaBb)
•dominant - type of trait, in which the characteristic is always expressed, or appears, in an individual.
•F1 generation - the first filial generation, offspring from the cross of the P(parent) generation.
•F2 generation - the second filial generation, offspring from the cross of the F1 generation
•filial generation - offspring of a cross of parent generations; the F2 generation or subsquent generations.
•Gene - a specific sequence of DNA that governs the expression of a particular trait and can be passed to an offspring
•genotype - genetic make-up of an organism; remains constant throughout an individual’s life. Usually indicated by the combination of letters in a Punnett square (BB, Bb, or bb)
•Heredity - the passing of genetic traits such as the color of hair or eyes from one generation to the next, resulting in similarities between members of one family or strain.
•Heterozygous - describes an individual with two different alleles at a locus.
•Hybrid - an organism heterozygous for a trait.
•Homozygous - describes an individual with two alleles at one locus that are identical.
•Inherited - having certain physical traits that are transmitted from one generation to the next
•law of segregation – Mendel’s first law of inheritance, in which the hereditary traits are determined by pairs of alleles from each parent. These alleles separate during gamete formation, giving each offspring only one allele from each parent.
•Mendelian ratio - ratio of dominant phenotype (homozygous dominant genotype and heterozygous genotypes) to recessive phenotype (homozygous recessive phenotype) of 3:1.
•monohybrid - a cross of two heterozygous individuals that differ in one trait; for example Aa X Aa
•P generation - the designation for the parent generation
•phenotype - the physical and physiological traits of an organism. Physical traits of an organism which are resultant from its genotype are called its phenotype (brown/blue eyes).
•principle of dominance - when individuals of contrasting traits are crossed, the offspring will express only the dominant trait.
•Punnett square - simple grid used to illustrate all possible combinations of gametes from a given set of parents.
•Purebred - having descended from ancestors of a distinct type, or breed. Purebred organisms in a given species or variety all share similar traits.
•Recessive - having an allele that is latent (present but inactive) and therefore is not usually expressed unless there is no dominant allele present.
•Traits - distinguishing characteristics or phenotypic features of an individual
•true breeding - organisms that are homozygous for a particular trait or set of traits and produce like offspring.
Objective 4 - The Study of Heredity
•Zygote formed from two gametes, one contributed by each parent
•Chromosomes of each gamete bring hereditary material to the new cell
•Hereditary material controls development and characteristics of the embryo and since material comes from two parents, offspring will be the same and differ from parents
•Genetics is the branch of biology that studies the ways in which hereditary information is passed from parents to offspring
Mendel's Experiment - (can also refer to class notes)
•Gregor Mendel was a monk who lived in town of Brunn (Czechoslovakia), teaching science at a high school, he experimented from 1857
to 1856 in the monastery garden on certain traits in pea plants
•Pea plants suitable for genetics experiment:
–Easy to grow
–Sharp contrast in traits (some tall, some short etc)
–Self pollination makes it easy to control, reduces cross pollination
•Mendel cross pollinated different plants and observed carefully the results
•Through mathematics he came to his results and published paper in the journal of his local scientific society
•In 1900 scientists came to same conclusions Mendel had, concerning heredity
Principle of Dominance
•Mendel noticed plants which self pollinated for several generations remained short. Came to conclusion they were pure short
•When Mendel crossed pure short plants with pure tall plants, all plants were tall
•Mendel let these plants (first filial/F1Generation) self pollinate to determine if short plants were lost forever, discovered F2 Generation was ¾ tall and ¼ short
•Mendel discovered traits shown in F1 Generation to be dominant and traits hidden to be recessive
Principle of Dominance states: when an organism is hybrid for a pair of contrasting traits, only the dominant trait
can be seen in the hybrid.
•Principle of dominance – when organisms with contrasting traits are crossed, the offspring will express only the dominant trait
• Mendel showed this when he crossed TT (tall) x tt (short) and all the offspring were tall (Tt). When the allele for the dominant trait
is present, that trait is the one that is expressed.
Law of Segregation
•Mendel hypothesized that each trait was controlled by a pair of factors
•He stated there was a factor for tallness and for shortness, with one being dominant and one recessive, in a cross, both factors are present, but only the dominant factor's trait is shown, but the recessive factor is still present so may be seen in future generations
•Law of Segregation states: factors that occur in pairs are separated from each other during gamete formation and
recombined at fertilization
Law of segregation – Mendel’s first law of inheritance, in which the hereditary traits are determined
by pairs of alleles from each parent. These alleles separate during gamete formation, giving each offspring
only one allele from each parent.
** If that didn’t happen, a DD could never result in future generations being
recessive…
D D D d
d Dd Dd D DD Dd
d Dd Dd d Dd dd**
•Mendel’s conclusions that led to the law of segregation:
•Each parent has two alleles (Mendel called them ‘factors’)
•Only one factor from each parent is received by the offspring (1+1 = 2 alleles =trait)
/ / (eye trait) \ \(height trait) two pairs of homologous chromosomes
XX XX each one replicated
meiosis 1:
XX XX two cells, each with 2 doubled chromosomes; each cell has one doubled chromosome for eyes, and one for height.
meiosis 2:
/ \ / \ / \ /\ four cells, each with 2 single chromosomes(one from each homologous pair); one for eyes, and one for height)
Objective 4C - Law of independent assortment
•Mendel - Two Trait Cross
•At first, one trait at a time
•however, organisms have many traits
•How are two or more traits inherited?
•wondered if inheriting one trait influenced inheritance of a different trait
•EX. Did pea shape influence pea color?
•His steps:
•produced purebreds (as he did in the first experiment)
•homozygous dominant for both traits: round and yellow (RRYY)
•homozygous recessive for both traits: wrinkled and green (rryy)
•Observing two traits in the cross
F1 : All round and yellow seeds (RrYy)
•all heterozygous for both traits
•Cross the F1's RrYy X RrYy (dihybrid cross)
•F2 generation: 9:3:3:1 phenotypic ratio
•9 round and yellow, 3 round and green, 3 wrinkled and yellow, one wrinkled and green
•page 537 – let’s do the cross
•This consistent ratio is explained if both traits were inherited independently of each other
I
Unit 3: Mendelian Genetics. Chapter 16. Starting on p. 524.
Objective 1
Heredity - the passing of genetic traits such as the color
of hair or eyes from one generation to the next, resulting in similarities
between members of one family or strain.
genetics - the branch of Biology dealing with the principles of variation and inheritance
in organisms; how traits are passed from generation to generation.
Objective 2
Unit characters - a term describing Mendel’s “factors” of inheritance (genes) which are inherited as independent units.
Unit theory of inheritance - a term describing Mendel’s laws of inheritance, from his discovery that genes (which he termed factors) are inherited as independent units.
Objective 3 - terminology
•allele - alternate form of a gene
•Different copies or forms of a gene controlling a certain trait are called alleles (B or b)
•If alleles for a certain trait in an organism are the same they are homozygous (BB or bb), if they are different they are heterozygous (Bb).
•dihybrid cross - cross of two heterozygous individuals that differ in two traits (AaBb X AaBb)
•dominant - type of trait, in which the characteristic is always expressed, or appears, in an individual.
•F1 generation - the first filial generation, offspring from the cross of the P(parent) generation.
•F2 generation - the second filial generation, offspring from the cross of the F1 generation
•filial generation - offspring of a cross of parent generations; the F2 generation or subsquent generations.
•Gene - a specific sequence of DNA that governs the expression of a particular trait and can be passed to an offspring
•genotype - genetic make-up of an organism; remains constant throughout an individual’s life. Usually indicated by the combination of letters in a Punnett square (BB, Bb, or bb)
•Heredity - the passing of genetic traits such as the color of hair or eyes from one generation to the next, resulting in similarities between members of one family or strain.
•Heterozygous - describes an individual with two different alleles at a locus.
•Hybrid - an organism heterozygous for a trait.
•Homozygous - describes an individual with two alleles at one locus that are identical.
•Inherited - having certain physical traits that are transmitted from one generation to the next
•law of segregation – Mendel’s first law of inheritance, in which the hereditary traits are determined by pairs of alleles from each parent. These alleles separate during gamete formation, giving each offspring only one allele from each parent.
•Mendelian ratio - ratio of dominant phenotype (homozygous dominant genotype and heterozygous genotypes) to recessive phenotype (homozygous recessive phenotype) of 3:1.
•monohybrid - a cross of two heterozygous individuals that differ in one trait; for example Aa X Aa
•P generation - the designation for the parent generation
•phenotype - the physical and physiological traits of an organism. Physical traits of an organism which are resultant from its genotype are called its phenotype (brown/blue eyes).
•principle of dominance - when individuals of contrasting traits are crossed, the offspring will express only the dominant trait.
•Punnett square - simple grid used to illustrate all possible combinations of gametes from a given set of parents.
•Purebred - having descended from ancestors of a distinct type, or breed. Purebred organisms in a given species or variety all share similar traits.
•Recessive - having an allele that is latent (present but inactive) and therefore is not usually expressed unless there is no dominant allele present.
•Traits - distinguishing characteristics or phenotypic features of an individual
•true breeding - organisms that are homozygous for a particular trait or set of traits and produce like offspring.
Objective 4 - The Study of Heredity
•Zygote formed from two gametes, one contributed by each parent
•Chromosomes of each gamete bring hereditary material to the new cell
•Hereditary material controls development and characteristics of the embryo and since material comes from two parents, offspring will be the same and differ from parents
•Genetics is the branch of biology that studies the ways in which hereditary information is passed from parents to offspring
Mendel's Experiment - (can also refer to class notes)
•Gregor Mendel was a monk who lived in town of Brunn (Czechoslovakia), teaching science at a high school, he experimented from 1857
to 1856 in the monastery garden on certain traits in pea plants
•Pea plants suitable for genetics experiment:
–Easy to grow
–Sharp contrast in traits (some tall, some short etc)
–Self pollination makes it easy to control, reduces cross pollination
•Mendel cross pollinated different plants and observed carefully the results
•Through mathematics he came to his results and published paper in the journal of his local scientific society
•In 1900 scientists came to same conclusions Mendel had, concerning heredity
Principle of Dominance
•Mendel noticed plants which self pollinated for several generations remained short. Came to conclusion they were pure short
•When Mendel crossed pure short plants with pure tall plants, all plants were tall
•Mendel let these plants (first filial/F1Generation) self pollinate to determine if short plants were lost forever, discovered F2 Generation was ¾ tall and ¼ short
•Mendel discovered traits shown in F1 Generation to be dominant and traits hidden to be recessive
Principle of Dominance states: when an organism is hybrid for a pair of contrasting traits, only the dominant trait
can be seen in the hybrid.
•Principle of dominance – when organisms with contrasting traits are crossed, the offspring will express only the dominant trait
• Mendel showed this when he crossed TT (tall) x tt (short) and all the offspring were tall (Tt). When the allele for the dominant trait
is present, that trait is the one that is expressed.
Law of Segregation
•Mendel hypothesized that each trait was controlled by a pair of factors
•He stated there was a factor for tallness and for shortness, with one being dominant and one recessive, in a cross, both factors are present, but only the dominant factor's trait is shown, but the recessive factor is still present so may be seen in future generations
•Law of Segregation states: factors that occur in pairs are separated from each other during gamete formation and
recombined at fertilization
Law of segregation – Mendel’s first law of inheritance, in which the hereditary traits are determined
by pairs of alleles from each parent. These alleles separate during gamete formation, giving each offspring
only one allele from each parent.
** If that didn’t happen, a DD could never result in future generations being
recessive…
D D D d
d Dd Dd D DD Dd
d Dd Dd d Dd dd**
•Mendel’s conclusions that led to the law of segregation:
•Each parent has two alleles (Mendel called them ‘factors’)
•Only one factor from each parent is received by the offspring (1+1 = 2 alleles =trait)
/ / (eye trait) \ \(height trait) two pairs of homologous chromosomes
XX XX each one replicated
meiosis 1:
XX XX two cells, each with 2 doubled chromosomes; each cell has one doubled chromosome for eyes, and one for height.
meiosis 2:
/ \ / \ / \ /\ four cells, each with 2 single chromosomes(one from each homologous pair); one for eyes, and one for height)
Objective 4C - Law of independent assortment
•Mendel - Two Trait Cross
•At first, one trait at a time
•however, organisms have many traits
•How are two or more traits inherited?
•wondered if inheriting one trait influenced inheritance of a different trait
•EX. Did pea shape influence pea color?
•His steps:
•produced purebreds (as he did in the first experiment)
•homozygous dominant for both traits: round and yellow (RRYY)
•homozygous recessive for both traits: wrinkled and green (rryy)
•Observing two traits in the cross
F1 : All round and yellow seeds (RrYy)
•all heterozygous for both traits
•Cross the F1's RrYy X RrYy (dihybrid cross)
•F2 generation: 9:3:3:1 phenotypic ratio
•9 round and yellow, 3 round and green, 3 wrinkled and yellow, one wrinkled and green
•page 537 – let’s do the cross
•This consistent ratio is explained if both traits were inherited independently of each other
I
Law of Independent Assortment - P. 536
•During Meiosis, genes for different traits are separated and distributed to gametes independently of one another
•Dihybrid cross - 9:3:3:1 ratio every time
•Therefore alleles for traits are not inherited together
•Mendel’s second law of inheritance (Law of Independent assortment) states that inheritance of alleles for one trait does not affect the inheritance of alleles for another trait •offspring may have new combinations not present in either parent
•another example: dark hair brown eyed man and light hair blue eyed woman can have dark hair and blue eyed child
•During Meiosis, genes for different traits are separated and distributed to gametes independently of one another
•Dihybrid cross - 9:3:3:1 ratio every time
•Therefore alleles for traits are not inherited together
•Mendel’s second law of inheritance (Law of Independent assortment) states that inheritance of alleles for one trait does not affect the inheritance of alleles for another trait •offspring may have new combinations not present in either parent
•another example: dark hair brown eyed man and light hair blue eyed woman can have dark hair and blue eyed child
obj_5_1_trait_punnett_square_2014.docx | |
File Size: | 14 kb |
File Type: | docx |
monohybrid_and_dihybrid_punnett_squares.docx | |
File Size: | 12 kb |
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genetics_problem_solving-_worksheet_3_practise.docx | |
File Size: | 16 kb |
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Answers to the above practice problems are posted on the whiteboard in the General Science Lab next to the door :)
Beyond Mendel’s Laws – p. 541 (Objective 6 & 7)
Some organisms do not follow Mendel's Laws for heredity
Incomplete Dominance
Some organisms do not follow Mendel's Laws for heredity
- Incomplete Dominance, Co-dominance,
and Multiple Alleles
- Mendel found that traits were either
dominant or recessive
- this means, that whenever a dominant
allele is present, it is expressed
- some organisms however, show
exceptions to that rule
Incomplete Dominance
- in some cases, neither allele is
dominant
- results in blending if the two traits appear together
- When both alleles contribute to produce a trait that is not exactly
like either parent, known as incomplete dominance
- Ex. When a red flower is crossed with a white flower, pink flowers
are produced. In the F2 Generation, ¼ will be red, ½ pink and ¼
white
- often found in species of plants. ex. Snapdragon
- white and red snapdragon flowers are
homozygous, while pink is heterozygous
- RR - red
- R’R’ - white (instead of lower case,
since white is not recessive)
- RR’ - pink
- Refer to crosses on page 541.
beyond_mendel_worksheet_2014.docx | |
File Size: | 14 kb |
File Type: | docx |
Multiple Alleles - Objective 6C - p. 542
•many genes have more than two alleles
•multiple alleles - pattern of inheritance when a gene may have more than two alleles for any given trait.
•examples: blood types, skin color, eye color
•end up with several variations of phenotypes (ex. Eye color: blue, brown, hazel, green)
•multiple alleles can be influenced by environmental factors, such as diet and climate.
•ex. It is important that anyone with a genetic disorder know the effects of diet or other behaviour on the symptoms (ex. A person genetically predisposed to have diabetes may delay or prevent diabetes by eating healthy and exercising)
•Three alleles involved: A, B, and O •Each person has two of the three alleles
•alleles IA, IB, and i
•IA & IB are dominant over i
•But, IA & IB are co-dominant
•possible blood types:
•IAIA - Type A (homozygous dominant)
•IAi - Type A (heterozygous)
•IBIB - Type B (homozygous dominant)
•IBi - Type B (heterozygous)
•IAIB - Type AB (co-dominant)
•ii - Type O (homozygous recessive)
•many genes have more than two alleles
•multiple alleles - pattern of inheritance when a gene may have more than two alleles for any given trait.
•examples: blood types, skin color, eye color
•end up with several variations of phenotypes (ex. Eye color: blue, brown, hazel, green)
•multiple alleles can be influenced by environmental factors, such as diet and climate.
•ex. It is important that anyone with a genetic disorder know the effects of diet or other behaviour on the symptoms (ex. A person genetically predisposed to have diabetes may delay or prevent diabetes by eating healthy and exercising)
•Three alleles involved: A, B, and O •Each person has two of the three alleles
•alleles IA, IB, and i
•IA & IB are dominant over i
•But, IA & IB are co-dominant
•possible blood types:
•IAIA - Type A (homozygous dominant)
•IAi - Type A (heterozygous)
•IBIB - Type B (homozygous dominant)
•IBi - Type B (heterozygous)
•IAIB - Type AB (co-dominant)
•ii - Type O (homozygous recessive)
multiple_allele_practise_problems.docx | |
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In-class activity - Mini Lab. P. 531
Objective 9 & 10 - p. 534 - Test Cross
•How can you determine if an organism is homozygous dominant or heterozygous?
•“normal-sized” malamute dogs are dominant to dwarf dogs. How can you tell if a normal-sized dog is homozygous or heterozygous?
•Cross of an individual of unknown genotype with a (known) homozygous recessive individual
•Used to determine whether or not an organism with a dominant trait is heterozygous or homozygous
•If the ‘unknown’ is homozygous, all offspring will show dominant trait.
•If a recessive offspring results (in this case, 50% should be recessive), the unknown genotype has to be heterozygous
•If a tall plant (either TT or Tt) is mated with a short plant (tt), if any of the offspring is short then the unknown organism must be heterozygous.
•If the offspring is tall then it is either heterozygous or homozygous
•(if the sample size is big enough, a recessive offspring should ultimately result)
Objective 9 & 10 - p. 534 - Test Cross
•How can you determine if an organism is homozygous dominant or heterozygous?
•“normal-sized” malamute dogs are dominant to dwarf dogs. How can you tell if a normal-sized dog is homozygous or heterozygous?
•Cross of an individual of unknown genotype with a (known) homozygous recessive individual
•Used to determine whether or not an organism with a dominant trait is heterozygous or homozygous
•If the ‘unknown’ is homozygous, all offspring will show dominant trait.
•If a recessive offspring results (in this case, 50% should be recessive), the unknown genotype has to be heterozygous
•If a tall plant (either TT or Tt) is mated with a short plant (tt), if any of the offspring is short then the unknown organism must be heterozygous.
•If the offspring is tall then it is either heterozygous or homozygous
•(if the sample size is big enough, a recessive offspring should ultimately result)