Unit vi mendelian genetics
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UNIT VI - MENDELIAN GENETICS. Baby Campbell – Ch 9 Big Campbell – Ch 14, 15. I. MENDEL. pea plants. Mendel’s Experiments Worked with ______________ Eliminated ________________________ and controlled ____________________

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UNIT VI - MENDELIAN GENETICS

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Unit vi mendelian genetics

UNIT VI - MENDELIAN GENETICS

Baby Campbell – Ch 9

Big Campbell – Ch 14, 15


I mendel

I. MENDEL

pea plants

  • Mendel’s Experiments

    • Worked with ______________

    • Eliminated ________________________ and controlled ____________________

    • P Generation - True-breeding pea plants with one trait X true-breeding pea plants with another trait

    • Produced hybrids also known as F1

      • ___________________________

      • F1 Phenotype =

      • F1 Genotype =

    • F1 X F1 → F2

      • ___________________________

      • F2 Phenotype Ratio =

      • F2 Genotype Ratio =

self-pollination

cross-pollination

TT x tt

4 tall : 0 short

0 TT : 4 Tt : 0 tt

Tt x Tt

3 tall : 1 short

1 TT : 2 Tt : 1 tt


I mendel cont

I. MENDEL, cont

alleles

  • Mendel’s Principles

    • Alternative versions of genes known as ______________ account for variations in inherited characters.

    • Organisms inherit _____ alleles for each trait

    • If alleles at a locus differ; that is; if the genotype is _______________, the allele that shows is known as the ________________ allele.

    • Law of Segregation – two alleles for a heritable character segregate during meiosis

    • Law of Independent Assortment – each pair of alleles segregates independently of each other pair of alleles during meiosis

2

heterozygous

dominant


Ii analyzing probability of trait inheritance

II. ANALYZING PROBABILITY OF TRAIT INHERITANCE

  • Test Cross

    • Organisms with dominant phenotype crossed with _____________________________ to determine genotype

  • Punnett Square

  • Multiplication Rule

    • States the probability of 2 or more independent events occurring together can calculated by multiplying individual probabilities

    • For example,

      • Determine the probability of a homozygous recessive short plant produced from F1 X F1

        • Cross = Tt x Tt

        • Probability of egg carrying t = ½

        • Probability of sperm carrying t = ½

        • Probability of tt offspring = ¼

homozygous recessive


Ii analyzing probabilities cont

II. ANALYZING PROBABILITIES, cont

  • Addition Rule

    • States that the probability of 2 or more mutually exclusive events occurring can be calculated by adding together their individual probabilities

    • For example,

      • Determine the probability of a heterozygous plant produced from F1 X F1

        • Tt x Tt

        • Chance of egg carrying T = ½

        • Chance of sperm carrying t = ½

        • Chance of sperm carrying T = ½

        • Chance of egg carrying t = ½

        • Probability of Tt offspring = ¼ + ¼ = ½


Ii analyzing probabilities cont1

II. ANALYZING PROBABILITIES, cont

  • Crosses Involving Multiple Characters

    • Determine the genotype ratios of the offspring for the cross BbDD X BBDd


Ii analyzing probabilities cont2

II. ANALYZING PROBABILITIES, cont

  • Crosses Involving Multiple Characters

    • Determine the genotype ratios of the offspring for the cross YyRr X YyRr


Ii analyzing probabilities cont3

II. ANALYZING PROBABILITIES, cont

  • Crosses Involving Multiple Characters

    • In the cross, PpYyRr X Ppyyrr, what is the probability of offspring that are purple, green, & round?

      • P= purple, p = white

      • Y = yellow, y = green

      • R = round, r = wrinkled


Probability practice makes perfect

Probability Practice Makes Perfect! 

In pea plants,

long stems are dominant to short stems

purple flowers are dominant to white, and

round seeds are dominant to wrinkled.

A plant that is heterozygous for all three loci self-pollinates and 2048 progeny are examined. How many of the resulting plants would you expect to be long-stemmed with purple flowers, producing wrinkled seeds?


Ii analyzing probabilities cont4

Pedigree Analysis

II. ANALYZING PROBABILITIES, cont


Recessive trait

Recessive Trait


Dominant trait

Dominant Trait…


Iii variations in inheritance

III. VARIATIONS IN INHERITANCE

  • Co-Dominance

    • Both alleles affect phenotype in separate & distinguishable ways

    • Often designated with 2 different “big letters”

  • Incomplete Dominance

    • Neither allele is dominant; heterozygotes show a blend of two homozygous phenotypes

    • One allele designated with “big letter’, the other with “big letter prime”; for example T T’


Iii variations in inheritance cont

III. VARIATIONS IN INHERITANCE, cont

  • Multiple Alleles

    • Many genes have more than 2 alleles

    • Example, ABO blood groups in humans

    • Three alleles

  • A woman with O blood has a child with Type A blood. The man she claims is the father has AB blood. Is it possible that he is the father of this child?


Iii variations in inheritance cont1

III. VARIATIONS IN INHERITANCE, cont

  • Polygenic Inheritance

    • For example, AABBCC = very dark skin; aabbcc = very light skin.

    • Intensity based on units; in other words, AaBbCc and AABbcc individuals would have the same pigmentation


Iii variations in inheritance cont2

III. VARIATIONS IN INHERITANCE, cont

  • Epistasis

    • Gene at one locus alters

      phenotypic expression of a

      gene at a second locus

    • For example,

      A dominant allele, P causes the production of purple pigment; pp individuals are white. A dominant allele C is also required for color production; cc individuals are white. What proportion of offspring will be purple from a ppCc x PpCc cross?


Iii variations in inheritance cont3

III. VARIATIONS IN INHERITANCE, cont

  • Pleiotropy


Iii variations in inheritance cont4

III. VARIATIONS IN INHERITANCE, cont

  • Environmental Impact on Phenotypes


Iv sex linked inheritance

IV. SEX-LINKED INHERITANCE

  • First recognized by Thomas Hunt Morgan

    • Drosophila melanogaster

      • Fruit flies

      • Excellent organism for genetic studies

        • Prolific breeding habits

        • Simple genetic make-up; 4 pairs of chromosomes → 3 pairs of autosomes, 1 pair of sex chromosomes

    • Crossed true-breeding wild-type females with true-breeding mutant males

    • Mutant trait showed up in ½ male F2 offspring ; was not seen in F2 females

  • Determined mutant allele was on X-chromosome; thus inherited differently in males versus females

    • In females,

    • In males,


Iv sex linked inheritance cont

IV. SEX-LINKED INHERITANCE, cont

  • Red-green colorblindness is caused by a sex-linked recessive allele. A color-blind man marries a woman with normal vision whose father was colorblind. What is the probability she will have a colorblind daughter?


Iv sex linked inheritance cont1

IV. SEX-LINKED INHERITANCE, cont

  • The gene for amber body color in Drosophila is sex-linked recessive. The dominant allele produces wild type body color. The gene for black eyes is autosomal recessive; the wild type red eyes are dominant. If males with amber bodies, heterozygous for eye color are crossed with females heterozygous for eye color and body color, calculate the expected phenotype ratios in the offspring.


Iv sex linked inheritance cont2

IV. SEX-LINKED INHERITANCE, cont

  • X Inactivation in Females

    • During embryonic development, one X chromosome in female cells is inactivated due to addition of methyl group to its DNA

    • Dosage compensation

    • Inactive X chromosome condenses; known as Barr body


Iv sex linked in inheritance cont

IV. SEX-LINKED IN INHERITANCE, cont

  • Occurs randomly

    • Females will have some cells where “Dad’s copy” of X is inactivated, some where “Mom’s copy” is inactive

    • Therefore, females are a mosaic of cells

    • Preserved in mitosis

    • In ovaries, Barr body chromosome is reactivated for meiosis and oogenesis


Iv sex linked inheritance cont3

IV. SEX-LINKED INHERITANCE, cont

  • X Inactivation

    • Calico coloration in female cats


V gene mutations

V. GENE MUTATIONS

  • Change in the nucleotide sequence

  • May be spontaneous mistakes that occur during replication, repair, or recombination

  • May be caused by mutagens; for example, x-rays, UV light, carcinogens

  • If changes involve long stretches of DNA, known as chromosomal mutations

  • Point mutations – change in a gene involving a single nucleotide pair; 2 types

    • Substitution

    • Frameshift – due to addition or deletion of nucleotide pairs


V gene mutations cont

V. GENE MUTATIONS, cont

  • Classification of Gene Mutations

    • Traits may be described as dominant, recessive, etc . based on the effect of the abnormal allele on the organism’s phenotype

    • Instruction encoded by genes carried out through protein synthesis

    • Vast majority of proteins are enzymes

    • Abnormal allele → Defective enzyme

      • If the enzyme produced by the normal allele is present in sufficient quantities to catalyze necessary reactions,

        • No noticeable effect on phenotype

        • Defective allele is classified as recessive

      • If the lack of normal enzyme production by defective allele cannot be overcome by normal allele,

        • Organism’s phenotype is affected

        • Defective allele is classified as dominant


Vi inherited genetic disorders

VI. INHERITED GENETIC DISORDERS

  • Due to gene mutations

  • Classified as autosomal or sex-linked, depending on chromosome location of affected gene

  • Autosomal Disorders – Grouped according to path of inheritance

    • Autosomal Recessive Disorders


Vi inherited genetic disorders1

VI. INHERITED GENETIC DISORDERS

  • Albinism


Vi inherited genetic disorders cont

VI. INHERITED GENETIC DISORDERS, cont

  • Cystic Fibrosis


Vi inherited genetic disorders cont1

VI. INHERITED GENETIC DISORDERS, cont

  • PKU


Vi inherited genetic disorders cont2

VI. INHERITED GENETIC DISORDERS, cont

  • Tay-Sachs


Vi inherited genetic disorders cont3

VI. INHERITED GENETIC DISORDERS, cont

  • Autosomal Co-Dominant Disorders

    • Sickle Cell Anemia


Vi inherited genetic disorders cont4

VI. INHERITED GENETIC DISORDERS, cont

  • Autosomal Dominant Disorders

    • Huntington’s Disease


Vi inherited genetic disorders cont5

VI. INHERITED GENETIC DISORDERS, cont

  • Autosomal Dominant Disorders

    • Marfan Syndrome


Vi inherited genetic disorders cont6

VI. INHERITED GENETIC DISORDERS, cont

  • Autosomal Dominant Disorders

    • Achondroplasia


Vi inherited genetic disorders cont7

VI. INHERITED GENETIC DISORDERS, cont

  • Hypercholesteremia


Vi inherited genetic disorders cont8

VI. INHERITED GENETIC DISORDERS, cont

  • Sex-Linked Disorders

    • All

    • Affect

    • Hemophilia


Vi inherited genetic disorders cont9

VI. INHERITED GENETIC DISORDERS, cont

  • Colorblindness

  • Duchenne Muscular Dystrophy


Vii testing for inherited genetic disorders

VII. TESTING FOR INHERITED GENETIC DISORDERS

  • Identification of Carriers/Genetic Counseling

    • Tests are available for Tay-Sachs, sickle cell, cystic fibrosis, Huntington’s, PKU, & many others

  • PGD – Preimplantation Genetic Diagnosis


Vii genetic testing cont

VII. GENETIC TESTING, cont

  • Fetal Testing

    • Amniocentesis

      • Performed between 14th-16th weeks of pregnancy

      • Cells collected, tested


Vii genetic testing cont1

VII. GENETIC TESTING, cont

  • Chorionic Villus Sampling (CVS)

    • Narrow tube inserted through mother’s vagina, cervix

    • Small tissue sample suctioned from placenta (organ that transmits nutrients, removes wastes from fetus)

    • Testing may be done earlier in pregnancy but not suitable for all types of testing

  • Newborn Screening

    • PKU


  • Viii chromosomal basis of inheritance

    VIII. CHROMOSOMAL BASIS OF INHERITANCE

    • Chromosomal Theory of Inheritance

      • States genes occupy specific loci on chromosomes

      • During meiosis, chromosomes undergo segregation & independent assortment

    • Linked Genes

      • During Thomas Morgan’s work with Drosophila, he recognized

        • Two genes located on same chromosome were linked; that is, inherited together

        • However, offspring phenotypes showed this wasn’t always true


    Viii chromosomal basis of inheritance cont

    VIII. CHROMOSOMAL BASIS OF INHERITANCE, cont

    • Linked Genes, cont

      • In fruit flies, normal wild-type phenotype is gray body, normal wings – both genes are located on same chromosome

        • G = wild-type (gray) body; g = black body

        • W = wild-type wings; w = mutant wings

      • True-breeding wild type flies X true-breeding mutants

      • F1 showed all

      • F1 X test cross

        • Counted 2300 offspring

        • Should have counted


    Viii chromosomal basis of inheritance cont1

    VIII. CHROMOSOMAL BASIS OF INHERITANCE, cont

    • 965 GWgw944 gwgw206 Gwgw185 gWgw

    • Morgan realized variation in probabilities due to


    Viii chromosomal basis of inheritance cont2

    VIII. CHROMOSOMAL BASIS OF INHERITANCE, cont

    • Linkage Maps

      • In crossing over, the further apart two genes are, the higher the probability that a crossover will occur between them and therefore, the higher the recombination frequency.


    Viii chromosomal basis of inheritance cont3

    VIII. CHROMOSOMAL BASIS OF INHERITANCE, cont

    • Recombination Frequency = # recombinants__ X 100

      total # offspring

    • One map unit = 1% recombination frequency

      ……………………………………………………………………………………..

      965 GWgw944 gwgw206 Gwgw185 gWgw


    Viii chromosomal basis of inheritance cont4

    VIII. CHROMOSOMAL BASIS OF INHERITANCE, cont

    • The genes for vestigial wings, black body color, and cinnabar eyes are linked genes.

    • In controlled crosses . ..

      • The gene for vestigial (vg) wings and body color (b) have a 17% crossover rate.

      • The gene for eye color (cn) and body color (b) have a 9% crossover rate.

      • The gene for eye color (cn) and vestigial wings (vg) have a 9 ½% crossover rate.

    • Draw the chromosome.


    Ix chromosomal disorders

    IX. CHROMOSOMAL DISORDERS

    • Alterations in Chromosome Number

      • Most commonly due to nondisjunction

    • Results in aneuploidgametes


    Ix chromosomal disorders cont

    IX. CHROMOSOMAL DISORDERS, cont


    Ix chromosomal disorders cont1

    IX. CHROMOSOMAL DISORDERS, cont

    • Detected with karyotype

    • Examples

      • Down Syndrome


    Ix chromosomal disorders cont2

    IX. CHROMOSOMAL DISORDERS, cont

    Turner Syndrome


    Ix chromosomal disorders cont3

    IX. CHROMOSOMAL DISORDERS, cont

    • Klinefelter Syndrome


    Ix chromosomal disorders cont4

    IX. CHROMOSOMAL DISORDERS, cont


    Ix chromosomal disorders cont5

    IX. CHROMOSOMAL DISORDERS, cont

    • Cri du Chat – Caused by deletion in chromosome 5

    • Chronic Myelogenous Leukemia – Caused by reciprocal translocation. Large piece of chromosome 22 exchanges places with tip of chromosome 9. Resulting chromosome 22 easily recognizable; known as Philadelphia chromosome.


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