genetics review
TRANSCRIPT
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Classical Genetics
Gregor Mendel
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The Work of Gregor Mendel
Genetics: the scientific study of heredity, or how traits are passed from one generation to the next
Gregor Mendel’s Peas- Mendel was an Austrian monk who is credited as the “father of genetics.”
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The Work of Gregor Mendel
- Mendel began working with pea plants that were true-breeding, meaning that if allowed to self pollinate, they would only produce offspring identical to themselves
-ex. Tall plants produce tall plants, green seeded plants produce green seeded plants
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The Work of Gregor Mendel
Genes and Dominance- Mendel studied 7 different plant traits. Traits are characteristics such as height or flower color.
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The Work of Gregor Mendel
Seed Shape Flower
PositionSeed CoatColor
Seed Color Pod Color Plant Height
PodShape
Round
Wrinkled
Round
Yellow
Green
Gray
White
Smooth
Constricted
Green
Yellow
Axial
Terminal
Tall
Short
Yellow Gray Smooth Green Axial Tall
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The Work of Gregor Mendel
- Mendel called the original plants the P (parent) generation. The offspring were the F1 (first filial) generation .- the offspring of crosses between parents of different traits are called hybrids
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The Work of Gregor Mendel
Mendel's F2 Generation
P GenerationF1 Generation
Tall Tall Tall Tall Tall TallShort Short
F2 Generation
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11-1 The Work of Gregor Mendel
From his experiments, Mendel drew two conclusions1) biological inheritance is determined by factors that are passed from one generation to the next. Today we call these factors genes.
- the different forms of a gene are called alleles
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The Work of Gregor Mendel
ex. gene (trait) is eye coloralleles (forms) are blue,
brown, green, etc.2) the second conclusion is called the principle of dominance- the principle of dominance states that some alleles are dominant and others are recessive
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The Work of Gregor Mendel
Segregation- Mendel saw that some forms of traits would disappear during the F1 generation, but reappear during the F2 generation- he explained this by showing that the alleles segregated during the formation of gametes, or sex cells.
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The Work of Gregor Mendel
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Section QuizGametes are also known as
genes. sex cells. alleles. hybrids.
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Section QuizThe offspring of crosses between parents
with different traits are called alleles. hybrids. gametes. dominant.
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Section QuizIn a cross of a true-breeding tall pea plant
with a true-breeding short pea plant, the F1 generation consists of
all short plants. all tall plants. half tall plants and half short plants. all plants of intermediate height.
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Section QuizIf a particular form of a trait is always
present when the allele controlling it is present, then the allele must be
mixed. recessive. hybrid. dominant.
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Probability and Punnett Squares
Genes and Probability- the likelihood that an event will occur is called probabilityex. a coin landing on heads has a probability of 50%- the principle of probability can be used to predict the outcome of genetic crosses
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Probability and Punnett Squares
Punnett squares- the gene combinations that might result from a genetic cross can be determined by drawing a diagram known as a Punnett square
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Probability and Punnett Squares
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Probability and Punnett Squares
Organisms that have two identical alleles for a particular trait are called homozygous.ex. TT
Organisms that have two different alleles for a particular trait are called heterozygousex. Tt
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Probability and Punnett Squares
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Probability and Punnett Squares
The physical characteristics of an organism are called its phenotypeex. tall plant
The genetic makeup of an organism is its genotypeex. TT or Tt
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Section QuizProbability can be used to predict
average outcome of many events. precise outcome of any event. how many offspring a cross will produce. which organisms will mate with each other.
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Section QuizCompared to 4 flips of a coin, 400 flips of
the coin is more likely to produce about 50% heads and
50% tails. less likely to produce about 50% heads and
50% tails. guaranteed to produce exactly 50% heads
and 50% tails. equally likely to produce about 50% heads
and 50% tails.
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Section QuizOrganisms that have two different alleles
for a particular trait are said to be hybrid. heterozygous. homozygous. recessive.
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Section QuizTwo F1 plants that are homozygous for
shortness are crossed. What percentage of the offspring will be tall?
100% 50% 0% 25%
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Exploring Mendelian Genetics
Independent assortment- the principle of independent assortment states that genes for different traits can segregate independently during the formation of gametesex. Seed color does not depend on seed shape
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Exploring Mendelian Genetics
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Exploring Mendelian Genetics
Beyond dominant and recessive alleles- some alleles are neither dominant nor recessive , and many traits are controlled by multiple alleles or multiple genes
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Exploring Mendelian Genetics
Incomplete dominance or Codominance- the heterozygous phenotype is somewhere between the two homozygous phenotypesex. red flower + white flower = pink
Punnett square animation
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Exploring Mendelian Genetics
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Exploring Mendelian Genetics
Multiple alleles- multiple alleles contribute to the phenotype ex. Blood type (i, IA, IB)Type O = i iType A = IA IA or IA iType B = IB IB or IB iType AB = IA IB
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Exploring Mendelian Genetics
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Exploring Mendelian Genetics
Polygenic traits- two or more genes control the outcome of a particular traitex. Skin color in humans is controlled by the combinations of 4 different genes
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Exploring Mendelian Genetics
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Section QuizIn four o'clock flowers, the alleles for red
flowers and white flowers show incomplete dominance. Heterozygous four o'clock plants have
pink flowers. white flowers. half white flowers and half red flowers. red flowers.
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Section QuizMendel's principles apply to
pea plants only. fruit flies only. all organisms. only plants and animals.
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Human Heredity
Human ChromosomesA typical human body cell contains
46 chromosomes- 44 autosomes and 2 sex chromosomes
Chromosomes are arranged in a karyotype, a picture of the chromosomes
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Human Heredity
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Human Heredity
Males and females differ in the sex chromosomes they contain- males are XY- females are XX
All egg cells carry a single X chromosome. However, half of all sperm cells carry a X chromosome while half carry a Y chromosome.
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Human Heredity
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Human Heredity
Human TraitsScientists use a pedigree to help
study how traits are passed from one generation to the next.
Pedigree: a chart which shows the relationships within a family
Pedigree animation
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Human HeredityCircle = Female
Square = Male
Marriage lineParental line
carrier of the trait
shaded = express the trait
not shaded = does not express the trait
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Human Heredity
Since most human traits are polygenic (many genes), they can not be traced to a single parent
Many genes have been discovered through the study of genetic disorders- they can be dominant or recessive
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Human Heredity
In both cystic fibrosis and sickle cell disease, a small change in the DNA of a single gene affects the structure of a protein, causing a serious genetic disorder
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Human Heredity
Cystic Fibrosis- caused by a recessive allele on chromosome 7- causes digestive and respiratory problems- only half of people with CF live into their 20s
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Human Heredity
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Human Heredity
Sickle Cell Disease- causes hemoglobin to be less soluble- changes the shape of red blood cells; become bent into the sickle-shape
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Human Heredity
Malaria and the Sickle Cell Allele
Regions where malaria is common
Regions where the sickle cell allele is common
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Section QuizA chromosome that is not a sex
chromosome is know as a(an) autosome. karyotype. pedigree. chromatid.
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Section QuizAn individual with a blood type phenotype
of O can receive blood from an individual with the phenotype
O. A. AB. B.
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Human Chromosomes
Human genes and chromosomes- on each chromosome there is the information for several hundred genes
ex. Gene for ALS is on 22nd chromosome
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Human Chromosomes
Sex-linked genes: genes located on the X or Y chromosomeex. colorblindness, hemophilia, muscular dystrophy
Males have only 1 X chromosome and cannot be heterozygous for the trait. Females can be carriers (heterozygous).
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Human Chromosomes
Father(normal vision)
ColorblindNormal vision
Mother (carrier)
Daughter(normal vision)
Son(normal vision)
Daughter(carrier)
Son(colorblind)
Male
Female
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Human Chromosomes
Chromosomal disordersThe most common error occurs
when homologous chromosomes fail to separate during meiosis. This is called nondisjunction.
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Human Chromosomes
Homologous chromosomes fail to separate
Meiosis I:Nondisjunction
Meiosis II
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Human Chromosomes
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Human Chromosomes
If nondisjunction occurs, abnormal numbers of chromosomes may find their way into gametes, and a disorder of chromosome numbers may result.- Down syndrome results from a nondisjunction of the 21st chromosome- Turner’s syndrome (XO) and Klinefelter’s syndrome (XXY)
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