Transcript Mendel Power Point

Gregory Mendel
• Gregory developed own
experiment to study
different traits in peas
• First scientist to study
genetics
• “Father of Genetics”
Genes
• Units of information about specific traits
• Passed from parents to offspring
• Each has a specific location (locus) on a
chromosome
Alleles
• Different forms of a gene
• Each person has at 2 alleles for each trait
• 2 types
• Dominant (A)
• Recessive (a)
Must KNOW Vocabulary!
Chromosomes-transmitted from one generation to the
next, contains many genes
Gene- sequence of DNA on the chromosome,
determines trait (about 30,000 in humans)
Alleles-alternative forms of a gene
More Vocab……
• Homozygous- 2 copies of allele are the same
– AA
– aa
• Heterozygous- 2 copies of allele are different
– Aa
And more Vocab…..
• Phenotype- what
you see
• (purple/white)
• Genotype- actual
alleles present
• (PP/Pp/pp)
Probability
• The chance that an outcome of a given event
will occur
• Punnett squares give probability for what
kinds of offspring will be born…..doesn’t tell
EXACTLY how many of each kind you will have
• EX: if you flip a coin
10 times, you would
predict 5 heads/5 tails.
• Is this always true???
Mendel’s First Law:
Principle of Segregation
• Alleles split apart
randomly in meiosis
Punnett-Square Method
• Draw a box
• Put genotype at the top, bring alleles down
• Put other genotype on the side, bring alleles
over
Pedigrees
• Write lines for all of your individuals
• Put in known alleles
• Work backwards to solve to missing alleles
Tracking Generations
• Parental generation (P)
• First-generation offspring (F1)
• Second-generation offspring (F2)
Mendel’s Second Law:
Principle of Independent
Assortment
• Traits don’t always stay
together
• EX: white/short tail
• Brown/long tail
Aren’t inherited together!
Dihybrid Crosses
• Always use to compare the possibility of
inheriting 2 different traits
– Figure out genotypes of parents
– Find all possible allele combinations for their
gametes
• F.O.I.L.- firsts, outers, inners, lasts
– Complete a Punnett Square to solve for
offspring
Question of the Day
• Brown eyes are dominant to blue eyes
• Freckles are dominant to no freckles
• Mom is heterozygous
• Dad is heterozygous
Epistasis
• One gene can mask the phenotypic effects
of a different gene
– Results when more than one gene codes for a
particular trait
– Common among genes for hair color in
mammals
• Black B is dominant to brown b
– BB Black
– Bb Brown
• Yellow the epistasis trait that is only
present when homozygous recessive
– BE black
– bE brown
– Ee yellow
Pleiotropy
• Alleles at a single locus may have effects
on two or more traits
– Eye color
– Skin color
• A rose breeder finds that when he crosses
a true-breeding climber with a truebreeding shrubby plant all F1 offspring are
climbers. Find the F2 generation.
• He also found that when he crossed sweet
smelling roses with no scent roses, all of
the F1 plants smelled sweet. Find the F2
generation.
• Using the information from above cross a
plant that is hetero for BOTH traits with a
plant that is hetero for BOTH traits. What
does your F1 generation look like?
Incomplete Dominance
• a cross between individuals with two
different phenotypes produces offspring
with a third phenotype that is different
• Heterozygous genotype displays a
different phenotype than either
homozygous parent
Codominance
• a cross between two different phenotypes
produces offspring with a third phenotype in
which both of the parental traits appear
together.
• Heterozygous produces phenotype with both
parent’s phenotypes visible
• Blood Typing
• Thorns on roses are controlled by 2
genes. Thorns are dominant to no thorns
for the first gene. However the other gene
will overshadow the first and will show the
phenotype of thorns if a dominant allele is
present.
• Solve the phenotypes of the offspring if
one plant that is hetero for both genes
crosses with another plant that is homoz
recessive for both genes.
• Solve for the possible parents genotypes if
there are 3 offspring in the F1 generation,
2 that do not have thorns and the other
does have thorns.
• If you cross a homoz red plant with a white
plant all F1 offspring are pink. However if
you cross homoz tall plant with a homoz
short plant all F1 offspring are tall.
• You cross a hetero tall, pink plant with a
short, white plant. What are the
genotypes and phenotypes of the
offspring?
• Identify the parents if you haveF1 offspring
that are tall/red, short/pink.
• What would you cross with a hetero tall
pink plant to get offspring that are short
and pink? Justify your answer.
Homework!
• Pg183-185 Genetics Problems
–2, 3, 5, 6, 7, 9,10,12,13,14,
Blood Types
• Gene that controls ABO type codes for
enzyme that dictates structure of a
glycolipid on blood cells
• Two alleles (IA and IB) are codominant
when paired
• Third allele (i) is recessive to others
Blood Types
– IAIA Type A
– IBIB Type B
– iiType O
– IAi
Type A
– IBi
Type B
– IAIB Type AB
Blood Transfusions
• Recipient’s immune system will attack
blood cells that have an unfamiliar
glycolipid on surface
• Type O is universal donor because it has
neither type A nor type B glycolipid
48.Mom is type A and has a child that is type O, what
is/are dads possible blood type/s?
49.If mom is hetero type B and dad is hetero A, what
is/are the possible blood types of the offspring going to
be?
50.Which blood type is recessive to the other types?
Answers:
a. Type A, Type B, Type AB
b. Type A, Type B, Type O
c. Type AB
d. Type O
e. All of these
Linkage and Cross-over
• Each chromosome becomes zippered to
its homologue
• All four chromatids are closely aligned
• Non-sister chromosomes exchange
segments
Effects of Crossing Over
• After crossing over, each chromosome
contains both maternal and paternal
segments
• Creates new allele combinations in
offspring
Linkage Groups
1. Two or more genes can be located on the
same chromosome
2. Genes that are close together tend to be
transmitted as a unit but not all genes are
transmitted together
Crossover Frequency
• Proportional to the distance that separates
genes
Pedigree Analysis
• Genetic Abnormality: A rare uncommon version
of a trait
– polydactyly
• Genetic Disorder: Inherited conditions that
cause mild to severe medical problems
– Why don’t they disappear?
• Mutation introduces new rare alleles
• In heterozygotes, harmful allele is masked,
so it can still be passed on to offspring
Symbols in
Predigrees
Phenotypic Treatments
• Symptoms of many genetic disorders can
be minimized or suppressed by
– Dietary controls
– Adjustments to environmental conditions
– Surgery or hormonal treatments
Genetic Screening
• Large-scale screening programs detect
affected persons
• Newborns in United States routinely tested
for PKU
– Early detection allows dietary intervention and
prevents brain impairment
Prenatal Diagnosis
• Amniocentesis
• Chorionic villus
sampling
• Fetoscopy
• All methods have some
risks
Preimplantation Diagnosis
• Used with in-vitro fertilization
• Mitotic divisions produce ball of 8 cells
• All cells have same genes
• One of the cells is removed and its genes
analyzed
• If cell has no defects, the embryo is
implanted in uterus
Question of the Day
• Identify what type of dominance is
happening here and justify your reasoning
• Identify what type of dominance is
happening here and justify your reasoning
Karyotype Preparation:
• Stopping the Cycle:
– Cultured cells are arrested at metaphase by
adding colchicine
– This is when cells are most condensed and
easiest to identify
Karyotype Preparation
• Arrested cells are broken open
• Metaphase chromosomes are fixed and
stained
• Chromosomes are photographed through
microscope
• Photograph of chromosomes is cut up and
arranged to form karyotype diagram
Karyotype Diagram
Chromosome Structure
• Alterations to chromosome structure are
usually bad
• Duplications are adaptive: one gene
functions normally - the other is free to
mutate
• Chromosome structure evolves
Nondisjunction
Aneuploidy
• Individuals have one extra or less
chromosome
• (2n + 1 or 2n - 1)
• Major cause of human reproductive failure
• Most human miscarriages are aneuploids
Polyploidy
• Individuals have three or more of each
type of chromosome (3n, 4n)
• Common in flowering plants
• Lethal for humans
– 99% die before birth
– Newborns die soon after birth
Duplication
• Gene sequence that is repeated several to
hundreds of times
• Duplications occur in normal
chromosomes
• May have adaptive advantage
– Useful mutations may occur in copy
Deletion
• Loss of some segment of a chromosome
• Most are lethal or cause serious disorder
Inversion
• Sequence of DNA is reversed within the
chromosome
Translocation
• A piece of one chromosome becomes
attached to another nonhomologous
chromosome
• Most are reciprocal
Comparing the X and Y
chromosome
• Y has about 225 genes and determines
male sex (SRY gene) if present forms
testes if absent ovaries form
• X contains more than 1,100 genes, deal
with nonsexual traits, can be expressed in
both males and females