Download Mendelian Genetics

Mendelian Genetics
Blue People of Kentucky
Methemoglobinemia
Genetics
• Genetics is the study of heredity.
• Heredity is the transmission of traits from parent to
offspring; an organisms genetic makeup.
• Genes are sections of a chromosome that code for a
specific trait. Ex: hair color, height, etc.
• A trait is any characteristic that can be passed from parent
to offspring.
Genetics
• Alleles are the form of the gene that is passed from
parent to offspring.
• Flower color = gene;
• Purple and white = alleles of the flower color gene
• Multiple alleles are genes with more than 2 alleles
• Eye color
Gregor Mendel
• An Austrian monk who is credited as the first person to study the
science of genetics.
• So he is referred to as “the Father of Genetics.”
• Mendel worked with garden pea plants in his experiments
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Easy to grow
Had many traits to study; height, seed shape, pod shape, flower color, etc.
Reproduced rapidly
Cross pollination
Gregor Mendel
• Mendel’s Experiment
• Crossed a Tall plant with a short plant
• This is the parent generation, P1
• All offspring were tall
• Crossed two plants from the P1 offspring
• This is the first filial or first generation of offspring, F1
• Crossed Tall plants from the next generation
• This is the second filial generation of offspring after the parents, F2
• Resulted in ¾ Tall plants and ¼ short plants
Mendel’s Findings
• Concept of Unit Characters: traits are
determined by “factors” that occur in pairs.
We now know that these unknown “factors”
are genes.
• Dominance: One factor of a pair may cover
up or prevent the expression of a trait
Example:
Your Mom gives you the gene for having a Unibrow (recessive) and
your father gives you the gene for having two eye brows (dominant)
Dad
Mom
What will you have?
Mendel’s Findings
• Law of Segregation: two alleles for a gene will separate during
meiosis
• Law of Independent Assortment: alleles separate randomly or
independently of each other. This means that seed shape does not
affect plant height.
Because of independent assortment and crossing over
during meiosis, there is an infinite number of possible
combinations of chromosomes in the gametes, this is called
genetic recombination.
Important Genetics Terms
• Dominant: the “stronger” gene; represented by an uppercase letter
B
R
• Recessive: the “weaker” gene; represented by a lowercase letter
b
r
Important Genetics Terms
• Genotype: combination of genes represented by a combination of letters.
We generally use the first letter of the dominant gene.
• RR, Rr, rr
• Phenotype: the expression of the gene/trait; what is actually seen or
expressed (phenotype = physical trait)
• Tall, short, green, round, wrinkled
Genotype & Phenotype
Genotype of alleles:
R = red flower
r = yellow flower
All genes occur in pairs, so 2 alleles
affect a characteristic
Possible combinations are:
Genotypes:
RR
Rr
Phenotypes: RED RED
rr
YELLOW
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Important Genetics Terms
• Homozygous: gene pairs that are identical
• Homozygous dominant: TT, AA, RR
• Homozygous recessive: tt, aa, rr
• Heterozygous: gene pairs that are different. The dominant gene will be
expressed in most heterozygous organisms.
• Tt, Aa, Rr
• Hybrid: offspring of parents with gene pairs that are different; another term
for heterozygous
Probability
• The traits you received from your parents were all randomly
combined due to chance.
• We use the mathematical study of probability in genetics to help
us determine the likelihood of passing on certain traits to future
offspring.
Mendelian Inheritance and Probability
• How do we know what the probability of a cross
will be?
• We use a device called a Punnett square to see
possible gene combinations.
Mendelian Inheritance and Probability
• Monohybrid Cross:
a cross between
organisms that
involves one trait.
• Dihybrid Cross:
a cross between
organisms that
involves two traits
Mendelian Inheritance and Probability
• The probability of a gene combination can be
represented by:
• A fraction: # of one kind of combination
# of all possible combinations
• A ratio: 1:4, 1:2, 3:4, 4:0, 1:2:1, etc.
• Or a percentage: 25%, 50%, ect.
Let’s practice…
Punnett squares
WHEN HEREDITY
ISN’T SIMPLE
INCOMPLETE DOMINANCE
• The phenotype of the heterozygous organism is “in between” the dominant
and recessive phenotype.
• Example: Snapdragon flowers
• Homozygous Dominant = Red (CRCR)
• Homozygous Recessive = White (CWCW)
• Heterozygous = Pink (CRCW)
CODOMINANCE
• Both alleles express themselves independently in the phenotype. This means
that both alleles are expressed equally; both are dominant in a heterozygous
organism.
• Cows, horses, people (sickle cell anemia)
• Homozygous dominant = Black (BB)
• Homozygous dominant = White (WW)
• Heterozygous = Checkered (BW)
Multiple Alleles
• Traits controlled by more than two alleles.
• Blood Type
Sex-Linked Traits
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Traits carried on the sex chromosome
Sex-linked traits can only be carried on an X chromosome.
Color Blindness
Male Pattern Baldness
• Can a father pass a sex-linked trait to his son?
Autosomal Disorders
• Nondisjunction
• Monosomy
• Turner Syndrome
• Trisomy
• Trisomy 21 = Down’s Syndrome
Sex Chromosome Disorders
• Turner’s Syndrome
• Kleinfelter’s Syndrome
• Superfemale
Dominant Disorders
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Achondroplasia (dwarfism)
Glaucoma
Polydactyly
Brown Teeth
Recessive Disorders
• Cystic Fibrosis
• Sickle Cell Anemia
• Albinism
Pedigrees
• Shows the pattern of inheritance within a family