Transcript 3-24-16 Genetics and Heredity 12.3

Genetics and
Heredity
March 24, 2016
Chapter 12.3
Chapter 12 Vocabulary
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Heredity
Trait
Genetics
Fertilization
Purebred
Gene
Allele
Dominant allele
Recessive allele
Hybrid
Probability
Punnett square
Phenotype
Genotype
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Homozygous
Heterozygous
Incomplete dominance
Codominance
Multiple alleles
Polygenic inheritance
Meiosis
Selective breeding
Inbreeding
Hybridization
Clone
Genetic engineering
Gene therapy
DNA
• DeoxyriboNucleic Acid
• Stores genetic information
• DNA < chromosome < nucleus < cell
Organizing DNA
• DNA is bundled together as chromosomes
• Different parts of a chromosome make up genes
Gene: the factors that control a trait. The sequence of
DNA that determines a trait and is passed from parent
to offspring.
• You can have different forms of a gene that does
the same thing. This is called an allele.
Allele: different form of a gene
Genes & Heredity
• When genes are passed on by reproduction, the
offspring will have traits based on those genes
• Asexual reproduction makes an exact genetic
copy of the original organism (+ random mistakes)
• Sexual reproduction can end up with a mix of 2
genes for the same thing, so it’s more complicated
to figure out which trait the offspring will have
Alleles & Inheritance
• Inheritance depends on what the genes say and show
(AKA which alleles the offspring get)
Genotype: what an organism’s genes say.
• Can’t know genotype without knowing organism’s exact
genes
Phenotype: what an organism’s genes show
• What the organism looks like (is the dominant allele there
or not?)
• Note: external factors (acquired traits) like dyeing hair or
cutting off a tail don’t change the original phenotype
Homozygous vs
Heterozygous
Homozygous: the 2 alleles for a gene are the same
Heterozygous: the 2 alleles for a gene are different
• Only the dominant trait will show up in the
phenotype, but the genotypes can be different,
even if they look the same
• E.g. Smooth pea pods are dominant. The smooth
pod could be SS or Ss, but the bumpy one must be
ss
Homozygous vs
Heterozygous
Phenotype
Genotype
Homozygous
or
Heterozygous
ss
Homozygous
recessive
SS
Homozygous
dominant
Ss
Heterozygous
More Complicated
Inheritance
• Sometimes it’s more complicated than that
Complications:
• More than 2 forms of an allele
• 2 dominant alleles
• Multiple genes controlling 1 visible trait
Incomplete Dominance vs
Codominance
Incomplete dominance: both alleles are dominant vs
other alleles. When they appear together, they make
a new phenotype that is a blend
Yellow x blue = green
Codominance: both alleles are dominant vs other
alleles. When they appear together, they make a new
phenotype where both show up at the same time
Yellow x blue = yellow & blue
Incomplete or
Codominance?
Multiple Alleles
• Previously looked at cases where there were only 2
alleles – sometimes you can have more
• You can have multiple alleles and incomplete
dominance or codominance happening at once
• E.g. blood types
• E.g. Rabbit fur has 4 alleles: brown, chinchilla,
Himalayan, and albino
Blood Types
• Blood can be A, AB, B, or O
• O is recessive
• Use Punnett squares to predict blood types for the
offspring of these parents:
• AO and AB
• O and BB
• AO and BO
• AB and AB
• O and AO
Rabbit Fur
Polygenic Inheritance
Polygenic inheritance: More than 1 gene can control
a visible trait. Gives you a broad range of phenotypes
(and even more genotypes)
• E.g. eye color, height
• Can be polygenic and codominance or
incomplete dominance at the same time
Eye Color
Inherited vs Acquired
• Inherited traits are things you are born with
• Acquired traits you get later
o A subtype of acquired traits can affect your DNA
Acquired or inherited?
• Learn to speak French
• Dye hair blonde
• Dog’s ears are cropped
• Adult’s height
• A baby’s blonde hair turns brown
Genes & the Environment
• Part of nature vs nurture debate
• Some people thought genes didn’t matter – what
environment you grew up in would matter most
• Turns out, environment can change the way genes
are expressed as well as what you do with them
• Environment can make small changes to your DNA
that turn genes “on” or “off”
• E.g. Changes how many copies of a protein you make
• Field known as epigenetics
o (if you want to research it)