Transcript Intro to Genetics - MacWilliams Biology

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Intro to Genetics
Mrs. MacWilliams
Biology
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Objectives
1.
Describe how homologous chromosomes carry
the same genes, but may be different alleles.
2.
Define the terms dominant, recessive, genotype,
phetotype homozygous, and heterozygous.
3.
Compare Mendel’s three laws of heredity.
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Key Terms
Genetics
The study of heredity
Heredity
The study of HOW parents pass certain
traits to offspring.
Chromosome
Rod shaped structures within the nucleus of
the cell that contain genes
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Key Terms continued
Genes
Units of heredity information located on
chromosomes
Gametes
Reproductive cell
Human: sperm & eggs;
Flowers: pollen (sperm) & pistil (eggs)
Alleles
Either member of a pair of GENES that
determines a single trait
Ex: gene pair Yy
+ Two factors involved in
development
1. Heredity
2. Environment
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Relationship of Genes to Each Other
1. DOMINANT
- trait that hides the recessive
2. RECESSIVE
- trait that is hidden by the
dominant
Homozygous
vs.
Heterozygous
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Homozygous (PUREBRED) (homo=same)
Two genes in a pair are identical
Homozygous Dominant – both genes in the pair are the
dominant trait
Example: AA
Homozygous Recessive – both genes in the pair are the
recessive trait
Example: aa
Heterozygous (HYBRID) (hetero=different)
There is one dominant gene and one recessive gene
Example: Aa
**ZYGOUS = ZYGOTE
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Ha Ha Just kidding… this is not
what they would look like!!!!
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Two Ways to Designate Organisms
1. GENotype (GENes)
a. Actual genetic info on the chromosome
b. Uses DOUBLE LETTERS to signify
 double letters because each parent
“sends” a trait
 double letters due to HOMOLOGUS nature
of chromosomes
 HOMO = SAME LOGOUS = LOCATION
c. Use only one letter per TRAIT
 uppercase letters for dominant traits
 lower case letters for recessive traits
 i.e. AA, Aa, aa (NOT AB)
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2. PHenotype (PHoto)
a. Outward appearance of
organism
Example: brown eyes, blonde
hair
+ GREGOR MENDEL
“The Father of Genetics”
Mendel was a pioneer in genetics, born 1822,
lived in a monastery, plant breeding
experiments.
Used pea plants. WHY?
1. Easy to grow
2. short gestation time
3. produced many offspring at a time.
Studied traits that had 2 contrasting forms:
Ex. Tall vs. short; yellow vs. green
Kept meticulous records and calculated ratios.
Did this through many generations several times
for each trait.
+ Mendel’s 1st Law of Heredity
DEALS WITH ONE GENE
1.
Law of Segregation
-In a pair of alleles (e.g. blue and brown eye
color) only ONE of the two are represented in a
gamete.
**Alleles SEGREGATE into different gametes
during meiosis (ensures each parent only donates
half of their genetic material to each offspring)
+ Mendel’s 2nd Law of Heredity
DEALS WITH 2 OR MORE GENES
2. Law of Independent Assortment
 Alleles
of different genes separate independently of
one another during gamete formation (ex. Alleles for
eye color separate independently from hair type)
 The combination of alleles in any one gamete is totally
random (allows for a great deal of variation in
organisms)
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Mother donates blue eyes allele and straight hair allele
Father donates brown eyes allele an curly hair allele
Offspring can get any combo
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Blue eyes straight hair
Blue eyes curly hair
Brown eyes straight hair
Brown eyes curly hair
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+Mendel’s
3rd Law of Heredity
3. Law of Dominance
One gene in a pair may prevent the other gene in the pair from
being expressed.
ALWAYS REPRESENTED BY A CAPITAL LETTER
Recessive- the gene that is hidden by the dominant gene
ALWAYS REPRESENTED BY lower case letters
Example
Yellow (A) Dominant
Green (a) recessive