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Introduction to Genetics
How Traits are Passed from
Parents to Offspring
Life Science
What is Inheritance?
In your lab notebook, please answer as best you can:
1. What are germ cells?
• Cells which divide by meiosis to become gam...
 Life begins when two gametes (sperm + egg) join
 A complete set of chromosomes results (23 + 23)
 The zygote starts as...
Differentiation
 Genes signal
different cells to
create proteins
that give them
unique shapes
& functions
 These cells g...
 The chromosomes from your mom and dad have
given your cells instructions to make YOU!
 Each characteristic you inherite...
Alleles: variations of a gene
Gene Alleles
Eye Color Blue, brown, green,
hazel
Pea height Tall, short
Pea color Yellow, gr...
1822-1884
Gregor Mendel
 An Austrian scientist-turned-monk
noticed patterns in the monastery's
garden
 Studied the inher...
Mendel's Experiments
 He wondered if traits seen in different
generations of pea plants were
• determined by environmenta...
Dominant and Recessive Traits
 Observed phenotype,
the outward expression
of the genes
 the F1 generation are
tall, showing that trait is
dominant
 T...
Genotypes: Genes and Alleles
 The genetic make-
up of an organism
is its genotype
 Every organism is
diploid (has 2 copi...
Genotype Genotype Phenotype
Homozygous
dominant
TT Dominant
Homozygous
recessive
tt Recessive
Heterozygous Tt Dominant
 H...
Punnet Square: Monohybrid Cross
 Used to predict the outcome of a genetic cross
The Law of
Segregation
 Diploid chromosomes
of parents undergo
meiosis
 Alleles separate as
they become haploid
egg or s...
Independent Assortment & Segregation
Which traits are dominant?
 Heterozygotes express an
intermediate phenotype
 Instead of overpowering
one another, both traits
are partially express...
Co-Dominance
 The inheritance of ABO blood groups
demonstrates co-dominant inheritance
 Two alleles are dominant (Type A...
Polygenic Traits
 The control of a trait by
more than one gene
• Skin color is controlled by at
least 6 alleles or genes
...
The Human Genome Project
 In the 1950's, scientists
were first able to view a
set of human
chromosomes
 In 2003, scienti...
Human Karyotype: 23 homologous
pairs
X + X = GIRLX + Y = BOY
 The X and Y chromosomes determines gender
Sex Chromosomes
 The mother always donates an X chrom...
Intro to Genetics
Intro to Genetics
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Intro to Genetics

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Mendelian genetics

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Intro to Genetics

  1. 1. Introduction to Genetics How Traits are Passed from Parents to Offspring Life Science What is Inheritance?
  2. 2. In your lab notebook, please answer as best you can: 1. What are germ cells? • Cells which divide by meiosis to become gametes (eggs or sperm). 1. How is metaphase I of meiosis different than metaphase in mitosis? • Homologous pairs line up in the middle and divided into the new cells. 1. A small segment of DNA that codes for a specific protein which determines a certain trait in an organism is called a… • Gene 1. What is the ploidy of a germ cell after it divides by meiosis? • Haploid (or n) 1. When homologous pairs line up during Metaphase 1 of meiosis, they often swap sections of DNA. This process increases genetic variation in the resulting gametes and is called… • Crossing over Week 10 Review Quiz Bonus: How are the daughter cells of mitosis different than those formed by meiosis? Mitosis ends with two, identical, diploid daughter cells while meiosis yields four, unique, haploid daughter cells.
  3. 3.  Life begins when two gametes (sperm + egg) join  A complete set of chromosomes results (23 + 23)  The zygote starts as a single cell, but soon begins to divide (via mitosis = identical cells)  Genes are "turned" on and off, causing cells to differentiate (change to have different forms/jobs) Fertilization: new life is formed
  4. 4. Differentiation  Genes signal different cells to create proteins that give them unique shapes & functions  These cells grow & divide to make tissues that form the organs of the developing baby
  5. 5.  The chromosomes from your mom and dad have given your cells instructions to make YOU!  Each characteristic you inherited from your parents is called a trait (eye color, earlobe shape, height, personality traits, etc.)  For each trait, you have a pair of alleles (one from your mother and one from your father) Heredity & Inherited Traits
  6. 6. Alleles: variations of a gene Gene Alleles Eye Color Blue, brown, green, hazel Pea height Tall, short Pea color Yellow, green Flower position Axial, terminal
  7. 7. 1822-1884 Gregor Mendel  An Austrian scientist-turned-monk noticed patterns in the monastery's garden  Studied the inherited traits of pea plants and found predictable, numerical ratios in the offspring  Observed some traits were dominant over others (i.e. yellow peas overpowered or occurred more often than green pea seeds)
  8. 8. Mendel's Experiments  He wondered if traits seen in different generations of pea plants were • determined by environmental factors (soil composition, temperature, sunlight) OR • "handed down" by parents (chromosomes weren't even discovered yet, so he had no idea how)  In his highly controlled experiments, he tested the hypothesis that each trait was determined by a set (not one, but TWO) inherited factors from each parent  Do you see the Scientific Method at work here?
  9. 9. Dominant and Recessive Traits
  10. 10.  Observed phenotype, the outward expression of the genes  the F1 generation are tall, showing that trait is dominant  The dwarf plant has the recessive trait (it is overpowered by the tall allele) Mendel’s Crosses
  11. 11. Genotypes: Genes and Alleles  The genetic make- up of an organism is its genotype  Every organism is diploid (has 2 copies of each chromosome)  Each trait is designated by a different letter  DOMINANT ALLELES ARE CAPITAL LETTERS  Recessive alleles are lowercase letters
  12. 12. Genotype Genotype Phenotype Homozygous dominant TT Dominant Homozygous recessive tt Recessive Heterozygous Tt Dominant  Homozygous means the two alleles are the same  Heterozygous means the two alleles are different Genotype determines Phenotype
  13. 13. Punnet Square: Monohybrid Cross  Used to predict the outcome of a genetic cross
  14. 14. The Law of Segregation  Diploid chromosomes of parents undergo meiosis  Alleles separate as they become haploid egg or sperm  They are combined again during fertilization to produce a diploid offspring
  15. 15. Independent Assortment & Segregation
  16. 16. Which traits are dominant?
  17. 17.  Heterozygotes express an intermediate phenotype  Instead of overpowering one another, both traits are partially expressed  Flower color traits separate again during meiosis and can be seen in the F2 generation Incomplete Dominance
  18. 18. Co-Dominance  The inheritance of ABO blood groups demonstrates co-dominant inheritance  Two alleles are dominant (Type A and Type B)  Both phenotypes are expressed in the heterozygote (Type AB)
  19. 19. Polygenic Traits  The control of a trait by more than one gene • Skin color is controlled by at least 6 alleles or genes  Each gene product is additive to others  The hallmark of a polygenic trait is • A bell curve distribution • A continuous distribution
  20. 20. The Human Genome Project  In the 1950's, scientists were first able to view a set of human chromosomes  In 2003, scientists finished mapping the human genome  Now every gene of each human chromosome is know by location and trait
  21. 21. Human Karyotype: 23 homologous pairs
  22. 22. X + X = GIRLX + Y = BOY  The X and Y chromosomes determines gender Sex Chromosomes  The mother always donates an X chromosome. Why?  The father gives either an X (female) or a Y (male).

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