Download Introduction to Genetics

CHAPTER 11
Introduction to Genetics
GENETICS & YOU
Something to keep in mind as we begin our discussion on genetics…
• Your traits are a combination of your genetic material (DNA) and the environment
around you.
• For Example: Why are people from poor countries often short?
 Malnutrition
• Because of this…
• The physical appearance of an individual cannot always be directly linked to
an individual’s genetic makeup.
NATURE VS. NURTURE
• What can we use to study how the environment affects the
expression of our genes?
GREGOR MENDEL
• Considered the “Father of Genetics”
• Performed Experiments to Study Heredity
• Heredity – the passing of traits or characteristics from parent to
offspring
• In his experiments Mendel used Pea Plants.
• Why?
MENDEL’S PEA PLANTS
1.
2.
3.
4.
5.
Cheap & Readily Available
Easy to Grow & Don’t Move (easy to contain & control/manage)
Grow fast –study multiple generations
Control their breeding/reproduction
Characteristics were easy to study because they came in easily
identifiable pairs.
a) Round vs. Wrinkled Pea Shape
b) Tall vs. Short Pea Plants
c) Green vs. Yellow Pea Pods
MENDEL’S EXPERIMENT
Mendel controlled the reproduction of his pea plants so he could study
heredity.
• He did this by:
 Removing the Stamen (male)
 Contains the Anther
 Pollen = Plant Sperm
 Carpel (contains the stigma, style, ovary) – female reproductive structures
• Crossed Plants that showed the same traits only.
• Created “true or pure bred” lines
MENDEL’S EXPERIMENT
• Once Mendel had his true or pure bred lines, he could cross
plants that had different traits.
• What did Mendel look for?
 Patterns!
OBSERVATIONS
So what did Mendel observe when he performed his experiments?
________________ X ___________________
All _________________________
____________________ x ______________________
Ratio
3(
) __________________: 1 (
) _________________
DOMINANT VS. RECESSIVE
• Traits like pea shape are said to be either dominant or recessive.
• A recessive trait become hidden by a dominant trait.
• In Mendel’s cross which trait was dominant?
• Which trait was recessive?
• How do we know recessive traits are present & get passed down?
MENDEL DIDN’T KNOW ANYTHING
ABOUT GENES!
• Gene – segment of DNA that codes for a specific protein which controls
a trait.
• Genes can exist in more than one form!
• For example
 Round or Wrinkled are 2 forms of the gene or protein for seed shape.
• We call these different forms of a gene: alleles
• Each parent has 2 alleles for each trait BUT only gives one to the
offspring!
• Which one? That’s all chance!
PROBABILITY & GENETICS
• Diploid Organisms have 2 copies of each numbers chromosome.
• Remember, chromosomes of the same shape and size are called:
 Homologous Chromosomes
• Homologous Chromosomes carry the same genes but can have
different forms or alleles of these genes.
• For Example:
Both chromosomes 18 carry the gene that controls the shape of
your hair line. (one chromosome 18 came from mom & one from dad)
18 A – Widow’s Peak
18 B – No Widow’s Peak
So, which one will you pass on to your child?
PROBABILITY & GENETICS
• Scientists can make predictions about which traits will get passed onto
offspring & therefore what offspring might look like.
• The study of these predications is called probability.
• Probability
 Expressed as a fraction or a percent.
 Equation: # of times a specific event occurs
total # of possible outcomes
 can be either dependent or independent
INHERITANCE OF ALLELES
• Mendel crossed plants that differed in one gene/trait: pea shape.
• This type of cross is called a monohybrid cross.
________________ X ___________________
All _________________________
____________________ x ______________________
Ratio
3(
) __________________: 1 (
) _________________
GENERATIONS & PUNNETT SQUARES
• The plants involved in the 1st cross are called the parental or P generation.
• The offspring of the P generation are called the F1 generation.
• The offspring of the F1 generation are called the F2 generation.
Punnett Square
• Capital Letter represents the: Dominant Allele
• Lowercase Letter represents the: Recessive Allele
• Place each parent’s allele combinations across the top & side of the box &
fill in the squares.
GENOTYPES & PHENOTYPES
• Both RR pea plants & Rr peal plants look round, but are they the same
genetically?
• Round is called a phenotype = physical appearance
• Rr or RR is called a genotype = actually genes or alleles of an individual
• Two Types of Genotypes
 Homozygous = two identical alleles (RR or rr)
 Heterozygous = two different alleles (Rr)
GENOTYPES & PHENOTYPES
Classify the following as either a genotype or phenotype.
For each genotype determine if it is homozygous or heterozygous.
RR
Round
Rr
GENOTYPES, PHENOTYPES, &
PUNNETT SQUARES
• Every time you make a Punnett Square you MUST indicate both
the Phenotypic & Genotypic Ratios!
• Let’s do an Example: homozygous round pea X heterozygous round pea