TOPIC
Genetics
ESSENTIAL
QUESTION
How does the crossing over of chromosomes that occurs during recombination result in
increased genetic variation in a population?
Which factors have the greatest influence on creating increased genetic variation within a
species?
In what ways do mutations play a part in the processes involved in the evolution of species?
REFLECT
RECORD
Review
• All cells are diploid: one copy of chromosomes from mom and one
copy from dad.
• How many chromosomes make up who you are?
New Vocab
• Genes:
• Alleles:
• Homologous Chromosomes:
• Heredity:
• Genetics:
• Traits:
SUMMARY
© Sunshine State Science 2017
TOPIC
Gregor Mendel
Reflect
Record
“Father of Genetics”
3 Laws of Inheritance:
1. Law of Inheritance
2. Law of Segregation
3. Law of Independent Assortment
Why Pea Plants?
• Reproduce sexually
• Male and female gametes in same flower
• Grow rapidly
• Easy to care for
• Distinctly separate characteristics (tall/short, wrinkled/round peas)
Mendel’s Experiments
• Had control over breeding
• Used only purebred plants
• Observed “either-or” traits
SUMMARY
© Sunshine State Science 2017
TOPIC
Monohybrid Cross
Reflect
Record
What is a Cross?
Cross:
P=
F1 =
F2 =
Monohybrid Cross
Hybrid:
First Generation
• Tall plant x short plant
• Offspring were all tall plants
•
Filial =
• Short trait seemed to have disappeared
Second Generation
• Two F1 hybrid plants were crossed
• 75% of offspring were tall; 25% were short
• The short trait seemed to reappear
SUMMARY
Summarize a monohybrid cross through two generations. (HINT: cross
the P generation then cross the F1 generation to get to F2)
© Sunshine State Science 2017
TOPIC
Law of Dominance
Reflect
Record
• Dominant:
Example:
• Recessive:
Example:
Genotype vs Phenotype:
• Genotype:
• Phenotype:
Significance of Alleles
• Alleles have assigned letters
• Each individual has two alleles (one from each parent)
• Homozygous:
• Heterozygous:
SUMMARY
1. How can I determine a phenotype of a horse?
2. How many dominant alleles must be present for a phenotype that
results from a dominant allele?
3. How would you describe the organism with the genotype Tt?
© Sunshine State Science 2017
TOPIC
More Laws
Reflect
Record
Law of Segregation
When chromosomes separate in meiosis, each gamete (egg or sperm)
will receive only one chromosome from each pair.
Example:
Law of Independent Assortment
The assortment of chromosomes for one trait doesn’t affect the
assortment of chromosomes for another trait.
Genes for different traits are inherited independently of one
another
Punnett Square
Example
SUMMARY
1. A couple has two children, both are girls. What is the chance the
parents’ next child is a girl?
2. A female dog homozygous for brown fur mates with a male
homozygous for yellow fur, what would the outcome of offspring be
for a litter of 8?
© Sunshine State Science 2017
TOPIC
Dihybrid Cross
Reflect
Record
Finding possible genotypes for offspring when considering two
genes at the same time.
Steps:
Example #1
Genotype:
Sort Alleles:
Phenotypic ratio:
Example #2
Genotype:
Sort Alleles:
Phenotypic ratio:
Example #3
Genotype:
Sort Alleles:
Phenotypic ratio:
SUMMARY
© Sunshine State Science 2017
TOPIC
Exceptions to Laws
Reflect
Record
Some alleles are neither dominant nor recessive, and many traits are
controlled by multiple alleles or multiple genes.
Incomplete Dominance
• Heterozygous phenotype is between the two homozygous
phenotypes.
• Neither allele is dominant or recessive
•
Example:
Codominance
• Both traits are fully and separately expressed.
•
Examples:
Blood Type  both codominance AND multiple alleles
• Codominance:
• Multiple Alleles:
© Sunshine State Science 2017
TOPIC
Exceptions to Laws
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Record
Multiple Alleles
• Having more than two alleles for one gene
•
Example:
Polygenic Inheritance
• A trait produced by two or more genes
•
Usually shows a RANGE in phenotype
•
Ex:
• Ocassionally, epistasis can occur
•
When one gene overshadows all of the other
•
Ex:
SUMMARY
© Sunshine State Science 2017
TOPIC
Linked Genes
Reflect
Record
• Genes that are physically located on the same chromosome will be
inherited together.
•
Ex:
•
Linked genes can only be separated or broken apart during
Crossing Over
Sex-Linked Traits
• Males and females have exactly the same chromosomes for pairs 122. These are called autosomes.
• The last pair of chromosomes determine the gender of the individual
and are called sex chromosomes.
• Females:
• Males:
• Sex-Linked Genes – genes on sex chromosomes (X and Y).
• Y chromosome carries ______ genes.
• X chromosome contains ________ genes that affect
________traits.
• X-Linked Genes – Genes on the X chromosome.
• Females inherit gene as normal and principle of dominance
applies.
• Males inherit gene on the X, ,but not the Y.
***Why do males express the trait whether it is dominant or
recessive??
Color Blindness Example:
SUMMARY
© Sunshine State Science 2017
TOPIC
Pedigree
Reflect
Record
A chart used to trace the phenotypes and genotypes in a family to
determine whether people carry diseases or traits.
• Similar to a family tree but traces a trait or disease
• Can be used by potential parents or genetic counselors to determine
probability of passing on the disease to children.
• Studying pedigrees can help scientists determine the inheritance
pattern for a trait (dominant or recessive, sex-linked or autosomal).
Autosomal Recessive
• most common inheritance pattern for genetic diseases.
• Disease is _______ in the family (only a few affected family members).
• ______ and __________ are equally likely to inherit this disease.
• Disease often _______ generations (a childe may inherit the disease
even though neither of the parents have the disease).
•
Examples:
Autosomal Dominant
• Disease is __________ in the family (affects many members).
• _______ and ___________ are equally likely to inherit this disease.
• Disease will _________ skip a generation – a child cannot inherit the
disease if both parents are healthy.
•
Examples:
SUMMARY
© Sunshine State Science 2017
TOPIC
Pedigree
Reflect
Record
Sex-Linked Recessive
• Disease is ______ in the family (only a few affected family members).
• Disease often _______ generations.
• _______ are more often affected than females.
• Affected fathers ___________ pass on to their sons! (why?)
•
Examples:
How to Determine the Pattern of Inheritance in a Pedigree:
1. If there are way more males than females affected (shaded in), than
the pedigree is tracing a ____________________.
2. If not, look for two parents that are the same shade that have a child
who is different from them. Label that child homozygous recessive
(Ex. rr) and the parents heterozygous (Ex. Rr).
a. If the child was shaded, the pedigree is tracing an
_____________________.
b. If the parents were shaded, the pedigree is tracing an
_____________________.
SUMMARY
© Sunshine State Science 2017