Transcript Genetics_regulars

Fundamentals of Genetics
Chapter 9
Genetics Goals
• Be able to explain the relationship
between genes, alleles, and traits
• Be able to distinguish between a species’
genotype and phenotype
• Be able to use a Punnett square to
calculate the probability of each phenotype
and genotype given a set of parents
• Know the three laws of genetics
2-25-10
What is Genetics
• Genetics is the scientific study of heredity.
• Heredity is what makes each species
unique.
UMBUKU Lizard
LIGER
ZEEDONK
Gregor Mendel
-
Austrian Monk, famous for
his work with pea plants.
known as the Father of
Genetics
chose traits that did not
appear to blend
was the first to follow single
traits from generation to
generation
• trait - a specific
characteristic that varies
from one individual to
another
• true-breeding (purebred) plants - always
produce offspring
identical to themselves.
• Hybrids - offspring from
parents with different
traits.
•
Alleles - different forms
of a gene
Genes – a short segment
of DNA on a
chromosome dthat
contains the instructions
for a single trait
Molecular genetics –
the study of the structure
and function of
chromosomes and genes
The Principle of Dominance
• Dominant alleles are
always expressed
– Ex: brown eyes are dominant.
• 2 brown alleles = brown eyes
• 1 brown allele and 1 blue allele =
brown eyes
• Recessive alleles are
only expressed if both
alleles are recessive
– Ex: blue eyes are recessive
• 2 blue alleles = blue eyes
Segregation & Independent
Assortment
• The Law of Segregation
– separation of alleles during meiosis to form
gametes (sex cells).
• The Law of Independent Assortment
– genes for different traits can segregate
independently during the formation of
gametes.
2.26.10
gametes
gene
A
a
Homologous chromosomes
A
a
gametes
gene
A
A
Homologous chromosomes
A
A
• Homozygous –
both alleles of a
pair are alike (BB)
– Purebred
• Heterozygous –
two alleles in the
pair are different
(Bb)
– Hybrid
• Genotype – genetic makeup (BB,
Bb, bb)
• Phenotype – physical characteristic
(eyecolor, haircolor etc.)
Students
should use
book here
Genetic Generations
• P generation –
pure-bred parents
are crossed
• F1 generation –
offspring of P
generation selfpollinate
• F2 generation –
offspring of the F1
generation
RR
rr
pollen
Parental
generation (P)
pollen
cross-fertilize
true-breeding,
purple-flowered
plant
true-breeding,
white-flowered
plant
Rr
First-generation
offspring (F1)
Punnett Squares
• Monohybrid – only one characteristic is studied
• Monohybrids have 2 possible phenotypes,
3 possible genotypes
Punnett Squares
–
1.
2.
3.
Key: use a letter to represent each allele
Cross: the genotypes of the parents.
Punnet square
Write the genotype: list all possible
genotypes, then the fractions and
percents shown in the Punnet square
4. Phenotypes: show all, with fractions and
percents.
Probability & Genetics
• Probability is the likelihood that an event
will happen.
• used to predict the outcomes of genetic
crosses
• Penny – 2 possible outcomes
3.1.10
Dominant-Recessive
Ex:
RR = Red
rr = White
Rr = red
- Dominant trait always shows up if present
- Recessive trait only shows up if dominant
trait is not present
- Dom. trait is capitalized, rec. trait is
lowercase
- 3 genotypes, 3 phenotypes
Trait
Seed
shape
Seed
color
Pod
shape
Pod
color
Dominant form
Recessive form
smooth
wrinkled
yellow
green
inflated
constricted
green
yellow
purple
white
at leaf
junctions
at tips of
branches
tall
(1.8 to
2 meters)
dwarf
(0.2 to 0.4
meters)
Flower
color
Flower
location
Plant
size
Dihybrid Cross
- Involves two
pairs of
contrasting
traits
Ex: color and
shape for peas
3.4.10
Chapter 14: The Human
Genome
Pedigree
• Circles – stand for females
• Squares – stand for males
• Colored circle or square – affected by
recessive trait
• Horizontal line – connects married couples
• Vertical line with bracket – connects
parents to children
March 8
A Mutation is:
A change in the
nucleotide-base
sequence of a gene
or DNA molecule
Examples:
• Down syndrome:
trisomy 21
• Klinefelter
syndrome: XXY
• albinism
Mutations can be either unimportant or
harmful