Transcript Genes - Dallas ISD

Genes and Inheritance
Chromosome
Genes contain the
information for the
production of proteins,
which specify traits.
Gene
Protein
Since genes are inherited,
traits are also inherited.
Trait
Location of Genes
In sexually reproducing
organisms, cells have
a homologous pair of
chromosomes (one from
each parent).
Chromosome
from egg
(mom)
Chromosome
from sperm
(dad)
Chromosomes from a
homologous pair have the
same genes but can have
different alleles.
Allele: different form of a
gene
May be dominant or
recessive.
Homologous pair
of chromosomes
Gregor Mendel: Father of Genetics
Genetics: branch of biology
dealing with heredity
Gregor Mendel (1822-1884)
was an Austrian monk who is
regarded as the father of genetics.
Mendel used pea plants to study the
inheritance patterns of many traits.
Mendel’s View of Inheritance
Parent A
Parent B
Parent A
Parent B
Offspring
Offspring
Old Idea
New Idea
(Mendel)
Blending of
parental traits
Inherited traits behave
as discrete units
Mendel’s Pea Experiments
Mendel examined a small number of phenotypic characters or
traits in peas.
Dominant alleles masked recessive alleles.
Seed color
yellow dominant over green
Pod color
green dominant over yellow
Seed shape
round dominant over wrinkled
Pod shape
inflated dominant over constricted
Using a Punnett Square: Monohybrid
Crosses
X
Parents
Pp
Pp
Each parent provides
two gametes for the grid
Calculates outcomes of
genetic crosses.
Important vocabulary:
P
Homozygous dominant
Gametes
p
Heterozygous
P
Gametes
Homozygous recessive
PP
Pp
Pp
pp
p
Offspring
Genotype and Phenotype
Genotype
Phenotype
PP
Purple
(homozygous)
Pp
The genotype of an organism refers
to its genetic make-up.
The phenotype of an organism refers
to its observable features or traits.
(heterozygous)
Pp
Purple
Purple
(heterozygous)
pp
(homozygous)
White
Results of Mendel’s Experiments
Seed shape
Round
Wrinkled
Seed color
Yellow
Green
Pod color
Green
Yellow
Flower position
Axial
Terminal
Pod shape
Inflated
Constricted
Stem length
Tall
Dwarf
5474
1850
7324
Round
Wrinkled
TOTAL
2.96 : 1
6022
2001
8023
Yellow
Green
TOTAL
3.01 : 1
428
152
580
Green
Yellow
TOTAL
2.82 : 1
651
207
858
Axial
Terminal
TOTAL
3.14 : 1
882
299
1181
Inflated
Constricted
TOTAL
2.95 : 1
787
277
1064
Tall
Dwarf
TOTAL
2.84 : 1
Mendel’s Law of Segregation
Each pair of alleles is separated into different gametes and into
different offspring.
Gametes contain only one copy of a gene since they only
receive one chromosome from each homologous pair.
Homologous pair of
chromosomes, each has a
copy of the gene on it (A or a)
Gametes (sperm
Or egg cells)
Law of Independent Assortment
Genotype: AaBb
Alleles for different traits are sorted
independently of each other.
All combinations of alleles are
distributed to gametes with equal
probability.
Intermediate
Cells
Gametes
Ab
Ab
aB
aB
Selected Hereditary Traits
Dominant
Recessive
Right handedness
Left handedness
Hitch-hiker’s thumb
Normal thumb
Polydactylism (extra digits)
Normal digits
Pattern baldness
Normal hair
Free ear lobes
Attached ear lobes
Hitch-hiker’s thumb
Free ear lobe
Handedness
Polydactylism is a
dominant trait
Attached ear lobe
In this crowd of men, almost all
show some degree of pattern
baldness, a dominant trait.
Human Tongue Roll
The ability to roll the tongue into a U-shape when viewed from
the front is controlled by a dominant allele.
Dominant
Recessive
Phenotype:
Can roll tongue
Phenotype:
Cannot roll tongue
Allele:
T
Allele:
t
Punnett Square Practice
1.
Brown hair (B) is dominant over lighter hair
colors (b). If two heterozygotes for this trait
mate, what are the:
a. genotype frequencies
b. phenotype frequencies
of the offspring?
Punnett Square Practice
2.
Dwarfism (D) is dominant over normal height (d).
If a person of normal height and a dwarf who is
homozygous dominant mate, what are the
chances of having a child that is also a dwarf?
Punnett Square Practice
3. Polydactyly, or having extra digits (P) is dominant over
having five digits on each limb (p). If a woman with
polydactyly mates with a normal male, then:
a. What are the possible genotypes of the woman?
b. What is the genotype of the male?
c. Create two Punnett Squares displaying their
possible children.
Punnett Square Practice
4. Tallness
in pea plants (T) is dominant to
shortness (t). Round seeds (R) are dominant to
wrinkled seeds (r). Set up a Punnett Square
showing the mating results of two plants that are
heterozygous for both traits.