Download BIOLOGY UNIT 6 STUDY GUIDE

BIOLOGY UNIT 6 STUDY GUIDE
Understand early
Blending Hypothesis
Understand
Particulate Hypothesis
Understand truebreeding plants
Monohybrid Cross:
Number of generations
and Identity of plants in
each generation
Understand Mendel’s
Principle of Segregation
Monohybrid Cross:
Genotypic ratio (F2)
Explains how offspring inherit traits from both parents. Example, redflowered plant crossed with yellow-flowered plant of same species; red &
yellow hereditary material in offspring blends producing orange-flowered
plants. All offspring of orange-flowered plants have orange flowers.
Parents pass on to their offspring separate & distinct factors (genes) that are
responsible for inherited traits. Mendel stressed that heritable factors
(genes) retain their identity generation after generation.
When self-fertilized, true-breeding plant produces offspring identical in
appearance to itself generation after generation.
Pairing in which parent plants differ in only one (mono) character
Parent Generation: True-breeding parents (Purple flowers x White flowers)
F1 Generation: All identical hybrids (Purple flowers self-fertilize…)
F2 Generation: ¾ same color as F1 plants, ¼ color of “disappearing” truebreeding parent
Mendel reasoned F1 plants carried 2 factors for flower color—one for purple
& one for white
Two alleles (alternative forms of genes) for a character segregate (separate)
during the formation of gametes (sex cells), so that each gamete carries only
one allele for each character.
R
r
R
p
RR
Rr
Rr
rr
Monohybrid Cross:
Phenotypic ratio (F2)
Understand when and
how a test cross is
performed. Know the
possible outcomes.
3 Purple : 1 White
An organism with a DOMINANT PHENOTYPE could have 2 POSSIBLE
GENOTYPES: DOMINANT HOMOZYGOUS (PP) or HETEROZYGOUS (Pp)
A testcross breeds an individual of unknown genotype, but dominant
phenotype with homozygous recessive individual
If RR, then:
If Rr, then:
R
R
R
r
r
Rr
Rr
r
Rr
rr
r
Rr
Rr
All offspring purple.
Dihybrid Cross:
Parental gametes
Dihybrid Cross:
Phenotypic ratio (F2)
1 RR : 2 Rr : 1 rr
r
Rr
rr
½ offspring purple & ½ offspring white.
Pairing in which parent plants differ in two (di) characters
True-breeding for round yellow seed x True-breeding for wrinkled greed seed
WWYY = gametes WY, WY, WY, WY
wwyy = gametes wy, wy, wy, wy
F1 generation: Heterozygous round yellow seeds, WwYy (Self-fertilize…)
WwYy = gametes WY, Wy, wY, wy
F2 generation: Four different pea phenotypes result
9/16: Round yellow, 3/16: Wrinkled yellow, 3/16: Round green, 1/16:
Wrinkled green 9:3:3:1
See Above
F2 Generation:
RY
rY
Dihybrid Cross:
Number of generations
and Identity of plants in
each generation
Understand Mendel’s
Principle of
Independent
Assortment
Understand Pattern of
Inheritance:
Intermediate
Inheritance
Know examples of
Intermediate
Inheritance and How to
construct an accurate
Punnett square
Ry
ry
RY RRYY
RrYY
RRYy
RrYy
rY RrYY
rrYY
RrYy
rrYy
Ry RRYy
RrYy
RRyy
Rryy
Ry RrYy
rrYy
Rryy
rryy
During gamete formation in an F2 cross, a particular allele for one
characteristic can be paired with either allele of another character. The
alleles for different genes are sorted into gametes independently of one
another.
For some characteristics, neither allele is dominant.
Heterozygotes have a phenotype that is intermediate between the
phenotypes of the two homozygotes
Although F1 phenotypes are intermediate, this inheritance pattern doesn’t
support blending hypothesis – because parent phenotypes can reappear in F2
generation.
Example: Andalusian chickens
P generation: Black chicken, CBCB x White chicken CWCW
F1 generation: All “Blue” chickens, CBCW (Mating among F1…)
F2 generation: 1 Black chicken, CBCB : 2 “Blue” chickens, CBCW : 1 White
chicken, CWCW
CB
CB
CW CBCW CBCW
CW CBCW CBCW
Understand Pattern of
Inheritance:
Multiple Alleles and
Codominance
Know examples of
Multiple
Alleles/Codominance
and How to construct
an accurate Punnett
square
For many genes, several alleles exist in a population, expanding the number of
possible genotypes & phenotypes.
Exhibiting codominance means that a heterozygote expresses both traits,
EQUALLY. This is different from intermediate inheritance – the individual’s
phenotype isn’t intermediate, but rather shows separate traits of both alleles.
Example: Human blood type
P generation: Any of six possible genotypes
(O: ii, A: IAIA or IAi, B: IBIB or IBi, AB: IAIB)
See example crosses below:
IA
i
IB
IB
IA
IB
i
IAi
IA i
IA IAIB
IAIB
IA IAIA IAIB
A
B
B
i
Ii
ii
i Ii
Ii
IB IAIB IBIB
Understand Polygenic
Inheritance
Know examples of
Polygenic Inheritance
and How to construct
an accurate Punnett
square
Know examples of the
Importance of the
Environment, specific
to Humans
Know and Understand
the modern
Chromosome Theory of
Inheritance
Understand Two
Scenarios Genetic
Linkage and Crossing
Over
Understand how SexLink Traits work
Know Fruit Fly example
for Sex-Linked Traits:
Each generation and
genotypes for
individuals
When two or more genes affect a single character
Each allele contributes one “unit” of its particular trait, like tallness or
darkness.
The potential combinations of alleles (and thus range of phenotypes) for
character increases with number of genes that affect that character.
Examples: In humans, height & skin color
Cannot cross more than two traits in a Punnett square
Trees’ leaves: Size, shape, greenness depend on exposure to wind & sunlight
Siamese cats: Cooler temperature at extremities activates enzyme for darker
fur color
Humans: Nutrition influences height, Exercise affects build, Exposure to
sunlight darkens skin
Human identical twins: Affected by diet, activity level, history of illness,
exposure to sunlight
Environment vs. Genes: Blood count (altitude, physical activity, infection)
States that genes are located on chromosomes & behavior of chromosomes
during meiosis & fertilization accounts for inheritance patterns –
chromosomes undergo segregation & independent assortment during meiosis
Scenario 1: Gene loci close together – Homologous chromosomes pair up at
prophase I of meiosis, then cross over. The alleles tend to stay together.
Scenario 2: Gene loci far apart – Homologous chromosomes pair up at
prophase I of meiosis, then cross over. New combinations of alleles are
created.
Most sex-linked genes are found on X chromosome. Thus females carry two
copies of gene for this character (XX) while males only carry one copy (XY).
A recessive trait will only appear in females if BOTH X chromosomes carry
recessive traits, while that trait will appear in males only carry the trait on the
X. Most often, sex-linked traits are observed in males more frequently.
P generation: Red-eyed female, XRXR x White-eyed male, XrY
F1 generation:
Xr
Y
R
R r
X XX
XRY
XR XRXr
XRY
2 red-eyed females, 2 red-eyed males
F2 generation:
XR
Y
R
X XRXR
XRY
Xr XRXr
XrY
2 red-eyed females, 1 red-eyed male & 1 white-eyed male