Download File - Biology by Napier

STAAR REVIEW - GENETICS
Female
Tt
Male
Tt
In pea plants, tallness(T) is dominant over shortness(tt). Both parents are heterozygous for this trait. Place the correct letters of the alleles in the rest of the circles
to the left.
Define these words.
homzygous
Homologous Chromosomes
F1 Generation
Segregation
Gametes
F2 Generation
heterozygous
dominant
recessive
gamete
Practice with Monohybrid crosses:
Use Punnett Squares to show the possible offspring genotypes and phenotypes.
1. A male fruit fly is Rr for having red eyes and the female is also Rr. Red Eyes are dominant while
white is recessive. What possible offspring could they have?
a. What is the probability that the offspring will have red eyes?
b. What is the probability that the offspring will have white eyes?
2. In guinea pigs, having a rough coat (R) is dominant over having a smooth coat of hair (rr). What
are the probabilities for the offspring with parents who are RR and rr
a. What is the probability that the offspring will have a rough coat?
b. What is the probability that the offspring will have a smooth coat?
3. In some birds, having a long beak (L) is dominant over a short beak (ll). In a cross of a
homozygous dominant bird and a homozygous recessive bird what are the outcomes possible?
a. What is the probability that the offspring will have a long beak?
b. What is the probability that the offspring will have a short beak?
Practice with Dyhibrid Cross, Incomplete Dominance, and Sex-Linked Traits
Dihybrid crosses consider two traits when predicting outcomes. The traits are on the same homolgous
chromosomes. The FOIL method of determining the gamete alleles is used by many to insure that the correct
allele combinations are used.
first
F- first letter of each trait
O - the outer letters of each trait
I - the inner letters of each trait
L- the last letters of each trait
Example:
inner
BbRr
last
outer
The alleles are: BR, Br, bR,br
Dihybrid Crosses
In fruit flies, red eyes (R) is dominant over white
eyes (rr) , and long front legs (L) is dominant
over short legs (ll).
Complete this cross: RrLl x RrLl
Incomplete Dominances
Cross two pink flowers (RW)
RR = red flower
WW = white flower
How many red flowers will result?
How many flies will have white eyes and
short legs?
Fill in the missing alleles in the chart. (B) is for
black hair in guinea pigs and bb is (white). (R)
is for rough texture and (rr) is for smooth.
bR
bR
bR
BbRr
Br
Br
Sex-Linked Trait
Hemophilia is a recessive trait (hh) in
which the blood will not clot. Show a
cross between these parents:
X HX h x
BbRr
Br
BbRr
How many pink flowers will result?
BbRr
BbRr
How many guinea pigs will have black hair?
How many guinea pigs will have smooth hair?
X HY
What is the
probability of any
child having
hemophilia?
What is the chance
of having a son with
hemophilia?