Transcript sex-linked traits

JOURNAL : EOCT BIOLOGY QUESTIONS
1. In Mendel’s experiment with a single trait, the trait that
disappeared in the first generation and reappeared in the next
generation is called the
a. Homozygous trait
b. Dominant trait
c. Recessive trait
d. Heterozygous trait
2. In fruit flies, the gray body color is (G) is dominant to the ebony
body color (g). What is the genotypic ratio of the offspring of a
heterozygous gray female and an ebony male?
a. 25% Gg, 75% gg
b. 50%Gg, 50% gg
c. 75% gray, 25% ebony
d. 100% gray
When is a trait said to display
incomplete dominance?
When the heterozygote has a
phenotype intermediate between the
phenotypes of two homozygotes
What is codominance?
The phenotype of the heterozygote is not
intermediate between the phenotypes of
the homozygotes; rather , the
heterozygote expresses both
homozygote phenotypes simultaneously
In horses, gray horses (GG) are codominant to white
horses (WW). The heterozygous horses(GW) is an
appaloosa horse (a white horse with gray spots on the
rump and loins). Cross a white horse with an appaloosa
horse.
Genotypic ratios:
Phenotypic ratios:
What is a test cross?
A cross that is made in which one
individual of unknown genotype is
crossed with another individual with a
homozygous recessive genotype
Ex. TTx tt = all tall (Tt)
Recessive will not appear
Tt x tt = 50% of offspring will show recessive
trait (tt), 50% heterozygous (Tt)
What is a backcross?
When a cross made between an F1 genotype
and either of the parental genotypes
Ex. Tt x tt or Tt x TT
Law of Dominance:
The trait that is observed when two alleles are
present
Ex. Pp
- purple
Law of Segregation
Alleles segregate (separate) during
the formation of gametes and one
allele goes into each gamete
Which law was formulated as a
result of Mendel’s dihybrid
crosses?
LAW OF INDEPENDENT
ASSORTMENT:
Alleles at different loci separate
independently of one another
Summary of Mendel’s laws
LAW
DOMINANCE
SEGREGATION
INDEPENDENT
ASSORTMENT
PARENT
CROSS
OFFSPRING
TT x tt
tall x short
100% Tt
tall
Tt x Tt
tall x tall
75% tall
25% short
RrGg x RrGg
round & green
x
round & green
9/16
pods
3/16
pods
3/16
pods
1/16
pods
copyright cmassengale
round seeds & green
round seeds & yellow
wrinkled seeds & green
wrinkled seeds & yellow
12
Dihybrid Cross
9:3:3:1
9 round yellow
3 wrinkled yellow
3 round green
1 wrinkled green
copyright cmassengale
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APRIL 10, 2012
EQ: HOW ARE SEX-LINKED TRAITS & MULTIPLE
ALLELES PASSED FROM ONE GENERATION TO THE
NEXT?
WARM-UP: WHAT DID YOU DO DURING YOUR
SPRING BREAK?
*When several genes affect
a character/trait
A
B
I ,I ,
i
*caused by nondisjunction of
chromosomes during anaphase
**Individuals
contain 3 copies of
chromosome 21
*
*1/700 births
characteristic facial
features, heart defects , &
leukemia
*
*Missing a sex chromosome
Caused by a gene
located on either an
X or Y chromosome.
Ex. Colorblindness
& Hemophilia
Sex-linked Trait Problem
• Example: Eye color in fruit flies
•
(red-eyed male) x (white-eyed female)
XRY
x
XrXr
• Remember: the Y chromosome in males does not
carry traits.
• RR = red eyed
Xr
Xr
• Rr = red eyed
• rr = white eyed
• XY = male
XR
• XX = female
Y
copyright cmassengale
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STANDARD SYMBOLS USED IN PEDIGREES: