Download Mendelian Genetics 4

Finishing Up Mendelian Genetics
AIM: How can our genes affect our health and
how can the environment affect our genes?
DO NOW: Handout
HOMEWORK: Review sheet
TEST ON TUESDAY, 2/15/11
Do Now
1. Which of the following crosses can never produce a child
with blood type O?
a) O x AB
b) A x B
c) A x O
d) O x O
Do Now
2. In squirrels, the gene for gray fur (G) is dominant over the
gene for black fur (g). If 50% of a large litter of squirrels are
gray, the parental cross that produced this litter was most likely
a) GG x Gg
b) GG x GG
c) Gg x gg
d) gg x gg
Do Now
3. Some individuals with blood group A may inherit the
genes for blond hair, while other individuals with blood
group A may inherit the genes for brown hair. This can be
explained by the principle of
a) dominance
b) multiple alleles
c) independent assortment
d) incomplete dominance
I. Genetic Disorders
What’s another way to say “two recessive traits”?
A. If mom or dad is heterozygous for a recessive
genetic disorder, would they be normal or sick?
What would their kid be?
Carriers – a parent that is heterozygous for a recessive
genetic disorder
B. If mom or dad is heterozygous for a dominant
genetic disorder, would they be normal or sick?
Could their kid be sick?
1. Huntington’s disease affects the nervous
system and causes a gradual loss of brain
function, uncontrollable movements, and
emotional disturbances. There is no cure.
Stop and think! Are there any
carriers in dominant genetic
disorders?
Huntington’s Disease
II. Sex-Linked Traits
What genotype makes an organism male?
What genotype makes an organism female?
XY
XX
A. Men only get one X chromosome. If there happens to be
a recessive gene on the X, men don’t have a dominant
gene that can cancel it out. They are going to express it.
B. Females have a far greater chance of having a dominant
gene to hide the recessive one.
C. Sex-linked traits – traits carried by either the X or the Y
chromosome
D. Sex-linked trait example: Color Blindness
Color blindness is a gene located on the
X-chromosome.
Who would be more likely to be affected by this gene?
Men or women?
E. Sex-linked trait example: Hemophilia
1. Hemophilia – characterized by really slow
clotting of the blood
III. Polygenic Traits
A. Most traits are the result of the action of many genes
(One trait = many genes).
ex. Skin color, hair color, and height depend upon the
interaction of many independent genes.
B. Polygenic traits are controlled by two or more genes.
1. They show a wide range of phenotypes
III. Environmental Influences on Heredity
Your genes are not the final answer!
A. There is so much that can be influenced by the environment,
including nutrition, exercise, and where you live.
B. Genes + Environment = Phenotype
Analyze the phrase,
“Heredity loads the gun,
but environment pulls
the trigger”
Ex. Diseases like diabetes or
ulcers may be in a genetic
code, but may never be
seen in the phenotype if the
person leads a healthy
lifestyle.
SUMMARY
How can our genes affect our health? Give at least 3
examples. They can be from any class on genetics!
How can the environment affect our genes? Give 3
examples (at least one not from class).
Complete the summary worksheet