Genetics

Melissa T. Emberton

Biology

Concepts

Instructions for specifying characteristics are carried in nucleic acids.

Mulitcellular organisms, including humans, form from cells that contain two copies of each chromosome. This explains many features of heredity.

History

Genetics: Study of inherited traits Heredity: Passing of traits from parents to

offspring. Gregor Mendel: Given credit for what we

know about genetics/heredity. Mendel studied garden peas and came up

with a model for inheritance.

How does the environment influence traits we have?

Students will… Construct Punnett squares in order to determine

phenotype of offspring. Predict what genes individuals carry based on traits they

have. Identify mechanisms of change that influence evolution Distinguish between mechanisms of change influencing

traits of organisms. Compare conditions necessary for populations to be in

Hardy-Weinberg equilibrium. Design animal with adaptations to help them survive.

Mendel’s Model For each trait, we have two copies of the gene—

one from the mother and one from the father. There are alternative forms of genes. These are

called alleles. For example, we possess two alleles for freckles. Their combination determine whether we will have freckles or not.

These alleles can be dominant or recessive. Dominant alleles, when present, will be expressed. Recessive alleles can be masked by dominant alleles. In order for recessive alleles to be expressed both must be recessive.

Gametes carry only one allele for each inherited trait. At fertilization each gamete contributes one allele.

If a person is carrying two alleles for a trait that are the same—they are homozygous for that trait. If the alleles are different they are heterozygous.

The genes we are carrying for traits is our genotype. The expression of those genes is our phenotype.

If Tall is dominant in pea plants and short is recessive. Which would

represent the genotype of a heterozygous plant

TT T

t tt ST

0% 0%0%0%

A. TT

B. Tt

C. tt

D. ST

20

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Which would represent the genotype of a short pea plant?

TT T

t tt ST

0% 0%0%0%

20A. TT

B. Tt

C. tt

D. ST

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How many plants would be tall if you cross a heterozygous parent

with a short parent?

¼ ½ ¾

All

woul

d be

tall

0% 0%0%0%

20A. ¼

B. ½

C. ¾

D. All would be tall

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Monohybrid cross:– Looks at only one trait at a time.

Dihybrid cross: – Looks at two traits at one time.– Each trait gets a different letter– Letters on Punnett Square are determined from

all possible combinations of parent alleles.

If black fur and long whiskers are dominant in rabbits.

A rabbit would need two letters for each trait.

homozygous dominant for color and homozygous recessive for whisker length

BBll—the rabbit would be black with short whiskers.

What about a rabbit who is heterozygous for both traits?

BbLl

What would the following rabbits look like?

BbLl– Black with long whiskers

bbLL– Grey with long whiskers

BBll– Black with short whiskers

Bbll– Black with short whiskers

Predicting offspring Cross two parents heterozygous for both

traits.

If Black is dominant and Long whiskers is dominant. What would the genotype of a rabbit that is grey and heterozygous for

whisker length be?

BBLL

Bbll

bbll

bbLl

0% 0%0%0%

A. BBLL

B. Bbll

C. bbll

D. bbLl

20

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What would the rabbits look like if you crossed one that is homozygous dominant for color and whisker length with a rabbit who is grey with

short whiskers?

¼ b

lack

long

, ¼ b

lac.

..

¼ b

lack

long

, ¼ b

lac.

..

All

grey

short

All

black

long

0% 0%0%0%

20A. ¼ black long, ¼ black short, ½ grey short.

B. ¼ black long, ¼ black short, ¼ grey long, ¼ grey short

C. All grey shortD. All black long

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Other Traits

Multiple Allele: Determine blood type. A & B are dominant—O is recessive.

Codominance: When two dominant alleles are expressed together. Ex: Roan coat.

Incomplete dominance: Intermediate trait is expressed in heterozygous individuals. Ex: In snapdragons a red (RR) and white (rr) cross makes pink flowers (Rr).

What color would the flowers be if you cross a red flower with a pink flower?

Red

& P

ink

Red

, Pin

k & W

hite

All

Red

All

White

53%

0%

47%

0%

A. Red & Pink

B. Red, Pink & White

C. All Red

D. All White

If a woman has type O blood, and a man has type A blood, what could the

children have?

Only

Typ

e O

Only

Typ

e A

Typ

e A o

r Typ

e B

Typ

e A o

r Typ

e O

18%

76%

0%6%

A. Only Type O

B. Only Type A

C. Type A or Type B

D. Type A or Type O

Inherited diseases

Genetic predisposition: Having an increased chance of a disease due to inheritance. Ex: Heart disease & Diabetes

Genetic disorder: If you have the genes for the disorder, you will definitely have the disease. Ex: Colorblindness & albinism

Autosomal Disorders

Autosomal traits mean that the genes are carried on one of the 22 autosomes. – BOTH male and females can be carriers of

autosomal disorders. – A carrier can pass on the genes but does not

have the disorder.– Some include: albinism, cystic fibrosis, and

sickle cell anemia

Sex-linked Traits

Sex-linked traits are carried on the X chromosome. – ONLY females can be carriers of sex-linked

disorders. – Some of these include: Colorblindness,

Muscular Dystrophy & Hemophilia. – Because males only have one X, they are more

likely to have sex-linked diseases than females.

If a man with MD marries a carrier, could they have a child with MD?

Yes

, but

only

a g

irl

Yes

, but

only

a b

oy

Yes

, cou

ld b

e a

boy or..

. N

o

0%

20%

67%

13%

A. Yes, but only a girl

B. Yes, but only a boy

C. Yes, could be a boy or girl

D. No

Pedigrees

Chart showing how a trait is inherited over several generations.

Males are squares—females are circles. Children are listed in order of birth. Shapes are colored completely if they

express the trait. Only half shaded if they carry are heterozygous for trait.