chapter 5 “heredity” p. 126

CHAPTER 5 “HEREDITY“HEREDITY”

P. 126

Chapter Five “I Cans” Heredity

1. I can draw a Punnett Square and determine the possible

outcomes of the crosses.

2. By using a pedigree, I can track a trait over several generations.

3. I can distinguish between genotypes / phenotypes and

heterozygous / homozygous traits.

4. I can identify dominant and recessive traits and use a Punnett

Square to identify the possible traits of the offspring.

Heredity- is the passing of traits from parent to offspring.

Genetics- the study of how traits are inherited through the action of alleles.- are different forms of the same trait

If the trait is If the trait is hair colorhair color,,

- are possible alleles.

blonde

brunette

red

If the trait is If the trait is eye color,eye color,

- are possible alleles.

blue

brown

hazel

Genetics was ‘started’ by Gregor Mendel.- he experimented

with pea plant traits in the 1800’s.

- is considered the ‘father’ of genetics. (p. 127 -128)

Purebred- an organism that

always produces the same traits in its offspring.Ex. St. Bernards produce St. Bernards

Ex. Siamese cats produce Siamese kittens

Mendel “crossed” traits and discovered that some traits appear more often.

- called dominant

Ex. Brown eyes over blue eyes.Ex. Tall pea plants over short plants.

The dominant trait “masks” the hidden trait:

Ex. Blue eyesEx. Red hairEx. Attached ear lobes

- called recessive.

Mendel then allowed the “crossed” tall and short plants to reproduce.

- surprising results.- out of 4 plants =

3 tall / 1 short(because the tall

were dominant)- always got a 3:1

ratio.

What is the ratio of girls to boys in your row?

What is the ratio of plants to people in this room?

Because of ratios, Mendel could create probabilities of what the offspring would be.- he could predict which

traits would appear.Ex. The offspring of the

tall and short plant cross75% chance of tall25% chance of short Coin

FlipProbability = 50% heads / 50% tails Ratio = 1:1

PUNNETT SQUARES

Purebred tall and purebred short cross= All Tall offspring

T T

t tTt TtTt Tt

The crossed offspring produce

3 talls and 1 short

Ratio? Probability? 4:0100% tall 0% short

T T

t tTt TtTt Tt

Tt is a hybrid - or mix.

Notice the 3:1 ratio

Ratio of short to tall?

1:3Probability of

having tall offspring?

75%Probability of

having short offspring?

25%

A punnett square shows the genotype of an organism.

- actual genetic traits (can’t see)

Ex. Bb, TT. -the alleles.

B bBb

BB Bb

Bb bb

phenotype - the visible traits. (can see or touch)

Hazel eyes

Attached ear lobes

If the alleles are the same (BB or tt)- they are called homozygous.

If the alleles are different (Bb or Tt)- they are called heterozygous.

(or purebred) (or hybrid)

(for animals only!)

ASSIGNMENT:WORKSHEET

“WHAT IS GENETICS?P. 132 SELF CHECK

1 - 4 (ON BACK)

Incomplete dominance - when one trait is not dominant over another.

Ex. four o’clock flowers

RR = redrr = white

R R

rr

Rr RrRr Rr

Results:

4 Pink! (Rr)Ratio:

Red:white:pink 0:0:4

Ratio: red/pink/white1:2:1

R r

Rr

RR RrRr rr

Results:1 red, (RR)2 pink, (Rr)1 white (rr)

Probability of a red flower?25%

Probability of a pink flower?50%Probability of a white flower?

25%

Ratio: red/pink/white2:2:0

R R

Rr

RR RRRr Rr

Results:2 red, (RR)2 pink, (Rr)0 white (rr)

Probability of a red flower?50%

Probability of a pink flower?50%Probability of a white flower?

0%

Polygenic inheritance - when a group of genes -not just two -combine to form a trait.

Ex. blood type, eye color, skin color, height, etc.

Codominance- a phenotype that is blended or

“mixed”

Sex Determination- the male determines the sex of the

offspring.XX = female (two X chromosomes)XY = male (one X, one Y chromosome)

Probability of having a girl?

50%Probabilty of having

a boy?50%Ratio of boys to girls?2:2 or 1:1

X X

XY

XX XX

XY XY

WORKSHEET

“PUNNETT SQUARES”

Sex-linked Disorders- inherited “conditions”

linked to the X chromosome.Ex. color blindness, hemophilia.

- these disorders are carried on the females’ X chromosome.

(the female is a carrier)

Results:XX - 1 normal girlXY - 1 normal

boyXXc - 1 carrier girlXcY - 1 colorblind boy

X Xc

XY

XX XXc

XY XcY

For a girl to be colorblind, the trait must appear on both alleles. (XcXc)

Colorblind TestsColorblind Tests

How a colorblind person would see a strawberry plant:

Hemophilia - a disease where the blood will not clot. It was common in the royal families of Europe.

Hemophilia Results:XXh =

two carrier femalesXY =

two normal malesXh

Y

X XXXh

XYXXh

XYProbability of having a hemophilic child?

0%

Probability of having a female carrier?

100%

Hemophilia Ratio of carrier females to normal males?

2:2or 1:1Xh

Y

X XXXh

XYXXh

XYProbability of having a hemophilic female?

0%

Probability of having a normal male?

100%

Hemophilia Results:XXh

= carrier femaleXY

= unaffected maleXhXh

= hemophilic femaleXhY

= hemophilic male

Xh

Y

X XhXXh

XYXhXh

XhY

Probability of having a hemophilic child?

50%

- a record of an organism’s ancestors.- it traces the occurrences of a trait.

(p. 139 in text)

Pedigree

Results:1 normal male1 normal female1 carrier female1 affected male

PedigreeIs the pedigree correct?

Do the punnett!

X XhX

YXXXY

XXh

XhY

The Symbols of a Pedigree:

Read pp. 137 - 138. “Human Genes and Mutations”.

?!!

Female (normal)Male (normal)Female with traitMale with trait

Female carrierMale carrier

ASSIGNMENT:WORKSHEET“GENETICS”

Chapter Five “I Cans” Heredity

1. I can draw a Punnett Square and determine the possible

outcomes of the crosses.

2. By using a pedigree, I can track a trait over several generations.

3. I can distinguish between genotypes / phenotypes and

heterozygous / homozygous traits.

4. I can identify dominant and recessive traits and use a Punnett

Square to identify the possible traits of the offspring.