CHAPTER 5 “HEREDITY” P. 126

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 hair color, blonde brunette - are possible alleles. red

If the trait is eye color, blue brown - are possible alleles. 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: - called recessive. Ex. Blue eyes Ex. Red hair Ex. Attached ear lobes

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 cross 75% chance of tall 25% chance of short Coin Flip Probability = 50% heads / 50% tails Ratio = 1:1

t t Tt Tt Tt Tt T PUNNETT SQUARES Purebred tall and purebred short cross = All Tall offspring The crossed offspring produce 3 talls and 1 short

t t Tt Tt Tt Tt T Tt is a hybrid - or mix. Notice the 3:1 ratio Ratio? Probability? 4:0 100% tall 0% short Tt is a hybrid - or mix. Notice the 3:1 ratio

1:3 75% 25% Ratio of short to tall? Probability 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 b BB Bb B b 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 ASSIGNMENT: WORKSHEET “WHAT IS GENETICS? P. 132 SELF CHECK 1 - 4 (ON BACK)

Incomplete dominance - when one trait is not dominant over another. R R Rr Rr r Rr Rr Ex. four o’clock flowers RR = red rr = white 4 Pink! (Rr) Results: Ratio: Red:white:pink 0:0:4

R r RR Rr R r Rr rr 25% 50% 1:2:1 25% Results: 1 red, (RR) 2 pink, (Rr) 1 white (rr) R r RR Rr R r Rr rr Probability of a pink flower? 50% Probability of a white flower? 25% Ratio: red/pink/white 1:2:1 Probability of a red flower? 25%

R R RR RR R r Rr Rr 0% 50% 2:2:0 50% Results: 2 red, (RR) 2 pink, (Rr) 0 white (rr) R R RR RR R r Rr Rr Probability of a pink flower? 50% Probability of a white flower? 0% Ratio: red/pink/white 2:2:0 Probability of a red flower? 50%

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)

X X X Y XX XX XY XY Probability of having a girl? 50% Probabilty of having a boy? Ratio of boys to girls? 2:2 or 1:1 X X X Y 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)

X Xc X Y XX XXc XY XcY Results: XX - 1 normal girl XY - 1 normal boy XXc - 1 carrier girl XcY - 1 colorblind boy X Xc X Y XX XXc XY XcY For a girl to be colorblind, the trait must appear on both alleles. (XcXc)

Colorblind Tests

How a colorblind person would see a strawberry plant:

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

X X Xh Y XXh XXh XY XY Hemophilia Results: XXh = two carrier females two normal males X X Xh Y XXh XXh XY XY Probability of having a hemophilic child? 0% Probability of having a female carrier? 100%

X X Xh Y XXh XXh XY XY Hemophilia Ratio of carrier females to normal males? 2:2 or 1:1 X X Xh Y XXh XXh XY XY Probability of having a hemophilic female? 0% Probability of having a normal male? 100%

X Xh Xh Y XXh XhXh XY XhY Hemophilia Results: XXh = carrier female XY = unaffected male XhXh = hemophilic female XhY = hemophilic male X Xh Xh Y XXh XhXh XY XhY Probability of having a hemophilic child? 50%

Pedigree a record of an organism’s ancestors. it traces the occurrences of a trait. (p. 139 in text)

X Y XX XXh XY XhY Pedigree Is the pedigree correct? Do the punnett! Results: 1 normal male 1 normal female 1 carrier female 1 affected male X Xh X Y XX XXh XY XhY

The Symbols of a Pedigree: Female (normal) Male (normal) Female with trait Male with trait Female carrier Male carrier ?!! Read pp. 137 - 138. “Human Genes and Mutations”.

ASSIGNMENT: WORKSHEET “GENETICS”