Chapter 10.2: Mendelian Genetics (Pgs 277-282)

Chapter 11: Complex Inheritance and Human Heredity (Pgs 294- 315)

Name: Hour: Date:

Biology I S409Notes: The Genetics Unit

How Genetics Began

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Heredity- the passing of traits from parent to offspring (the next generation)

Genetics – is the science of heredity

The Father of Genetics: Gregor Mendel An Austrian monk & plant breeder in 1866)Studied pea plants (a “true-breeding” simple,

predictable plant; consistently produce offspringwith only one form of a trait = complete dominance)

Kept precise records of 7 traitsSeed shape and colorFlower color and positionPod color and shapePlant height

www.acad.swarthmore.edu/.../ the_history_of_gene_testin.htm

T: 1, 2a

The Inheritance of Traits

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2 different plants crossed. (P1) “cross pollinate”Tall plant X short plantResults (offspring): F1 generation

Found all were tall (Same for all 7 traits)One trait “masks the other”

F1 was allowed to “self pollinate” to produce F2

Results: Majority tall and some shortFound ¾ tall : ¼ short3:1 ratio for all 7 traits

Must be a pair of factors (genes)one gene from each parent

Genes & Dominance

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Genes are represented by letters of the alphabet Good letters = Aa, Bb, Rr Bad Letters = Cc, Oo, Ww (look too similar! )

Genes represented in pairs (1 individual has 2 letters) One from mom, one from dad

Principle of Dominance One gene masks the other from being expressed

A gene that “masks” is Dominant = R A gene that gets “masked” is Recessive = r

Two identical genes are homozygous (purebred) RR = homozygous dominant (shows dominant trait) rr = homozygous recessive (shows recessive trait)

One of each gene is heterozygous (hybrid) Rr = heterozygous (shows dominant trait)

T: 2 f, g, h

Vocabulary Summary

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Allele – different forms of the same gene; tall/short, brown/blue (represented by letters)

Chromosome- DNA containing structure that carries genetic material from one generation to another

Gene- functional unit that controls inherited trait expression that is passed from one generation to another; section of DNA found on a chromosome; i.e. the gene for eye color

Genotype – an organism’s allele pairs (letters)Phenotype – observable characteristic; what organism looks

like (words)

Homozygous – an organism with two of the same alleles for a particular trait (RR or rr)

Heterozygous – an organism with 2 different alleles (Rr) ; called hybrids

Dominant- allele that will mask a recessive gene (R)Recessive- allele that is masked (r)

T: 2 b-i

Probability & Genetics

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Probability = likelihood an event occursExample: coin flip

Either heads or tailsThere is a 1 out of 2 chance it is heads½ or 50% probability

Each flip is independent of otherWhat if you flip a coin 3 times?The probability of all heads ½ X ½ X ½ = 1/8

You can use this to predict genetic cross outcomes

Punnett Squares(Dr. Reginald Punnett)

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Used to predict & compare results of a cross

Types of gametes (sex cells) produced are shown along the top and left side of the square

Possible combinations of the offspring appear in the boxes (zygotes; a.k.a. fertilized egg)

Consider one of Mendel’s Experiments: Tall plants are considered dominant to short plants regarding pea plant height. If two pea plants heterozygous for height are crossed, the following genotypes and phenotypes may be determined regarding the possible offspring.

One Trait is being considered: plant height (T, t)

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Key: TT = tall Tt = talltt = short

P1: Tt x Tt

Punnett Square:

Genotype: (letters) 1 TT: 2 Tt : 1 ttPhenotype: (words) 3 Tall Pea Plants: 1 Short Pea Plant

T t

T TT Tt

t Tt tt

Probability & Segregation

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In the previous example the results of the cross were…Genotype

¼ TT ; 2/4 or ½ Tt; ¼ tt

Phenotype¾ tall; ¼ short75% tall; 25% short

Remember these are predictions;They hold true for large #sNot necessarily for individual/small events

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Trait: shape (R, r)Key: R R = round

R r = round r r = wrinkled

P1 R r X r rPunnett Square:

Genotype: (letters) 2 Rr : 2 rrPhenotype: (words) 2 Round Peas: 2 Wrinkled Peas

R r

r Rr rr

r Rr rr

Complete Dominance Cross (4 Boxes 1 trait)

When looking at the shape of peas on pea plants, round peas are dominant to wrinkled peas. Using a Punnett Square, determine the genotype and phenotype of the possible offspring when you cross a plant that is heterozygous for pea shape WITH a homozygous recessive plant for the same trait.

T: 3a

Trait: Flower color (R, r)

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Key: RR = red Rr = pink rr = white

P1: RR x rrPunnett Square:

Genotype: (letters) 4 RrPhenotype: (words) 4 Pink (All Pink)

R R

r Rr Rr

r Rr Rr

Incomplete Dominance CrossIn four o’clock plants, the alleles for red and white flowers

show incomplete dominance. When alleles are mixed, pink flowers result. If a red flower is crossed with a white flower, the following genotypes and phenotypes may be determined regarding the possible offspring.

T: 3b

Trait: fur color (R, r)

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Key: RR = red fur Rr = red & white spots rr = white fur

P1: RR x rr Punnett Square:

Genotype: (letters) 4 RrPhenotype: (words) 4 (All) red & white spots

R R

r Rr Rr

r Rr Rr

Co-Dominance CrossIn cows, the alleles for fur color show co-dominance. Fur color may be red or white in cows, however, when alleles are mixed fur will have red and white spots. If a red cow is crossed with a white cow, the following genotypes and phenotypes may be determined regarding the possible offspring.

T: 3b

Trait: attitude (L, l)

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Key: LL = snotty cat Ll = snotty & lazy cat ll = lazy cat

P1: Ll x Ll Punnett Square:

Genotype: (letters) 1 LL : 2 Ll : 1 llPhenotype: (words) 1 snotty : 2 snotty & lazy: 1 lazy

L l

L LL Ll

l Ll ll

Co-Dominance CrossIn cats, the alleles for attitude show co-dominance. Cats can have attitudes that are snotty or lazy, however, when alleles are mixed a cat with a snotty & lazy attitude results. If two heterozygous cats are crossed, what are the genotypes and phenotypes of the possible offspring?

T: 3b

Set of 3 or more alleles determine 1 traitIn fruit flies, there are multiple alleles for eye color. 3 alleles produce different eye colors. Red eyes are dominant to purple and white eyes, however, purple eyes are dominant to white eyes. If you cross a heterozygous red eye fly that carries the white eye allele with a heterozygous purple eye fly will the offspring be? Trait: eye color (E, eR, er)

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Key: EE = red eyes EeR = red eyes Eer = red eyes eReR = purple eyes eRer = purple eyes erer = white eyes

Genotype: (letters) 1 EeR: 1 Eer: 1 eRer : 1 erer

Phenotype: (words) 2 red eye : 1 purple eye : 1 white eye

E er

eR EeR eR er

er Eer erer

P1: Eer x eRer

Punnett Square:

Multiple Alleles CrossT: 3d

Trait: ear length (E, eL, el)

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Key: EE = Long ears EeL = Long ears Eel = Long ears eLeL = Floppy ears eLel = Floppy ears elel = short ears

Genotype: (letters) 2 Eel: 2 eLel Phenotype: (words) 2 long ears : 2 floppy ears

E eL

el Eel eL el

el Eel eLel

P1: EeL x elel

Punnett Square:

Multiple Alleles CrossIn bunnies, there are multiple alleles for ear length. Different combinations of 3 alleles produce ear lengths. Long ears are dominant to floppy ears and short ears, however, floppy ears are dominant to short ears. If you cross a heterozygous long ear bunny that carries the floppy ears allele with a short ear bunny what offspring will result?

T: 3d

Sex-Linked Traits

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Each cell in your body, except your gametes, contains 46 chromosomes (23 from mom, 23 from dad)22 pairs of chromosomes are called autosomes1 pair of chromosomes is called your sex chromosomes (determines

gender)

Sex chromosomes (gametes) are called: X & Y Males = XY Females = XX

Thomas Hunt Morgan (Early 1900’s) discovered sex-linked genes in Drosophila. (Fruit flies)

Most Sex-linked genes are on the X, not the Y. Why? The X chromosome is physically larger!

Most sex-linked genes are recessiveOne gene, from mom, gives males mutant trait.Two genes, from each parent, are needed

to give a female offspring the mutant trait(that’s why there are fewer females with sex-linked traits)

T: 3e

Examples of Sex-linked TraitsAgain, females are less likely to express a

recessive X-linked trait because the other X chromosome may mask the effect of the trait!Red-green color blindness

(~8% of males in US)

Hemophilia(inability to clot blood)

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T: 3e

Sex-Linked Cross

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In fruit flies, eye color is sex-linked. Normal eye color is red, and recessive eye color is white. If you cross a white-eyed male with a normal red-eyed female what offspring result?

XR = female sex chromosome w/ normal dominant gene for red eyes

Xr = female sex chromosome w/ mutant recessive gene for white eyes

Y = male sex chromosome

T: 3e

Trait: eye color (XR, Xr, Y)

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Key: XRXR = Normal Female, Red EyesXRXr = Carrier Female, Red EyesXrXr = Mutant Female, White EyesXRY = Normal Male, Red EyesXrY = Mutant Male, White Eyes

P1: XrY x XRXR

Punnett Square:

Genotype: (letters) 2 XRXr: 2 XRY Phenotype: (words) 2 Carrier Females, red eyes :

2 Normal Males, red eyes

XR XR

Xr XR Xr XR Xr

Y XR Y XR Y

T: 3e

Sex-Linked Cross

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Hemophilia is a disease that results from the bloods inability to clot. This disease has been found to be a sex-linked trait in humans. The hemophilia allele is recessive to the normal allele. If you cross a female carrier with a normal male what offspring result?

T: 3e

Trait: blood’s ability to clot (XB, Xb, Y)

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Key: XBXB = Normal Female; Can ClotXBXb = Carrier Female; Can ClotXbXb = Mutant Female, hemophiliacXBY = Normal Male; Can ClotXbY = Mutant Male, hemophiliac

P1: XBY x XBXb

Punnette Square:

Genotype: (letters) 1XBXB: 1XBXb : 1XBY : 1XbYPhenotype: (words) 1 Normal Female Can Clot : 1 Carrier

Female Can Clot:1 Normal Male Can Clot: 1 Mutant Male, hemophiliac

.

XB Xb

XB XB XB XB Xb

Y XB Y Xb Y

T: 3e

Dihybrid CrossTwo Traits (16 Boxes)

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Principle of Independent AssortmentStates that genes for different traits segregate (separate) independently during gamete formation

This holds true for more than one trait

Plant height and flower color are being studied. Tall plants are dominant to short plants and red flowers are dominant to white. A white plant heterozygous for height is crossed with a short plant heterozygous for flower color. Using this cross, the following genotypes and phenotypes may be determined regarding the possible offspring.

T: 3c

Traits: height (H, h)color (R, r)

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Key: HH = TallHh = Tallhh = ShortRR = RedRr = Redrr = White

P1: Hhrr x hhRr

T: 3c

Traits: height (H, h) Cont. color (R, r)

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P1: H h r r x h h R r

Punnett Square:

Genotype: (letters) 4 HhRr : 4 hhRr : 4 Hhrr : 4 hhrrPhenotype: (words) 4 Tall & Red : 4 short & red :

4Tall & white : 4 short & white

Hr Hr hr hr

hR HhRr HhRr hhRr hhRr

hr Hhrr Hhrr hhrr hhrr

hR HhRr HhRr hhRr hhRr

hr Hhrr Hhrr hhrr hhrr

T: 3c

Dihybrid Cross

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Number of spots and tail length are being studied in leopard. Even numbers of spots are dominant to odd numbers of spots and long tails are dominant to short tails. A leopard with a odd number of spots a short tail is crossed with a leopard who is heterozygous for both traits. Using this cross, the following genotypes and phenotypes may be determined regarding the possible offspring.

T: 3c

Traits: Number of spots (E, e)Tail length (L, l)

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Key: EE = Even #Ee = Even #ee = Odd #LL = Long TailLl = Long Tailll = Short Tail

P1: eell x EeLl

T: 3c

Traits: Number of spots (E, e) Tail length (L, l)

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P1: eell x EeLl Punnett Square:

Genotype: (letters) 4 EeLl : 4 Eell : 4 eeLl : 4 eellPhenotype: (words) 4 Even #ed Spots & Long Tail

: 4 Even #ed Spots & Short Tail : 4 Odd #ed Spots & Long Tail : 4 Odd #ed Spots & Short Tail

el el el el

EL EeLl EeLl EeLl EeLl

El Eell Eell Eell Eell

eL eeLl eeLl eeLl eeLl

el eell eell eell eell

T: 3c

11.1: Basic Patterns of Human InheritanceRecessive Genetic Disorders

Mendels work was ignored for about 30 years and “rediscovered” in the early 1900’s by Dr. Garrod & genetic studies now continue today…

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11.1: Basic Patterns of Human InheritanceDominant Genetic Disorders

Not all genetic disorders are caused by recessive inheritance. Some are caused by dominant alleles. That means those who do NOT have the disorder are homozygous recessive for the trait.

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Pedigrees – Pg 299Pedigrees can be used to track

genetic information through generations of a family “family history”

Pedigrees have a few simple rules:Men are shown as squaresWoman are shown as circlesEach generation is given a

Roman Numeral (I, II, III, IV, V)Each individual within a

generation is given a number (1, 2, 3, 4, 5)

Shaded individuals have the trait being tracked in the pedigree

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T: 3f

Pedigree Practice Problem #1: The trait shown below is the ability to taste PTC

(phenylthiocarbamide) paper. This trait is controlled by a dominant gene represented by T, and is transmitted by normal inheritance. Nontasters are, therefore, Homozygous for the recessive trait and are represented by tt. The shaded figures below are both homozygous recessives (tt) and are nontasters. All unshaded symbols have two possible genotypes: TT or Tt. Determine the genotypes of all the individuals in the pedigree below:

tt Tt

Tt Tt Tt Tt tt Tt/TT

Tt

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T:f

Problem #2 Write the correct Roman

numeral for each generation.

Write the correct number for each individual.

Assume the shaded symbols represent the recessive homozygous genotype rr. Which, individuals show the homozygous recessive trait?

In the spaces below each symbol, write as much of the genotype of each individual as can be determined from the information provided.

Pedigree Practice

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I

II

III

1 Rr 2 rr

1 Rr 2 Rr 3 rr 4 Rr 5 Rr 6 rr

1 rr 2 Rr 3 Rr

T: 3f

Problem #3 Colorblindness in humans is caused by a sex-linked recessive gene on the X-chromosome. In this pedigree chart, both of the first generation parents are colorblind. Assuming that none of the in-laws are colorblind or are carriers, what is the maximum number of descendants that could be colorblind?

a.3b.4c.5d.12

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Pedigree PracticeT: 3f

11.3: Chromosomes & Human Heredity

Karyotypes are a way of studying chromosomesUsed to identify genetic

disorders.

You can not see changes in genes, but you can see changes in chromosome number.

There are 22 autosomes matched together with 1 pair of nonmatching sex chromosomes. (find X & Y)

Is this karyotype from a male or female?

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T: 4,5

NondisjunctionNondisjunction: when sister chromatids fail to separate properly during cell division

Down syndrome: one of the earliest known human chromosomal disorders. It is usually the result of an extra chromosome 21; often called trisomy 21

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T: 4, 5