Characteristic #4All living things reproduce using the

same genetic mechanism (code)

• Each organism reproduces its own species• Offspring inherit genetic instructions from their

parents through a molecule called DNA• Offspring can differ from their parents (genetic

variation)

HeredityHeredityInheritance of traits from

parent to offspring

Genetics: the study of how traits are passed from parent to

offspring

Genetics: the study of how traits are passed from parent to

offspring• Trait: a characteristic,

like eye color, blood type or ear shape

• Inheritance (heredity): the traits that a parent passes to the offspring

What are some traits that you got from one of your parents?

Widows peek?

• Central function of life: to produce more life.

• Central problem: how to transfer information from one generation to the next.

All the information for each organism is found in the cell. How do cells pass

information from one cell to the next?

History of Genetics

The understanding of trait inheritance been around from early times.

It was obvious to early societies that certain disorders or traits ran in families (hemophilia, dwarfism, mental illness).

History of Genetics• Early civilizations exploited the

understanding of inherited traits through selective breeding, particularly in agriculture.

• Crops and plants were developed for consumption (corn, yams).

Gregor MendelFather of Genetics

Gregor MendelFather of Genetics

• A monk in a monastery

• Born in 1822.

• Used pea plants to show how traits are passed from parents to offspring.

Monohybrid CrossMonohybrid Cross

• Breeding individuals that differ in one trait only

• Example: crossing a green pea plant with a yellow pea plant

Green peas X Yellow peas

What happened?

ALL of the offspring had GREEN PEAS!

P1 = X

F1=

• Trait: observable characteristic (pea color)

• Dominant trait: strong trait (green peas)

• Recessive trait: weak trait (yellow peas)

• Alleles: the different forms of a trait (green and yellow)

dominant recessive

What did Mendel do next?

• Crossed the offspring

Offspring green peas X Offspring green peas

X

What do you think happened in the next generation?

~3/4 of the new baby peas were green

~1/4 of the new baby peas were yellow

X

Questions Mendel had:

Questions Mendel had:

1. Why did this happen?

2. Where was the yellow trait in the first set of offspring?

3. How did the yellow trait come back in the second set of offspring?

Next Mendel tried a di-hybrid cross:

• Dihybrid cross: breeding plants that differ in two traits:

X

What happened:• Again, all of the offspring only showed the

dominant trait for both characteristics:

X =

Again, he crossed the offspring:

9/16 3/16

3/16 1/16

X =

• Each trait was inherited in the same pattern as a monohybrid cross

• Of 16 plants:– 9 (3/4) were green– 3 (1/4) were yellow– 9 (3/4) were tall– 3 (1/4) were short

• The traits were inherited independently

Write these:• Inheritance: the way traits are passed

from parent to offspring

• Gene: a section of a chromosome that controls a single trait

• Allele: one alternative for the way a trait can be expressed

• Dominant allele: will always be expressed if present

• Recessive allele: only expressed if no dominant allele is present

Write these down:

• Monohybrid cross: crossing individuals that differ in a single trait

• Dihybrid Cross: crossing individuals that differ in two traits

• Independent Assortment: Genes for specific traits follow normal patterns of inheritance without interference from other genes

Mendel's 4 Laws of Inheritance

• There are genes of inheritance, and these genes carry traits. In peas, there is an gene for tallness, and one for pea color.

• Each parent contributes half of an individual’s genes.

• Genes come in different forms (alleles), that are dominant or recessive.

• Different genes are expressed independently of each other (tall/short is inherited independent of yellow/green)

Mendel’s Laws of Heredity1. Law of Segregation – two alleles for a

trait separate when gametes are formed (meiosis)

i.Chance determines which traits a gamete gets

2. Law of Independent Assortment- Alleles of different genes separate independently of one another during gamete formation.

i.hair color not affected by characteristics for eye color (different chromosomes)

Gene s

Gene s

• Genes are on chromosomes

• Genes control traits

Where are genes found?

• DNA carries all genetic information

• DNA is divided into strands called chromosomes

• Humans have 46 chromosomes

• Chromosomes are divided into genes

• This chromosome has 3 genes

KaryotypeKaryotype A karyotype shows the 46

human chromosomes arranged in 23 homologous

pairs

Homologous Pairs

• Chromosomes come in matching pairs

• Homologous chromosomes have all of the same genes

• One chromosome in each pair comes from mom (in the egg) & the other comes comes from dad (in the sperm)

• This means that all body cells have two copies of each gene – one from mom & one from dad

Alleles

• A gene codes for a trait

• Each trait may have different options, or possibilities

• Each possible version of the gene is an allele

– Gene = hair color

– Alleles = brown, blond, black, red

What would be other possible alleles for each gene?

Notice this chromosome has 5 genes:• Gene: Eye color Allele: blue• Gene: Hair texture Allele: smooth• Gene: Hemoglobin Allele: normal• Gene: Blood type Allele: type A• Gene: Eye shape Allele: round

Each individual has two copies of each gene/allele

One copy comes from the mom’s chromosome

One copy comes from the dad’s chromosome

Genes on Homologous Chromosomes

have to be for same type of trait, but alleles can code for different

colors

Non-homologous chromosomes

Genes and alleles• Gene: pea plant height.

Alleles: tall, short

• Gene: pea texture. Alleles: smooth, wrinkled

• Gene: flower color. Alleles: pink, white

• Gene: Leaf edge. Alleles: smooth, toothed

• Gene: Hand preference. Alleles?

• Gene: Hair color. Alleles?

• Gene: Blood type. Alleles?

• Alleles:▲ ■ ● Gene?

• Alleles:

Gene?

Review

• Some alleles are dominant (green, tall) over the other traits

• Some alleles (yellow, short) are recessive to the dominant trait

• The alleles present and the way they combine in an individual determines how the trait will appear

Dominant alleles: • always show up if

present. • represented by an

uppercase letter.

Recessive alleles: • will only show up if a

dominant allele is not present.

• A dominant allele will hide the recessive trait.

• Represented by a lowercase letter.

Rule of DominanceRule of Dominance

When a dominant allele is present, the trait it represents will always show up, no matter

what the other allele is.

Remember:Remember:• Each individual has two copies of each gene/allele

(one from mom and one from dad). • Say a gene, H, for hair texture has two alleles

– H: straight hair– h: curly hair

• There are 3 possible combinations:– HH (two dominant alleles) – straight hair– Hh (a dominant and a recessive allele) - straight– hh (two recessive alleles) – curly hair

• Gene: pea color

• Alleles: Green is dominant (G) and yellow (g) is recessive

An individual with: Will have:

GG green peas

Gg green peas

gg yellow peas

Examples:Examples:

• Gene: pea plant height:

• Alleles: tall (T) and short (t)

• Which is the dominant allele?

An individual with: Will be:

TT Tall

Tt Tall

tt Short

Examples:Examples:

• Gene: pea texture.

• Alleles: smooth (dominant) and wrinkled (recessive).

• Which texture would be “s” and which would be “S”?

An individual with: Will have:

SS ?

Ss ?

ss ?

Examples:Examples:

• Alleles: pink flowers (P) and white flowers (p)

• Gene: What is the gene?

An individual with: Will have:

? Pink Flowers

? Pink Flowers

? White Flowers

Examples:Examples:

Some terminologySome terminology• Genotype: combination of alleles.

Examples: Gg, GG or gg

• Phenotype: how the trait shows up: Examples: green peas; yellow peas.

• Genotype: GG• Phenotype:

Genotype or Phenotype?Genotype or Phenotype?

1. Hh =

2. Hairy arms =

3. Baldness =

4. UU =

5. Mm =

6. Colorblindness =

7. Black Hair =

8. Ll =

What about these:• Gene: pea plant height. T = tall; t = short.

What will the phenotype be for the following genotypes:– TT?– tt?– Tt?

• Gene: flower color. P = pink; p = white. Give the genotype for the following phenotypes:– Pink flowers: __________ & __________– White flower: __________

Sex Chromosomes

• The last pair of chromosomes (pair #23) are different from the others

• They can be “X” or “Y”

• An individual with XX will be a girl

• An individual with XY will be a boy

• More about this later

A little more terminology…• Homozygous = individual has the same

alleles for a gene. Examples: HH, bb, gg, JJ, aa, OO, mm, RR.– Homozygous Dominant: 2 dominant alleles.

Which of the above are homozygous dominant?

– Homozygous recessive: 2 recessive alleles. Which above are homozygous recessive?

• Heterozygous = individual has different alleles for a gene: Aa, Bb, Cc, Dd.

Quiz• Match:a) Tt, TT, tt d) wrinkledb) Tall e) RRc) Tt f) rr

1. ___ Homozygous Dominant2. ___ Homozygous Recessive3. ___ Heterozygous4. ___ Genotype5. ___ phenotype

• Class work

• Pg 163

• 1, 3, 4 Restate questions

• Bonus # 5

• Vocab Quiz #7 Weds

• Ch 8 Quiz Friday

Predicting OffspringPredicting Offspring

Punnett Square: Used to predict the offspring that will be formed in a

monohybrid cross

Named after Reginald Punnett

Punnett square for GG X ggPunnett square for GG X gg

Offspring ratios:

Phenotype: 4 green: 0 yellow or 100% greenGenotype:0 GG: 4 Gg: 0 gg or 100% Gg

A GG green plant is crossed with a Gg green plant. Predict the genotype and phenotype of the offspring.

• Genotype ratio:

1 GG: 2 Gg: 1 gg

25% GG, 50% Gg, 25% gg

• Phenotype ratio:

3 Green, 1 yellow

75% green, 25% yellow

Try these:1. Pea plants have a gene for height.

T = tall and t = short. What is the genotype and phenotype of the offspring resulting from a Tt X tt cross?

2. In pea plants, S = smooth peas, and s = wrinkled peas. What are the genotype/phenotype ratios of a cross between ss X ss?

Tt X ttTt X tt• Genotype:

2 Tt: 2 tt

50% Tt; 50% tt

• Phenotype:

2 tall; 2 short

50% tall; 50% short

ss X ssss X ss• Genotype:

0 SS: 0 Ss: 4 ss

100% ss

• Phenotype:

0 smooth:4 wrinkled

100% wrinkled

Dihybrid Cross

• Cross between individuals that differ in two traits

• Law of independent assortment: each gene/trait follows its own pattern of inheritance without interference from other traits/genes

Dihybrid Cross between GGTT X GgTtG=green / g=yellow T=tall / t=short

GT GT GT GT

GT GGTT GGTT GGTT GGTT

Gt GGTt GGTt GGTt GGTt

gT GgTT GgTT GGTT GGTT

gt GgTt GgTt GgTt GgTt

Di-hybrid Cross between GgTt X GgTt

GT Gt gT gt

GT GGTT GGTt GgTT GgTt

Gt GGTt GGtt GgTt Ggtt

gT GgTT GgTt ggTT ggTt

gt GgTt Ggtt ggTt ggtt

G=green / g=yellow T=tall / t=short

Review:Mendel's 4 Laws of Inheritance

• Chromosomes have genes - one gene per trait.

• Each parent contributes half of an individual’s genes though his or her gametes.

• Genes come in different forms (alleles), that are dominant or recessive.

• Different genes are expressed independently of each other (tall/short is independent of yellow/green)

Review Terminology

• Genotype: the alleles that an individual has for a specific gene (Aa, or aa)

• Phenotype: the trait that is displayed (brown eyes, or hitchhiker’s thumb)

• Heterozygous: a dominant & a recessive allele (Aa)

• Homozygous dominant: two dominant alleles (AA)

• Homozygous recessive: two recessive alleles (aa)

Non-Mendelian Inheritance

Non-Mendelian Inheritance

• Sometimes genetics don’t follow the rules that Mendel outlined.

• Not all genes are represented by only 2 alleles.

• Not all alleles are strictly dominant and/or recessive.

Incomplete Dominance• Phenotype is halfway between that of the two

alleles.• Red snapdragon (RR) crossed with white

snapdragon (R’R’) will give pink offspring (RR’)

PracticePractice

For the following, give an example of incomplete dominance:

• A alligator is heterozygous for the egg laying gene, with one allele for laying 12 eggs and the other allele for laying 6 eggs

• A heterozygous flower with an allele for 6 petals and an allele for 2 petals

• A heterozygous lizard with an allele for a blue tail and an allele for a yellow tail

Co-dominance Both alleles are dominant and will show up

equally in the individual.Chickens have a gene for feather color. Black

(B) feathers are codominant with white (W) feathers.

BB WW BW Black White Black and white

feathers feathers feathers

Identify each as co-dominant, incomplete dominance, or dominant/recessive

• A lizard with spots is crossed with a lizard with stripes. The offspring has both spots and stripes

• A shrub with toothed leaves is crossed with a shrub with smooth-edged leaves. The offspring have wavy leaves

• A purple iris is crossed with a rare scarlet iris. All of the seeds produce purple plants

• A cat with kinky whiskers mates with a cat that has whiskers. They have kittens that have kinky whiskers and straight whiskers.

Identify each as codominant, incomplete dominance, or dominant/recessive

• A flower with cream colored petals is crossed with a flower with black petals. The offspring have gray petals

• A man who is double-jointed has 6 children with a woman who is not double-jointed. Four of the children are double-jointed and two are not

• A spaniel with solid-colored hairs is crossed with a spaniel that has hairs with frosted tips. The offspring have some hairs that are solid and others with frosted tips

Multiple AllelesMultiple Alleles When there are more than two

alleles for one trait

• Gene = flower color

• Alleles:– Fy (yellow)

– Fr (red)

– Fw (white)

Polygenic trait• When several

genes control one trait, resulting in a range of possibilities for the trait

• Human height is polygenic, and has a range of possibilities, from less than 4 feet to about 8 feet.

Identify each as multiple alleles or polygenic inheritance:

Identify each as multiple alleles or polygenic inheritance:

1. Eye color can be one of the following: brown, green, blue, hazel

2. The broken pattern (presence of white mixed with color) of rabbits can range from having a rabbit with only a small spot of white to having a rabbit that is almost completely white

Identify the following as multiple alleles or as

polygenic inheritance:

3. Human foot size ranges from petite to quite large, from 4 through size 15 (or larger!)

4. Some species of flowers have individuals with either 2, 4 or 6 stamen

5. One species of ground cover can have flowers that are blue, white or yellow

Sex-linked TraitsSex-linked Traits• In humans, there are 23 pairs of

chromosomes.• In 22 pairs, the chromosomes are

homologous – they have the same genes.• In the 23rd pair, the sex chromosomes, the

pair is not homologous. There is an X chromosome and a shorter Y chromosome.

• The Y chromosome is missing some of the genes that are in the X chromosome.

• An XX is a female and an XY is a male.

Sex-linked TraitsSex-linked Traits• In humans females, all 23 pairs of

chromosomes are homologous – they have the same genes. The 23 pair in girls are the same size (XX)

• In boys, the 23rd pair does not match – it has a longer X and a shorter Y chromosome (XY)

• The Y chromosome is missing some of the genes that are in the X chromosome.

• This 23rd pair are the sex chromosomes

• Notice that the Y chromosome is missing the top four genes

• This individual (a male) will have two copies of the bottom 6 genes, but only one copy of the top four genes.

• On the top genes, whatever allele the X chromosome has will be expressed.

• Color-blindness is a recessive trait.

• Pretend that the brown gene at the top codes for color-blindness

• This male will have whatever phenotype is expressed by the gene on the X chromosome.

• A girl can only be colorblind if both parents pass the trait on, but a boy can receive the trait from only the mom.

Brown gene = color-blindnessColor-blindness is recessive to normal vision

• This is the 23rd pair from a female.

• What is her genotype for color-blindness?

• Bb• What is her

phenotype for color-blindness?

• Normal vision

Brown gene = color-blindnessColor-blindness (b) is recessive to normal vision (B)

• This is the 23rd pair from a male.

• What is his genotype for color-blindness?

• b

• What is his phenotype for color-blindness?

• He will be color blind

Hemophilia is an X-linked recessive (h) disorder which prevents normal clotting of blood, often resulting in massive bleeding from minor injuries. Normal clotting (H) is dominant. Which of the following will have the disorder?

A B C

What is a Pedigree?

• A graphic representation of genetic inheritance

• Uses symbols to show traits and genotypes of each generation in a family

• Useful for diagnosing carriers of genetic disorders, and predicting affected offspring

Analyzing a Pedigree

• Recessive disorders: pedigree shows affected individuals that come from unaffected parents

• Sex-linked disorders: disproportionate number of affected individuals in one gender only (usually males)

• Which individuals are affected?

• Which individuals are definitely carriers?

• What are the chances that individual IV-5 has the recessive allele (is a carrier)?

• Which individuals are homozygous recessive?

• Which individuals are heterozygous?

• If III-1 marries an affected male , what will be the chances that their children will inherit the disease?

Lethal Recessive DisordersSome homozygous recessive genotypes are lethal

• Tay-Sach’s is a lethal recessive disorder of the nervous system that is fatal in early childhood

• Tay-Sach’s babies lack an enzyme that breaks down fats – the fats accumulate in the cells, leading to blindness, retardation, and death

• Cystic Fibrosis is a recessive disorder that affects the lungs, and is fatal by late adolescence

• Mucus builds up in the lungs system, affecting the ability to breath & exchange oxygen in the tissues

Recessive Disorders/TraitsCystic Fibrosis

Disease that interfers with breathing &

causes early death

Tay Sach’sDisease that leads to retardation/death due to

buildup of lipids in the CNS

Pedigree for Tay-Sach’s

Dominant Disorders

• Each carrier has the trait

• The phenotype is passed on as a heterozygous trait

• Inheritance is equal among boys and girls

Tongue RollingA dominant trait

Huntington’s DiseaseA Lethal Dominant Disorder

• Neurological disorder with late life onset (30 – 50)

• Individuals are unaware that they have the illness until they reach middle age

• Due to late onset, individuals often reproduce and pass on the lethal allele to offspring

Huntington’s Disease

Sex-linked Inheritance

• In sex-linked traits, there is a difference between the inheritance patterns for males and females

Sex-linked Disorders

• Hemophilia is found only on the X chromosome

• Hemophiliacs do not have clotting factors in their blood and cannot control bleeding

• Color-blindness also on the X chromosome

• Color-blindness interferes with the ability to distinguish certain colors

HemophiliaA sex-linked recessive disorder

What pattern of inheritance is this?

What pattern of inheritance is this?

What pattern of inheritance is this?

What type of inheritance is this?

What pattern of inheritance is this?

Karyotype• A karyotype can help doctors and geneticists

identify genetic diseases and deformities

• Missing, extra, or damaged chromosomes create physical or mental problems, or even death

How a karyotype is done:

• DNA is extracted so that chromosomes are visible

• Chromosomes are placed in homologous pairs

• Pairs are arranged from largest to smallest, with the sex chromosomes at the end

Creating a Karyotype

• Matching sex chromosomes (xx) = girl

• Non-matching sex chromsomes (xy) = boy

A normal karyotypeBoy or Girl?

Boy or Girl?

Boy or Girl?

• Pairs that have one too many or one too few indicate a genetic disorder

Where is the problem?

Trisomy 18Patau’s Syndrome

An Abnormal Karyotype Where is the problem?

Answer: Trisomy-21• Three chromosomes in the 21st pair, and

47 total chromsomes

• Also called Down Syndrome

• Leads to physical defects and mental retardation

Normal or Abnormal?Girl or Boy?

Abnormal Male with trisomy-18 Edward’s Syndrome

Abnormal KaryotypeWhere’s the problem?