GeneticsGenetics is the

science of inheritance. 

It requires sexual reproduction..

wherein a sperm

and egg combine

to form a zygote.

Patterns of Inheritance: Genetics Chapt. 10

• Interest in genetics is as old as humankind…

• Modern genetics began in 1860’s

• Czech Monk- Gregor Mendel

• Playing with peas in his garden

Gregor Mendel

• Used peas to study how physical traits passed from parent to offspring

• Mendel measured 7 traits in peas, each trait with 2 forms.

• How were these traits passed on?

• Mendel came up with rules….

• Text pg. 178

Examples of two Pea traits (Shape & Color) that Mendel studied

Mendel’s 1st Rule

The Law of Segregation:

• For each trait (i.e. pod color or plant height) an individual has 2 factors

• The 2 factors may be the same or different

• When making kids, each parent will contribute only 1 factor

• The 2 factors a parent has will separate when making a kid (plant or human)

The Law of Segregation

• Each parent will pass on 1 factor during sex (gamete production)

• Kids get 1 factor (for each trait) from each parent...

Text pg 181

The Factors

• Each individual has 2 factors for each trait…pod color, height, eyes, hair...

• If both factors for a trait are the same, you are homozygous for that trait…

• If you have 2 different

factors for a trait, you are heterozygous for that trait

How to Label these factors?

• G for Green pods

• Y for yellow pods

• B for brown hair

• x for blond hair

But…we don’t do this!!

The Factors

• You have 2 factors, but only 1 factor for each trait is typically used (expressed)..

• This is the dominant factor

• The other one is the recessive factor

So; How we do Label the factors?

• Dominant factor is written in upper case… i.e. “B”

• Recessive factor in lower case, using the dominant abbreviation.. i.e. “b”

• B is for brown hair (which is dominant)

• b is for blond

Quiz

• If the you are heterozygous for brown hair, what two factors will you have?

• If homozygous, what two factors?

How to Predict which factor you’ll give your

kids? • Each parent has 2 factors for each trait

• But, each gamete you produce has only 1 factor for each trait

• Which factor goes to which kid?

• Best described by a Punnett Square

Punnett Square..• Used to predict how offspring will get

their share of factors…

• Parents mate (x): BB X bb

• What possible offspring will each make?

B B

b

b

FemaleGametes

Male Gametes

Possible Offspring…. Or, F1 Generation

B B

b

b

Bb Bb

Bb Bb

Each F1 Offspring has the same traits for hair color… Bb

Another Example..Trait for Seed Shape (S)

Text pg 181

Mendel’s 2nd Law

• Factors for each trait segregate into gametes independently of each other

• The factor for hair color (B or b) will segregate independently of the factor for height (T or t)

• Consider a dihybrid cross… Two traits at once

• Example: Say Parents are Bbtt x bbTT

Dihybrid Cross

• If a Bbtt male mates with a bbTT female?

• What are the possible gametes for each?

Male Bbtt x

Female bbTT

Bt bt

bT

bT

BbTt bbTt

BbTt bbTt

gametes

gametesNew individuals (with two factors for each trait)

So What?

• What does Mendel and his Peas have to do with you?

• Chromosomes and Heredity…

Mendel’s Factors = Genes

• Every normal human has thousands of genes

• Each gene describes the information for one human trait.

• You have two genes for each trait

• Where are these genes located?

On Chromosomes• We each have 46

chromosomes in each cell

• 23 chromosomes came from Mom, 23 from Dad

• Each chromosome contains hundreds of genes…

An example using the FISH techniqueof identifying the location of one geneon a chromosome.

Gene location on Chromosomes

Quiz

• If the human trait for Hairy knuckles is located on 1 gene…how many copies of this gene will you have?

• If Hairy knuckles is a dominant trait, how would you characterize the genotype?

• Use H for Hairy knuckles• HH or Hh

Why should you care about Chromosomes?…

Have a Baby!

• Karyotype…spread out a fetus’s chromosomes to check for normalcy

• Amniocentesis (Text pg. 768-769) …Enables us to karyotype a fetus

• What are they looking for?

Chromosomal Abnormalities: Downs Syndrome• An extra chromosome # 21

(3 copies)• Also referred to as Trisomy 21• Slow development, flat face,

slanted eyes, intelligence varies greatly

• 50% of children die before age 1

• Karyotype tests can predict the disorder but not its severity

Karyotyping reveals lots of information

• Normal 23 pairs of chromosomes

• Of the 23 pairs, 22 are autosomal pairs and 1 pair are the sex chromosomes

• Females have two identical sex chromosomes (XX),

• While males have one X and one smaller chromosome called Y

Sex Chromosomes

Male vs. Female

• Females are determined by XX chromosomes

• Males by XY chromosomes

• Males get the X from Mom, the Y from Dad

• Females get one X from each parent

Sex Chromosomes

Male or Female?

Sex-linked Traits

• Each X chromosome carries ~1,000 genes, whereas Y contains very few

• So, if a male gets an X chromosome from his Mom with a bad gene, he is going to suffer from it

• A female has a second X copy to work with…

Example: Hemophilia• A sex-linked recessive

disorder in which blood does not clot effectively

• Therefore, cuts are slow to heal

• Disease is carried on the X chromosome

• Queen Victoria and extended family suffered from this

Female Carriers for Hemophilia

Genetic Defects:Can be due to chromosomal

disorders…

Genetic Defects: Or, at the level of Genes

Sickle Cell anemia; autosomal recessive. 9 % of US blacks are heterozygous, while 0.2% are homozygous recessive. The recessive allele causes a single amino acid substitution in the beta chains of hemoglobin. When oxygen concentration is low, sickling of cells occurs.

Heterozygotes make enough good beta-chain hemoglobin that they do not suffer as long as oxygen concentrations remain high, such as at sea-level.

Genetic Defects: at the level of Genes

Huntington’s Disease; (also referred to as Woody Guthrie's disease) is an autosomal dominant resulting in progressive destruction of brain cells. If a parent has the disease, 50% (or more) of the children will have it. The disease usually does not manifest until after age 30.

Cystic Fibrosis; CF is the most common genetic disease in Caucasians. An individual must inherit a defective copy of the CF gene from each parent to have cystic fibrosis. CF causes the body to produce an abnormally thick, sticky mucus, due to the faulty transport of sodium and chloride (salt) within cells