Genetics

1
Genetics

• Genetics is the
• science of inheritance. 
• It requires sexual reproduction..
• wherein a sperm
• and egg combine
• to form a zygote.

2
Patterns of Inheritance Genetics Chapt.
10

• Interest in genetics is as old as humankind
• Modern genetics began in 1860s
• Czech Monk- Gregor Mendel
• Playing with peas in his garden

3
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.

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

• Text pg. 178

4
Mendels 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)

5
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
6
The Factors

• Each individual has 2 factors for each traitpod
  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

7
How to Label these factors?

• G for Green pods
• Y for yellow pods
• B for brown hair
• x for blond hair
• Butwe dont do this!!

8
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

9
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

10
Quiz

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

11
How to Predict which factor youll 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

12
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?

Male Gametes
Female Gametes
13
Possible Offspring. Or, F1 Generation
B B
b
Bb
Bb
Bb
Bb
b
Each F1 Offspring has the same traits for hair
color Bb
14
Another Example..Trait for Seed Shape (S)
Text pg 181
15
Mendels 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

16
Dihybrid Cross

• If a Bbtt male mates with a bbTT female?
• What are the possible gametes for each?

17
Male Bbtt x Female bbTT
Bt
bt
gametes
bT
BbTt
bbTt
New individuals (with two factors for
each trait)
gametes
bbTt
bT
BbTt
18
So What?

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

19
Mendels 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?

20
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 technique of
identifying the location of one gene on a
chromosome.
21
Gene location on Chromosomes
22
Quiz

• If the human trait for Hairy knuckles is located
  on 1 genehow 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

23
Why should you care about Chromosomes?Have a
Baby!

• Karyotypespread out a fetuss chromosomes to
  check for normalcy
• Amniocentesis (Text pg. 768-769) Enables us to
  karyotype a fetus
• What are they looking for?

24
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

25
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
26
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
27
Male or Female?
28
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

29
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

30
Female Carriers for Hemophilia
31
Genetic DefectsCan be due to chromosomal
disorders

32
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.

33
Genetic Defects at the level of Genes

• Huntingtons 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