Genetics

Contents:

  1. Genetics

  2. Sex Linked Traits

  3. Environment and Heredity

 

Genetics

 

Genetics- science of heredity

Heredity- passing of traits from one generation to the next (Greeks were the 1st people to notice anything about heredity)

Gregor Mendel- �Father of Genetics�- Australian, monk, went to a university (catholic church didn�t like science), experimented with green peas, conducted breeding experiments

Peas:

  1. Easily distinguishable traits

  2. Large number of offspring (sample number)

  3. They grow fast (short generation span)

  4. They are easy to grow

  5. They carry both self and cross pollination- pollen is a reproductive part in a plant

Pollination- when sperm goes from male part to female part (because of bees or winds)

Self Pollination- pollination with in the same plant

Cross Pollination- pollination with in two different plants

Mendel is well known because:

  1. Conducted controlled experiments

  2. Kept accurate results

  3. Studied one trait at a time

  4. Used a large sample number

  5. First to use statistics and probability

Dominant- a trait which expressed itself even if only one dose of the gene is present

Recessive- a trait which expresses itself only if two doses of the gene are present

Types of cells:

a)     Somatic cells- cells which are not directly involved in reproduction- 46 of them in a cell

b)    Gametes- sperm and egg cells, cells directly involved in reproduction

Somatic Cells-

46 chromosomes- made of genes (genes for all traits)

                      2 genes per trait per cell

Gametes Cells � you need two gametes to form offspring

                   23 chromosomes per cell

                   1 gene per trait per cell

Eye Color (pretend only brown and blue)

B = brown

b = blue

Possible outcomes: BB= brown

                             Bb= brown

                             bb= blue

Homozygous- the 2 genes for the trait are the same (ex: BB and bb)

Heterozygous- the 2 genes for the trait are different (ex. Bb)

Zygote- fertilized egg

Phenotype- external appearance of a trait

Genotype- the actual gene combination for the trait

Allele- gene (different form/ variation)

Factors- Mendel�s terms for genes

Mendel�s Experiment: watched the high of pea plants (T or t). He bred a tall plant and a short plant and all the offspring were tall. From this he concluded that tall was dominant.

Law of Dominance � when pure alternate forms of a trait are crossed all offspring resemble the dominant parent. The trait that does not appear in the offspring is recessive.

Punnet Square

Law of Segregation � when F1 hybrids are crossed with each other the trait that did not appear in the F1 reappears in about � of the F2.

Law of Independent Assortment- (3rd law of genetics) when two traits are studied at the same time, the inheritance of one trait is independent of the inheritance of the 2nd trait

Exception to Independent Assortment- when genes for different traits are found on the same chromosomes they tend to be inherited together. This is called linked genes (ex. Blonde hair, blue eyes).

Incomplete Dominance- (blending inheritance) the hybrid doesn�t resemble either parent but instead shows a blend of both parental traits.

Ex. Four O�clocks (petal colors)

          Red-dominant

          White- dominant

RR x WW = RW (pink)

    

Alusian Fowl (feather colors)

          Black- dominant

          White- dominant

BB x WW = BW (blue)

Sickle Cell Disease

Blood Cell Types:

HbA- hemoglobin A- normal

HbS- hemoglobin S- abnormal

Gene Combinations:

1.       HbA HbA � normal (your blood cell looks like a blob)

2.     HbA HbS- sickle cell trait ( your have both types of cells but more blood cells are normal)

3.     HbS HbS- sickle cell anemia ( your blood cells are moon shaped)

Sickle Cell Anemia- (HbS HbS) your red blood cells don�t hold as much oxygen as the normal cells do. It is also harder for these blood cells to get around the body.

Sickle Cell Trait- (HbA HbS) you have both types of blood cells (more normal ones then abnormal ones), most of them are normal, they have a higher resistance to malaria than either of the other two (HbA HbA, HbS HbS)

 

Multiple Alleles- there are 3 or more different genes for a trait in the population. Individuals still only have 2 genes.

Blood Groups- there are 4 major blood groups (A, B, AB, O)

Antigen- a foreign substance usually a protein that stimulates production of antibodies.

Antibody- a substance produced in response to an antigen.

 

Phenotype

Genotype

Antigen

Antibody

             A

IA ,IA , IA , i

             A

Anti-B

             B

IB,  IB, IB, i

             B

Anti- A

           AB

IA, IB

            AB

None

            O

ii

          None

Anti-A, Anti-B

 

Universal Recipient- AB- can receive blood from anybody, but can�t give blood to anybody. (Example of incomplete dominance)

Universal Donor- O- can give blood to anybody, but can�t receive blood from anybody.

Agglutination Reaction- can happen if you mix the bloods that can�t be mixed (ex. Mix A and B)

Rh (Rhesus) Factor- not multiple alleles

Rh= + (positive) dominant

Rh= - (negative) recessive

 

RhRh=  +

Rhrh=   +

rhrh=    -

 

Possible Blood Types

A+    B+   AB+   O+

A+    B-    AB-    O-

 

Placenta- only found in pregnant women. Provides oxygen and nutrients to the developing fetus (baby). Carries away fetus�s wastes.

Rh Disease- the only possible way to get it is if mother is negative, father is positive, and baby is positive.  A few drops of the baby�s blood mixes into the mother�s blood while the baby is in the placenta, the mother�s antibodies will start trying to find its way to kill the baby�s blood. The baby doesn�t have anti-bodies ( gets antibodies from breastfeeding) so it can get hurt. But usually even if the blood breaks the antibodies don�t have enough time to enter the baby�s blood (It takes a while to produce the antibodies and by that time the baby is out). This won�t harm the mother but might harm the baby. If the mother has another baby that comes out positive if there is a breakage and blood leaks the baby will be harmed.

 

Back to Top

 

Sex Linked Traits

 

Sex- Linkage (sex linked traits)- traits were genes are located on the X chromosome only. There are no genes for these traits on the Y.

 

Colorblindness

C- normal color vision

c- color blindness (more common in male)

 

*c gene is only found in X chromosome (not found in Y chromosome)

 

Genotypes (for females)                     Genotypes (for males)

CC- dominant (normal)                         CY- dominant (normal)

Cc- carriers (normal                            cY- recessive (colorblind)

cc- recessive (colorblind)

 

    C (mother) c

CC

Cc

 CY

cY

 C (father)

 Y

 

50% of the sons will be colorblind

The ratio of males: females who have colorblindness is 10:1. This is because it is easier for a male to inherit the recessive gene than for a female since the male only needs to inherit one gene recessive gene and the female needs to inherit two of them.

 

Synthesize- produce

 

Hemophilia- the inability of the blood to clot, can�t synthesize factor VIII, the chemical for clotting)

H- dominant (blood clots)

h- recessive (hemophilia)

 

-There are no hemophiliac women only hemophiliac men because it�s very rare to have two of the recessive gene, and most fathers who have it die young so they can�t pass it down.

 

Back to Top

 

Environment and Heredity

 

  1. Green Color in Plants- plants are green because of chlorophyll, light is needed to activate the chlorophyll

C- dominant (chlorophyll) green

c- recessive (no chlorophyll) white

  1. Baldness in Humans- a minimum level of testosterone is needed to activate the dominant gene

B- dominant (bald)

b- recessive (hair)

  1. Intelligence-

Twin Studies

          Identical twins rose apart

                       v.

          Fraternal twins raised together

                                     

Back to Top

Return to Freshman Review Sheets

Review Sheets Central
www.reviewsheetscentral.com