Study guide- Heredity

What is a gene?

A unit of heredity information

What does a gene normally code for?

for a specific trait or protein.

Who is the father of genetics?

Gregor Mendel

What was “the father’s” test organism?

Pea plants

Give a couple of reasons why these were a great choice

• Easy to grow

• Self-pollinating plants

• 7 easy identifiable traits

What about them lent to controlling fertilization?

Their ability to self-pollinate

Describe in general terms the advantage of Mendel’s choice for the seven characteristics he chose to study

The characteristics had easy observable traits, allowing for tracking or patterns in generations

Define Allele

Alternative forms of a gene controlling a specific trait

P -

Parent generation

_{F1 -}

Result of cross between 2 parents

F2 -

Result of cross between two F1’s

Phenotype - 

Physical Appearance

Examples of Phenotype:

• Eye color

• Height

• Skin tone

• Flower color

Genotype -

The genetic make up of an organism

Examples of Genotype:

• Bb (heterozygous)

• bb (homozygous recessive)

Dominant -

A genetic trait that is expressed in the phenotype even when only one copy is present in the genotype

Recessive -

A genetic trait that is only expressed in the phenotype when two copies are present in the genotype

Homozygous dominant -

Ex:

A genetic trait where two identical dominant alleles are present in the genotype

Ex: BB

Homozygous recessive -

Ex:

A genetic trait where two identical recessive alleles are present in the genotype

Ex: bb

Heterozygous -

Ex:

A genetic trait where two different alleles, one dominant and one recessive, are present in the genotype

Ex: Bb

Would pure or true breeding individuals be homozygous or heterozygous?

Pure or true breeding individuals are homozygous

Mendel’s Law of segregation -

• Alleles separate when gametes are formed ensuring that each gamete carries only one allele for each gene

Law of independent assortment - 

• the alleles of different genes segregate independently from one another

Give an example of polygenic inheritance in people

• Human skin color

• height

• intelligence

Give an example of two traits that are closely linked

• Red hair and freckles

Does crossing over separate these very often?

No

Incomplete dominance - 

EX:

• Effect of 1 allele
  is modified by the
  presence of
  another Allele

• Red flower + white flower = pink flower

Codominance - 

EX:

• When a single gene has more than one dominant allele

• Red cow + white cow = red and white spotted cow

Give an example of a trait influenced by temperature

• Siamese cats have a darker fur color on cooler temperatures

Give an example of a trait influenced by pH

• Hydrangea flower color can change based on soil pH levels

• blue in acidic soil and pink in alkaline soil

 Autosomes -

• Chromosomes that are alike in males and females

• do not determine sex

Sex chromosomes - 

• Chromosomes that determine the sex of an individual, designated as X and Y

Sex chromosomes in Males

• Males have one X and one Y chromosome

Sex chromosomes in females

• Females have two X chromosomes

Who determines the sex of the baby?

• The male

 Compare X vs. Y chromosomes with the relative amount of genes they carry

• X chromosomes carry significantly more genes than Y chromosomes;

• X chromosome contains approximately 1,100 genes

• Y chromosome has about 50-200 genes

What are X-linked or sex-linked genes?

Genes located on the X chromosome, which is one of the two sex chromosomes

Give a couple of examples in people of x linked genes

• Colorblindness

• Hemophilia

• Muscular dystrophy

Who passes on the defective gene to the son?

• The mother

What do we call someone that has one normal gene and one defective gene?

A carrier

Why is Achondroplasia called Lethal Dominance?

• because individuals with two copies of the gene typically do not survive to term, while those with one copy have the disorder

Explain the possible genotypes and phenotypes

Genotypes -

Homozygous dominant

Heterozygous

Homozygous normal

Phenotypes -

1 lethal

2 little people

1 normal

Example of Codominance

• ABO Blood Typing System

Example of Complete Dominance

• Rh Blood Typing System

When are antibodies made in ABO Blood typing system?

• born with

When are antibodies made in Rh blood typing system?

• only if exposed with RH positive blood

What is erythroblastosis fetalis?

• a disorder that happens with a fetus where they have excessive red blood cell destruction due to an incompatibility between the mother's and fetus's blood types

 When does erythroblastosis fetalis occur? 

It occurs when an Rh-negative mother carries an Rh-positive fetus,

 How is erythroblastosis fetalis prevented?

• with rhogam shot given to Rh-negative mothers during and after pregnancy to prevent the formation of antibodies against Rh-positive blood

What are the antigens and antibodies associated to A blood type

• has A antigens

• and anti-B antibodies

What are the antigens and antibodies associated to B blood type

• has B antigens

• and anti-A antibodies

What are the antigens and antibodies associated to AB blood type

• has A and B antigens

• no anti-A or anti-B antibodies

What are the antigens and antibodies associated to O blood type

• has no A or B antigens

• has anti-A and anti-B antibodies

Be able to figure out what blood type someone has if given the reactions in Anti-A, Anti-B, and Anti-D serum.

• If a blood sample reacts with Anti-A antibodies, the person has either blood type A or blood type AB

• If it reacts with Anti-B antibodies, they have either blood type B or AB

• reactions with Anti-D serum indicate the presence or absence of Rh factor, which determines if the blood type is positive or negative

Who is the universal donor?

O- blood type

The universal recipient?

AB+ blood type