Applied Biology Genetics Notes

Genetics Introduction

• Genetics is the study of heredity

• Heredity explains why you look like your parents or siblings (similar traits)

• Traits (ex. Color, shape) are inherited or passed down to offspring in genetic crosses

Essential Vocabulary!

• Gene – parts of DNA that control traits

• Gregor Mendel – “Father of Genetics”, studied inheritable information & performed plant-cross experiments

Dominant vs Recessive

Dominant gene – trait ALWAYS shows itself

Recessive gene – trait hidden when dominant gene is present

Allele – forms of a particular gene (we use caps & lower case letters)

(R = round and r = wrinkled…….but both code for shape)

Homozygous vs. Heterozygous

• Homozygous – 2 of same allele for a trait (RR or rr)

• Heterozygous – 2 different alleles for a trait (Rr)

Phenotype vs. GenotypePhenotype vs. Genotype

• Phenotype – physical observable trait (shape, color ect.)

• Genotype – genetic make-up, combination of alleles (RR, Rr, rr)

Genotype

Phenotype (purple)

Solving Genetics ProblemsSolving Genetics Problems

1. Designate letters for traits (R=Round, r=wrinkled)

2. Determine parent alleles

3. Set up Punnett square

4. Fill – in Squares

5. Determine possible offspring genotypes & Phenotypes

Practice ProblemBlack hair (B) is dominant over brown hair (b). A man heterozygous for black hair and a woman with brown hair have children. What are the genotypes and phenotypes of their offspring?

Step #1 B = black b = brown

Step #2 Dad = Mom = Step #3 (punnett square)

Step #4 (fill-in offspring squares)

Step #5 (Genotypes & phenotypes)

Blood Typing Genetics(Codominance & Multiple Alleles)

• In simple genetics…there are usually 2 alleles– 1 dominant (R) & 1 recessive (r)

• In Codominance…neither allele is dominant over the other!

• Since they are COdominant…they both show up in the heterozygous phenotype!

Blood Typing Genetics (cont.)

• Usually in simple genetics problems we have:– 1 Dominant Allele– 1 Recessive Allele R or r

• In Blood typing, we have:–2 Dominant Alleles = A & B–1 Recessive Allele = o

EXAMPLE: Blood Types!

Blood Typing - Codominance• In humans, there are 4 possible blood

types: A, B, AB, and O.

• Type O individuals are considered to be the “universal donors”, whereas type AB individuals are said to be “universal recipients”!

Blood Type Genotypes

Type A Blood– AA is homozygous– Ao is heterozygous

Type B Blood– BB is homozygous– Bo is heterozygous

Type AB Blood– AB (this is the co-dominant blood type!)

Type O Blood– oo (only 1 way to have Type O blood because o is

recessive!)

Blood Typing – Practice Problem

A man heterozygous for Type A blood and woman homozygous for Type B blood have children. What are the possible genotypes and phenotypes of their offspring?

Practice Problem #2Two babies are ready to go home from the hospital…

Which baby belongs to which parents?

• Here’s what you know about the babies:– Baby A bas blood type A– Baby B has blood type O

Parents #1 - Father (Homozygous Type A) & Mother (Type O)

Parents #2 - Father & Mother (Heterozygous A)

Sex Linkage – Hemophilia

Some traits are carried on the X chromosome!! Hemophilia is the most well-known sex-linked disease!

Males = X Y

Females = X X

Hemophilia Lacking the ability for blood to clot…can’t stop bleeding

Possible Genotypes:

Hemophilic Male Genotype = X Y

Hemophilic Female = X X

Normal Male Genotype = X Y

Normal Female Genotypes = X X X X (CARRIER)

Practice Sex Linkage (Hemophilia)

ProblemA man with hemophilia and a normal women (but carrier for hemophilia) have a child. What are the possible genotypes and phenotypes of their offspring?

Man = X Y

Woman = X X

Offspring Genotypes:

Offspring Phenotypes:

Human GeneticsKaryotype - the complete set of chromosomes in a species. Can show chromosomal disorders such as:

1.Down Syndrome (Trisomy 21)

2.Turner Syndrome (X missing pieces)

3.Klinefelter Syndrome (XXY)

Chromosomal Disorders occur due to NONDISJUNCTION – error in meiosis where chromosomes don’t separate correctly during anaphase!

Human Genetics - Pedigrees