Genetics Test ReviewTest is Tuesday, April 21st

Vocabulary:

Who is the “father of genetics”? Gregor Mendel

What is a trait? Physical characteristics of organisms

What is heredity? Passing of traits from parent to offspring

What is genetics? Scientific study of heredity

Vocabulary: What are genes?

Factors that control traits What are alleles?

Different forms of a gene One allele is inherited from each parent Alleles can be dominant or recessive

Dominant and Recessive Alleles:

What is a dominant allele? Always seen if present Indicated by a capitol letter (T)

What is a recessive allele? Masked or hidden if dominant allele is present Indicated by a lower case letter (t)

Hybrid and Purebred:

What is a hybrid? Organism has two different alleles for the trait – one

dominant and one recessive. What is a purebred?

Organism has two identical alleles for a trait – two recessive OR two dominant.

Homozygous and Heterozygous:

What is homozygous? An organism that has two identical alleles for a trait TT – homozygous dominant tt – homozygous recessive

What is heterozygous? An organism that has two different alleles for a trait Tt – heterozygous – will show the dominant trait

Let’s Practice:

• Homozygous (HO) or Heterozygous (HE):

AA ____Bb ____Cc ____Dd ____

Ee ____ff ____GG ____ HH ____

HO

HE

HE

HE HO

HO

HO

HE

Phenotypes and Genotypes:

What is a phenotype? Physical appearance or visible trait Example is flower color, stem height, etc.

What is a genotype? The genetic makeup or allele combination Examples are TT or Tt

Genotypes determine phenotypes

Determine the Phenotype:

Purple flowers are dominant to white flowersPP _____________Pp _____________pp _____________

Brown eyes are dominant to blue eyesBB ____________Bb ____________bb ____________

Purple

Purple

White

Brown

Blue

Brown

For each phenotype list the genotype:

Straight hair is dominant to curly.____________ straight____________ straight____________ curly

Pointed heads are dominant to round heads.____________ pointed____________ pointed____________ round

SS

Ss

ss

PP

Pp

pp

What are Punnett Squares?

Punnett Squares chart that shows all possible

combinations of alleles that can result from a genetic cross. Used to determine the probability of a particular outcome. The probability is the likeliness that an event will occur.

Punnett Square Practice:

• ________ x ________ • In pea plants, purple flowers are

dominant over white flowers, which are recessive. Cross a homozygous dominant parent with a homozygous recessive parent. What is the outcome for this cross?

PP pp

P P

p

p

Pp

PpPp

Pp

100% Purple Flowers

What does the term codominace mean?

Both alleles of a gene pair are equally dominant.

Neither allele is dominant or recessive to the other and as a result both alleles are expressed in a heterozygous offspring.

Punnett Square for Codominance:

X

100% mixed curly and straight hair (CS)

Curly HairCC

Straight HairSS

Curly and Straight HairCS

C C

S

S

CS CS

CS CS

What does the term Incomplete Dominance mean?

One allele of a gene pair is only partially dominant over the other.

In these cases an intermediate form of the trait is expressed in heterozygous organisms.

Often seen in flowers.

Punnett Square for Incomplete Dominance:

X

100% gray mice (Bb)

Black mouseBB

White mousebb

B B

b

b

Bb Bb

Bb Bb

Gray mouseBb

What are sex-linked traits?

• Traits that are controlled by genes located on the sex chromosomes (X or Y).

• These traits are more common in males than females.

• Females: XX• Males: XY

Female & Male Genotypes:

• What is the genotype for a female?

• XX• What is the genotype

for a male?• XY

Sex Linked Example:Girls = XX Boys = XY

Consider a case where hemophilia is a recessive disorder that is inherited on the X chromosome. Complete the Punnett Square to find out the results of the offspring if the mom does not have hemophilia and the dad has hemophilia.

• 100% the daughters will be carriers (XHXh), but will not have hemophilia.

• 100% of the sons will not have hemophilia (XHYØ)

XH

Xh

XH

YØ

XHXh XHXh

XHYØ XHYØ

What are multiple alleles?

• Traits that are controlled by three or more alleles.

• Even though more than two alleles exist for a particular trait, humans only carry two at a time.

• ABO Blood Type is a good example!

ABO Blood Type:Consider a family where the mother is blood type B and the father is blood type A. Is it possible for them to have a blood type O baby? Why or why not? Set up a Punnett Square to support your answer.

B

A

O

O

AB AO

BO OO

Yes, it is possible for the baby to have blood type O, if the mother’s genotype is BO and the father’s genotype is AO.

What is a pedigree used for?

• A pedigree is a chart or “family tree” that tracks which members of a family have a particular trait.

What is the shape of DNA?

Double Helix

How do the nitrogen bases in DNA pair?

Adenine pairs with Thymine

Guanine pairs with Thymine

What is a nucleotide?A molecule made up of a nitrogen base, a sugar, and a phosphate group.

Why are Watson, Crick, and Franklin so important?

• Watson and Crick built a model that showed how the smaller molecules of DNA bond together and form a double helix.

• Franklin used X-rays to study DNA, which indicated that DNA has a helix shape.

What is DNA replication?

• DNA replication is the process of copying a DNA molecule to make another DNA molecule.

Steps of DNA replication: 1. DNA strand separates and

nitrogen bases are exposed.2. Nucleotides move into place

and form new nitrogen base pairs.

3. Two identical strands of DNA are produced.

DNA Replication:

Determine the other DNA strand that forms during DNA replication:

Original strand: A T T C G C G A T A G COther strand: T A A G C G C T A T C G

Original strand: C G A A T T G G C A C COther strand: G C T T A A C C G T G G

What are the differences between DNA and RNA?

• DNA– 2 strands– Sugar – deoxyribose– Nitrogen bases – A, T, G, C– Pairing of bases• A with T• G with C

• RNA– 1 strand– Sugar – ribose– Nitrogen bases – A, U, G, C– Pairing of bases• A with U• G with C• *Uracil replaces Thymine

What are the function of mRNA, tRNA, and rRNA?

• Messenger (mRNA): carries coded instructions for protein synthesis.

• Transfer (tRNA): carries specific amino acids to ribosomes during protein assembly.

• Ribosomal (rRNA): helps form chemical bonds that attach one amino acid to the next.

Genetic Code:

• What is the genetic code?• The order of nitrogen bases along a gene

forms a genetic code that specifies what type of protein will be produced. The type of protein produced determines the trait!

• What are the building blocks of protein? • A group of three nitrogen bases codes for a

specific amino acid.

What are the steps of protein synthesis?

• DNA “unzips” between the nitrogen base pairs.• Genetic information from DNA is copied by the

mRNA which leaves the nucleus and attaches to a ribosome in the cytoplasm.

• Transfer RNA (tRNA) picks up amino acids according to the mRNA code of nitrogen bases.

• Each tRNA molecule attaches the amino acid to the growing protein chain.

What is TRANSCRIPTION?

• The process by which mRNA is made from DNA. It occurs in the nucleus.

What is TRANSLATION?

• Translation occurs in the cytoplasm, specifically on the ribosomes. The mRNA made in the nucleus travels out to the ribosome to carry the message of the DNA. Translation is the process of making a protein from RNA.

Identify the following in protein synthesis:tRNA, mRNA, protein chain, ribosome, and amino acid

1

2

3

4

Ribosome5

How To Read A Codon Chart:Codon: series of three nitrogen bases on

mRNA

1. When looking at the chart, the first letter in the codon is located on the left hand side of the chart.

2. The second letter is at the top of the chart. Find when these two letters intersect.

3. Then look at the third letter. It is found on the right hand side of the chart, in the box where one and two intersect.

4. This is the name of the amino acid that is made when that codon is read during protein synthesis.

https://www.youtube.com/watch?v=Z4wZxraE59o

Suppose one strand of DNA has the following nitrogen base sequence:

TAC CGC TCC GCC ACT

• What would be the order of nitrogen bases on the other strand of DNA?

• What would be the order of nitrogen bases on mRNA that would be transcribed (copied) from the initial DNA sequence? (TAC CGC TCC GCC ACT)

• Using this mRNA sequence and the genetic code, what amino acids, in order, would be included in the protein chain? (you can write the 3-letter abbreviation for each amino acid)

• Would any additional amino acids be attached to this particular protein chain? Explain.

AUG GCG AGG CGG UGA

ATG GCG AGG CGG TGA

MET ALA ARG ARG STOP

No, because the protein chain ends with a stop codon.

Suppose one strand of DNA has the following nitrogen base sequence:CCC ATA ATG AAA ATC

• What would be the order of nitrogen bases on the other strand of DNA?

• What would be the order of nitrogen bases on mRNA that would be transcribed (copied) from the initial DNA sequence? (CCC ATA ATG AAA ATC)

• Using this mRNA sequence and the genetic code, what amino acids, in order, would be included in the protein chain? (you can write the 3-letter abbreviation for each amino acid)

• Would any additional amino acids be attached to this particular protein chain? Explain.

GGG UAU UAC UUU UAG

GGG TAT TAC TTT TAG

GLY TYR TYR PHE STOP

No, because the protein chain ends with a stop codon.

What is a mutation?

• A change in the nucleotide sequence of a gene, which is a mistake that occurs in one gene of a chromosome. This causes the cell to produce an incorrect protein, which results in a different physical trait or phenotype.

Identify the type of mutation:

Substitution Mutation: one nitrogen base is replaced by a different nitrogen base

Deletion Mutation: one or more nitrogen bases are left out of the DNA sequence

Insertion Mutation: one or more nitrogen bases are added to the DNA

The mice ran away.

The rice ran away.

Thei cera naway.

The migukce ran away.