Goal 3 Genetics

Cell Cycle

Cell Cycle

• Interphase= majority of the life of a cell–the time during which it grows and prepares for replication

• Mitotic Phase- Mitosis and Cytokinesis

Mitosis• Mitosis = division of the nucleus– Four phases:• Prophase – chromatin condenses to show individual

chromosomes; centrioles replicate and spindle begins to form; nucleus dissolves• Metaphase– chromosomes line up along the center of the cell;

each chromosome is attached to spindle fiber at centromere• Anaphase – sister chromatids separate into opposite sides of

the cell• Telophase– chromatids gather at opposite ends of cell; nuclei

reform; spindle disappears

Mitosis

– Two IDENTICAL cells are formed (diploid)• Asexual reproduction

– Occurs in somatic cells (body cells)

Mitosis

Cytokinesis

• Cytokinesis – division of the cytoplasm – occurs directly after telophase of mitosis and telophase I and II of meiosis

Meiosis– Two divisions with 4 phases in each:• Meiosis I–During prophase I, crossing over occurs between

homologous chromosomes–During metaphase I, homologous chromosomes

line up at center of cell–During anaphase I and telophase I, homologous

chromosomes are separated into different sides of the cell

• Meiosis II–Looks much like mitosis in that sister chromatids

are separated

Meiosis

– Four DIFFERENT cells are formed• Genetic variation!!!!!!• Sexual reproduction

– Occurs in sex cells (gametes = sperm and egg)– Daughter cells have ½ the number of

chromosomes that the parent cell had (haploid)

Mendelian Genetics• Gregor Mendel was a monk that studied cross-

pollination in pea plants and recognized predictable patterns of inheritance.

• Probability and Punnett Squares• Vocabulary to KNOW:

Mendelian Genetics– trait —a characteristic– allele —different forms of a gene– dominant —allele that is always expressed, capital letter– recessive —weaker allele, only expressed if dominant is

not present, lower-case letter– homozygous —2 of the same alleles, TT or tt– heterozygous —2 different alleles, Tt– genotype —the genetic makeup, the letters of the

alleles– phenotype —the physical characteristic the letters stand

for

Non-Mendelian Genetics

• Codominance – two alleles are equally dominant, therefore the heterozygote shows both alleles.– Example: In cows, Black (BB) and White (WW) are

codominant; BW is spotted.– Problem: If a Black Cow and a Spotted Bull are

mated, what is the probability of a spotted baby?

Non-Mendelian Genetics

• Problem: If a Black Cow and a Spotted Bull are mated, what is the probability of a spotted baby?

B B

B

W BW

BB BB

BW

BB = black (2)BW= spotted (2)

50% spotted or 1/2

Non-Mendelian Genetics

• Incomplete Dominance– one allele is not completely dominant over another, therefore the heterozygote is a blend of the two alleles.– Example: In snapdragons, Red (RR) and White

(WW) are incompletely dominant. RW is a pink flower.

– Problem: If two pink flowers are crossed, what is the probability of a red flower?

Non-Mendelian Genetics

• Problem: If two pink flowers are crossed, what is the probability of a red flower?

R

R

W

W

RR RW

RW WW

RR = red (1)RW= pink (2)WW= white (1)

¼ or 25% red

Non-Mendelian Genetics• Multiple Alleles : there are more than 2 alleles

for a trait– Example: Human Blood types. Type A and Type B

are codominant over Type O. – There are 4 possible blood types and 6 possible

genotypes: Phenotype Genotype

A **IAIA (AA) or IAi (AO)

B **IBIB (BB) or IBi (BO)

AB IA IB (AB)

O ii (OO)

** IAIA and IBIB are homozygous**IAi and IBi are heterozygous

Non-Mendelian Genetics

Problem: Bob has type AB blood and his wife, Annie, is heterozygous for type A blood. What is the probability of their child having type B blood?

Non-Mendelian GeneticsIA

IA

IB

i

IAIA IAIB

IAi IBi

IAIA = A (1)IAIB = AB (1)Iai = A (1)Ibi = B (1)

¼ or 25% B blood

Non-Mendelian Traits

• Sex-Linked Traits – traits for which the gene is carried on the X chromosome.– Diseases are more common in males because they

only have 1 X chromosome.– Females who are heterozygous for the trait are

called carriers– Problem: Colorblindness is a sex-linked recessive

trait. If Suzie is a carrier for colorblindness and Joe has normal vision. What is the probability of the two having a son with colorblindness?

Non-Mendelian Traits

• Problem: Colorblindness is a sex-linked recessive trait. If Suzie is a carrier for colorblindness and Joe has normal vision. What is the probability of the two having a son with colorblindness?

XH Xh

XH

y XHy

XHXhXHXH

Xhy

XHXH = normal female (1)XHXh = carrier (1)XHy = normal male (1)Xhy = colorblind male (1)

¼ or 25% of having a son with colorblindness

Non-Mendelian Genetics

• Polygenic Traits – traits for which the genes are carried in multiple locations on multiple chromosomes. – Results in a wide variety of phenotypes.– Examples: Skin Color & Height

Pedigree

• A_pedigree shows the relationship and inheritance patterns of a family– Males are squares, females are circles– Unshaded are unaffected, shaded are affected, half

shaded are carriers– Horizontal lines between two people indicate

matings, vertical lines indicate children– People are numbered from left to right– Generations are numbered going down with Roman

Numerals.

Pedigree

• Autosomal or Sex-Linked? Dominant or Recessive?

Pedigree

• Autosomal or Sex-Linked? Dominant or Recessive?

DNA & Protein Synthesis• DNA Form– Structure of DNA = double helix– discovered by Watson

& Crick in 1954– nucleotides = building blocks• Phosphate• Sugar – Deoxyribose• Nitrogen Base–Adenine & Thymine–Guanine & Cytosine

– Nucleotides are held together by weak hydrogen bonds.

DNA & Protein Synthesis

Give the complementary DNA Strand

• ATAGCATTCCGACGTCAG

DNA & Protein Synthesis

Give the complementary DNA Strand

• ATAGCATTCCGACGTCAG• TATCGTAAGGCTGCAGTC

DNA & Protein Synthesis

• DNA _Replication– DNA makes an exact copy of itself before cell division– DNA molecule separates into 2 strands.– Each strand of DNA serves as a template or model

for the new strand.– Two identical DNA molecules are created

• DNA replication is aided by the enzymes helicase and DNA polymerase

DNA & Protein Synthesis

• RNA Form– RNA is single stranded instead of double stranded

like DNA– The sugar deoxyribose is replaced with the sugar

ribose.• The base Adenine pairs with Uracil instead of

Thymine

DNA & Protein Synthesis

– Types of RNA:•Messenger RNA (mRNA) brings message

from DNA in the nucleus to the ribosome in the cytoplasm.• Transfer RNA (tRNA) brings correct amino

acids to the ribosome to assemble the protein being made.• Ribosomal RNA (rRNA) the structure of

the ribosome

DNA & Protein Synthesis

• Protein Synthesis–Transcription= DNA mRNA, occurs in

nucleus•RNA polymerase separates DNA

strands and DNA serves as a template for the formation of mRNA.• Transcribe the following:

• ATAGCATTCCGACGTCAG

DNA & Protein Synthesis

• Transcribe the following:• ATAGCATTCCGACGTCAG (DNA)• UAUCGUAAGGCUGCAGUC (mRNA)

DNA & Protein Synthesis

–Translation= mRNA proteins•Making protein at the ribosome from

the mRNA•What sequence of amino acids would

make up the protein for the DNA strand above?

DNA & Protein Synthesis

• UAUCGUAAGGCUGCAGUC (mRNA)

• Split the mRNA into codons (groups of 3)– UAU= ?– CGU= ?– AAG=?– GCU=?– GCA=?– GUC=?

DNA & Protein Synthesis

• Now look at your amino acid chart to determine the amino acid that goes with each codon of mRNA– UAU= Tyr– CGU= ?– AAG=?– GCU=?– GCA=?– GUC=?

DNA & Protein Synthesis

–UAU= Tyr–CGU= Arg–AAG=Lys–GCU=Ala–GCA=Ala–GUC=Val

DNA & Protein Synthesis

• Mutations any change in a genetic sequence–Creates genetic variation–Harmful mutations are associated with

many genetic diseases and some forms of cancer.• Cancer is uncontrolled cell growth or

continuous mitosis

DNA Technology

• DNA Fingerprint – DNA fragments are run through a gel and bands are compared for similarities

• Recombinant DNA – pieces of DNA from 2 different organisms are joined together.– Can be used to produce human insulin for diabetic

patients• Cloning – creating genetically identical individuals

from a single cell.

DNA Technology• Human Genome Project – identify the genes and

sequence bases that make up the human chromosomes.– Completed in 2003– Information can be used to detect and possibly

treat many genetic diseases.• A karyotype is a picture which shows all the

chromosomes in each cell– It is used to detect if there are more than two

copies of each chromosome and the sex or gender of the individual• 3 copies of Chromosome 21 = Down’s Syndrome