DNA&

MENDELIAN GENETICS REVIEW

DNA Genetic material found in the nucleus of

eukaryotic cells; in the cytoplasm of prokaryotes (no nucleus)

A library of genetic information (genes) located in the nucleus of eukaryotic cells

Made up of one long DNA molecule wrapped around chunks of protein

CHROMOSOME

Number of Chromosomes Organisms have 2 different types of

cells

Body (somatic) cells: skin, liver, brain These cells each have a Complete Set of chromosomes (46, or 23 pairs)

Sex cells (gametes): sperm and egg

Because sperm and egg need to meet and combine their chromosomes to form a new individual, they have ½ the number of chromosomes as body cells (23)

Karyotype

One complete set

of chromosome

s(23 Pairs)(46 total)

Chromosomes are counted on karyotypes

Normal Human Karyotype: 46 chromosomes

23 pairs 44 autosomes

22 pairs 2 sex chromosomes

1 pair XX = female XY = male

Down’s Syndrome Karyotype

“TRISOMY 21”

Structure of DNA

A Double helix ladder of connected nucleotides forming a sugar-phosphate “backbone” and nitrogen base “steps”

Each nucleotide of DNA consists of: A sugar “deoxyribose” A phosphate A nitrogenous base:

Adenine Thymine Cytosine Guanine

When nucleotides are bonded, they compose a DNA molecule

Double-helix/spiral ladder Sugar-phosphate “backbone” Bases are rungs of ladder Long sequences of bases make up genes

The Making of New Prokaryotes

Bacteria make a copy of their DNA strand Then splits in two, creating two bacteria.

The Making of New Body Cells Mitosis: Division of a cell into BODY cells.

(Body cells = Somatic = liver, brain, skin, etc) First, DNA is copied, then the nucleus of eukaryotic cells divide, each new nucleus has a complete set of chromosomes.

(Really, mitosis = nuclear division) Cytokinesis: Cell Division. The eukaryotic cell divides into two cells,

each with its own nucleus***These two parts of the cell cycle are often

combined and called ‘mitosis’

MITOSIS

Mitosis + Cytokinesis = 2 new cells with the same genetic information as the original cell

Cell Cycle: An Interactive Animation

Cycle of growth and division. Interphase (cell growth) is most active.

KEY TERMS:

Haploid Cells: The number of chromosomes in a sex cell

n = 23 in humans(Sex cells = Gametes = sperm, egg)

Diploid Cells: The number of chromosomes in a somatic cell

2n = 46 in humans

Meiosis

The division of a cell into sex cells. The number of chromosomes in the nucleus is halved. (46 to 23)

Mitosis vs. Meiosis

Spermatogenesis

2n=46

humansex cell

diploid (2n)

n=23

n=23

n=23

n=23

n=23

n=23

sperm

haploid (n)

Crossing-over occurs at this stage

4 genetically different gametes are produced

Crossing Over =

Genetic Variation

When chromosomes exchange corresponding

segments of DNA- no longer identical

Crossing Over = Variation

homologous pairs

This causes geneticvariation

TetradTetrad, homol. pairs together

Nondisjunction causes errors in chromosome numbers

Nondisjunction is when the chromosomes don’t split evenly in meiosis, resulting in too many or too few chromosomes in the sperm or egg.

Examples of diseases/conditions caused by non-disjuction: Down’s Syndrome = 47 Turner’s Syndrome = 45 Klinefelter’s Syndrome = 47http://www.biostudio.com/d_%20Meiotic%20Nondisjunction%20Meiosis%20I.htm

Why do these errors cause physiological problems?

Protein Synthesis: How DNA turns the base sequence into proteins

DNA RNA Protein

DNA REPLICATION:

Copying DNA before Cell Division

1.The Double Helix ‘unzips’ 2. A

matching(complementary)strand is made of each side,making two molecules of DNA

Copying DNA

before the nucleus divides

and before cell

division

RNA: The copied ‘page’A working copy of DNA genes

that leaves the nucleus

As the ‘original copy’ of ALL the cells genetic information, DNA cannot leave the nucleus

DNA has ALL the genetic material, and cells only need to use specific information

So a ‘working copy’ is made that can leave the nucleus and make the needed proteins for the cells to function.

DNA holds the instructions for the manufacturing of protein.

This is done through protein synthesis -the making of proteins from the instructions coded by the sequence of bases in the DNA

1. Transcription: In the nucleus, the genetic info is ‘copied’ from DNA to RNA in code.2. Translation: The RNA leaves the nucleus and the code is translated on ribosomes to make specific proteins for gene expression

http://www.biostudio.com/demo_freeman_protein_synthesis.htm

1865 Paper Published by Gregor Mendel based on his research with garden peas

1. Principle of Dominance and Recessiveness:There are alternate forms of genes called alleles.

One factor in a pair of genes may mask the effect of another.

Dominant allele: When only ONE of the alleles affects the trait. (Use a CAPITAL letter)

Recessive allele: the allele that is NOT expressed if there is a dominant allele present. (Use a small letter).

1865 Paper Published by Gregor Menel based on his research with garden peas

Homozygous – an individual who has the same alleles for a trait. Ex. 2 genes for cystic fibrosis

(BB = homozygous dominant or bb = homozygous recessive)

Heterozygous – an individual who has different alleles for a trait. Ex. One gene for cystic fibrosis, one for normal (Bb)

Genotype – the genetic makeup of an organism “Genes”

The many different alleles that an organism can possess: BB or Bb or bb

Phenotype – the external appearance of an organism. An organisms physical appearance, determined by it’s alleles “Photo”

Genetics Terminology

Generations

Parent generation = POffspring of P generation = F1Offspring of F1 generation = F2

Cross a homozygous dominant purple flowerwith a homozygous recessive white flower.

Givethe F1 genotype and phenotype percents.

Purple = PP, white = pp

Sex-linked inheritance

Males and females inherit some diseases with different frequency. This is because the Y-chromosomes have

fewer genes, and with only one X for males, there are no heterozygotes.

Examples: hemophilia and color-blindness

Punnett squares that separate the chances of males and females getting diseases

How males and females inherit:XN Y or Xn YXN XN or XNXn or XnXn

Pedigree Charts

Pedigree charts follow a genetic mutation/disease through several generations of a family.

You can determine what chance offspring has of having a disease based on family history and Punnett Square.

The main diseases that are tracked this way are: Tay-sachs Huntingtons Colorblindness Hemophilia Cystic fibrosis

Basic Symbols

PHENOTYPESClear = unaffectedShaded = affectedGENOTYPESNot usually

indicated, but often can be determined by the phenotypes

How to read a pedigree

Pedigree:recessivegeneticdisorder

1. An individual

who is affected may have parents

who are unaffected.

2. ALL children of 2

affected parents are

affected

Pedigree:DominantInheritance

1.Every affected

individual has at least one

affected parent2. Affected who mate with an

unaffected have a 50% chance

to pass the trait.

3. Two affected MAY have unaffected children

Sex-Linked Recessive

males get their X from their mother

fathers pass their X to daughters only

females express it only if they get a copy from both parents.

expressed in males if present

recessive in females Outsider rule for

recessives (only affects females in sex-linked situations): normal outsiders are assumed to be homozygous.

#1 – sickle-cell

Autosomal Recessive (nn)

#4 - colorblindness

X-linked Recessive (Xn)

The factors for different traits are sorted into the gametes independent of each other.

S = Smooth peaY = Yellow Color

1. Determine all possible combinations of alleles in the gametes for each parent.

DiHybrid Cross: Independent Assortment

DiHybrid Crosses

2. List the gametes for Parent 1 along one edge of the punnett square, and the gametes for Parent 2 along the other edge

DiHybrid Cross

3. Fill out the squares with the alleles from Parent 2 The result is the prediction of all possible combinations of genotypes for the offspring of the dihybrid cross, SsYy x SsYy.

A phenotypic ratio of 9:3:3:1 is predicted for the offspring of a SsYy x SsYy dihybrid cross.

9 spherical yellow : 3 spherical green : 3 wrinkled yellow : 1 wrinkled, green