Gregor Mendal – discovered heredity is transmitted in discrete “units” later called genes.

James Watson and Francis Crick – showed DNA is a double helix

Stored in the Nucleus Determines the nature of each cell in the body and how it will function Made up of nucleotides

C = cytosine G = guanine T = thymine A = adenine

4 bases: adenine can only

pair with thymine (AT)

cytosine can only pair with guanine (CG)

The combination of base pairs cannot vary p. 172

1. Which side of the ladder each base comes from2. The order in which the base pairs occur along

the ladder3. The overall number of base pairs

These variations account for differences between species.

All organisms use just these 4 bases, but with different numbers and arrangements

Uncondensed DNA

Chromosome

P 176

Condensed DNA Rod shaped

Each sperm and each egg (gametes) contains 23 chromosomes.

The chromosomes contain genes (a certain length of the chromosome).

The fertilized egg (zygote) and all the body cells that develop from it (except the sperm cells and the egg) contain 46 chromosomes.

Two types1. Autosomes

22 pairs numbered from largest to smallest.

2. Sex chromosomes: 1 pair (23rd pair)

XX in females XY in males

Karotype: picture of chromosomes

P. 177

Question: A liver cell from a human male has:

A) 22 pairs of autosomes, an X and a Y chromosome.

B) 22 pairs of autosomes and two X chromosomes. C) 46 pairs of autosomes, an X and a Y

chromosome. D) 23 pairs of autosomes and two X chromosomes. E) 23 pairs of autosomes, an X and a Y

chromosome.

Answer: A

Each of us has two sets of chromosomes (homologous pairs) one from our mother and one from our father

Each homologous pair contains lengths of genetic information (genes)

Many matched pairs of genes are not exactly alike (alleles)

Differences in our genes account for our uniqueness (green eyes vs. blue eyes)

Genes are a recipe. Alleles are different forms of the same recipe (e.g. chocolate cake and vanilla cake)

23 Pairs = 46 chromosomes total in every cell of your body (except egg and sperm)

HOMOLOGOUS PAIRS

Gene for eye color (blue)

Gene for eye color (green)

allele

Basic unit of genetic information Determine nature and the function of

the cell. The human genes (about 120,000) are

referred to as the human genome. A genome is the full set of genes in

each cell of an organism.

A nuclear enzyme attaches to a segment of DNA causing nucleotide bonds to separate.

Transcription occurs resulting in messenger RNA (mRNA). T is now U (uracil)

Transfer RNA (tRNA) initiates translation into amino acid.

Ribosomes move along the RNA bonding amino acids into polypeptide chains which make proteins.

mRNA

tRNA

NOTE TO STUDENTS: During the cell lecture we learned a part of this process, now we are just inserting one more step (translation using tRNA to tell the ribosome in the right language how to make proteins)

1. Transcription: the transfer of information from a DNA molecule into mRNA molecule.

2. Translation: the transfer of information from an RNA molecule into a Polypeptide, in which language of the nucleic acids is translated into that of amino acids.

Transcription and Translation

DNA staircase unwinds and two chains separate

each chain attracts new biochemical material from the cell to synthesize a new and complementary chain

Ultimately a new cell is formed Process is known as MITOSIS

In the first step of mitosis, all chromosomes are copied, so that instead of 2 copies, the cell briefly has 4 copies of each chromosome.

Shortly afterwards, the cell divides in half, resulting in two cells each has a complete copy of the genetic information.

These cells grow larger and eventually undergo mitosis.

Hint: Mitosis happens in “my toes” and my liver and my mouth etc.

MITOSIS

Homologous pair copied

Gametes: Sex cells (ovum or sperm)

Diploid cells: Cells having 2 copies of each chromosome

Haploid gametes: Gametes having 1 copy of each

chromosome

testicles and ovaries. A diploid cell (having 2 copies of each

chromosome) undergoes a special form of cell division to create haploid gametes (having 1 copy of each chromosome).

An egg and a sperm fuse together to form a new diploid cell called zygote (a process called fertilization).

Meiosis

Mitosis: each cell divides and duplicates itself exactly (46 chromosomes in each cell)

Meiosis: How reproductive cells (eggs and sperm) are produced Results in gametes, cells that contain only

23 chromosomes

Austrian Monk Mathematical principles Classical Genetics

Garden Pea as a model “Basic units” in pairs

p. 210

Example: Pea is wrinkled or smooth

Sexually Reproducing Organism Cross-Pollination (2 different plants) Self-Pollination (same plant)

The seeds in a pod of one of Mendel's pea plants are each the result of a separate fertilization event

Self-pollination occurs as pollen from the anthers falls on the stigma.

1

4

3

2

male anthers

ovaries

Seeds in ovary(peas in pod)

Female stigma

pollination = fertilization

Pollen carry sperm

Pollen falls

Parent generation

(yellow seeds) (green seeds)1

3 2cross-pollination

offspring(yellow seeds)

x

How to cross-pollinate: Mendel’s method

Cross pollinate Wait for Mature plant to

develop Observe characteristics

Phenotype – The observable physical characteristics of an organism, as determined by genetic makeup

Genotype - The combination of alleles located on homologous chromosomes that determines a specific characteristic or trait.

Dominant – when two different alleles are present, the one that is expressed. (Usually represented with a capital letter)

Recessive - when two different alleles are present, the one that is not expressed. (Usually represented with a lower case letter)

Homozygous - with identical alleles at the same locus (location) on homologous chromosomes. (e.g. BB or bb)

Heterozygous - with two different alleles at the same locus on homologous chromosomes. (e.g. Bb)

Monohybrid Cross True-breeding stocks (homozygous)

P (Parental) generation F1

first filial generation

Mendel’s Crosses

Uses letters to represent genes Capital letter denotes dominant gene

and lowercase letter denotes recessive E.g. a tall plant is dominant to a short

Use “T” to represent tall Use “t” to represent short (not s)

HOW TO READ A PUNNETT SQUARE

female gametes

P p P p

P

p

P

pmal

e ga

met

es

pp Pp

1 2

YYYY

YY YY yyyyyyyy

Y Y y y

Y Y y y

Y

Y yy

Yy

YyYy

Yy

YyYy

Yy Yy

female male

female

gamete

s malegametes

possible outcomes in fertilization

P generation

1

2

3

4

5 F1 generation

Question Cross an F1 heterozygous yellow pea with a F1 Heterozygous yellow pea

Y y

Y

y

YY Yy

Yy yy

Genotypic ratio of offspring?

Phenotypic ratio of offspring?

YY

yy

Yy Yy

y y

Y Y

YY

yy

Yy Yy

YY Yy Yy yy

yellow green

threegenotypes

twophenotypes

Y Y

y y

Heterozygous

Homozygous

Applied Mathematical Principles

dominantallele

recessiveallele

maternal paternal maternal paternalmaternal paternal

homozygousdominant heterozygous homozygous

recessive

yellow seeds yellow seeds green seeds

Yy

YYYy Yy

yy

“pure” green

F1 generation

F2 generation

self-pollination

“pure” yellowmixed

YyYY

Yy

yy

YY yyYy

YY F3 generation

YYYY

YYYY

YYYy Yy

yy

yy

yyyyyy

Yy

YYYy

yy yy

Heterozygous or Homozygous?AA _____Ee ____Ii _____mm _____ In guinea pigs, the allele for short hair is

dominant.  What genotype would a heterozygous short haired guinea pig have?  _______

A heterozygous round seeded plant is crossed with a homozygous round seeded plant. (Round is dominant to wrinkled)

What percentage of the offspring will be homozygous dominant (RR)? 

A homozygous round seeded plant is crossed with a homozygous wrinkled seeded plant. What are the genotypes of the

parents?  What percentage of the offspring

will also be homozygous? 

Questions:

P generation

smoothyellow

wrinkled green

cross-pollinationx

F1 generation

100% smooth yellowself-fertilization

F2 generation

3159

1013

1083

321

smoothyellow

wrinkledyellow

smoothgreen

wrinkledgreen

: : :

Dihybrid Cross• 2 characters

F1 cross with F1

SY Sy sY sy

SY

Sy

sY

sy

SSYY SSYy SsYy SsYy

SSYy SSyy SsYy Ssyy

SsYY SsYy ssYY ssYy

SsYy Ssyy ssYy ssyy

Phenotypic ratio?

P generation

SSYY ssyy

SY sygametes gametes

F1 generation

100% SsYy

F2 generationPollen

EggSY Sy sY sy

SY

Sy

sY

sy

x

SS YY

SS Yy

Ss YY

Ss Yy

SS Yy Ss YY Ss Yy

SS yy Ss Yy Ss yy

Ss Yy ss YY ss Yy

Ss yy ss Yy ss yy

Who are the major players and what did they do?

DNA: what is it? What is it made from? Nucleotide bases: For DNA, for RNA?

What are they? How are they matched? DNA replication, transcription,

translation? What can vary in DNA? What is a Karotype? What are chromosomes? How many do

we have in our cells?

What are genes? Alleles? What is a genome? What are mitosis and meiosis? Which

cells undergo which process. What are the final results?

What are genotype, phenotype, homozygous, heterozygous, dominant, recessive? Example? Recognize?

What is the P and F1 generation?

What are the products of a monohybrid cross? A dihybrid cross? Ratios?

Punnett squares