GENETICS

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Unit 2: GENETICS QUIZ

The Nature of Heredity:

All organisms use cell division and cell reproduction to grow and reproduce

Multicellular organisms use cell division for growth/ repair, whereas unicellular organisms use it as a means of reproduction

Key feature: Passing of chromosomes from the parent cell to the daughter cells(NOTE: Chromosomes carry info. for traits, so traits are passed from parents to offspring - a process called heredity

Genetic Material:

Genetics: The scientific study of heredity and variation

Genetic MAterial: All material in an organism that stores genetic info.

NOTE: In a chromosome, genetic info is contained in a molecule of deoxyribonucleic acid (or DNA)

Instructions occur as distinct sequences of info. along a DNA molecule - Each of these sequences of genetic info is called a gene.

Genes carry info that helps to produce a particular trait of an organism

EACH gene occupies a specific location or locus on a chromosome

Chromosomes:

Found in the nucleus of all eukaryotic cells in most multicellular organisms

Chromosomes occur in sets;

Diploid cells have two sets of chromosomes

Haploid cells have half the normal number of chromosomes

NOTE: Both mitochondria and chloroplast contain small amounts of genetic material

Reproduction:

Asexual reproduction:

almost always involves cell division

cell division: two chromosomes of the parent cell are divided such that each of two daughter cells receives one copy of each chromosome

ADVANTAGES

parent organism does not have to seek out a mate

doesn't need to perform specialized mating behaviors

results in heredity that is direct and invariable.

Sexual Reproduction:

individuals are reproduced from the fusion of two cells

cells usually come from diff. parent cells

offspring obtain half genetic material from one parent and the other half from the other parent

results in genetically variable offspring and contain equal amounts of genetic info. from each parent.

DISADVANTAGES:

must have specialized organisms to produce sex cells

producing mating calls can attract mates AND prey

sex is biologically costly and possibly risky

offspring can inherit genetic info that can make them weak and UNABLE TO SURVIVE

DNA and The Code of Life:

Chromosomes are passed to offspring through Gametes

Genetic material is contained in the nucleus

The Chemical Composition of DNA:

DNA has main components:

Pentose sugar(cyclic, 5-carbon sugar)

prophase group with a negative charge

nitrogenous base

Together, all three are a nucleotide - repeating unit of DNA

Possible bases for the nucleotides of DNA - Adenine(A), guanine (G), thymine ( T), and cytosine(C)

Key relationships among the nitrogenous bases in DNA:

The Amount of Adenine is always equal to the amount of thymine

The amount of guanine is always equal to the amount of cytosine

The structure of the DNA molecule:

The molecular structure of DNA is a double helix

The model accounted for:

DNA is made o pentose sugar, a phosphate group, and one of four nitrogenous bases

The proportion of adenine and thymine is equal, and the proportion of guanine and cytosine is equal

DNA has the shape of a helix or corkscrew

DNA is made up of 2 strands of repeating NA nucleotides that run in opposite directions

The chemical backbone of a DNA strand is made up of alternating phosphate groups and pentose sugars

Attached to backbone - nitrogenous bases

The bases of one strand are paired with the bases of other strands - ie. thymine with adenine and cytosine with guanine

This is called complementary base pairing!!!

Sine bases = complementary, there is no need to know the nucleotide base sequence for both strands

QUESTION:

What is the complementary base strand for TTGACAGTAAAA?

= AACTGTCATTTT

Cloning and Reproduction:

In both plant and animal cell cytokinesis, separation occurs at the midpoint along the original spindle fibers

Cloning:

many organisms reproduce asexually by mitotic cell division

CLoning - the process of forming identical offspring from a single cell or tissue

Plant cloning - some plants have the ability to reproduce through their seeds

Animal cloning: ie/ dolly the sheep, obtained a body cell from the adult sheep he wished to clone and an unfertilized egg from a second sheep

Sexual Reproduction: adding variety

Sexual reproduction offers variety as the offspring inherit traits from 2 parents

2 processes:

The formation of haploid sex cells or gametes ( contain genetic info from parents)

the second process is fertilization - when 2 sex cells produce a zygote(first cell of the new individual)

Modes of sexual reproduction:

Most species have two types of sex cells

Animals: reproductive organs produce sex cells are the tests(which produce sperm cells) and the ovaries(produce egg cells)

Many species - distinct male and female individuals

They possess only one type of sex organ and have the ability to make 1 kind of sex cell

Other species = hermaphroditic -composed of individuals that take both male and female gametes

Meiosis:

2 stage cell division in which the resulting daughter cells have half the # of chromosomes as the parent cell

The process where haploid cells are formed

2 stages

Since gametes half only half chromosomes, they are haploid

In humans, the haploid number is 23 chromosomes, diploid is 46.

REsu;t of sexual reproduction is offspring receive genetic material from each parent in a form of haploid gametes, combined - 2 gametes produce a zygote that contains a complete set of chromosomes

Each of the 23 chromosomes you receive from your father is matched by 23 chromosomes from your mother

Paired chromosomes = homologous chromosomes

Similar in shape, size and carry genetic info for the same genes

Fertilization occurs when a haploid sperm cell (n = 23) unites with a haploid egg cells (n = 23) to form a diploid zygote cell(2n = 46)

Meiosis I:

DNA replication occurs

Beginning of prophase I, chromosomes start to shorten and thicken

Each chromosome is replicated during interphase and now consists of 2 sister chromatids joined at the centromere

Nuclear membrane dissolves, centrioles separate to opposite poles, spindle fibers for,

Chromosomes come together in homologous pairs

Each chromosome of pair is composed of a pair of sister chromatids

Structure = tetrad because each pair of chromosomes is composed of four chromatids

sister chromatids intertwine, mating homologous chromosomes, called synapsis

Prohphse continues, intertwined chromatids from different chromosomes break and reattach to each other

Exchanges sections in a process called crossing over - results in recombination of genetic info. between nonsister chromatids

During metaphase I:

tetrads migrate toward the center of the cell and align centromeres across the middle of the cell

anaphase I:

homologous chromosomes head to opposite poles of the cell

reduction division occurs

Once chromosomes from each pair will be found in the daughter cell

*Each chromosome in new cell consists of sister chromatids

Telophase I:

membrane begins forming around chromosomes at each end of cell divides

each daughter nucleus receives only one member of each original chromosome pair

Cells are now haploid

meiosis II:

Begins immediately after telophase I and the first cell division

Haploid daughter cells - contain 1 set of chromosomes(chromosomes with 2 chromates)

Due to crossing over, sister chromatids are not identical

No duplication of DNA between mI and mII

Prophase II:

beginning of cell division

Nuclear membrane dissolves and spindle fibers form

Metaphase II:

arrangement of chromosomes (each with 2 chromatids) across the center of the cell

Anaphase II:

sister chromatids separate and move to opposite poles of the cell

nuclear membrane beings to form around chromatids (now chromosomes)

Telophase II:

The second nuclear division is completed and the second division of cytoplasm follows

4 daughter haploid cells have been produced

Random assortment of Homologous chromosomes:

In meiosis I. homologous chromosomes pair up during prophase I and metaphase I

Separated during anaphase I

Each daughter cell now = haploid(receiving one chromosome from each pair)

The daughter can recive another chromosome of each homologous pair

RANDOM ASSORTMENT

# of possible combinations of chromosomes depends on the # of chromosome pairs

Diploid organism - # of pairs/combinations = 2^n

In humans - 2^23 - over 8 million possible combinations

Gametogenesis:

formation of sex cells - gametogenesis

Production of sperm cells - spermatogenesis

Production of egg cells - oogenesis

In oogenesis, the cytoplasm of the female gametes do not divide equally during each cell division of meiosis

one daughter cells receive most of the cytoplasm

Other cells die and the final product of oogenesis is a single egg cell

In spermatogenesis, the cytoplasm divides equally during each cell division, resulting in the formation of four equal sized sperm cells

Males produce many sex cells compared to females

Karyotypes:

a picture of chromosomes that have been arranged according to #, size, and shape

Sex chromosomes and sex determination:

Sex chromosomes consist of matching homologous chromosomes in female and a partially matching pair in males

Males - one chromosome is much smaller than the other

Females - larger 2 chromosomes is a homolog to the sex chromosomes in a female

Parts of Z and Y chromosomes contain matching regions that let them undergo synapsis and behave as a homologous pair during meiosis

Auotsomes = non sex chromsomes

Pattern = XX - Female, XY - Male

Individuals inherit an X chromosome from father and X from mother are Female,

Individuals who Received a Y from father and X from mother are Male

Abnormal Meiosis or Fertilization:

During meiosis, entire chromosomes can be lost or gained from cells

Result of nondisjunction - occurs when homologous chromosomes fail to separate during meiosis

Result: One of the daughter cells will have an extra chromosome, whereas the other one will have a missing one

Cells with extras chromosomes or are missing one cannot function normally

In humans, nondisjunction results in gametes with 24 or 22 chromosomes

If a gamete with 24 chromosomes joins with a normal gamete(23 chr.) from opposite sex, resulting zygote will have 47 chromosomes instead of 46

Zygote has; 22 pairs of chromosomes and 3 copies of one chromosome, referred to as trisomy

If a gamete with 22 chromosomes jins with a normal gamete, the resulting zygote will have 45 chromosomes

It will be missing one of its homologous chromosomes for the remaining pair, known as monosomy.

nondisjunction Disorders:

Down syndrome - a chromosomal abnormality in which there is an extra chromosomes number 21 ( trisomy 21)

There is extra genetic info and unpaired chromosomes in every cell

Cytoplasmic Inheritance:

DNA can be found in the mitochondria and chloroplasts

Origin of cytoplasmic DNA:

Chloroplasts and mitochondria originated as a prokaryotic organism

Mitochondria and chloroplasts are able to reproduce independently with the cytoplasm, thereby producing copies of their DNA

Asexual reproduction and cytoplasmic inheritance:

As the parent cell divides, each daughter cell obtains approximately equal numbers of cytoplasmic material

Most male gametes are small and contain little cytoplasm unlike females

During fertilization, male gametes do not usually contribute organelles to new zygote

Zygote inherits cytoplasmic DNA from the female gamete

MATERNAL INHERITANCE

mitochondria in an individual are always genetic clones of the mitochondria from the mother

Parental inheritance - inheritance if cytoplasmic DNA from only the male gamete

Sometimes both female and male gametes contribute

Cytoplasmic inheritance and genetic variations:

Mitochondria in daughter cells are not really genetically identical

Chloroplast can be separated at random during cell division making it possible for each daughter cell to receive a different mix of chloroplasts

In humans, a number of rare genetic disorders are attributed to mitochondrial DAN. Since the genes in mitochondria often influence cellular respiration these disorders are associated with energy metabolism.

POWERPOINTS:

Introduction to Genetics and Mitosis:

Terminology:

Genetics: Science of genes, heredity, and variation of inherited characteristics

Chromosomes: Found within cells - made up of many molecules of DNA

DNA: A molecule that carries genetic information

Gene: A portion or subunit of DNA that codes for a particular trait/characteristic

Locus(pl. LOCI): Where a particular gene is located on a chromosome

Sexual vs Asexual Reproduction:

Asexual: w individual produced by a single parent through cell division

Genetically identical offspring

No need to mate

Sexual = Individuals produced through the fusion of sex cells

Genetic variability - Adaptability?

costly

Principles of cell Division:

A single cell makes two ells by an equal split of nuclear contents in a process called mitosis

Cytokinesis refers to the equal split of cytoplasm and the organelles within it

The parent cell is the cell that divides

Daughter or sister cells - the 2 cells that result from the division, they are genderless!

The cell cycle:

Interphase(the period between cell divisions)

growth, duplication of genetics info, preparation for mitosis

Cloning

Forming identical offspring from a single cell or tissue

Structure of DNA and Mutations:

Chemical composition of DNA:

3 main components:

pentose sugar(5 carbon ring)

phosphate group with a negative charge

Nitrogenous Base

*3 components together = nucleotide

Thymine and Cytosine = single ringed - Pyrimidines

Guanine and adenine = double-ringed - Purines

DNA has a phosphate sugar backbone and bases pair up in the middle of the molecule - a with t and g with c

Point Mutations:

Replicating cells do not copy genetic info in DNA accurately;

Base pair substitutions - One nitrogen base is accidentally replaced with another base

Insertions - One or more nitrogenous bases are inserted during the copying process

Deletions - One or more nitrogenous bases are deleted during the copying process

Meiosis:

Meiosis vs Mitosis:

e goal of mitosis is to create 2 genetically identical diploid daughter cells from one parent cell

The goal of meiosis is to create 4 gametes(haploid sex cells(ie sperm, egg) from one parent cell

Homologous chromosomes:

Pair of chromosomes containing the same gene sequences (each derived from one parent)

the same genes found on homologous chromosomes BUT NOT necessarily the same alleles

Allele: Different version of the same gene

ie/ curly hair vs straight hair allele

Meiosis:

Sexual reproduction

occurs in germ cells

one parent cell produces 4 gametes

eachgamete cells contain different genetic inforamtin

2 divisions(starts with 46 double-stranded chromosomes):

after 1st division - 23 double-stranded chromosomes

after 2nd division - 23 single-stranded chromosomes

Meiosis I:

DNA Replications

Two identical copies of each chromatid(sister chromatids) are attached at the centromere to form a double-stranded chromosome

Early Prohphas I:

nuclear envelope dissolves

Asters form

Centrioles move towards the poles of the cell

Metaphase I:

Homologous pairs align along the equator of the cell

Spindle fibers attach to the pair of sister chromatids

Anaphase I:

Homologs separate and move to opposite poles

Sister chromatids remain attached at their centromeres

Telophase I:

Nuclear envelope resembles

Pairs of sister chromatids are found in each haploid daughter cell

Cytokinesis

Meiosis II:

Prophase II:

Nuclear envelope dissolves

Spindle fibers form

Centrioles move towards poles

*NOTES: Don't need interphase as you don't need to duplicate DNA

Metaphase II:

Chromosomes align along the equator of the cell

Spindle fibers attach to centromeres of sister chromatids

Anaphase II:

Spindle fibers contract and pull sister chromatids apart

Telophase II:

Nuclear envelope reassembles

Chromosomes uncoil becoming chromatin

Spindle fibers disappear

Cytokinesis divides each cell into 2 nonidentical haploid cells

RESULT:

23 single chromosomes

Gamete Production:

Spermatogenesis: Sperm production

Diploid spermatogonia - primary spermatocytes - 4 spermatids

Oogensis: Egg production

Oogonia - primary

oocytes - 1 egg +polar bodies

Polar bodies - Nonfunctioning reproductive cell; a by-product of meiosis, dies overtime

How does meiosis produce variations?

Crossing over - exchange of genetic info. between homologous chromosomes

Occurs in prophase in meiosis I generates diversity

Independent assortment:

The homolog of one chromosome can be inherited with either homolog of a second chromosomes

Lining up

Mistakes In meiosis:

Karyotyping:

To study human chromosomes

A karyotype is a photographic inventory of individual chromosomes

A karyotype usually shows 22 pairs of autosomes and one pair of sex chromosomes

Alteration of chromosomes number:

Non-disjunction: Results in abnormal chromosomes numbers

Failure in chromosomes separation

homologous chromosomes fail to move apart properly during meiosis I

Sister chromatids separate during meiosis II

Monosomy - Fertilized egg cell is missing a chromosome - 45 chromosomes

Trisomy - Fertizlied cell has an extra chromosome - 47 chromosomes

An abnormal number of sex chromosomes:

Non-disjunction can also produce gametes with extra or missing sex chromosomes

Unusual numbers of sex chromosomes do not upset the genetic balance as much as the unusual number of autosomes

Usually offspring are viable

Sexual Reproduction:

Male and female gametes do not contribute equal amounts of cytoplasm

Male gametes have much less cytoplasm than female eggs

Sperm do not contribute mitochondria - or chloroplasts to the zygote

The zygote will have the same mitochondrial DNA as a mother - maternal inhertiance

Mitochondria / chloroplasts often do not separate evenly during cell division - genetic variation in an organism

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