heredity

Mendel’s Law of Segregation (Segregate means “to separate”)

A. This states that alleles on homologous chromosomes move independently of one another. They separate

to opposite poles of the germ cell during Anaphase I.

B. This occurs at Anaphase I and II in Meiosis.

XI. Mendel’s Law of Independent Assortment . This law describes the behavior of pairs of homologous

chromosomes during Metaphase I.

A. Each pair of homologous chromosomes moves to the metaphase plate during Metaphase I

independently of any other chromosome pair. The random placement of the homologous maternal and

paternal chromosome pairs along the Metaphase plate illustrates independent assortment.

XII. Probability “Chance”

A. This refers to the likelihood of a certain outcome actually happening. (What are the chances

of…occurring?)

B. C. D. Probability ranges on a scale between 0 and 1.00. (From 0% to 100% essentially.) 0.5 is 50% and so on.

On a monohybrid Punnett square, each square represents a 25% chance of outcome.

Add all boxes that have the same genotypes together to get the total probability.

XIII.Complete Dominance

A. The dominant allele has information and it is expressed, even if there is only one copy. Geneticists call

this “100% penetrance”.

XIV.Incomplete Dominance

A. Information from both alleles is expressed in the cell. Neither phenotype is completely penetrant,

therefore the heterozygous phenotype appears “blended”. (Red + White = Pink)

XV. Codominance

A. Both alleles are expressed in the cell. They are both equally present in terms of phenotype, i.e. black and

white coats in animals, AB blood type in humans expresses both A AND B cell markers.

XVI. A. B. C. D. Multiple Alleles-Many human genes are complex with multiple alleles.

There are multiple (more than 2) versions of the same basic allele

The extracellular glycoproteins of red blood cells are a classic example. These antigens(glycoproteins)

identify the blood types

1. One dominant allele results in the presence of A antigens on the surface of red blood cells

2. Another dominant allele results in the presence of B antigens on the surface of red blood cells.

3. A third allele results in no antigen and is a recessive allele. This condition is referred to as Type

O. Since it is recessive, the gene or stretch of DNA that codes for these proteins has no code for

A or B antigens, so neither is made.

Universal Donor – Type O can give blood to anyone. Since the O type blood has neither A nor B

antigens, it is not recognized at all and does not cause a reaction in the bodies of people who have A, B,

AB or O blood types.

Universal Recipient – Type AB can receive blood from anyone. Since the AB blood cells have both A and

B antigens, there is no reaction if those cells are mixed with A, B, AB, or O blood types.

XVII. Pedigree

A. This is a family history of trait occurrence in chart form.

B. A pedigree indicates the past occurrences of traits and can be useful in predicting the future occurrence

of traits.

C. The power of pedigrees is their ability to predict possible genotypes and thus phenotypes of future

generations.

XVIII. Recessive Disorders

A. B. Only occur in the homozygous recessive genotypes.

Carriers – These are organisms that are heterozygous in genotype and therefore have a 50% chance of

passing on a recessive allele. Carriers usually appear normal for the trait as they possess one dominant

allele.

C. Human recessive disorders:

1. Cystic Fibrosis (Also referred to as “CF’.)

a) This is the most common lethal genetic disease among people of European descent.

b) This disorder affects 1 in 2,500 births.

c) In Caucasians, 1 in 25 people is a carrier for the disorder.

d) The disorder creates a faulty Chloride ion (Cl-) protein carrier on cell membranes in the

lungs. This causes fluid (water) to build up in the lung tissues.

(1) People drown in their own fluid.

(2) They are also prone to get multiple infections in the lungs

e) Treatment? Since it is genetic there is no cure. Patients have to get the fluid drained

from the lungs periodically for their entire life. There are medicines to help reduce the

number of times this has to occur.

2. Sickle-cell Disease

a) This disorder is the most common genetic disorder among people of African

descent.

b) c) It affects 1 in 400 births.

The 6th Amino Acid in the hemoglobin molecule is changed (Glutamine -> Valine) in the

primary sequence needed to make red blood cells

d) Carriers express a mild form of Sickle- cell anemia

(1) These individuals have resistance to Malaria because of the one recessive allele

they possess prevents infection by the Malaria parasite but carriers mainly

have normal red blood cells for carrying oxygen.

(2) This is referred to as the Heterozygote Advantage. They have an advantage

over individuals that are homozygous dominant or homozygous recessive.

Homozygous dominant are not resistant to Malaria. Homozygous recessive are

also resistant to Malaria; BUT they have the sickle cell condition to contend

with.

e) These sickle shaped cells have reduced oxygen carrying ability. They also are painful

when the points of the cell jab into the walls of the blood vessels.

f) Treatment? There is no cure as it is genetic. Some medicines help with the pain or low

oxygen levels.

XIX.Dominant Disorders

A. Only need one allele for these disorders to be present or “expressed”.

B. If an individual is homozygous dominant, usually the disease is much worse and often fatal.

C. Human Dominant Disorders:

1. Achondroplasia (This is referred to as Genetic Dwarfism.)

a) This disorder affects 1 in 10,000 births.

b) Most people are homozygous recessive and therefore much taller than these individuals.

2. Huntington’s Disease

a) This disorder affects 1 in 10,000 births.

b) It has a late life onset – usually in the 40-50 age range. (Usually after children are born.)

c) The dominant gene has a locus on the tip of Autosome 4.

d) Family history is important in diagnosis of this disorder. (Pedigree can help.)

e) It is a slow degenerative disorder affecting the brain that is almost always fatal

XX. Genetic Counseling and Counselors

A. These are individuals who run pedigrees, using family history data, to look at potential outcomes or

carrier recognition and give advice on whether or not to pursue trying to have children based on the

“probability” of a genetic disorder occurring within the offspring.

B. C. Remember, chance has no memory. Each mating can potentially have a different outcome.

Need to perform karyotypes to help confirm diagnosis sometimes.

Unit 9 Genetics

NonMendelian Genetics

I. Linked Genes

A. This term is usually to describe genes found on the Autosomes (1 – 22). These are usually inherited as a

linked unit because they are found on the same chromosome. These genes are not independently

assorted but rather they are inherited as a package.

B. Genetic Recombination occurs during crossing over in Prophase I when chromosome segments are

exchanged between homologous paired chromosomes.

1. Parental types – These offspring organisms look like their parents.

2. Recombinant types – These offspring organisms look like a combination of both parents because

of crossing over creating a mixture of the genes.

II. Sex-Linked Genes

A. This term refers to genes found on the sex chromosomes; 95% of the time it refers to the X

chromosome. (Think X when it is seX linked.)

1. This is because both sexes have at least one X chromosome in their genome.

2. XX (Female and homologous); XY (Male and heterologous)

B. C. Sex chromosomes undergo very little crossover during Prophase I of Meiosis.

Sex of the organism will be determined at conception when the egg is fertilized by the sperm. You will

either get a sperm containing an X chromosome or a sperm containing a Y chromosome.

D. Everyone starts out female.

1. At about two months of age in the womb, the Y chromosomes’ SRY (sex determining region of Y)

gene becomes active to convert estrogen to testosterone to finish development of the male.

2. After development is complete, testosterone production is turned off until puberty. At puberty

it is turned back on so as to make the secondary sexual characteristics, such as facial hair.

E. Patterns of Inheritance and some Human Sex-Linked Genetic Disorders: (No cure exists, because the

problem is in the DNA.)

1. Color Blindness

a) This is the result of a faulty gene (recessive) on the X chromosome for making a

particular type of color absorbing protein in cones of the retina of the eye.

b) The most common type is Red/Green Colorblindness. (Red and Green appear gray.)

2. Hemophilia (Means “love of bleeding”)

a) These individuals cannot make Anti-Hemolytic Factor. (AHF for short.)

b) They experience problems with bleeding to death.

c) This was a disorder associated with the “Royal Blue-Bloods of Europe” – They were

inbreeding to keep the crown “In the Family”. The “carrier” is traced to Queen Victoria.

Also a trait found in the royal Russian Romanov family.

d) Treatment? These individuals have to keep AHF with them at all times in case they get

hurt. If they do get hurt and start to bleed they will require a shot of AHF to stop the

bleeding. Even a bruise (bleeding under the skin) can possibly lead to death.

3. THE PATTERN ON A PEDIGREE: It will appear to mainly affect males (as they only have one X

chromosome). This is because if the inherited X chromosome has a recessive gene on it; it will

not be covered up by a dominant one on another X chromosome (as is the case in most

females). Females can still get these disorders, but they must inherit two recessive X

chromosomes. The females tend to be carriers, so they appear unaffected and tend to

pass the recessive X on to their sons. The son will be a sufferer, IF he gets the recessive X, of the

disorder. It appears to “skip” a generation, because the mother is a carrier and the sons are

showing the disorder

Unit 9 Genetics

Meiosis

I. Heredity

A. This refers to the transmission of traits from one generation to the next by inheriting DNA from the

parent (for asexual reproduction) or parents (for sexual reproduction).

II. Genetics

A. B. This is the science that deals with the transmission of information in the form of DNA. It can range from

studying how traits are passed from one generation to the next using Punnett squares or identifying

DNA segments (what we call genes) and the proteins or enzymes that they make. It is a huge field of

science.

This field has had a tremendous impact on society as a whole. Such things as cloning and new medicines,

using bacteria and yeast to make human hormones, or even making biological weapons such as Super

Anthrax.

III. Gene

A. A basic physical and functional unit of hereditary that can vary from a hundred DNA bases to more than

2 million bases.

1. Most genes code for some type of protein or enzyme. The DNA is first transcribed into RNA

which can be directly functional, or then further translated into a protein

2. Genes may acquire mutations which can be either harmful or lead to adaptations within a

population.

3. Genes can contain exons, regions of DNA that directly code for RNA or proteins, and introns, or

non-coding regions of DNA which may be regulatory in nature

IV. Genome

A. B. This refers to an organism’s entire genetic make-up. All the DNA within a cell. It would be like the

“blueprint” for making the whole functioning car.

Half of the DNA comes from the mother (“half” is represented by “n”); The other half of the DNA comes

from the father ( n ). Therefore, a half plus a half equals 2 halves which is equal to 1 organism. ( n + n )

= 2n. (“half” is also called haploid/monoploid and “two halves” is called diploid). Of each homologous

pair present in the genome, one chromosome is maternal and the other is paternal.

V. Locus

A. The location of a gene on a chromosome. Important when you are talking about autosomes vs. sex

chromosomes.

VI. The two types of reproduction that can occur by living organisms:

A. Asexual Reproduction

1. This involves only one parent. The parent is producing genetic clones of itself. The parent and

offspring are 100% identical in terms of DNA content and DNA nucleotide sequence.

2. Benefits – Reproduction can occur very quickly (Good for taking over a new area). It is a simple

process. You only need one parent.

3. Risks – Every organism is the same. So if a disease affects one; it will affect all. (There is no

variation!)

a) This caused the Irish Potato Famine. Potatoes are originally from South America. One

species of potato plant was taken to Ireland. This became the only species that the

farmers could plant, as no new species were brought over afterwards. A pathogenic

fungus, called Potato Blight, began attacking the plants. Since they were all alike in

terms of DNA because they were clones, the fungus wiped them out quickly causing the

famine to occur.

B. Sexual Reproduction

1. This requires two parents to contribute DNA. This process “creates” variation, which is

important in terms of survival in the environment. The offspring does not EXACTLY resemble

either parent.

2. Benefits – It produces variation. This is why some organisms have advantages over others within

the same species in terms of survival and the ability to reproduce. Variety means there exists

the possibility to evolve over time while living in an ever changing environment

3. For example, Wooly Mammoth. Those with less hair survived and passed on those genes for less

hair to their offspring as the environment became warmer over time. This lead to the evolution

of our modern elephant, which has very little hair. The mammoths with more hair died before

they could reproduce; thereby “wiping” out those genes and eventually causing the extinction

of the old species.

4. Risks – It takes two to be able to reproduce and they must be of the opposite sex for the

Physical Reproduction to occur. This is not good for an endangered species. It also takes more

time. It also involves the more complicated process or meiosis to create the gametes that have

half the DNA content.

VII. Human Life Cycle is Diploid Majority

A. Somatic (“soma” means “body”) cells make up most of our body-body cells.

1. These cells contain 46 chromosomes inside them. They are 2n – diploid. 2n=46)

2. Karyotypes will display all 46. (A karyotype is basically pictures of the chromosomes.) (“kary”

refers to “nucleus”)

3. Homologous “same” Chromosomes can be seen. (These are called Autosomes) 44 = 22 pairs

exist in all human cells. If female, the two sex chromsomes are the same too… two X

chromosomes.

4. Heterologous “different” Chromosomes may be seen in males. These may be the 2 sex

chromosomes. In males, there is one X and one Y chromosome.

5. Female (XX); Male (XY)

B. Germ (“germ” means “beginning”) cells. Also known as gametes and sex cells)

1. These cells contain 23 chromosomes. They are n – haploid. n=23

2. Fertilization, which is the fusion of egg (from the female) and sperm (from the male) together,

must occur to be able to reproduce.

3. This fusion between egg and sperm produces a single diploid cell called a zygote.

a) Haploid + Haploid = Diploid; n + n = 2n; 23+ 23=46

4. The zygote goes on, through repeated mitosis, to produce the new multicellular organism.

VIII.Meiosis - means “The process of Gamete Formation”

A. B. This process occurs in the sex organs of the organism. These organs are called Gonads

This process has 1 DNA replication followed by 2 cell DIVISIONS therefore the result is 4 haploid cells.

1. Remember that the S phase doubles the amount of DNA. In humans, when all 46 chromosomes

are replicated, therefore the parent cell has 2x (96 chromosomes) the DNA of a non-dividing cell.

2. Meiosis I (This division is the separation of chromosome pairs.) This takes the cell back to

diploid (a full set of chromosomes (e.g. 46 in humans).

3. Meiosis II (This division is the separation of sister chromatids.) In humans, 46 -> 23

chromosomes.

C. D. In this process, Males produce 4 haploid sperm; each having 23 chromosomes.

In this process, Females produce 1 haploid egg with 23 chromosomes due to the need for additional

cytoplasm and cell membrane. The other three cells (polar bodies) degrade.

E. Stages to the process of Meiosis

1. These stages are very similar to the stages of Mitosis

2. Three major differences from Mitosis are present to increase variation. (Remember, Mitosis is

normal cell division. It basically makes clones of the adult. No variation exists.)

IX. X. 3. Crossover “genetic swapping” between homologous pairs occurs in Prophase I. (Creates

4. 5. variation.)

Chromosome pairs independently assort as they line up in Metaphase I (Creates variation.)

Sister Chromatids separate in Anaphase II. (Creates Variation.)

Crossover “genetic swapping” between homologous chromosomes.

A. This occurs to create variation from the parent’s genome. (They are then called Recombinant

Chromosomes.)

B. Synapsis – Chromosomes are in a state of being intertwined together during metaphase I. (“syn” means

“together”; “sis” means “process of”)

C. Tetrad - Four chromosomes twisted together (“tetra” means “four”… Like the game Tetris has four

different shapes.)

D. Chiasmata – Where the chromosomes physically overlap making an “x”. (“Chi” is the Greek letter for

“X”.)

Major differences between Mitosis and Meiosis

A. B. The number of divisions (Mitosis has 1; Meiosis has 2)

The final products of each process. Mitosis – “cloned” or identical daughter cells; Meiosis – variable

haploid gametes

C. D. Crossover, in Prophase I, creates variation--No crossover in Mitosis.

Chromosome pairs vs. sister chromatids separating in the second division to REDUCE chromosome

number to haploid.

XI. Evolution Implications

A. The genetic variation within individuals, produced during meiosis (both prophase – crossing over, and

metaphase – segregation and independent assortment), along with random fertilization (the

recombination of two haploid genomes) between individuals emerges as genotypic and phenotypic

variety within a population. Natural selections occur as a result of this variety and drives the adaptation

of a population over time

XII. Chromosomal Errors than can occur:

A. These could occur during Mitosis or Meiosis

1. They could occur during the Anaphase Stages where chromosomes are moving

2. They could also occur during Crossover where gene DNA segments are moving

B. Two types of errors can occur:

1. Chromosomal Number-Aneuploidy means “Abnormal number of chromosomes”

a) This is the result of nondisjunction. (Failure to separate during Anaphase.) Can you

“see” a possible definition in the term? 3 possible results

(1) Trisomic -Three of 1 kind of chromosome

(2) Monosomic- Missing one, the other half of the pair. The Trisomic gamete

contains the extra chromosome.

(3) Polyploidy (Many extra sets of chromosomes.)

(a) 3n (triploid) Three “halves” are

in this cell.

(b) 4n (tetraploid) Four “halves” are in this

cell.

considered larger and better tasting due to the extra chromosomes.

Ex. Strawberries are octoploid.

2. Individual Chromosome Structure

XIII.Syndrome

A. B. C. a) b) c) d) e) These occur because of faulty crossover and affect sections of a chromosome generally

larger than an individual gene.

Deletion – Chromosome segment is “missing”. It got stuck on the other homologous

chromosome during crossover.

Duplication – A chromosome segment was “copied” twice. (Two genes on one

chromosome. It is “missing” from the other homologous chromosome.)

Inversion – A chromosomal segment is “backwards”. It was inverted backwards during

crossover.

Translocation – A chromosomal segment is attached to a different autosome. It

accidentally broke loose and ended up on another chromosome.

This term refers to an organism “possessing” the identifying traits of a particular genetic disorder.

Human Genetic Disorders due to two abnormal chromosomal number (#) or structure:

1. Down’s Syndrome

a) This affects about 1 in 700 births.

b) These individuals possess an Extra 21 Autosome (A.K.A. Trisomy 21)

c) General syndrome features

d) Mainly the result of women of advanced age having babies.

2. Turners Syndrome (XO)

a) General characteristics: These individuals appear fairly normal. They just are lacking the

“sexual” characteristics we normally see in individuals. The “sexual” traits are missing

because there is no second sex chromosome to help create those traits. These

individuals are usually raised as females

Remember, there are no cures for all of these disorders; only treatments because the problem is Genetic

Flashcards are learning tools that use a simple question-and-answer format to reinforce memory and understanding of concepts. Typically, a flashcard has a term or question on one side and the definition or answer on the reverse. Flashcards are useful for self-testing, active recall, and spaced repetition, which enhances long-term retention of information. They can be created for various subjects and tailored to an individual’s learning goals.