Genetics NotesObjective: We will learn about Mendel, traits, probabilities and Punnett Squares.

Vocabulary:

Gregor Mendel

Trait

Allele

Dominant

Recessive

Self-pollination

Cross-pollination

Offspring

Homozygous

Heterozygous

True Breeding

Hybrid

Genotype

Phenotype

Probability

Punnett square

Monohybrid

Dihybrid

Independent Assortment

Incomplete Dominance

CoDominance

Segregate

Multiple Alleles

Polygenic Traits

Gamete

Chromosomes

Meiosis I and II

Haploid

Diploid

Cross-over

Polar Bodies

Gene Linkage

Gene Map

Karyotype

Autosomes

Sex Chromosomes

Pedigree

ABO Blood Groups

Genetic Disorders

Sex-linked Traits

Gregor Mendel

Gregor Mendel was a ________________ born in 1822. He became a Priest and spent years studying science and math. He also worked in a monastery and taught high school. Besides his teaching duties, Mendel was in charge of taking care of the monastery garden. Mendel worked with _________ plants for 14 years! He is the founder of genetics and heredity research!

He found that pea flowers contained both male and female parts. The male parts produced ____________________ (male sex cells) and the female parts produced ________ (female sex cells). When pollen and egg combine, a seed is formed.

When this occurs in a single flower, it is called self-pollination. Seeds produced this way only contain genes from the single plant that produced them (like a __________________).

o True-Breeding is the term for plants that self-pollinate on their own in nature, and produce offspring that look identical to the single parent plant.

Pea Plants can also cross-pollinate, meaning the male sex cells in the pollen of one flower will _______________________ the egg cells of another flower. The seeds produced will contain genes from two different parents.

To perform cross-pollination, Mendel had to select which plants he wanted to cross (breed together). To do this, he had to _____________________________ them from self-pollinating. So, he cut the male part off, and dusted the flower with pollen from another flower.

Genetics Intro

A trait is a specific characteristic, such as seed color or plant height, that ____________ from one individual to another.

The traits Mendel studied had ____________________________ (opposite) characteristics, for example the trait for seed color could be yellow or green. And the trait for height could be tall or short.

When Mendel crossed plants with contrasting characteristics he watched to see which traits were ___________________ from the parents. He called the parents the "P" generation, and the plants they produced from their seeds (offspring) the "F1" generation.

F is for the latin word filia meaning son. The offspring produced by crossing two _________________________ parents are called hybrids.

After cross breeding two opposite plants, Mendel noticed that the F1 generation looked like only _________ parent. Why did the traits of the second parent disappear? To find out, Mendel let the F1 generation self-pollinate to produce the F2 generation. The offspring now had traits from both the original P generation plants! Mendel concluded there had to be a _______________ factor that passes traits from one generation to the next; we call it genes.

Principle of Dominance

There are 2 possible forms of each gene, these forms are called Alleles. When one allele ___________________ over another, it is due to the Principle of Dominance: some alleles are "dominant" (capital letter) and some are "recessive" (lower case letter).

We only see recessive alleles if there is _____ dominant allele present.

The Principle of Dominance explains why some genes show over others, but it doesn't explain why the F1 generation only looks like 1 parent and the F2 generation looked like both P generation parents.

Mendel found the _____________ for the alleles of traits are __________________________ during gamete (sex cell) formation. Pollen and eggs (sex cells = gametes) contain only 1 allele (letter) for each trait.

When they combine and make a seed, each seed contains 2 copies of the gene (2 letters).

Think-Pair-Share!

Which type of pollination will produce a clone of a flower? Self-pollination or Cross-pollination?

What is a gamete? Give an example

Explain the difference between Dominant and Recessive. Give an example

Parents are the ____ generation, and offspring are the ____ generation.

Warm-up Questions:

What plant did Mendel work with?

What is the chemical factor that passes traits on in families?

Plants with different traits from both parents are known as ______.

Genes & Probability

Whenever Mendel performed a cross with pea plants, he carefully categorized and counted all of the offspring. Every time Mendel repeated a particular cross, he noticed that he obtained __________________________ results.

For example, whenever Mendel crossed two plants that were _________________ for height (Tt): the resulting offspring were ¾ tall and ¼ short every time! Mendel realized the Principal of Probability could be used to explain the results of genetic crosses.

Probability is the likelihood a particular event will occur.

Punnett Squares

Punnett Squares are used to ________________ the possible gene combination that might result from a particular cross. The parent’s genes are segregated and written on the outside left and top of the square, then combined on the inside to show the _______________________ combinations in the offspring.

When working with only one gene/trait, the Punnett square is referred to as Monohybrid.

The two genes for each allele of a traits are represented with capital (dominant) and/or lower case (recessive) letters. There are 3 different arrangements for alleles: TT or Tt or tt, depending on how the gamete genes combined during fertilization.

Homozygous: Refers to 2 ______________________________ alleles (letters). Can be dominant or recessive. o Homozygous Dominant = TT (both capital), and Homozygous Recessive = tt (both lower case)o These organisms are True-breeding, meaning if identical parents are crosses, all offspring will also

be identical. Heterozygous: Refers to 2 ____________________________ alleles, Tt, having one capital and one lower case letter.

In this case, only the dominant trait will show. Another word for heterozygous is _____________________.

When talking about the parents and offspring, we use different words to describe their DNA genetics and the way they look on the outside with our eyes.

Genotype: The type of genes an organism has, the way genes are written out with _______________________. This is where we use the terms dominant, recessive, homozygous, and heterozygous.

Phenotype: A physical _____________________________ of what the organisms looks like on the outside, as if looking at a photograph.

Probability & Punnett Squares

Probabilities _____________________ the average outcome of a large number of events, however, it cannot predict the exact outcome of an individual event.

Ex. If you flip a coin twice, you may get 1H and 1T… or 2H… or 2T. But, if you keep flipping that coin 100x, you will get a 50/50 ratio of heads and tails.

The same is true for genetics, if there are very few offspring, it can be difficult to see the expected ___________________. However, this is easier to see when there are many offspring.

Parents Genotypes: ______________________________________

Parents Phenotypes: _____________________________________

Offspring Genotypes: _____________________________________

Genotype Ratio: __________________________________________

Offspring Phenotypes: ___________________________________

Phenotype Ratio: _________________________________________

Parents Genotypes: _____________________________________

Parents Phenotypes: ____________________________________

Offspring Genotypes: ___________________________________

Genotype Ratio: _________________________________________

Offspring Phenotypes: __________________________________

Phenotype Ratio: ________________________________________

Think-Pair-Share!

What does the Principle of Probability tell us about genetics?

What are Punnett Squares used for?

What type of Punnett Square analyzes only one trait?

Independent Assortment

Mendel knew that alleles (traits represented by letters) segregated apart when using a Punnett square, and combined back together in different combinations in offspring. He wondered if genes segregated independently, or if some genes were __________________________/stuck together during the segregation process.

For example, does the gene that determines whether a seed is round (R) or wrinkled (r) have anything to do with what color the seed is? Yellow (Y) or green (y)

To answer this question, Mendel performed an experiment that followed these two different genes as they passed from one generation to the next, this is known as a Two-Factor Cross.

Each F1 plant was formed by fusion of a gamete carrying the dominant RY alleles, with a gamete carrying the recessive ry alleles. Did this mean that the two dominant alleles would always stay together? Or would they ______________________________ independently? To find out, Mendel let the F1 hybrids self-pollinate.

In Mendel's experiment, the F2 plants produced 556 total seeds. Mendel compared the _________________________ in the seeds. He observed that 315 seeds were round and yellow, another 32 were wrinkled and green (the two parent phenotypes). However, 209 of the seeds had combinations of phenotypes- and therefore a new combinations of alleles- not found in either parent. This clearly meant that the alleles for seed shape segregated independently of those for seed color- a principle known as independent assortment.

Genes that segregate independently, such as the genes for seed shape and seed color in pea plants, do ______ influence each other's inheritance. Mendel's experimental results showed a 9:3:3:1 ratio when he made a dihybrid Punnett square that compared the inheritance 2 traits at once.

Summary of Mendel’s Principles

Mendel's principles form the basis of the modern science of genetics.

The inheritance of biological characteristics is determined by chemicals known as genes. Genes are passed from parents to their offspring.

In cases where two or more forms (alleles) of the gene for a single trait exist, some forms of the gene may be dominant and others may be recessive.

In most sexually reproducing organisms, each adult has two copies of each gene- one from each parent. These genes are segregated from each other when gametes are formed.

The alleles for different genes usually segregate independently of one another.

How to set up a dihybrid Punnett Square:

_______________________ x ________________________

Rouge Alleles

Not all of Mendel's work can be considered "law". Genetics can be more complex than just simple dominant or recessive. Some traits are not dominant or recessive, and some traits have more than two alleles possible.

Incomplete Dominance occurs when neither allele of a gene is dominant. For example, when two homozygous plants for contrasting colors are crossed, the offspring are all heterozygous and show a _______________/mix of both parent phenotypes. A red flower RR and white flower WW will produce pink RW flowers.

Codominance occurs when the expression of the genes are both _____________________ shown. For example a red cow crossed with a white cow will produce a roan (speckled) cow. And a black chicken crossed with a white chicken will produce an erminette (spotted) chicken.

Some genes have more than two alleles, and are said to have multiple alleles. This does not mean that an individual can have more than two alleles, it only means that more than two possible alleles exist.

One example is coat color in rabbits. A rabbit’s coat color is determined by a single gene that has at four different alleles. The different possible alleles are represented by a _______________________________ above the letter used for the allele. These different alleles display a pattern of simple dominance that can produce four possible coat colors.

Polygenic Traits

Many different traits are produced by the ______________________________________ of several genes. Traits controlled by more than two genes are called Polygenic Traits, and show a wide range of phenotypes. For example, human eye and skin color are influenced by many different genes in the body.

Think-Pair-Share!

Match these term to their definitions:

Incomplete Dominance More than 2 possible alleles for a trait

Multiple Alleles A blending of traits (red + blue = purple)

CoDominance Many genes interact to create different looks

Polygenic Traits Both alleles for a trait exist at the same time (spots)

Inheritance

Gregor Mendel didn’t know that genes were located in the cell. Fortunately, his predictions of how genes should behave were so specific that it was not long before biologists were certain they had found them. Genes are located on _______________________________ in the cell’s nucleus.

Each organism must inherit a single copy of every gene from both its parents. Because each pea plant had two parents, each plant must carry _________ complete sets of genes. And when an organism produces its own gametes, those two sets of genes must be separated from each other so that each gamete contains just one set of genes.

This means that when gametes are formed, there must be a process that separates the two sets of genes so that each gamete ends up with just _______ set. Although Mendel didn’t know it, gametes are formed through exactly such a process.

Chromosomes

For example, consider the fruit fly that has 8 chromosomes. Four came from the female parent, and the other 4 from the male parent. These two ___________ of chromosomes are called Homologous Chromosomes, meaning that the 4 chromosomes from the female parent have _________________________________ chromosomes from the male parent. They carry the same genes and are the same size.

A cell that contains both sets of homologous chromosomes is diploid, which means "two sets". The number of chromosomes in a diploid cell is represented by the symbol _________.

For example, the fruit flies cells are 2N = 8. Two complete sets of chromosomes means two complete sets of genes. Remember, Mendel predicted that the cells of adult organisms contain 2 copies of each gene.

The ________________________________ of sexually reproducing organisms contain only a single set of chromosomes, and therefore a single set of genes; these cells are haploid, and are written as N. Fruit flies gametes would be N = 4.

Meiosis

How are haploid (N) gamete cells made from diploid (2N) cells? This is done through the process of Meiosis, where the number of chromosomes per cell is reduced by ______________.

The stages of Meiosis are very similar to Mitosis: PMAT, except in Meiosis, PMAT is performed ________ times.

Meiosis involves two distinct stages: the first stage is Meiosis I, and the second stage is Meiosis II (where reduction occurs: diploid to haploid).

Meiosis I Summary

Like mitosis, prior to division each cell replicates its chromosomes (Remember that each chromosome is made of 2 sister chromatids). In ______________________________ of meiosis I, homologous chromosomes combine to form a tetrad: here, the 4 chromatids exchange portions of their genes in a process called crossing-over. This process results in __________ combinations of alleles on each chromatid.

After crossing-over, the homologous chromosomes separate and make two new diploid cells, each with different alleles from the parent cell. These 2 cells then go on to meiosis II.

Meiosis II Summary

The two cells produced by meiosis I now enter a second division. Unlike the first division, neither cell goes through chromosome replication before entering meiosis II. Thus, each of the cells contains just 2 chromosomes made of 2 chromatids at the start.

During metaphase II of meiosis II, the 2 chromosomes line up in the center of each cell, then in anaphase II the paired chromatids are separated into individual new cells.

Each of the __________ daughter cells produced in meiosis II receives 2 chromatids. Those four daughter cells are now haploid (N) and each is __________________ from each other and the original cell that entered the meiosis process.

Gamete Formation

In male animals, the haploid gametes produced by meiosis are called sperm. In plants, male gametes are called pollen and are also haploid. In females, the cell divisions at the end of meiosis are ________________________, so only a single haploid cell is produced that receives most of the cytoplasm and genetic information, this is the egg. The three other cells that do not contain enough cytoplasm or information are known as ___________________________________ and are not used for reproduction.

Mitosis vs. Meiosis Comparison

These two processes are very different. Mitosis results in the production of two genetically identical _________________ cells, where meiosis produces four genetically different _______________________ cells.

A diploid cell that divides by mitosis makes two identical diploid (2N) daughter cells. The 2N daughter cells have sets of chromosomes and alleles that are identical to each other and to the original parent cell. This is asexual reproduction = makes clones/copies of original cells, for ex: our body cells perform mitosis every day (skin, hair, ect).

Meiosis begins with a diploid cell, but produces four haploid (N) cells. These are all genetically different from the diploid parent cell, and from one another. Meiosis is how sexually reproducing organisms produce __________________.

Gene Linkage

Each chromosome is actually a group of linked genes; Mendel’s principle of Independent Assortment still holds true. It is the chromosomes, however, that separate independently, not individual genes.

If two genes are found on the _____________ chromosome, does this mean that they are linked forever? Not at all. Crossing-over during meiosis can separate genes on the same chromosome. Cross-over events occasionally separate and exchange linked genes, and produce new combinations of alleles. This is important because it helps to generate genetic ____________________________.

Gene Maps

In 1911 a Columbia University student Alfred Sturtevant hypothesized that the farther ____________________ two genes were, the more likely they were to be separated by a crossover in meiosis.

The rate at which linked genes were separated and recombined can be used to produce a “map” of ___________________ between genes. Sturtevant gathered data on fruit fly DNA and developed a gene map showing the relative ______________________ of each known gene on a Drosophila (fruit flies) chromosomes.

We now use gene maps for human chromosomes as well; this is especially helpful when analyzing a person’s DNA for known genetic disorders carried on certain chromosomes.

Human Genetics

Chromosomes – Made of tightly coiled DNA around histone proteins. Humans have ______ total, counted in 23 pairs. There are 2 types of chromosomes:

Autosomes: (# _________) are all the other chromosome pairs except the sex chromosomes. Sex Chromosomes: (# _____: either XX = female, or XY = male), they determine a person’s sex (gender).

Karyotype: ___________________ of chromosomes arranged in pairs. Grouping chromosomes by _________ and ___________. Autosomes are 1-22, and 23 is the sex chromosomes.

We can use a Punnett square to predict the possible sex of offspring, there is always a ______________ ratio in humans.

Pedigree Chart

Shows how a single natural trait is __________________________________ from one generation to the next within a ____________________. Many traits are strongly influenced by environmental, or non-genetic factors: like nutrition and exercise; these would not be used in a pedigree chart.

Human Blood Types

The Human Genome – is our ______________________________ set of genetic info, includes thousands of genes. Some of the very first genes to be identified were those that controlled blood type: the ABO blood group.

The ABO blood group – has ________________________ alleles: IA, IB, and i. Alleles IA and IB are ___________________________. In blood types, both A and B are _______________________________, and O is recessive. We use the letter “I” to represent dominance in blood types, there are 3 possible alleles: A = IA, B = IB, and O = i.

There are 4 possible ___________________________________, both A and B blood types can be homozygous or heterozygous.

Think-Pair-Share!

Cross a man who is Homozygous for type B blood

with a woman who has type AB blood.

Cross a woman who has type AB blood

with a man who is heterozygous for type A blood.

Genetic Disorders

Recessive Alleles: some genetic disorders are ______________________________ when two defective recessive alleles are passed to the offspring, one from each parent.

Ex 1: PKU (phenylketonuria) occurs when 2 recessive alleles are inherited on chromosome 12. Causes an inability to digest the _________________________________ phenylalanine, because their body does not produce the necessary enzyme to break it down. When phenylalanine is not digested it builds up in the tissues of the body and can cause mental disorders in infants. Thankfully, there is a test for newborns and special milk formulas for PKU babies so they can live normal lives.

Ex 2: Tay-Sachs Disease: caused by an autosomal recessive allele, found most commonly in those of European ancestry. Causes a progressive break down of the __________________________ system and sometimes death in infants.

Ex 3: Cystic Fibrosis is a fatal disease that originated in Europe, and is caused by a recessive allele on chromosome _______. Produces a protein that has a deletion of 3 base pairs (_______________) so the protein made is not able to function properly, causing those with Cystic Fibrosis to produce thick _________________ that clogs their airways and makes it very difficult to breathe.

Dominant Allele Disorders: are expressed when only _________ copy of the gene is present (heterozygous).

Ex 1: Dwarfism (achondroplasia) is ______________________________ dominant. Ex 2: Huntington’s Disease causes progressive ______________________ loss, and loss of mental function until

death occurs. Symptoms begin to show in someone’s thirties/forties.

Codominant Disorders: When one allele of a gene is good and one allele is bad.

Ex: Sickle Cell Anemia occurs in 1 out of every 500 African Americans, and causes them to have both normal and _____________________ (bent) shaped blood cells. The sickle cells cannot carry ______________________ like normal blood cells can, and cause damage or even blockages of blood vessels and tissues. Sickle Cell Anemia causes physical _____________________________ and can sometimes be fatal. People with Sickle Cell Anemia are resistant to the deadly disease ________________________, the sickle cells actually help to destroy the malaria parasite.

Sex-Linked Disorders

Most sex-linked disorders, or traits, are carried on the _____ chromosome.

Ex. 1: Colorblindness: the inability to distinguish between certain colors, caused by an X-linked ___________________________ allele. Color blindness is rare in females because they have 2 X-chromosomes for gender; males have just 1 X-chromosome: this means all X-linked alleles on the X-chromosome for sex are more likely to be inherited in males (even if they are recessive). In order for a recessive allele to be expressed in females, there must be 2 copies of the allele, one on both of her two X-chromosomes. Women are more likely to be a _________________________ of sex linked disorders.

Ex. 2: Hemophilia: disorder that _________________________________ blood from clotting properly, caused by an X-linked allele. The gene for producing the proper protein necessary for normal blood clotting is missing due to a deletion mutation. Ex: Queen Victoria

Ex. 3: Muscular Dystrophy: progressive weakening and _______________ of skeletal muscle, caused by a defective version of the gene that codes for muscle ___________________________ on the X-chromosome.

Ex. 4: X-inactivation - one X chromosome is switched ___________. In females, some cells have one X turned on and the other turned off, the one that is off creates dark ________________ in the nucleus called Barr Bodies. This can also create two differently expressed genes on either X-chromosome. In males, they only have 1 X-chromosome, so if its off/inactivated, then the genes it coded for would not be expressed. Ex: IN CATS one X = orange spots, another X = black spots

Non-Disjunction is the failure of one or more homologous chromosomes (pairs) to ________________________ during meiosis. It can involve autosomal or sex -Chromosomes. Abnormal numbers of chromosomes can end up in the ________________________, and a disorder of Chromosome numbers may result.

Autosomal Chromosome Disorders

1. Down Syndrome - Trisomy on chromosome 21 (______ copies of this chromosome). Results in mild to severe ____________________ illness, increased susceptibility to disease, and birth ______________________________.

Sex Chromosome Disorders -

2. Klinefelters Syndrome- __________ have an extra X chromosome (XXY) – are sterile. 3. Turner Syndrome- _____________________ inherit only one X chromosome (X) - women are sterile.

Think-Pair-Share!

How are recessive disorders inherited?

Are autosomal disorders dominant or recessive?

Which chromosome are sex-linked disorders carried on?