Introduction to Genetics

these alleles are listed in order of their dominance. What would be the possible genotypes of each of these rabbits?

full color: CC, Ccch, Cch, Cc Chinchilla: Cch, cch, cch, cchc Himalayan: ch, ch, ch, c Albino: cc

where did the man get his gene for colorblindness?

mother

a phenotype is:

physical characteristics of an organism, what the organism looks like

Mendel crossed true-breeding ____________ plants with true-breeding ________ plants. Tall * dwarf-> _____________

tall, dwarf, all tall offspring,

What did he found

- He found that 3/4 of the offspring were tall and 1/4 of the offspring were dwarf. -Evidently the F1 "tall" offspring must have been carrying the dwarf trait but it had been hidden -The dwarf trait had been passed down to the offspring and it reappeared in the F2 generation

Homozygous or Heterozygous

-An offspring will inherit two alleles for a trait, one allele from each parent. The combination of alleles received by the offspring may be either homozygous or heterozygous.

Mendel's Two conclusions

-Biological inheritance is determined by "factors" that are passed from one generation to the next. Today, we know these factors to be genes. Each of the traits that Mendel observed in the pea plants was controlled by 1 gene that occurred in two contrasting form (For example: The gene for the height of pea plants occurs in a tall form and ina dwarf form. The different forms of a gene are called allele

What you need to know about sexual reproduction in flowers:

-Flowers contain: Both male and female reproductive structures -The female part of the flower: pistil produces egg cells -The male part of the flower: Stamen produces pollen which contains sperm cells -When the pollen is delivered to the pistil, the sperm travels to the egg cell, and the result is fertilization -Fertilization produces: tiny embryo, which is enclosed inside a seed

Genes and the environment

-Gene expression is always the result of the interaction of genetic potential with the environment -A seedling may have the genetic capacity to be green, to flower, and to fruit, but it will never do these things if it is kept in the dark,. A tree may never grow tall if the soil is poor and no water is available -In other words, the presence of the gene is not all that is required for the expression of a trait. The gene must be present along with the proper environment conditions -The phenotype of any organism is the result of interaction between genes and the environment

The contributions of Mendel part 1

-Gregor Mendel was an Austrian monk who was born in 1822 -He is known as the Father of genetics. He discovered 3 laws of genetics that would forever change biology. He conducted a series of experiments in a quiet monastery garden. Mendel spent 14 years growing and experimenting with the pea plants grown in his garden

Chromosomes: sex determination

-Human cells contain 23 pairs of chromosomes. There are 22 pairs of autosomes, and one pair of sex chromosomes -In males and females, all of the pairs of chromosomes are the same except one pair. The pairs that are the same are called Autosomes. Autosomes are all of the chromosomes within a cell except for: the sex chromosomes -One pair differs between males and females. This pair is called the sex chromosomes. The sex chromosomes differ in structure -Females have 2 copies of a large X chromosome. Males have one X and one small Y

Codominance

-In humans, four blood types are possible: A, B, AB, and O -There are 3 alleles that determine blood type. These three alleles are written as follows: IA, IB, and i -Alleles IA and IB are codominant and the allele "i" is recessive

Polygenic Inheritance

-In polygenic inheritance, the determination of a given characteristic is the result of: the interaction of many genes -some traits, such as size, height, shape, weight, color, metabolic rate, and behavior are not determined by one pair of alleles. These traits are the cumulative results of the combined effects of many genes. This is known as polygenic inheritance -a trait affected by a number of genes- or polygenes-does not show a clear difference between groups of individuals. Instead, it shows a graduation of small differences -many normal human traits are thought to be polygenic -Examples: hair color, eye color, height, weight, skin color

The Principle of Independent Assortment: Mendel needed to answer one more question: When alleles are being segregated during gamete formation, does the segregation of one pair alleles have any effect on the segregation of a different pair of alleles? In other words, does the gene that determines if a pea plant is tall or dwarf have any effect on the gene for seed color?

-Mendel designed a second set of experiments to follow two different genes as they passed from parent to offspring. This is known as Dihybrid cross, two-factor cross

The contributions of Mendel part 2

-Mendel gave us the three basic laws of inheritance which are still used today: Law of Dominance and recessiveness, the principle of segregation, the principle of independent assortment -Mendel's great contribution was to demonstrate that: inherited characteristics are carried by genes

The Principle of Segregation

-Mendel had another question: Had the dwarf trait (recessive allele) disappeared, or was it still present in the F1 offspring -Mendel allowed the Hybrid tall offspring form the first generation to self-pollinate F1 tall * F1 Tall -> Offspring: 3/4 tall and 1/4 dwarf

This meant ....

that the alleles for seed shape had segregated independently of the alleles for seed color. The alleles for one gene had no effect on the alleles of another trait. This known as independent assortment

Genetics

the science that studies how genes are transmitted from one generation to the next

When the first generation was allowed to self-pollinate (RrYy x RrYy), it resulted in the production of 556 seeds:

315 round yellow ( dominant, dominant) 105 round, green ( dominant , recessive) 104 wrinkled, yellow (recessive, dominant) 32 wrinkled, green (recessive, recessive)

Gene

A segment of DNA that controls a hereditary trait

what are the four alleles for these rabbits in order of dominance are as follows:

C-full color (often called wild type agcuti) cch-light gray or chinchilla ch-albino with black extremities or himalayan c-albino

Heterozygous means that:

Two alleles are different: Tt

must the fathers of all colorblind girls be colorblind? Explain

Yes, for a girl to be colorblind, she must inherit the colorblind of each gene

The gene for colorblindness is carried on the X chromosome and is recessive. A man, whose father was colorblind, has a colorblind daughter Is this man colorblind? How do you know?

Yes, the colorblind daughter had to get O

Why did the recessive allele seem to disappear in the F1 generation and then reappear in the F2 generation?

-Mendel realized that organisms have two alleles for every triati. These two alleles are inherited, one from each parent. If the offspring receives a dominant allele from one parent, that dominant trait will appear in the offspring. Recessive traits show up in the offspring only if: The offspring receives 2 recessive alleles from each parent

Mendel's two conclusions part 2

-Mendel realized that some alleles are dominant over other alleles -Principal of Dominance and Recessiveness: Some alleles are dominant and others are recessive. A dominant allele can cover up/ mask a recessive allele -Dominant allele: If the dominant allele is present in an offspring: the dominant trait will show up in the offspring -Recessive allele: This trait will show up in the offspring only if: the dominant allele is not present

Mendel's work

-Mendel wanted to produce seeds by joining the egg and sperm from two different plants -To do this, he had to first prevent the possibility of self-pollination -Mendel cut away the stamens, the male reproductive parts of the flower, and then dusted the remaining female structure with pollen from a different plant -This is known as a cross-pollination and produces offspring from two different parents -Now Mendel could easily crossbreed plants and experiment with different characteristics

Mendel's Use of Pea plants for Genetics Experiments

-Pea flowers are normally self-pollinating. Since the male and female reproductive structures are relatively enclosed inside the flower, the sperm of the flower will fertilize the egg of the same flower -The resulting embryos will have the same characteristics as the parent plant -Mendel knew that these pea plants were "true breeding." This means that if they are allowed to self-pollinate, they would produce: offspring identical to themselves -(For example; If allowed to self-pollinate, tall plants would always produce tall plants. Plants with yellow seeds would always produce offspring with yellow seeds. -These true breeding plants were the cornerstone of Mendel's experiments

Using Probability and Punnett Squares to Work Genetics Problems Part 2

-The alleles of the first parent will be placed across the top of the square -The alleles of the second parent will be placed along the left side of the square -The possible gene combinations of the offspring will be placed inside the squares -Letters will represent the alleles -A capital letter represents a dominant allele -A lower case letter represents a recessive allele

Genes and Chromosomes

-The chromosomes are contained in the nucleus of the cell -Chromosomes are made of DNA -Two alleles must be present in order for a trait to show up in the offspring. One must come from mom and the other from dad. When fertilization occurs, the new offspring will have 2 alleles

Sex-linked genes

-There are many genes are found on the X chromosomes. The Y chromosome appears to contain only a few genes -Since the X and Y chromosomes determine the sex of an individual, all genes found on these chromosomes are said to be sex-linked -More than 100 sex-linked genetic disorders have now been associated with the X chromosome. -Sex-linked traits include color blindness, hemophilia, and muscular dystrophy -these are caused by recessive alleles -Since males have only one copy of the X chromosome, "they will have the disorder if they inherit just 1 copy of the allele. Females must inherit 2 copies of the allele, one on each of their X chromosomes, in order for the trait to show up. Therefore, sex linked genetic disorders are much more common in males than females

Mendel chose for his experiments the garden pea. It was a good choice because

-They were readily available -They were easy to grow -Grew rapidly -The sexual structures of the flower are completely enclosed within the petals as that there would be no accidental cross-pollinate between plants

genealogy tables (pedigree charts

-a pedigree chart shows relationships within a family -squares represent males and circles represent females -a shaded circle or square indicates that a person has the trait

Incomplete dominance or nodominance

-all traits are not clear-cut as dominant and recessive traits -Some genes appear to blend together -For example: In some flowers, such as snapdragons and for o'clocks, a homozygous red flower crossed with a homozygous white flower yields a heterozygous flower. -This is known as incomplete or nondominance -since there is no recessive allele, use only capital letters. For example: a red flower would b RR, and white flower would be WW, and the pink hybrid would be RW

multiple alleles

-many genes have two or more alleles and are said to have multiple alleles -there are two or more alleles for the trait -The best example for multiple alleles involves coat color in rabbits. Coat color in rabbits is determined by a single gene that has at least 4 different alleles. These four alleles demonstrate a dominance hierarchy in which some alleles are dominant over others.

Using a Punnett Square for a two-factor or dihybrid cross: When two traits are being considered, the Punnett Square will need _______. Each parent will pass one allele of each gene pair to the offspring. Given the following parental genotypes, what alleles could each parent pass to their offspring?

16

F1 Generation

1st generation of offspring

F2

2nd generation of offspring

Punnett Square

A diagram showing the allele combinations that might result from a genetic cross between two parents

Chromosome

A long chain of genes

If the parent was AABB:

AB, AB, AB, AB

If the parent was AaBb:

AB, aB,Ab, ab

If the parent was Aabb:

Ab, Ab, ab, ab

what types of offspring could be produced by a full color rabbit that had a genotype of C c ch that was bred with a Himalayan rabbit that was chc?

Ccch+chc

after

F1 hybrids were all tall -All of the offspring had the appearance of only one of parents -The trait of the other parent seemed to have disappeared. Mendel thought: that the dwarf trait had been lost

The possible genotypes for blood types are as follows: genotypes and phenotypes

IAIA type A blood IAi Type A blood IBIB Type B blood IBi Type B blood IAIB Type AB blood ii Type O blood

what types of offspring might be expected if one parent has type AB blood and the other parent is heterozygous for type A blood? What is the genotype of the first parent? What is the genotype of the second parent?

IAIB IAi

What type of offspring might be produced by two pink flowering plants? What are the genotypes of the parents?

RW and RW

Using Probability and Punnett Squares to Work Genetics Problems

If we know the genetic makeup of parents, what type of offspring might they produce? What is the probability of producing different types of offspring?

Practice problem: In a certain plant, flower color shows non dominance, but the stem length shows dominance. The allele for long stem is dominant over the allele for short stem. Cross a heterozygous long stemmed, red plant with a short stemmed pink plant what is the genotype of the first parent? What is the genotype of the second parent?

LlRR IIRW

a summary of Mendel's principles

Mendel's principles form the basis of modern genetics. Mendel's principles include the following: -the inheritance of traits is determined by individual units known as genes -genes are passed from parent to offspring -Each gene has two or more forms called alleles -Some alleles are dominant, while other alleles are recessive -Each parent has 2 alleles for a particular trait that they inherited from the their parents. They will pass 1 allele to their offspring when the alleles are segregated into gametes -The alleles for one trait segregate independently of the alleles for another trait

what are the exceptions from these principles

Not all genes show a pattern of dominance and recessiveness. For some genes, there are more than two alleles. Many times, traits are controlled by more than one gene. Now we will begin to examine some of these exceptions to Mendel's rules

P generation

Parent generation

If round and yellow are dominant, what is the genotype of all of the F1 offspring?

R1Yy, RrYy

First, Mendel crossed true-breeding parents. The following is a diagram of this cross:

Round, yellow peas (RRYY) X wrinkled, green peas (rryy) --> All F1 offspring had round, yellow peas

Mendel's principle of Segregation

Says that every individual carries 2 alleles for each trait. These two alleles separate or segregate during the formation of the egg and sperm cells

Trait

The characteristics that an organism has, such as hair color, eye color, tall or short, skin color

Probability

The likelihood that a particular event will occur

Hybrids

The offspring of parents with different traits

The principle of Independent Assortment states that:

When gametes are formed, the alleles of a gene for 1 trait segregate independently of alleles of a gene another trait NOTE: This is assuming that the two genes are located on separate chromosomes and are not linked on the same chromosome

the genotypes for color blindness would be written as follows:

XCXC=normal vision female (carrier) XCXc=normal vision female, but a carrier of the colorblind allele XcXc=colorblind female XCY=normal vision male XcY=colorblind male

The genotypes for hemophilia would be written as follows

XHXH=normal blood clotting female XHXh=normal clotting female, but a carrier of hemophilia XhXh=hemophilia XHY=normal blood clotting male XhY=hemophilia male

a genotype is:

a genetic makeup of an organism

If the parent was aaBb:

aB, ab, aB, ab

codominance

both dominant alleles are apparent in the phenotype of the heterozygous offspring

One parent had peas that were round and yellow and the other parent had peas that were wrinkled and green. The round and yellow traits were ______________.

dominant

The capital letter, T, represents ___________

dominant allele

If a parent has two alleles for a trait, how does the parent pass only one allele to the offspring? Today, we know that the answer to this lies in the type of cell division known as:

meiosis, the formation of gametes

what is an example of presence of the gene is not all that is required for the expression of a trait. The gene must be present along with the proper environment conditions

primrose plants that are red flowered at room temperature are white flowered when raised at hotter temperatures. Himalayan rabbits are white at high temperatures and black at low temperatures. Snow shoe rabbits are white at low temperatures and brown at high temperatures.

The lower case letter, t, represents a _________________

recessive allele

During Meiosis, the DNA is ____________ and then separated into ______________

replicated and 4 gametes

Gametes are:

sex cells or egg and sperm cells

Homozygous

two alleles are the same: TT or tt