Introduction to Introduction to GeneticsGenetics

Chapter 11 - BiologyChapter 11 - Biology

Gregor MendelGregor Mendel

1822-1884 - The father of genetics1822-1884 - The father of genetics Mendel discovered the basic principles Mendel discovered the basic principles

of heredity by breeding garden peas in of heredity by breeding garden peas in carefully planned experiments carefully planned experiments

True-breeding peas – self-pollinateTrue-breeding peas – self-pollinate Wanted to stop self pollination he cut Wanted to stop self pollination he cut

away the pollen-bearing male parts and away the pollen-bearing male parts and dusted pollen from another plant onto dusted pollen from another plant onto the flower – cross-pollinationthe flower – cross-pollination

Mendel’s 7 TraitsMendel’s 7 Traits

TraitTrait – specific characteristic, such as – specific characteristic, such as seed color or plant height – makes one seed color or plant height – makes one different from the otherdifferent from the other

Mendel crossed plants with each of the 7 Mendel crossed plants with each of the 7 traits and studied their offspring traits and studied their offspring ((hybridshybrids)) P (parental) – original pair of plantsP (parental) – original pair of plants FF11 (first filial) – offspring (first filial) – offspring FiliusFilius and and filiafilia are Latin for “son” and are Latin for “son” and

“daughter”“daughter”

Mendel’s 7 Traits cont.Mendel’s 7 Traits cont.

He first concluded that biological He first concluded that biological inheritance is determined by factors inheritance is determined by factors that are passed from one generation that are passed from one generation to the next.to the next. Factors that determine traits are Factors that determine traits are genesgenes Different forms of a gene are called Different forms of a gene are called

allelesalleles

His second conclusion: the principle His second conclusion: the principle of dominance (some alleles are of dominance (some alleles are dominant & others are recessive)dominant & others are recessive)

Mendel’s 7 Traits cont.Mendel’s 7 Traits cont.

Did the recessive alleles disappear, or Did the recessive alleles disappear, or were they still present in the Fwere they still present in the F11 plants? plants?

7 kinds of F7 kinds of F11 to produce an F to produce an F2 2 through through self-pollinationself-pollination Recessive alleles disappeared in FRecessive alleles disappeared in F11 and and

reappeared in Freappeared in F22

Alleles in FAlleles in F11 separated from each other separated from each other during the formation of sex cells (aka during the formation of sex cells (aka gametes) gametes)

When similar crosses were repeated, When similar crosses were repeated, similar results were obtainedsimilar results were obtainedie. Crossed 2 plants that were hybrid for ie. Crossed 2 plants that were hybrid for

stem height (stem height (TtTt), about ¾ were tall and ), about ¾ were tall and ¼ were short¼ were short

ProbabilityProbability – likelihood that a – likelihood that a particular event will occurparticular event will occur This can be used to predict the This can be used to predict the

outcomes of genetic crossesoutcomes of genetic crosses

Punnett SquarePunnett Square Chart that shows all Chart that shows all

the possible the possible combinations of combinations of alleles that can result alleles that can result from a genetic crossfrom a genetic cross

used to show all the used to show all the possible outcomes of a possible outcomes of a genetic cross and to genetic cross and to determine the determine the probability of a probability of a particular outcomeparticular outcome

T t

T

t

Tt

Tt

tt

TT

Coin Toss LabCoin Toss Lab

Please take out your handoutPlease take out your handout We will use the remainder of the We will use the remainder of the

period to work on and complete this period to work on and complete this lablab

How are dimples How are dimples inherited?inherited? Page 268 in Biology Text BookPage 268 in Biology Text Book

1. Write the last 4 digits of your telephone 1. Write the last 4 digits of your telephone number. These 4 random digits represent number. These 4 random digits represent the alleles of a gene that determines the alleles of a gene that determines whether a person will have dimples. whether a person will have dimples.

Odd = allele for the dominant trait of Odd = allele for the dominant trait of dimples dimples

Even = allele for the recessive trait of no Even = allele for the recessive trait of no dimples dimples

2. First 2 digits represent a certain father’s 2. First 2 digits represent a certain father’s genotype. Symbols genotype. Symbols DD and and d d to write his to write his genotype.genotype.

3. Use the last 2 digits the same way to 3. Use the last 2 digits the same way to find the mother’s genotype.find the mother’s genotype.

4. Construct a Punnett square for the 4. Construct a Punnett square for the cross of these parents. Then, using cross of these parents. Then, using the Punnett square, determine the the Punnett square, determine the probability that their child will have probability that their child will have dimples.dimples.

5. Determine the class average of the 5. Determine the class average of the percent of children with dimples.percent of children with dimples.

Homozygous Homozygous – organisms that have – organisms that have 2 identical alleles for a particular 2 identical alleles for a particular trait (ie. TT or tt) – true-breeding.trait (ie. TT or tt) – true-breeding.

HeterozygousHeterozygous – organisms that – organisms that have 2 different alleles for the same have 2 different alleles for the same trait (ie. Tt) – hybrid.trait (ie. Tt) – hybrid.

PhenotypePhenotype – physical characteristics – physical characteristics Things you can seeThings you can see

GenotypeGenotype – genetic makeup – genetic makeup Things you cannot see – ie. genes (made of Things you cannot see – ie. genes (made of

DNA) on chromosomesDNA) on chromosomes

Mendel performed an experiment to see if Mendel performed an experiment to see if seed shape affects seed color – crossed seed shape affects seed color – crossed plants and recorded the two traitsplants and recorded the two traits One did not effect the other One did not effect the other

(independent assortment) (independent assortment) – – genes for different traits can genes for different traits can segregate independently during segregate independently during formation of gametes.formation of gametes.

Summary of Mendel’s Summary of Mendel’s PrinciplesPrinciples

Inheritance of biological characteristics Inheritance of biological characteristics is determined by genes.is determined by genes.

When two of more forms of the gene for When two of more forms of the gene for a single trait exist, some forms may be a single trait exist, some forms may be dominant and others recessive.dominant and others recessive.

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

Alleles for different genes usually Alleles for different genes usually segregate independently of one another.segregate independently of one another.

Cases in which one allele is not Cases in which one allele is not completely dominant over another are completely dominant over another are called called incomplete dominanceincomplete dominance (heterozygous phenotype is between the (heterozygous phenotype is between the two homozygous phenotypes.two homozygous phenotypes.

CodominanceCodominance – both alleles contribute – both alleles contribute to the phenotype. (ie. in chickens, the to the phenotype. (ie. in chickens, the alleles for black feathers is codominant alleles for black feathers is codominant with the allele for white feathers.with the allele for white feathers.

Dominant & Recessive Dominant & Recessive AllelesAlleles

Incomplete Incomplete dominance - dominance - neither allele is neither allele is dominant,dominant, red x white = red x white =

pinkpink

Codominance - Codominance - both are both are expressed in expressed in some way,some way, red x white = red x white =

white/red spotswhite/red spots

Many genes have more than two Many genes have more than two alleles, known as alleles, known as multiple allelesmultiple alleles. . Does not mean that an individual can have Does not mean that an individual can have

more than two allelesmore than two alleles Means that more than two possible alleles Means that more than two possible alleles

exist in a population – ie. rabbit coat colorexist in a population – ie. rabbit coat color

Traits controlled by two or more genes Traits controlled by two or more genes are said to be are said to be polygenic traitspolygenic traits – – “having many genes.”“having many genes.” Often show a wide range of phenotypesOften show a wide range of phenotypes ie. wide range of skin color in humans – ie. wide range of skin color in humans –

more than 4 different genes control this more than 4 different genes control this traittrait

Mendel’s principles of genetics requires; Mendel’s principles of genetics requires; Each organism must inherit a single copy of Each organism must inherit a single copy of

every gene from each “parent” every gene from each “parent” When an organism produces its own When an organism produces its own

gametes, those 2 sets of genes must be gametes, those 2 sets of genes must be separated so that each gamete contains just separated so that each gamete contains just one set of genesone set of genes

ie. Body cell in an adult fruit fly has 8 ie. Body cell in an adult fruit fly has 8 chromosomes (4 from male parent, and 4 chromosomes (4 from male parent, and 4 from female parent) – these two sets of from female parent) – these two sets of chromosomes are chromosomes are homologoushomologous

Chromosomal Chromosomal InheritanceInheritance

A cell that contains both sets of A cell that contains both sets of homologous chromosomes is said to be homologous chromosomes is said to be diploid diploid – 2 sets– 2 sets Represented by the symbol 2NRepresented by the symbol 2N ie. For the fruit fly the diploid number is 8 ie. For the fruit fly the diploid number is 8

or 2N=8or 2N=8 Diploid cells contain two complete sets of Diploid cells contain two complete sets of

chromosomes and two complete sets of chromosomes and two complete sets of genesgenes

Single set of chromosomes – single set Single set of chromosomes – single set of genes are of genes are haploidhaploid – 1 set or N=4 for – 1 set or N=4 for a fruit flya fruit fly

Phases of MeiosisPhases of Meiosis

MeiosisMeiosis – process of reduction – process of reduction division in which the number of division in which the number of chromosomes per cell is cut in half chromosomes per cell is cut in half through the separation of through the separation of homologous chromosomes in a homologous chromosomes in a diploid celldiploid cell

Usually involves 2 distinct divisions Usually involves 2 distinct divisions known as meiosis I and meiosis IIknown as meiosis I and meiosis II

Meiosis IMeiosis I Before meiosis I, each chromosome is Before meiosis I, each chromosome is

replicated. replicated. Cells start to divide – 4 chromosomes line up Cells start to divide – 4 chromosomes line up

in the middle of the cell and 2 chromatids in the middle of the cell and 2 chromatids that make up each chromosome separatethat make up each chromosome separate

ProphaseProphase – each chromosome pairs – each chromosome pairs with its corresponding homologous with its corresponding homologous chromosome to form a structure called a chromosome to form a structure called a tetradtetrad 4 chromatids in a tetrad4 chromatids in a tetrad As tetrads are formed, they exchange As tetrads are formed, they exchange

portions of their chromatids in a process portions of their chromatids in a process called called crossing-overcrossing-over

Meiosis I cont…Meiosis I cont…

Crossing-over, results in the Crossing-over, results in the exchange of alleles between exchange of alleles between homologous chromosomes and homologous chromosomes and produces new combos of allelesproduces new combos of alleles

Homologous chromosomes separate, Homologous chromosomes separate, and two new cells are formedand two new cells are formed

SEE PAGE 276 FIG. 11-15 SEE PAGE 276 FIG. 11-15 (MEIOSIS)(MEIOSIS)

Meiosis IIMeiosis II

2 cells produced by meiosis I now enter a 2 cells produced by meiosis I now enter a second meiotic divisionsecond meiotic division Each of the cell’s chromosomes has 2 Each of the cell’s chromosomes has 2

chromatidschromatids

Metaphase II - chromosomes line up in Metaphase II - chromosomes line up in the center of each cellthe center of each cell

Anaphase II – paired chromatids separateAnaphase II – paired chromatids separate

See Page 278 Fig. 11-17See Page 278 Fig. 11-17

Meiosis produces four genetically Meiosis produces four genetically different haploid cellsdifferent haploid cells

In males, meiosis results in four equal-In males, meiosis results in four equal-sized gametes called spermsized gametes called sperm

In females, only one large egg cell In females, only one large egg cell results from meiosis (the other 3 cells results from meiosis (the other 3 cells are polar bodies and are not involved in are polar bodies and are not involved in reproduction)reproduction)

Mitosis vs. MeiosisMitosis vs. Meiosis Mitosis results in the production of two Mitosis results in the production of two

genetically identical diploid cellsgenetically identical diploid cells Allows an organism’s body to grow and Allows an organism’s body to grow and

replace cellsreplace cells In asexual reproduction, a new organism is In asexual reproduction, a new organism is

produced by mitosis of the cell or cells of produced by mitosis of the cell or cells of the parent organismthe parent organism

Meiosis produces four genetically Meiosis produces four genetically different haploid cellsdifferent haploid cells Begins with a diploid cell but produces four Begins with a diploid cell but produces four

haploid (N) cellshaploid (N) cells Is how sexually reproducing organisms Is how sexually reproducing organisms

produce gametesproduce gametes

Gene LinkageGene Linkage

Thomas Hunt Morgan researched fruit Thomas Hunt Morgan researched fruit flies which led to the principle of linkageflies which led to the principle of linkage Each fruit fly has four pairs of chromosomes Each fruit fly has four pairs of chromosomes

– each chromosome is a group of genes– each chromosome is a group of genes It is the chromosomes that assort It is the chromosomes that assort

independently, not the genesindependently, not the genes If two genes are found on the same If two genes are found on the same

chromosome they are not linked forever - chromosome they are not linked forever - crossing-over during meiosis sometimes crossing-over during meiosis sometimes separates genesseparates genes