heredity & genetics part one mendel and genetics i: mendel and genetics : a.what are dominant...

Heredity & GeneticsPART ONE

I: Mendel and Genetics Mendel and Genetics :A. What are dominant & Recessive

traits?B. What is a Punnett Square? C. What is incomplete dominance?

A- GeneticsGenetics: Similarities and differences among parents and offspring. It studies how offspring inherit characteristics from their parents and how DNA is involved.

B- MendelMendel: in 1866, this Austrian monk studied traits of pea plants.

1. Mendel studied 7 traits one at a time. Each trait had two forms. Height Tall Vs. Short.

2. Mendel grew short and tall pea plants.3. Mendel let these plants self-pollinate for

several generations to get pure breed seeds. Self-pollinate = Pollination within one plant

4. Mendel cross-pollinates the pure tall with the pure short pea plants.

Cross-pollination Cross-pollination = Take pollen from one plant and put it on another plant.

5. The seeds Mendel collects are Hybrids. HybridHybrid = combination of two varieties of

organisms.6. Mendel plants the hybrid seeds to see if

they will grow talltall, short, or mediummedium. They all grow talltall.

7. Mendel self-pollinates the hybrid for several generations, and plants the seeds from the hybrids. 3:1 ratio some grew tall some grew short.

8. Conclusion the trait for tallness was visible and the trait for shortness was hidden. Visible trait = dominantdominant, prevents

the expression of recessive trait in organism.

Hidden trait = recessiverecessive.

C-C-What we learned from Mendel.1.1.TraitsTraits (characteristics) are

determined by Genes.2.2.GenesGenes = a section of chromosomes

that determines a trait. { eye color, hair color, etc..}

3. 3. Two genes for every trait. Example tallness in pea plants if pure tall two tall genes, if short two short genes, if a hybrid one tall gene and one short gene.

4. 4. The different forms of a gene are ALLELESALLELES {recessive & dominant}

D- Punnett SquaresPunnett Squares.1.1.GenotypeGenotype = the genetic make-up

of an organism. HomozygousHomozygous: alleles of a gene are

the same. HeterozygousHeterozygous: alleles of a gene

are different; one allele for tall one for short. Hybrids are heterozygous.

2.2.PhenotypePhenotype = What the organism looks like.

3.3.Punnett SquaresPunnett Squares: predict the genotypes & phenotypes of offspring.

Symbols for different alleles of a gene. DominantDominant is capital and recessive is

lower case letter.Height = T for dominant & t for

recessive.TT or tt= homozygousTt = heterozygous or hybrid.

4. Offspring receive one allele for each trait from each parent.

5. Heterozygous pass on either T or t.

D-D- Incomplete DominanceIncomplete Dominance: Condition in which the two alleles of a gene are both dominant.1-1-It produces a blended phenotype.Blended phenotype = hybrid.Example: cross a pure red snapdragon Example: cross a pure red snapdragon

with a pure white snapdragon, and you with a pure white snapdragon, and you get a pink snapdragon. RW is the hybrid get a pink snapdragon. RW is the hybrid note both are dominant. note both are dominant.

Part Two Genes and Traits:Part Two Genes and Traits:

A.In the nuclei of a human cell you find two sets of chromosomeschromosomes 23 pairs. This is a diploiddiploid number of chromosomes.

1.One pair of the chromosomes comes from the fatherfather the other set comes from the mothermother.

2.Genes are sections of DNADNA, each human chromosome may contain 1,000’s1,000’s of genes.

3.The way chromosomes pairpair up results in different genetic make-make-upsups in the offspring.

B.B. MeiosisMeiosis: is the formation of sex cells or gametesgametes.

1.Eggs are produced in the female sex organ the ovariesovaries, sperm is produced in the male sex organ the testestestes.

2.Meiosis produces sex cells with only oneone set of chromosomeschromosomes these cells are monoploidmonoploid.

3.In meiosis the chromosomes separate twicetwice as do the cells.

4. Steps of Meiosis:a.a.11stst everything that occurs in

MitosisMitosis happens with Meiosis. Except the 22ndnd time the chromosomes DO NOT DOUBLE.DO NOT DOUBLE.

b.Sometimes the twin chromosomes that are similar pair with each other. If they exchangeexchange DNA this is known as crossingcrossing over this increases the differencesdifferences in the offspring compared to the parent.

3.At the end of meiosis we have 44 cells with a monoploidmonoploid number of chromosomes. {HALFHALF THAT OF PARENT CELL}

4.When the egg and sperm cells unite the two monoploidmonoploid cells combine their DNA forming a diploid zygotezygote.

2n Diploid2n Diploid

4n4n

2n Diploid2n Diploid n Monoploidn Monoploid

PART THREEPART THREE

I. How Sex is InheritedInherited: Sex of an offspring is determined by a pair of chromosomeschromosomes.

A.The malemale body cell has XYXY The femalefemale body cell has XXXX

1.During meiosismeiosis the eggs of

the female receive an XX

chromosome.

2.During meiosis the spermsperm

cell

of the male receive either X X

or YY.

B.B. Twins:Twins:1.IDENTICAL TWINS: ONEONE EGG IS

FERTILIZED BY ONEONE SPERM. THE ZYGOTEZYGOTE SPLITS. ALWAYS THE SAME SEXSEX.

SpermSperm Egg

ZygoteZygote

Same Sex AlwaysAlways

2.2.FRATERNAL TWINSFRATERNAL TWINS: TWOTWO EGGS AND TWOTWO SPERM CELLS. THEY DODO NOTNOT CONTAIN THE SAME DNADNA. CAN BE DIFFERENT SEX.

2 Egg

2 Sperms

2 Zygote

C. X-LinkedLinked Traits: are traits determineddetermined by genes on the x-chromosome.

1.Several diseases are moremore common in males then in females.

• Women may notnot be affectedaffected by the disease, but pass it on to their sons. These womenwomen are known as carrierscarriers.

• X-chromosomes are largerlarger so they carry more genesgenes. The ability to see

colorcolor is on the x-chromosomex-chromosome.

2)2)X-chromosomesX-chromosomes have genes that tell whether or not you see colorcolor. (RedRed, GreenGreen)

• Women are seldomseldom color-blind because the gene is a recessiverecessive gene on the X-chromosome and they have two x-chromosomestwo x-chromosomes..X’=recessive

gene for color-color-blindnessblindness

3)3)HemophiliaHemophilia: is another x-linked diseasedisease it is a blood disorder that prevents the blood from clottingclotting properly.

X’X’ = recessive trait for hemophiliahemophilia

IV.Source of Gene Variations: When cells divide each DNA molecule in the cell makes exactexact copies of itself. But sometimes the cell makes a mistakemistake; bases may pair up incorrectlyincorrectly. The codoncodon are changed the alteredaltered gene is passed on to the new cell.

A- MutationMutation is any permanentpermanent change in the DNADNA of a cell.

1.Mutation increasesincreases with the exposure of DNADNA to some chemicalschemicals ands radiation that damagedamage the DNA molecule.

B.Chromosome Mutation: When a piecepiece of chromosome breaksbreaks and are rearrangedrearranged or lostlost. During meiosis chromosomes mutationmutation may occur when chromosomes do not separate evenlyevenly.

1.Muscular DystrophyDystrophy= Weak muscles.

2.Down Syndrome or TrisomyTrisomy 21= is caused as a result of a sex cell having too many 21st21st chromosomeschromosomes. The fertilized egg, contains threethree 21st chromosomeschromosomes instead of two.

3.Importance of Mutations= are a source of newnew traits or new formsforms of traits.